JP3217279B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for supplying a stabilized DC voltage to industrial or consumer electronic equipment.

[0002]

2. Description of the Related Art In recent years, with the reduction in price, size, performance, and energy saving of electronic devices, there has been a strong demand for switching power supplies having smaller sizes, higher output stability, and higher efficiency.

Hereinafter, a first conventional switching power supply device will be described. FIG. 13 is a circuit diagram of a first conventional half-bridge converter type switching power supply 1A. In FIG. 13, the voltage of DC power supply 1 is V
_IN . An input terminal 2A of the switching power supply 1A,
DC power supply 1 is connected to 2B. The first switching element 3 and the second switching element 5 are connected in series between the input terminals 2A and 2B, and alternately turn on and off.

A first capacitor 7 and a second capacitor 8
Are connected in series between the input terminals 2A and 2B. The potential at the connection point 7A between the first capacitor 7 and the second capacitor 8 is set to V _C. The transformer 9 has a primary winding 9A, a first secondary winding 9B, and a second secondary winding 9C. Primary winding 9
A, the turn ratio of the first secondary winding 9B and the second secondary winding 9C is n: 1: 1 (n is a real number). The primary winding 9A of the transformer has one end connected to a connection point 5A between the first switching element 3 and the second switching element 5, and the other end connected to a connection point 7A between the first capacitor 7 and the second capacitor 8. Connecting. The anodes of the first rectifier diode 14 and the second rectifier diode 15 are connected to the first secondary winding 9B and the second secondary winding 9C of the transformer 9, respectively. The cathodes are commonly connected.

The inductance element 16 and the smoothing capacitor 17 are connected in series. One end of the inductance element 16 is connected to a connection point between the first rectifier diode 14 and the second rectifier diode 15, and the other end is connected to the transformer 9. It is connected to a connection point 9E between the first secondary winding 9B and the second secondary winding 9C. Thereby, the first rectifier diode 14 and the second
The voltage rectified by the rectifier diode 15 is smoothed. The capacitance of the smoothing capacitor 17 is sufficiently large and the output terminal 1
DC output voltage V _OUT is output to 8A and 18B. The load 19 is connected to the output terminals 18A and 18B and consumes power. Output terminals 18A, 18B are connected to the input terminal of the control circuit 20, the DC output voltage V _{OU T} control circuit 2
Detected by 0. The control circuit 20 controls the first switching element 3 and the second switching element 3 to stabilize the output DC voltage V _OUT .
Are controlled at a predetermined on / off ratio.

The operation of the switching power supply configured as described above will be described below with reference to the waveform diagram of FIG. In FIG. 14, the driving pulse signals v _G1 , v _G2
Are control signals for turning on and off the first switching element 3 and the second switching element 5, respectively. Voltage v _D is the voltage applied to the first switching element 3. The currents i _D1 and i _D2 are the first switching element 3 and the second
To the switching element 5.

When the first switching element 3 is turned on at time T ₁ , the voltage V _C is applied to the primary winding 9A of the transformer 9 and the voltage V _C / n is applied to the first secondary winding 9B. appear. As a result, the first rectifier diode 14 is turned on,
Is turned off, and a voltage (V _C / n−V _OUT ) is applied to the inductance element 16. A current i _{D1, which} is the sum of the exciting current of the transformer 9 and the primary-side converted current of the exciting current of the inductance element 16, flows through the first switching element 3.

When the first switching element 3 is turned off at time T ₂ , the secondary current of the transformer 9 is supplied to the first secondary winding 9 B so that the excitation energy of the transformer 9 becomes continuous.
And flows into the second secondary winding 9C. As a result, the first rectifier diode 14 and the second rectifier diode 15 are turned on, and the induced voltage of the first secondary winding 9B and the second secondary winding 9C becomes zero. And the inductance element 16
Is applied with a voltage V _OUT .

When the second switching element 5 is turned on at time T ₃ , the voltage (V _IN) is applied to the primary winding 9 A of the transformer 9.
−V _C ) is applied, and the second secondary winding 9C of the transformer 9 is applied.
, A voltage (V _IN -V _C ) / n is generated. As a result, the rectifier diode 14 turns off and the second rectifier diode 15 turns on. A voltage [(V _IN
−V _C ) / n−V _OUT ]. The current i _D2 of the sum of the exciting current of the transformer 9 and the primary-side converted current of the exciting current of the inductance element 16 is supplied to the second switching element 5.
Flows.

When the second switching element 5 is turned off at time T ₄ , the secondary current of the transformer 9 is supplied to the first secondary winding 9 B so that the excitation energy of the transformer 9 becomes continuous.
And flows into the second secondary winding 9C. As a result, the first rectifier diode 14 and the second rectifier diode 15 are turned on, and the induced voltage of the first secondary winding 9B and the second secondary winding 9C becomes zero. And the inductance element 16
, The voltage V _OUT is applied in a direction opposite to the case where the second switching element 5 is on.

[0011] At time T ₅ when the first switching element 3 is turned on, the primary winding 9A of the transformer 9, the voltage V _C
Is applied. Thereafter, the above operation is repeated.

In the above operation, the on-period (T ₁ -T ₂ ) of the first switching element 3 and the on-period (T ₃ -T ₄ ) of the second switching element 5 are made equal to each other, which is defined as P _ON I do. Similarly OFF period _{(T 2 ~T 3), (} T 4 ~T 5)
And make it P _OFF . Let P _ON / P _OFF be the on / off ratio. Setting the ON and OFF period as described above, in the stable operation state, the flux state of the transformer 9 is reset back to an initial state every one cycle (T ₁ ~T _5). The reset of the state is called a reset condition. From the reset condition, the following equation (1) is satisfied.

(V _IN −V _C ) × P _ON = V _C × P _ON (1)

From equation (1), V _C is expressed as follows.

V _C = V _IN / 2

Equation (2) is satisfied by the reset condition under which the magnetic flux of the inductance element 16 returns to the initial state.

(V _IN / 2−V _OUT ) × P _ON = V _OUT × P _OFF (2)

From equation (2), V _OUT is expressed as follows.

V _OUT = δ × V _IN / 2

Here, δ is expressed as follows.

Δ = P _ON / (P _ON + P _OFF )

That is, by adjusting the _ON / OFF ratio P _ON / P _OFF of the first switching element 3 and the second switching element 5, the output voltage V _OUT can be stabilized. In the circuit configuration of FIG. 13, a voltage exceeding the input voltage is not applied to the first switching element 3 and the second switching element 5, and the transformer 9 is not DC-excited.

Hereinafter, a second conventional switching power supply device 31A will be described. FIG. 15 shows a second conventional switching power supply device 3 of a push-pull converter type.
It is a circuit diagram of 1A. In FIG. 15, the voltage of the DC power supply 1 is assumed to be V _IN . DC power supply 1 is connected to input terminals 2A and 2B of switching power supply device 31A. Transformer 27
Are the first primary winding 27A, the second primary winding 27B, the first
, And a second secondary winding 27D. The first primary winding 27A, the second primary winding 27
B, the turn ratio of the first secondary winding 27C and the second secondary winding 27D is n: n: 1: 1. A series circuit of the first primary winding 27A of the transformer 27 and the first switching element 3 is connected between the input terminals 2A and 2B. The second
Of the primary winding 27B and the second switching element 5 are connected between the input terminals 2A and 2B.

The anodes of the first rectifier diode 14 and the second rectifier diode 15 are connected to the transformer 27, respectively.
Are connected to one ends of a first secondary winding 27C and a second secondary winding 27D. First and second rectifier diodes 14,
The 15 cathodes are commonly connected. An inductance element 16 and a smoothing capacitor 17 are connected in series, and an end of the inductance element 16 is connected to the first rectifier diode 1.
4 and the cathode of the second rectifier diode 15. Connect the end of the smoothing capacitor 17 to the transformer 27
Is connected to a connection point 27E between the first secondary winding 27C and the second secondary winding 27D. The voltage rectified by the first rectifier diode 14 and the second rectifier diode 15 is smoothed by an inductance element 16 and a smoothing capacitor 17, and is output to output terminals 18A and 18B. The capacitance of the smoothing capacitor 17 is sufficiently large and the output terminal 18
DC output voltage V _OUT is output to A and 18B. The load 19 is connected to the output terminals 18A and 18B and consumes power.

The control circuit 29 detects the DC output voltage V _OUT and controls the first switching element 3 and the second switching element 5 at a predetermined on / off ratio in order to stabilize the output voltage V _OUT .

The operation of the switching power supply configured as described above will be described below. FIG. 16 shows a waveform diagram of the operation. In FIG. 16, the driving pulse signal v _G1 ,
v _G2 is a control signal for turning on / off the first switching element 3 and the second switching element 5, respectively. Voltage v _D1
Is applied to the first switching element 3. Voltage v _{D 2}
Is applied to the second switching element 5. The current i ₁ ,
i ₂ denotes a current flowing through the first switching element 3 and the second switching element 5, respectively.

[0027] At time T ₁ the first switching element 3 is turned on, the input voltage V _IN is applied to the first primary winding 27A of the transformer 27, the voltage V to the first secondary winding 27C _IN / n occurs. As a result, the first rectifier diode 1
4 is on, and the second rectifier diode 15 is off. Voltage (V _IN / n−V _OUT ) is applied to the inductance element 14.
Is applied. A current i _{1, which} is the sum of the exciting current of the transformer 27 and the primary-side converted current of the exciting current of the inductance element 14, flows through the first switching element 3.

[0028] When the first switching element 3 at time T _2, is turned off, as the excitation energy of the transformer 27 becomes continuous, secondary current, the first secondary winding 27C and the second secondary winding The flow is divided into lines 27D. As a result, the first rectifier diode 14 and the second rectifier diode 15 are turned on, and the induced voltage of the first secondary winding 27C and the second secondary winding 27D becomes zero. Then, the voltage V _OUT is applied to the inductance element 16 in a direction opposite to the case where the first switching element 3 is turned on.

[0029] When the second switching element 5 at time T ₃ is turned on, the voltage V _IN is applied to the second primary winding 27B of the transformer 27, the voltage V _IN to the second secondary winding 27D
/ N occurs. As a result, the first rectifier diode 14 is turned off, the second rectifier diode 15 is turned on, and the voltage (V _IN / n−V _OUT ) is applied to the inductance element 16. Is applied. The second switching element 5 includes a transformer 27
Of the exciting current of the inductance element 16
Current i ₂ flows in the sum of the following side in terms of current.

When the second switching element 5 is turned off at time T ₄ , the secondary current is supplied to the first secondary winding 27 C and the second secondary winding 27 so that the excitation energy of the transformer 27 becomes continuous. The flow is divided into lines 27D. As a result, the first rectifier diode 14 and the second rectifier diode 15 are turned on, and the induced voltage of the first secondary winding 27C and the second secondary winding 27D becomes zero. Then, the voltage V _OUT is applied to the inductance element 16 in a direction opposite to the case where the second switching element 5 is on. The ON period (T _{1 to} T ₂ ) of the _first switching element 3 and the second switching element 5
And the ON period (T ₃ ~T ₄₎ P _ON of equal values. Similarly, the off periods (T _{2 to} T ₃ ) and (T _{4 to} T ₅ ) are set to the same value P
_Set to _OFF . As described above, when the ON and OFF periods are set, the reset condition of the inductance element 14
Equation (3) holds.

(V _IN −V _OUT ) × P _ON = V _OUT × P _OFF (3)

From equation (3), V _OUT is expressed as follows.

V _OUT = δ × V _IN

Here, δ is expressed as follows.

Δ = P _ON / (P _ON + P _OFF )

That is, the output voltage V _OUT can be stabilized by adjusting the on / off ratio P _ON / P _OFF of the first switching element 3 and the second switching element 5.

[0037]

In the constructions of the first and second conventional examples, the first switching element 3 or the second switching element 5 is turned on when the switching element 3 or 4 is turned on in FIG. 13 or FIG. The parasitic capacitance indicated by the dotted line and the distributed capacitance of the transformer 9 are short-circuited, and the electric charges charged therein are discharged. Therefore the surge current S _I shown in FIG. 14 is generated, resulting in power loss and noise. Further, when the first switching element 3 and the second switching element 5 are turned off, a surge voltage _SV is generated due to the leakage energy of the transformer and the excitation energy held by the parasitic inductance of the wiring. Since the surge current S _I is generated during turn-on of the first and second switching elements 3 and 5, also increases the number generated in proportion to the switching frequency. As a result, the power loss increases due to the increase in the switching frequency, and the noise also increases.

Therefore, it was difficult to increase the switching frequency in the conventional switching power supply. In a switching power supply, a higher switching frequency is desirable. The reason is that when the switching frequency is increased, the capacity of the transformer 9, the capacitors 7, 8 and the like can be reduced, so that the switching power supply can be downsized.

[0039]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching power supply which prevents a surge current and a surge voltage from occurring, reduces power loss, improves efficiency, and reduces noise. .

The switching power supply of the present invention is connected in series between a terminal of a DC power supply and alternately turned on and off in series.
A DC connection of a first capacitor and a second capacitor connected between terminals of the DC power supply, a primary winding and at least one secondary winding, and one end of the primary winding is First
And the other end of the primary winding is connected to a connection point of a series connection of the first and second switching means, and the first and second switching means are connected to each other. Is turned on, a transformer for storing energy, a bidirectional switching means connected in parallel to a primary winding of the transformer, a rectifying / smoothing means connected to a secondary winding of the transformer, and an output of the rectifying / smoothing means. And when the first and second switching means are both off,
After a predetermined period after the first or second switching means is turned off, the bidirectional switching means is turned on to short-circuit the primary winding of the transformer, and the current of the primary winding is continuous. The first and second switching means are turned off before the first or second switching means is turned on, and the first and second switching means are turned off before the first or second switching means is turned on. Control means for controlling the first and second switching means and the bidirectional switching means so as to charge and discharge a parasitic capacitor equivalently connected in parallel with the means, the bidirectional switching means and the transformer. .

A switching power supply according to another aspect of the present invention is a series connection of a first switching means and a second switching means which are connected between terminals of a DC power supply and alternately repeat on and off, and a terminal of the DC power supply. The first connected between
DC connection of a capacitor and a second capacitor, a primary winding, an auxiliary winding, and at least one secondary winding. One end of the primary winding is connected to the first and second capacitors. The other end of the primary winding is connected to the first and second
A transformer for storing energy when the first and second switching means are turned on, a bidirectional switching means connected in parallel to an auxiliary winding of the transformer, The rectifying / smoothing means connected to the secondary winding of the transformer and the output of the rectifying / smoothing means are applied, and the first or second switching means is turned off while both the first and second switching means are off. After a predetermined period of time after the power supply is turned off, the bidirectional switching means is turned on to short-circuit the primary winding of the transformer, and the current of the primary winding is continuously supplied and stored in the transformer. The bidirectional switching means is turned off before the first or second switching means is turned on, and the first and second switches are held. The parasitic capacitor equivalently connected in parallel with the etching means to the transformer so as to charge and discharge, having a control means for controlling said bidirectional switching means and said first and second switching means.

According to another aspect of the present invention, there is provided a switching power supply device comprising: a first primary winding and a second primary winding each having one end connected to one terminal of a DC power supply;
Transformer with two secondary windings to store energy
A first terminal which is connected in series to the first primary winding and has an end connected to the other terminal of the DC power supply and which repeatedly turns on and off;
Switching means, connected in series to the second primary winding, and an end connected to the other terminal of the DC power supply,
A second switching unit that alternately turns on and off with the first switching unit, a connection point between the first primary winding and the first switching unit, the second primary winding and the second switching unit; A bidirectional switching means connected between the connection points of the switching means, a rectifying / smoothing means for rectifying / smoothing the current of the secondary winding, and an output of the rectifying / smoothing means applied to the first and second switching means. After turning on the bidirectional switching means for a predetermined period after the first or second switching means is turned off while both of the switching means are off, the stored energy of the transformer is maintained continuously. Holding the energy stored in the transformer, turning off the bidirectional switching means before turning on the first or second switching means, And second, as the switching means and a parasitic capacitor wherein it is equivalently connected in parallel to the transformer is charged and discharged, the first and second switching means and control means for controlling said bidirectional switching means,
Having. A switching power supply device according to another aspect of the present invention includes a first primary winding and a second primary winding each having one end connected to one terminal of a DC power supply, and at least one secondary winding. A transformer for storing energy, connected in series with the first primary winding,
An end is connected to the other terminal of the DC power supply, and the first switching means that repeats on / off is connected in series to the second primary winding, and an end is connected to the other terminal of the DC power supply. Second switching means that alternately turns on and off with the first switching means, bidirectional switching means connected in parallel to the auxiliary winding, rectifying and smoothing means for rectifying and smoothing the current of the secondary winding, The output of the rectifying / smoothing means is applied, and the bidirectional switching means passes a predetermined period after the first or second switching means is turned off while both the first and second switching means are off. Is turned on, the energy stored in the transformer is held so as to keep the energy stored in the transformer continuous, and the first or second switching means is turned off. Before turning on, the first and second switching means are turned off, and the first and second switching means and the first and second switching means and the parasitic capacitor equivalently connected in parallel to the transformer are charged and discharged. And switching means for controlling the bidirectional switching means. By turning on the bidirectional switching means, during the period from turning off the first switching means to immediately before turning on the second switching means, and from turning off the second switching means to turning on the first switching means. The energy stored in the transformer can be maintained during the period immediately before. Immediately before the turn-on, the charge of the parasitic capacitor equivalently connected in parallel to each switching means is discharged, and thereafter, the turn-on is performed. Therefore, no surge current is generated.

In addition, the clamping action for short-circuiting the primary winding of the transformer by the bidirectional switching means prevents generation of a surge voltage due to the influence of the leakage inductance of the transformer when the first and second switching means are turned off.

Further, in this configuration, there is no generation of a surge voltage when the bidirectional switching means is turned on and a surge voltage when the bidirectional switching means is turned off. Therefore, power loss is reduced, efficiency is increased, and noise is reduced. Further, a smaller switching power supply having a higher switching frequency can be realized.

[0045]

BEST MODE FOR CARRYING OUT THE INVENTION

<< First Embodiment >> Hereinafter, a first embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. FIG. 1 is a circuit diagram of a switching power supply device according to a first embodiment of the present invention.

The voltage of the DC power supply 1 is assumed to be V _IN . The input terminals 2A and 2B of the switching power supply 1B are connected to the DC power supply 1. The first switching unit 34 is constituted by a parallel connection of the first switching element 3 and the first diode 4. A second switching unit 56 is configured by a parallel connection of the second switching element 5 and the second diode 6. The first switching unit 34 and the second switching unit 56 are connected in series and connected between the input terminals 2A and 2B.

First capacitor 7 and second capacitor 8
Are connected in series and connected between the input terminals 2A and 2B.
Connection point 7A between first capacitor 7 and second capacitor 8
Is _VC . The transformer 9 has a primary winding 9A,
Of the secondary winding 9B and the second secondary winding 9C. The turns ratio of the primary winding 9A, the secondary winding 9B and the secondary winding 9C is n: 1: 1 (n is a real number). The primary winding 9A is connected to the connection point 7A between the first capacitor 7 and the second
Is connected to the connection point 5A between the switching unit 34 and the second switching unit 56.

The anode of the first rectifier diode 14 is connected to one end of the first secondary winding 9B of the transformer 9. The anode of the second rectifier diode 15 is connected to the second
Of the secondary winding 9C. The cathodes of the first rectifier diode 14 and the second rectifier diode 15 are commonly connected. The inductance element 16 and the smoothing capacitor 17 are connected in series, and the end of the inductance element 16 is connected to the first rectifier diode 14 and the second rectifier diode 1.
5 is connected to the connection point 14A of the cathode. An end of the smoothing capacitor 17 is connected to a connection point 9E between the first secondary winding 9B and the second secondary winding 9C. The voltage generated in the secondary windings 9A and 9B of the transformer 9 is rectified and smoothed, and the output voltage _Vout is supplied to the load 19 via the output terminals 18A and 18B. The above is the same as the configuration of the conventional half-bridge converter.

A parallel connection of the third switching element 10 and the third diode 11 and the fourth switching element 12
And the parallel-connected body of the fourth diode 13 are connected in series such that the anode of the third diode 11 and the anode of the fourth diode 13 are connected to form the bidirectional switching unit 25. The bidirectional switching unit 25 turns on the third switching element 10 to enable conduction only in the first direction through the fourth diode 13. Conversely, the fourth switching element 12
Is turned on, the conduction through the third diode 11 is enabled only in the second direction, which is opposite to the above. When both the third switching element 10 and the fourth switching element 12 are turned on, bidirectional conduction is possible. The bidirectional switching unit 25 is connected in parallel to the primary winding 9A of the transformer 9.

The control circuit 40 detects an output voltage between the output terminals 18A and 18B. Then, a control signal for controlling the on / off ratio of the first switching element 3, the second switching element 5, the third switching element 10, and the fourth switching element 12 is generated so that the output voltage V _OUT becomes constant. I do. Switching elements 3, 5, 10, 12
Is preferably composed of a semiconductor element. As the semiconductor element, for example, a bipolar transistor or FET is used.
In the case of the FET, since diodes connected in parallel are built in, the diodes 4, 6, 11, and 13 become unnecessary.

The operation of the switching power supply configured as described above will be described below with reference to FIG.

In FIG. 4, the drive pulse signal v _G1 is applied from the control circuit 40 to the first switching element 3. The drive pulse signal v _G2 is applied from the control circuit 40 to the second switching element 5. The drive pulse signal v _G3 is applied from the control circuit 40 to the third switching element 10. The drive pulse signal v _G4 is applied from the control circuit 40 to the fourth switching element 12. Voltage v _D shows the voltage applied to the first switching unit 34. Current i
_D1 indicates a current flowing through the first switching unit 34. The current i _D2 is supplied to the second switching unit 56
Shows the current flowing through. The current i _P is 1 of the transformer 9
The current of the next winding 9A is shown. The current i _L indicates a current flowing through the inductance element 16.

When the first switching element 3 is turned on by the drive pulse signal v _G1 of the control circuit 40 at time T ₁ ,
Voltage V _C is applied to primary winding 9A of transformer 9. In this case the voltage V _C / n in the first secondary winding 9B of the transformer 9 is turned on the rectifying diode 14 occurs. The inductance element 16 is the voltage _{(V C / n-V OUT} ) is applied, the current flowing through the inductance element 16 increases linearly. The current i _{P of the} primary winding 9A of the transformer 9 is the sum of the exciting current of the transformer 9 and the primary-side converted current of the current flowing through the first secondary winding 9B. Therefore, the current i _P increases linearly, and the transformer 9 and the inductance element 16
The excitation energy is stored in the. At this time, the control circuit 40
Therefore, the second switching element 5 is off, the third switching element 10 is off, and the fourth switching element 12 is on, but the second diode 6 and the third diode 11 are reverse-biased and off. There is no effect on circuit operation.

At time T ₂ , the drive pulse signal v _G1 of the control circuit 40 turns off and the first switching element 3 turns off. The current i _P flowing through the primary winding 9A of the transformer 9 tends to continuously flow under the influence of the leakage inductance of the transformer 9. Therefore, the current i _P is generated by the parasitic switching indicated by the dotted line equivalently connected in parallel to the first switching unit 34, the second switching unit 56, the third switching element 10 and the transformer 9 in the bidirectional switching unit 25, respectively. Charge and discharge the capacitor. As a result, the voltage v _D applied to the first switching unit 56
Rises. When the voltage V _D exceeds the voltage v _C, the third diode 11 is turned on by a voltage applied through the fourth switching element 12 is turned on, the bidirectional switching unit 25 is turned on.

At time T ₃ , the third switching element 10 is turned on by the drive pulse signal v _G3 of the control circuit 20.
The current flows through the third diode 11 and the third switching element 10. There is no difference in operation whether the on-current flows through the third diode 11 or the third switching element 10. At this time, the primary winding current i _P of the transformer 9 temporarily decreases because the energy stored in the transformer 9 is consumed by charging and discharging the parasitic capacitor.
When the diode 11 or the third switching element 10 is turned on, the primary winding 9A of the transformer 9 is short-circuited, and the energy stored in the leakage inductance and the exciting inductance of the transformer 9 is retained. Hereinafter, when energy is referred to, it indicates the energy stored in the leakage inductance and the excitation inductance of the transformer. As a result, the first secondary winding 9B and the second secondary winding 9C of the transformer 9 are formed.
Is zero, and the inductance element 1
The voltage applied to 6 becomes V _OUT . A current is divided and flows through the first secondary winding 9B and the second secondary winding 9C of the transformer 9 so as to keep the excitation energy continuous.
Therefore, the first rectifier diode 14 and the second rectifier diode 15 are turned on.

When the bidirectional switching unit 25 is turned off by turning off the fourth switching element 12 at time T ₄ , the first switching unit 34 and the second switching unit are turned on by the energy held in the transformer 9. 56, the parasitic capacitor equivalently connected in parallel to the fourth switching element 12 and the transformer 9 in the bidirectional switching unit 25 is charged and discharged. As a result, the voltage v applied to the first switching unit 34
_D rises. When the voltage V _D reaches the input voltage V _IN, the second
Is turned on. Turning on the second switching element 5 with the driving pulse signal v _G2 of the control circuit 40 at time T _5. The operation does not change whether the ON current flows through the second diode 6 or the second switching element 5.

Current i flowing through primary winding 9A of transformer 9
_P temporarily decreases due to the charging and discharging of the parasitic capacitance,
When the second switching means 56 is turned on, a voltage (V _C -V _IN ) is applied to the primary winding 9A of the transformer 9, and
The next winding current i _P decreases rapidly. When a sufficient reverse current is supplied to the primary winding 9A of the transformer 9, the first rectifier diode 14 is turned off, and the voltage (V _IN −V) is applied to the second secondary winding 9C.
_C ) / n occurs. As a result, the inductance element 16
, A voltage [(V _IN −V _C ) / n−V _OUT ] is applied, and the current i _L flowing through the inductance element 16 increases linearly. The current i _{P of the} primary winding 9A of the transformer 9 is
Of the current flowing through the secondary winding 9B and the primary-side converted current of the current flowing through the secondary winding 9B. Therefore, the excitation energy is stored in the transformer 9 and the inductance element 16. At this time, the first switching element 3 is turned off, the third switching element 10 is turned on, and the fourth switching element 12 is turned off by the control circuit 40.
The diode 6 and the fourth diode 13 are reverse-biased and off, so that there is no effect on the circuit operation.

When the drive pulse signal v _G2 of the control circuit 40 disappears at time T ₆ and the second switching element 5 is turned off, the current i _P flowing through the primary winding 9 A of the transformer 9 becomes equal to the leakage inductance of the transformer 9. Attempts to flow continuously under the influence of. The current i _P is supplied to the first switching unit 34,
A parasitic capacitor equivalently connected in parallel to the third switching element 10 and the transformer 9 in the second switching unit 56 and the bidirectional switching unit 25 is charged and discharged. As a result the voltage v _D applied to the first switching unit 34 decreases. When the voltage V _D reaches the voltage v _C, the fourth diode 13 is turned on by a voltage applied through the third switching element 10 of which is on, the bidirectional switching unit 25 is turned on.

At time T ₇ , the fourth switching element 12 is turned on by the drive pulse signal v _G4 of the control circuit 40. Regardless of whether the ON current flows through the fourth diode 13 or the fourth switching element 12, the bidirectional switching unit 2
The operation of No. 5 does not change. Primary winding current i _{P of} transformer 9
, The energy stored in the transformer 9 is consumed as negative-polarity energy during charging and discharging of the parasitic capacitor, and temporarily increases. When the fourth diode 13 or the fourth switching element 12 is turned on, the primary winding 9A of the transformer 9 is short-circuited, and the negative energy stored in the leakage inductance and the exciting inductance of the transformer is retained.

The voltage induced in the first secondary winding 9B and the second secondary winding 9C of the transformer 9 due to the short circuit of the primary winding 9A also becomes zero. As a result, the voltage applied to the inductance element 16 becomes V _OUT . A secondary current is divided and flows through the first secondary winding 9B and the second secondary winding 9C of the transformer 9 so as to keep the excitation energy of the transformer 9 continuous. Therefore, the first rectifier diode 14 and the second rectifier diode 15 are turned on.

At a time T ₈ , the bidirectional switching unit 25 is turned off by turning off the third switching element 10. The parasitic capacitors connected equivalently in parallel to the first switching unit 34, the second switching unit 56, the fourth switching element 12, and the transformer 9 are charged and discharged by the energy held in the transformer 9. As a result, the first switching unit 34
Voltage v _D applied to the drops. When it reaches zero, the first diode 4 is turned on.

At time T ₉ , the first switching element 3 is turned on by the drive pulse signal v _G1 of the control circuit 40. There is no change in the operation whether the on-current i _D1 flows through the first diode 4 or the first switching element 3.

Current i flowing through primary winding 9A of transformer 9
_P once increases due to charging and discharging of the parasitic capacitance,
When the first switching unit 34 is turned on, the voltage V _C is applied to the primary winding 9A of the transformer 9, and the primary winding current i _P rapidly increases. Primary winding 9A of transformer 9
When sufficient current is supplied to the second rectifier diode 1
5 is turned off, and a voltage V _C / n is generated in the first secondary winding 9B. Therefore, the voltage [(V _IN -V
_C ) / n-V _OUT ] is applied. Thereafter, the above operation is repeated.

The ON periods T _{1 to} T ₂ of the _first switching unit 34 and the ON periods T _{5 to} T ₆ of the second switching unit 56 are set to the same value P _ON . The first OFF period T ₂ ~ from the switching unit 34 is turned off to the second switching unit 56 is turned on
The OFF periods T _{6 to} T ₉ from the time when T ₅ and the second switching unit 56 are turned off to the time when the first switching unit 34 is turned on are set to P _OFF having the same value. The on / off ratio is represented by P _ON / P _OFF . Flux of the transformer 9 and the inductance element 16 is reset back to the initial state in one cycle (T ₁ ~T _9). This is hereinafter referred to as a reset condition. Equation (3) is established by the transformer 9 reset condition.

(V _IN −V _C ) × P _ON = V _C × P _ON (3)

Periods T _{2 to} T ₃ , T _{4 to} T ₅ , T _{6 to} T ₇ , T ₈
When ~T ₉ is ignored because short, the inductance element 16
Equation (4) holds from the reset condition of.

[(V _IN −V _C ) / n−V _OUT ] × P _ON = V _OUT × P _OFF (4)

Therefore, from equation (4), V _C and V _OUT are expressed as follows.

V _C = V _IN / 2

V _OUT = δV _IN / 2n

Here, δ is represented as follows.

Δ = P _ON / (P _ON + P _OFF )

Therefore, the output voltage V _OUT can be controlled by adjusting the on / off ratios P _ON / P _OFF of the first switching unit 34 and the second switching unit 56. The expression representing δ is the same conversion expression as that of the conventional half-bridge converter. Period _{T 2 ~T 3, T 4 ~T} 5, T 6
T ₇ and T _{8 to} T ₉ are considered, the output voltage V _OUT becomes low, but a predetermined voltage can be obtained by increasing δ accordingly. By the above operation of this configuration, the switching elements 3, 5, 10, 12 immediately before the first switching element 3, the second switching element 5, the third switching element 10, and the fourth switching element 12 are turned on.
Of the transformer 9 and the distributed charge of the transformer 9 are discharged. As a result, generation of surge current due to short-circuit can be reduced, and generation of noise can be suppressed.

Further, since the power loss is reduced due to the reduction of the surge current, the efficiency of the switching power supply is improved. Further, the surge voltage at the time of turning off the first switching element 3 and the second switching element 5 due to the leakage inductance of the transformer 9 is increased by the third diode 11 and the fourth diode 12 in the bidirectional switching unit 25. Is turned on, the first capacitor 7 and the second capacitor 8 and the input DC power supply 1 are effectively absorbed. Therefore, no surge voltage occurs.

Further, the surge voltage generated when the third switching element 10 and the fourth switching element 12 in the bidirectional switching unit 25 are turned off is also reduced by the first diode 4 and the second diode 6 being turned on. And the second capacitor 8 and the DC power supply 1. Therefore, no surge voltage occurs.

The energy for charging and discharging the parasitic capacitance depends on the energy stored in the exciting inductance and the leakage inductance of the transformer. If the leakage inductance is relatively small and the energy for charging / discharging the parasitic capacitance is insufficient, the primary winding 9A or 2
An inductance element may be connected in series to the next winding 9B to intentionally increase the leakage inductance. The charge / discharge energy of the parasitic capacitance can be increased by increasing the leakage inductance. Further, the first and second switching units 34 and 56 are reduced by reducing the exciting inductance value of the transformer 9 and reversely exciting the transformer.
Of the parasitic capacitance and the distributed capacitance of the transformer 9 can also be assisted.

Another example of the first embodiment is shown in FIGS. In the configuration of FIG. 1 of this embodiment, the DC input voltage V _IN is divided by a series connection of a first capacitor 7 and a second capacitor 8. When only the first capacitor 7 is connected between the input terminal 2A and the primary winding 9A as shown in FIG. 2, or when only the second capacitor 8 is connected between the input terminal 2B and the primary winding 9A as shown in FIG. Even when connected between lines 9A,
The switching power supply of the present invention operates normally. In addition, in the configuration of FIGS. 1 to 3, in addition to the parasitic capacitors equivalently connected in parallel to the first switching unit 34, the second switching unit 56, the bidirectional switching unit 25, and the transformer 9, external capacitors are provided. The addition does not affect the basic operation. Since the added capacitor works as a snubber circuit, the rise of the current becomes slow and noise is reduced. In addition, since the slope of the voltage applied when the switching elements 3, 5, 10, and 12 are turned off is reduced, there is an effect that the loss generated during switching can be further reduced. Further, the voltage applied to each switching unit does not exceed the input voltage V _IN , and the transformer 9 is not DC-excited as in the conventional half-bridge converter.

According to the first embodiment, the first, second, third,
Immediately before the fourth switching elements 3, 5, 10, and 12 are turned on, the electric charges charged in their parasitic capacitance and the distributed capacitance of the transformer are discharged, so that the surge current is reduced. Therefore, the noise is reduced and the power loss is also reduced, so that the efficiency is improved. Further, since the surge current is reduced, the switching frequency can be increased. A high-efficiency, low-noise, high-frequency switching power supply can be realized.

<< Second Embodiment >> A second embodiment of the present invention will be described below with reference to FIGS. FIG.
Is a switching power supply 1 according to a second embodiment of the present invention.
It is a circuit diagram of C.

In FIG. 5, a DC power supply 1, first and second
Switching units 34 and 56, first and second capacitors 7 and 8, and bidirectional switching unit 2
5 is the same as that of the first embodiment shown in FIG.

The transformer 21 has a primary winding 21A, a first 2
Secondary winding 21B, second secondary winding 21C, and auxiliary winding 21
D. The turns ratio of the primary winding 21A, the secondary winding 21B, the secondary winding 21C, and the auxiliary winding 21D is n: 1: 1: n.
(N is a real number). The primary winding 21A includes a connection point 7A between the first capacitor 7 and the second capacitor 8, a first switching unit 34, and a second switching unit 56.
Is connected to the connection point 5A.

The anode of the first rectifier diode 14 is connected to one end of the first secondary winding 21B of the transformer. The anode of the second rectifier diode 15 is connected to one end of the second secondary winding 21C of the transformer 21. The cathodes of the first rectifier diode 14 and the second rectifier diode 15 are commonly connected.

The inductance element 16 and the smoothing capacitor 17 are connected in series, and the end of the inductance element 16 is connected to the first rectifier diode 14 and the second rectifier diode 15.
Is connected to the connection point 14A of the cathode. The end of the smoothing capacitor 17 is connected to the first secondary winding 21B and the second secondary winding 21B.
Connected to connection point 21E of next winding 21C. The voltage generated in the secondary winding of the transformer is rectified and smoothed and the output voltage V
_OUT is supplied to the load 19 via the output terminals 18A and 18B.

The bidirectional switching unit 25 is connected to both ends of the auxiliary winding 21D.

The control circuit 41 detects the voltage between the output terminals 18A and 18B and controls the first switching element 3, the second switching element 5, the third switching element 10 and the fourth switching element so that the output voltage becomes constant. A control signal for controlling the switching element 12 by changing the on / off ratio is generated.

The operation of the switching power supply 1C configured as described above will be described below with reference to FIG.

In FIG. 8, the drive pulse signal v _G1 is applied from the control circuit 41 to the first switching element 3.
The drive pulse signal v _G2 is applied from the control circuit 41 to the second switching element 5. The drive pulse signal v _G3 is applied from the control circuit 41 to the third switching element 10.
The drive pulse signal v _G4 is applied from the control circuit 41 to the fourth switching element 12. Voltage v _D is applied to the first switching unit 34. The current i _D1 is a current flowing through the first switching unit 34, and the current i _D2 is a current flowing through the second switching unit 56.
The current i _P is a current flowing through the primary winding 21A. Current i _A
Is a current flowing through the auxiliary winding 21D of the transformer 21,
The current i _L is a current flowing through the inductance element 16.

At time T ₁ , the first switching element 3 is turned on by the drive pulse signal v _G1 from the control circuit 41,
Voltage V _C is applied to primary winding 21A of transformer 21. At this time, a voltage V _C / n is generated in the first secondary winding 21B of the transformer 21, and the rectifier diode 14 is turned on. A voltage (V _C / n−V) is applied to the inductance element 16.
_OUT ) is applied, and the current i _L flowing through the inductance element 16 increases linearly. Primary winding 2 of transformer 21
The current i _P of 1 A is equal to the exciting current of the transformer 21 and the first 2
Since the current is the sum of the current flowing through the secondary winding 21B and the primary-side converted current, the current increases linearly, and the excitation energy is accumulated in the transformer 21 and the inductance element 16. At this time, based on the output of the control circuit 41, the second and third switching elements 5 and 10 are off and the fourth switching element 12 is on, but the second diode 8 and the third
Since the diode 11 is reverse-biased and off, there is no effect on the circuit operation.

At time T ₂ , when the drive pulse signal v _G1 of the control circuit 41 disappears and the first switching element 3 is turned off, the current i flowing through the primary winding 21 A of the transformer 21
_P tends to flow continuously under the influence of the leakage inductance of the transformer. Therefore, the current i _P is supplied to the first switching unit 34 and the second switching unit 56.
And a parasitic capacitor equivalently connected in parallel to the transformer 9. As a result the voltage v _D applied to the first switching unit 34 increases, the voltage applied to the primary winding 21A of the transformer 21 is reduced. At the same time, the voltage induced in the auxiliary winding 21D decreases. When this voltage reaches zero, the third diode 11 is turned on by the voltage applied through the fourth switching element 12 that is on, and the bidirectional switching unit 25 is turned on.

At time T ₃ , the third switching element 10 is turned on by the drive pulse signal v _G3 of the control circuit 41.
There is no change in operation whether the on-current flows through the third diode 11 or the third switching element 10. The excitation energy stored in the transformer 21 is consumed by the charging and discharging of the parasitic capacitor and once decreased, but when the third diode 11 or the third switching element 10 is turned on, both the auxiliary windings 21D of the transformer 21 are connected. The excitation energy stored in the leakage inductance and the excitation inductance of the transformer is short-circuited by the directional switching unit 25. The voltage induced in the first secondary winding 21B and the second secondary winding 21C of the transformer 21 is zero, and the voltage applied to the inductance element 16 is
V _OUT . The secondary current is divided and flows through the first secondary winding 21B and the second secondary winding 21C of the transformer 21 so as to keep the excitation energy continuous. Therefore, the first rectifier diode 14 and the second rectifier diode 15 are turned on.

When the fourth switching element 12 is turned off at time T ₄ and the bidirectional switching unit 25 is turned off, the first switching unit 34 and the second switching A parasitic capacitor equivalently connected in parallel to the unit 56 and the transformer 21 charges and discharges. Therefore the voltage v _D applied to the first switching unit 34 increases. When the voltage v _D reaches the input voltage V _IN , the second diode 6 turns on.

At time T ₅ , the second switching element 5 is turned on by the drive pulse signal v _G2 of the control circuit 41.
There is no change in operation whether the on-current i _D2 flows through the second diode 6 or the second switching element 5.

The second switching unit 56 is turned on.
Then, the voltage (V) is applied to the primary winding 21A of the transformer 21._C-V
_IN) Is applied, and the current of the primary winding 21A of the transformer 21 is
i_PDecreases sharply. Primary winding 21A of transformer 21
When sufficient reverse current is supplied to the first rectifying diode
14 turns off, and the voltage (V) is applied to the second secondary winding 21C._IN−
V_C) / N occurs. The inductance element 16
Pressure [(V_IN-V_C) / NV_{OU T}Is applied and the inductor
Current i flowing through the sensing element 16_LIncreases linearly. G
Current i of primary winding 21A of lance 21_PIs a transformer 21
Of the exciting current and the primary current of the current flowing through the secondary winding 21B.
It decreases linearly to be the sum with the calculated current. Trance
21 and the inductance element 16 have excitation energy.
Stored. At this time, the output of the control circuit 41
Switching element 3 is off, third switching element 1
0 is on, the fourth switching element 12 is off,
However, the first diode 6 and the fourth diode 13
Since it is reverse biased and off, there is no effect on the circuit operation.

When the drive pulse signal v _G2 of the control circuit 41 is extinguished at time T ₆ and the second switching element 5 is turned off, the current i _{P of the} primary winding 21 A is continuously affected by the leakage inductance of the transformer 21. And try to flow. Therefore, the current i _P charges / discharges the first switching unit 34, the second switching unit 56, and the parasitic capacitor equivalently connected in parallel to the transformer 21. As a result, the voltage v _D applied to the first switching unit 34
Falls, and the voltage applied to the primary winding 21A of the transformer 21 decreases. At the same time, the voltage induced in the auxiliary winding 21D decreases. When this voltage reaches zero, the fourth diode 13 is turned on by the voltage applied through the third switching element 10 that is on, and the bidirectional switching unit 25 is turned on.

At time T ₇ , the fourth switching element 12 is turned on by the drive pulse signal v _G4 of the control circuit 41. There is no change in the operation whether the ON current flows through the fourth diode 13 or the fourth switching element 12. At this time,
The negative excitation energy stored in the transformer 21 is consumed by charging and discharging the parasitic capacitor. Therefore, current i _{P of} primary winding 21A temporarily increases. When the fourth diode 13 or the fourth switching element 12 is turned on, the auxiliary winding 21D of the transformer 21 is short-circuited, and the energy of the negative polarity stored in the leakage inductance and the excitation inductance of the transformer 21 is retained. As a result, the voltage induced in the first secondary winding 21B and the second secondary winding 21C of the transformer 21 becomes zero, and the voltage applied to the inductance element 16 becomes V _OUT . First secondary winding 21B and second secondary winding 21C of transformer 21
Since the secondary current is divided and flows so as to keep the excitation energy continuous, the first rectifier diode 14 and the second rectifier diode 15 are turned on.

When the third switching element 10 is turned off and the bidirectional switching unit 25 is turned off at time T ₈ , the first switching unit 34 and the second switching unit 56 and the parasitic capacitor connected equivalently parallel with the transformer 21 are charged and discharged, the voltage v _D applied to the first switching unit 34 decreases. When the voltage v _D reaches zero, to turn on the first diode 4.

[0097] The first switching element 3 by the driving pulse signal v _G1 of the control circuit 41 at time T ₉ are turned on. There is no change in the operation whether the on-current i _D1 flows through the first diode 4 or the first switching element 3. The current i _P flowing through the primary winding 21A of the transformer 21 temporarily increases due to charging and discharging of the parasitic capacitance. When the first switching unit 34 is turned on, the voltage V _C is applied to the primary winding 21A of the transformer 21, and the primary winding current i _P rapidly increases. When a sufficient current is supplied to the primary winding 21A of the transformer 21, the second rectifier diode 15 is turned off. Since the voltage V _C / n is generated in the first secondary winding 21B, the voltage [(V _IN −V _C ) / n is applied to the inductance element 16.
−V _OUT ] is applied. Thereafter, the above operation is repeated.

The ON periods of the first switching unit 34 and the second switching unit 56 are assumed to be P _ON having the same value. An off period from when the first switching unit 34 is turned off to when the second switching unit 56 is turned on and an off period from when the second switching unit 56 is turned off to when the first switching unit 34 is turned on. Let P _OFF be an equal value. Once you set the on and off periods as described above,
Equation (5) holds according to the reset condition of the transformer 21.

(V _IN −V _C ) × P _ON = V _C × P _ON (5)

From the reset condition of the inductance element 16, the periods T _{2 to} T ₃ , T _{4 to} T ₅ , T _{6 to} T ₇ , and T _{8 to} T ₉ are short.

[(V _IN −V _C ) / n−V _OUT ] × P _ON = V _OUT × P _OFF (6)

Therefore, from equation (6), V _C and V _OUT are expressed as follows.

V _C = V _IN / 2

V _OUT = δV _IN / 2n

Here, δ is expressed as follows.

Δ = P _ON / (P _ON + P _OFF )

Therefore, the _ON / OFF ratio P _ON / P of the first switching element 3 and the second switching element 5
_The DC output voltage V _OUT can be controlled by adjusting _OFF . Taking the period _{T 2 ~T 3, T 4 ~T} 5, T 6 ~T 7, T 8 ~T 9 into account, the direct current output voltage V _OUT decreases. By increasing δ by that amount, a predetermined DC output voltage V _OUT can be obtained.

In the second embodiment, immediately before the first to fourth switching elements 3, 5, 10 and 12 are turned on, the charges charged in the parasitic capacitance of each switching element and the distributed capacitance of the transformer 21 are discharged. Turns on after discharge. Therefore, generation of surge current due to short circuit can be reduced,
Generation of noise can be suppressed. Efficiency is improved because power loss due to surge current is reduced. Also, the surge voltage at the time of turning off the first and second switching elements 3 and 5 due to the leakage inductance of the transformer 21 turns on the third and fourth diodes 11 and 12 in the bidirectional switching unit 25. It is effectively absorbed by the first and second capacitors 7 and 8 and the DC power supply 1. Therefore, no surge voltage is generated.
In addition, the third and fourth switches in the bidirectional switching unit 25
The surge voltage generated when the switching elements 10 and 12 are turned off is also absorbed by the first and second capacitors 7 and 8 and the DC power supply 1 by turning on the first and second diodes 4 and 6. Therefore, no surge voltage is generated.

The energy for charging and discharging the parasitic capacitance depends on the energy stored in the exciting inductance and the leakage inductance of the transformer 21. Transformer 1
By connecting an inductance element in series with the secondary winding 21A or the secondary winding 21B, the leakage inductance can be increased intentionally. The discharge energy of the parasitic capacitance can be increased by increasing the leakage inductance. Further, by reducing the exciting inductance value of the transformer 21 and reversely exciting the transformer 21, it is possible to assist the discharge of the parasitic capacitance of the first and second switching units 34 and 56 and the distributed capacitance of the transformer 21. Another example of the second embodiment is shown in FIGS. In the configuration of FIG. 5 of the present embodiment, the input voltage V _IN is divided by connecting the first capacitor 7 and the second capacitor 8 in series. When only the first capacitor 7 is connected between the input terminal 2A and the primary winding 21A as shown in FIG. 6, or when only the second capacitor 8 is connected to the input terminal 2B as shown in FIG.
The switching power supply of the present invention operates normally even when it is connected between the power supply and the primary winding 21A.

In the configuration shown in FIG. 5, the connection point 10A between the third switching element 10 and the fourth switching element 12 of the bidirectional switching unit 25 is connected to the negative terminal 2B (circuit ground) of the DC power supply 1. . Therefore, the degree of freedom in setting the voltage levels of the drive pulse signals v _G3 and v _G4 of the control circuit 41 is increased, and the configuration of the control circuit 41 is simplified. In the configuration of FIG. 5, in addition to a parasitic capacitor equivalently connected in parallel to the first and second switching units 34 and 56, the bidirectional switching unit 25, and the transformer 21, an external capacitor may be added. , Does not affect basic operation. When such a capacitor is added, the rising slope of the voltage applied when each switching element is turned off is reduced, so that there is an effect that the power loss generated at the time of switching can be further reduced. First and second switching units 34, 5
The voltage applied to 6 does not decrease. The voltage applied to the first and second switching units 34 and 56 is the input voltage V _IN . The characteristic that the transformer 21 is not DC-excited is maintained, and a switching power supply device with high efficiency, low noise, and high switching frequency can be realized. << 3rd Example >>

Hereinafter, a third embodiment of the present invention will be described with reference to FIGS. 9 and 10. FIG. 9 is a circuit diagram of a switching power supply device 31B according to the third embodiment. In FIG. 9, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Input terminal 2 of switching power supply 31B
A and 2B are connected to the DC power supply 1. First and second
Of the switching units 34 and 56 and the bidirectional switching unit 25 are the same as those in FIG. The transformer 27 has a first primary winding 27A, a second primary winding 27B, a first secondary winding 27C, and a second secondary winding 27D. A first primary winding 27A, a second primary winding 27B, a first secondary winding 27C, and a second secondary winding 2
The turns ratio of 7D is n: n: 1: 1. A series circuit of the first primary winding 27A and the first switching unit 34 is connected to the input terminals 2A and 2B. The second one
A series circuit of the secondary winding 27B and the second switching unit 56 is also connected to the input terminals 2A and 2B. A first primary winding 27A and a second primary winding 27B of the transformer 27;
Are tightly coupled so that current commutation can be performed smoothly.

The bidirectional switching unit 25 includes a first
Is connected between a connection point 34A between the primary winding 27A and the first switching unit 34 and a connection point 56A between the second primary winding 27B and the second switching unit 56. The anode of the first rectifier diode 14 is connected to one end of a first secondary winding 27C of the transformer 27. The second rectifier diode 15 has an anode connected to one end of a second secondary winding 27D of the transformer 27. The cathodes of the first rectifier diode 14 and the second rectifier diode 15 are commonly connected. The inductance element 16 and the smoothing capacitor 17 are connected in series,
An end of the inductance element 16 is connected to a connection point between the cathodes of the first rectifier diode 14 and the second rectifier diode 15. The end of the smoothing capacitor 17 is connected to a connection point 2 between the first secondary winding 27C and the second secondary winding 27D.
7E. Voltages generated in the first and second secondary windings 27C and 27D of the transformer 27 are rectified by the first and second rectifier diodes 14 and 15, and smoothed by the inductance element 16 and the smoothing capacitor 17, and output terminals. 18A and 18B. A load 19 is connected to the output terminals 18A and 18B.

The control circuit 42 controls the output terminals 18A and 1
Detecting the output voltage V _OUT of the output voltage V _OUT between 8B so is constant, the first switching element 3, the second switching element 5, the third switching element 10 and fourth
A control signal for controlling the on / off ratio of the switching element 12 is generated.

The operation of the switching power supply configured as described above will be described below with reference to the waveform diagram of the operation shown in FIG. In FIG. 10, the drive pulse signal v _G1 is supplied from the control circuit 42 to the first switching element 3.
Is applied to The drive pulse signal v _G2 is applied from the control circuit 42 to the second switching element 5. The drive pulse signal v _G3 is supplied from the control circuit 42 to the third switching element 10.
Is applied to The drive pulse signal v _G4 is applied from the control circuit 42 to the fourth switching element 12. The current i _P1 flows through the first primary winding 27A of the transformer 27. Current i
_P2 flows through the second primary winding 27B of the transformer 27. The current i _D1 flows through the first switching unit 34. The current i _D2 flows through the second switching unit 56. The voltage v _D1 is applied to the first switching unit 34. The voltage v _D2 is applied to the second switching unit 56. The voltage v _S is applied between the cathodes of the rectifier diodes 14 and 15 and the connection point 27E. The current i _L indicates a current flowing through the inductance element 16.

At time T ₁ , when the drive pulse signal v _G1 is input from the control circuit 42 and the first switching element 3 is turned on, the input voltage V _IN is applied to the first primary winding 27A of the transformer 27. Is done. The voltage V _IN / n is generated in the first secondary winding 27C of the transformer 27, and the rectifier diode 14 is turned on. Voltage (V _IN / n−V _OUT ) is applied to the inductance element 16. Is applied, and the current i _L flowing through the inductance element 16 increases linearly. Transformer 2
7, the current i _P1 of the first primary winding 27A is
And the current flowing through the first secondary winding 27C.
It increases linearly to be the sum with the secondary conversion current. Exciting energy is stored in the transformer 27 and the inductance element 16. At this time, the second switching element 5 is turned off, the third switching element 10 is turned on, and the fourth switching element 12 is turned off under the control of the control circuit 42, but the second diode 6 and the fourth diode 13 are turned off.
Is reverse-biased and off, so there is no effect on circuit operation.

At time T ₂ , when the drive pulse signal v _G1 of the control circuit disappears and the first switching element 3 is turned off, the current i _D1 flowing through the first switching element 3
Tends to flow continuously due to the influence of the leakage inductance of the transformer 27, so that the first switching unit 3
4. Second switching unit 56 and transformer 27
To charge and discharge a parasitic capacitor equivalently connected in parallel to. As a result, the voltage v _D1 applied to the first switching unit 34 increases, and the second switching unit 5
6 The applied voltage v _D2 decreases. When the voltage v _D1 increases and reaches the voltage V _IN , the first primary winding 27 of the transformer 27
A and the voltage applied to the second primary winding 27B become zero. As a result, a voltage is applied through the third switching element 10 that is on, the fourth diode 13 turns on, and the bidirectional switching unit 25 turns on. Fourth diode 13 at time T ₃ during the on, the fourth switching element 12 is turned ON by the driving pulse signal v _G4 of the control circuit 42. There is no change in the operation whether the ON current flows through the fourth diode 13 or the fourth switching element 12.

When the bidirectional switching unit 25 is turned on, the series circuit of the first primary winding 27A and the second primary winding 27B of the transformer 27 is short-circuited and stored in the leakage inductance and the excitation inductance of the transformer 27. The energy is retained. When the bidirectional switching unit 25 is turned on, the first primary winding 27A and the second
Since the secondary winding 27B is connected in series, the number of turns of the primary winding is equivalently doubled. As a result, the current i _P1 of the first primary winding 27A of the transformer 27 is halved.

The first operation of the transformer 27 is performed by the above operation.
The voltage induced in the secondary winding 27C and the second secondary winding 27D becomes zero, and the voltage applied to the inductance element 16 becomes V _OUT . A secondary current is divided and flows through the first secondary winding 27C and the second secondary winding 27D of the transformer 27 so as to keep the excitation energy continuous. Therefore, the first rectifier diode 14 and the second rectifier diode 15 are turned on.

When the third switching element 10 is turned off at time T ₄ and the bidirectional switching unit 25 is turned off, the first switching unit 34 and the second switching unit Parasitic capacitors equivalently connected in parallel to 56 and the transformer 27 are charged and discharged. The voltage v _D1 applied to the first switching unit 34 increases, and the voltage v _D2 applied to the second switching unit 56 decreases. When the voltage v _D2 decreases and reaches zero, the second diode 6 turns on. During the ON of the second diode 6, the driving pulse signal v _G2 of the control circuit 42 at time T ₅
As a result, the second switching element 5 is turned on. There is no change in operation whether the on-current i _D2 flows through the second diode 6 or the second switching element 5.

When the second switching unit 56 is turned on
Then, the input voltage is applied to the second primary winding 27B of the transformer 27.
Pressure V_INIs applied and the current flows through the second primary winding 27B.
i_P2Increases rapidly. Second secondary winding of transformer 27
When sufficient current is supplied to line 27D, the first rectifying die
The arm 14 turns off and the voltage V is applied to the second secondary winding 27D._IN/
n occurs. Therefore, a voltage is applied to the inductance element 16.
(V_IN/ NV_OUT) Is applied and the inductance element
Current i flowing through 16_LIncreases linearly. Transformer 2
7, the current i of the second primary winding 27B._P2Is the transformer 27
Primary side of exciting current and current flowing through first secondary winding 27C
It increases linearly to be the sum of the converted current. The result
To the transformer 27 and the inductance element 16
Energy is accumulated. At this time, the control circuit 42
And the first switching element 3 is off and the third switch
The switching element 10 is off, and the fourth switching element 12 is off.
The first diode 4 and the third diode 1
Since 1 is reverse-biased and off, circuit operation is not affected.
There is no.

When the drive pulse signal v _G2 of the control circuit disappears at time T ₆ and the second switching element 5 is turned off, the current i _D2 flowing through the second switching element 5 is reduced by the leakage inductance of the transformer. The first switching unit 34 and the second switching unit 34
And the parasitic capacitor equivalently connected in parallel to the switching unit 56 and the transformer 27. Therefore, the voltage v applied to the second switching unit 56
_D2 is increased, the voltage v _D1 applied to the first switching unit 34 decreases. When the voltage v _D2 reaches the input voltage V _IN , the voltage applied to the first primary winding 27A and the second primary winding 27B of the transformer 27 becomes zero. The third diode 11 is turned on by the voltage applied through the fourth switching element 10 that is turned on, and the bidirectional switching unit 25 is turned on. The third diode 11 is in the ON period of the third switching element 10 is turned on by the driving pulse signal v _G3 of the control circuit 42 at T _7. There is no change in operation whether the on-current flows through the third diode 11 or the fourth switching element 12.

When the bidirectional switching unit 25 is turned on, a series circuit of the first primary winding 27A and the second primary winding 27B of the transformer 27 is formed and stored in the leakage inductance and the excitation inductance of the transformer 27. The energy is retained. When the bidirectional switching unit 25 is turned on, the first primary winding 27A and the second
Since the secondary winding 27B is connected in series, the number of turns of the primary winding is equivalently doubled. As a result, the first primary winding 27A
Of the current i _P1 is halved.

The voltage induced in the first secondary winding 27C and the second secondary winding 27D of the transformer 27 by the above operation becomes zero, and the voltage applied to the inductance element 16 becomes V _OUT. . The secondary current is divided and flows through the first secondary winding 27C and the second secondary winding 27D of the transformer 27 so as to keep the excitation energy continuous. Therefore, the first rectifier diode 14 and the second rectifier diode 15
Turns on.

When the fourth switching element 12 is turned off at time T ₈ and the bidirectional switching unit 25 is turned off, the first switching unit 34 and the second switching unit The parasitic capacitor equivalently connected in parallel to the unit 56 and the transformer 27 is charged and discharged. When the voltage v _D1 applied to the first switching element 3 decreases and reaches zero, the first diode 4 turns on. While the first diode 4 is on, the first switching element 3 is turned on by the drive pulse signal v _G1 of the control circuit 42. Even if the on-current i _D1 flows through the first diode 4, the first
The operation does not change even if the current flows through the switching element 3 of FIG.

The current i _P1 flowing through the first primary winding 27A of the transformer 27 once decreases due to the charging and discharging of the parasitic capacitance, but when the first switching unit 34 is turned on, the current i _P1 of the transformer 27 The input voltage V _IN is applied to the first primary winding 27A, and the current i _P1 of the first primary winding 27A sharply increases. When a sufficient current is supplied to the first secondary winding 27C of the transformer 27, the second rectifier diode 15C
Is turned off, and a voltage V _IN / n is generated in the first secondary winding 27C. As a result, the voltage (V
_IN / n-V _OUT ) Is applied. Thereafter, this operation is repeated.

The ON periods of the first switching unit 34 and the second switching unit 56 are assumed to be P _ON having the same value. An off period from when the first switching unit 34 is turned off to when the second switching unit 56 is turned on, and an off period from when the second switching unit 56 is turned off to when the first switching unit 34 is turned on. Is equal to P _OFF . From the reset condition of the inductor 16, the period _{T 2 ~T 3, T 4 ~T} 5, T 6 ~T 7 and T ₈ through T ₉
Is short and, if ignored, equation (8) holds.

2 (V _IN / n−V _OUT ) × P _ON = 2V _OUT × P _OFF (8)

Therefore, V _OUT is expressed as follows from equation (8).

V _OUT = δV _IN / n

Here, δ is represented as follows.

Δ = P _ON / (P _ON + P _OFF )

Therefore, the on / off ratio (P _ON / P 1) of the first switching element 3 and the second switching element 5
_OFF ) can be adjusted to control the output voltage V _OUT . Period T ₂
When _{~T 3, T 4 ~T 5,} T 6 ~T 7 and T ₈ through T ₉ to take into account, the output a voltage V _OUT decreases, to obtain a predetermined voltage by increasing the amount δ Can be.

In this embodiment, immediately before the first to fourth switching elements 3, 5, 10 and 12 are turned on, the charges of the parasitic capacitances of these switching elements 3, 5, 10 and 12 and the distributed capacitance of the transformer 27 are removed. Discharge. Therefore, generation of spike-like short-circuit current can be reduced, and efficiency can be improved and generation of noise can be suppressed. In addition, the first and the second due to the leakage inductance of the transformer 27
When the third diode 11 and the fourth diode 13 in the bidirectional switching unit 25 are turned on, the spike voltage when the switching elements 3 and 5 are turned off is effectively absorbed through the transformer 27. Therefore, generation of a spike voltage is reduced. In addition, a surge voltage generated when the third switching element 10 and the fourth switching element 12 in the bidirectional switching unit 25 are turned off is also transmitted through the transformer 27 by turning on the first diode 4 and the second diode 6. It is absorbed by the DC power supply 1 and no surge voltage is generated.

The first and second switching units 34 immediately before the first switching unit 34 is turned on.
And the discharge energy of the parasitic capacitance of 56 and the distributed capacitance of the transformer 27 depend on the energy stored in the exciting inductance and the leakage inductance of the transformer 27. An inductance element may be connected in series with the first secondary winding 27C and the second secondary winding 27D of the transformer 27, and the discharge energy may be further increased. Further, by reducing the inductance value of the transformer 27 and reversely exciting the transformer 27, it is possible to assist discharge of the parasitic capacitance of the first and second switching units 34 and 56 and the distributed capacitance of the transformer 27.

Even if external capacitors are added in addition to the parasitic capacitors equivalently connected in parallel to the first switching unit 34, the second switching unit 56, the bidirectional switching unit 25 and the transformer 27,
Has no effect on basic operation. Since the slope of the voltage applied when the switching units 34 and 56 are turned off is reduced by the additional capacitor, there is an effect that the loss generated at the time of switching can be further reduced. as a result,
A high-efficiency, low-noise, high-frequency switching power supply can be realized. << 4th Example >>

Hereinafter, a fourth embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. FIG. 11 is a circuit diagram of a switching power supply according to the fourth embodiment. 11, the same components as those in FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted. The transformer 39 includes a first primary winding 39A and a second primary winding 39A.
It has a secondary winding 39B, a first secondary winding 39C, a second secondary winding 39D, and an auxiliary winding 39E. The turns ratio of the first primary winding 39A, the second primary winding 39B, the first secondary winding 39C, the second secondary winding 39D, and the auxiliary winding 39E is as follows. n: n: 1: 1: n. The first primary winding 39A and the first switching unit 3
4 is connected between input terminals 2A and 2B. A series circuit of the second primary winding 39B and the second switching unit 56 is also connected between the input terminals 2A and 2B. The first switching element 3 and the second switching element 5 alternately turn on and off. The first primary winding 39A, the second primary winding 39B, and the auxiliary winding 39E of the transformer 39 are tightly coupled so that current commutation can be performed smoothly.

The anode of the first rectifier diode 14 is connected to one end of the first secondary winding 39C of the transformer 39. The anode of the second rectifier diode 15 is connected to one end of a second secondary winding 39D of the transformer 39. The cathodes of the first rectifier diode 14 and the second rectifier diode 15 are commonly connected. An inductance element 16 and a smoothing capacitor 17 are connected in series, and an end of the inductance element 16 is connected to the first rectifier diode 14.
And the connection point 2 of the cathode of the second rectifier diode 15
4A. An end of the smoothing capacitor 17 is connected to a connection point 39F between the first secondary winding 39C and the second secondary winding 39D.
Connected to. Secondary winding 39C, 39D of transformer 39
Generated at the output terminals 18A, 18A are rectified and smoothed.
B. A load 19 is connected between the output terminals 18A and 18B.

The bidirectional switching unit 25 has the same configuration as that shown in FIG. The bidirectional switch unit 25 is connected to both ends of the auxiliary winding 39E of the transformer 39. Third and fourth switching elements 10 and 12
Is connected to the negative terminal 2B of the DC power supply 1. The control circuit 43 detects the voltage between the output terminals 18A and 18B, and controls the first switching element 3, the second switching element 5, and the third switching element 10 so that the output voltage V _OUT becomes constant. And the fourth
A control signal for controlling the switching element 12 is generated.

The operation of the switching power supply configured as described above will be described below with reference to the waveform diagram of the operation shown in FIG.

In FIG. 12, the drive pulse signal v _G1 is applied from the control circuit 43 to the first switching element 3.
The drive pulse signal v _G2 is applied from the control circuit 43 to the second switching element 5. The drive pulse signal v _G3 is applied from the control circuit 43 to the third switching element 10.
The drive pulse signal v _G4 is applied from the control circuit 43 to the fourth switching element 12. The current i ₁ is supplied to the first switching unit 34 and the first primary winding 3 of the transformer 39.
Flow through 9A. The current i ₂ flows through the second switching unit 56 and the second primary winding 39B of the transformer 39. The current i ₃ flows through the auxiliary winding 39E of the transformer 39. The voltage v _D1 is applied to the first switching unit 34. The voltage v _D2 is applied to the second switching unit 56.

At time T ₁ , when the first switching element 3 is turned on by the input of the driving pulse signal v _G1 from the control circuit 43, the voltage V _IN is applied to the first primary winding 39A of the transformer 39. . At this time, a voltage V _IN / n is generated in the first secondary winding 39C of the transformer 39, and the rectifier diode 14 is turned on. The inductance element 16 has a voltage (V _IN / n-V _OUT ) Is applied, and the current i _L flowing through the inductance element 16 increases linearly. Transformer 3
Current i ₁ of the first primary winding 39A of the 9, trans 39
Of the current flowing through the first secondary winding 39C and the primary-side converted current of the current flowing through the first secondary winding 39C. As a result, the excitation energy is stored in the transformer 39 and the inductance element 16. At this time, the second switching element 5 is turned off, the third switching element 10 is turned on, and the fourth switching element 12 is turned off by the control circuit 43, but the second diode 6 and the fourth diode 1 are turned off.
Since 3 is reverse-biased and off, there is no effect on circuit operation.

At time T ₂ , when the drive pulse signal v _G1 of the control circuit 43 disappears and the first switching element 3 turns off, the current i _P1 flowing through the first primary winding 39A of the transformer 39 becomes , And becomes continuous due to the influence of the leakage inductance of the transformer 39. This current i _P1 charges and discharges a parasitic capacitor equivalently connected in parallel to the first switching unit 34, the second switching unit 56, and the transformer 39. As a result, the voltage v _D1 applied to the first switching unit 34 increases, and the voltage v _D2 applied to the second switching unit 56 decreases. At the same time, when the voltage induced in the auxiliary winding 39E also decreases and reaches zero, a voltage is applied through the third switching element 10 that is on, the fourth diode 13 turns on, and the bidirectional switching unit 45 turns on. .

At the time T while the fourth diode 13 is on.
_{In the third} , the fourth by the drive pulse signal v _G4 from the control circuit 43
Is turned on. The operation does not change whether the on-current i ₃ flows through the fourth diode 13 or the fourth switching element 12. When the bidirectional switching unit 45 is turned on, the auxiliary winding 39E of the transformer 39 is short-circuited, and the energy stored in the leakage inductance and the excitation inductance of the transformer 39 is maintained.

By the above operation, the first of the transformer 39
The voltage induced in the secondary winding 39C and the second secondary winding 39D becomes zero, and the voltage applied to the inductance element 16 becomes V _OUT . The secondary current is divided and flows through the first secondary winding 39C and the second secondary winding 39D of the transformer 39 so as to keep the excitation energy continuous. The second rectifier diode 15 is turned on.

Time T_FourAnd the third switching element 10
Turns off and bidirectional switching unit 45 turns off
The energy stored in the transformer 39
Thus, the first switching unit 34 and the second switch
Equivalent parallel connection to the switching unit 56 and the transformer 39
The connected parasitic capacitor is charged and discharged, and the first switch
Voltage v applied to the switching unit 34_D1Increases. same
Voltage applied to the second switching unit 56
v_D2Decreases. Voltage v_D2Reaches zero, the second
Ide 6 turns on. The second diode 6
Time T _FiveAnd the driving pulse signal from the control circuit 43
v_G2As a result, the second switching element 5 is turned on. Oh
Current i_TwoFlows through the second diode 6, the second switch
There is no change in operation even when flowing through the switching element 5.

When the second switching unit 56 is turned on, the voltage V is applied to the second primary winding 39B of the transformer 39.
_IN is applied, the current i ₂ of the second primary winding 39B rapidly increases. When a sufficient current is supplied to the second primary winding 39B of the transformer 39, the first rectifier diode 14 is turned off, and a voltage V _IN / n is generated in the second secondary winding 39D. Therefore, the voltage (V _IN / n) is applied to the inductance element 16.
−V _OUT ) Is applied, and the current i _L flowing through the inductance element 16 increases linearly. Current i ₂ of the second primary winding 39B of the transformer 39 and exciting current of the transformer 39, linearly to the sum of the primary-side conversion current of the current flowing through the second secondary winding 39D To increase. Therefore, the excitation energy is stored in the transformer 39 and the inductance element 16. At this time, the first switching element 3 is turned off, the third switching element 10 is turned off, and the fourth switching element 12 is turned on by the control circuit 43, but the first diode 4 and the third diode 11 are reverse-biased. Since it is turned off, there is no effect on the circuit operation.

At time T ₆ , when the drive pulse signal v _G2 of the control circuit 43 disappears and the second switching element 5 is turned off, the current i ₁ of the first primary winding 39 A becomes the leakage inductance of the transformer 39. Because of the continuous flow due to the influence, the parasitic capacitor equivalently connected in parallel to the first switching unit 34, the second switching unit 56, and the transformer 39 is charged and discharged. As a result, the voltage v _D2 applied to the second switching unit 56 increases. At the same time, the voltage v _D1 applied to the first switching unit 34 decreases, and the first primary winding 3 of the transformer 39
The voltage applied to 9A decreases. When the voltage induced in the auxiliary winding 39E also decreases and reaches zero, the fourth ON state is turned on.
Is applied through the switching element 12, and the third diode 11 is turned on, and the bidirectional switching unit 45 is turned on. The third diode 11 is the driving pulse signal v from the control circuit 43 at time T ₇ is ON
The third switching element 10 is turned on by _G3 . There is no change in operation whether the on-current flows through the third diode 11 or the third switching element 10. When the bidirectional switching unit 25 is turned on, the auxiliary winding 39E of the transformer 39 is short-circuited, and the energy stored in the leakage inductance and the exciting inductance of the transformer 39 is maintained.

The voltage induced in the first secondary winding 39C and the second secondary winding 39D of the transformer 39 becomes zero, and the voltage applied to the inductance element 16 becomes V _OUT . The first secondary winding 39C and the second secondary winding 39D of the transformer 39 are so controlled as to keep the excitation energy continuous.
Since the secondary current is divided and flows, the first rectifier diode 14 and the second rectifier diode 15 are turned on.

When the fourth switching element 12 is turned off at time T ₈ and the bidirectional switching unit 25 is turned off, the first switching unit 34 and the second switching unit 56 are turned on by the energy held in the transformer 39. And a parasitic capacitor equivalently connected in parallel to the transformer 39 is charged and discharged. The voltage v _D1 applied to the first switching unit 34 decreases. When it reaches zero, the first diode 4 turns on. The control circuit 43 at time T ₉ first diode 4 is on
The first switching element 3 by the drive pulse signal v _G1 of
Turn on. There is no change in operation whether the on-current flows through the first diode 4 or the first switching element 3.

The current i ₁ flowing through the first primary winding 39A of the transformer 39 decreases once due to the charging and discharging of the parasitic capacitance. However, when the first switching unit 34 is turned on, the current i ₁ of the transformer 39 is reduced. The voltage V _IN is applied to the primary winding 39A of No. 1.
Is applied, and the current i _{1 of the} primary winding 39A sharply increases. When a sufficient current is supplied to the first primary winding 39A of the transformer 39, the second rectifier diode 15 is turned off, and a voltage V _IN / n is generated in the first secondary winding 39C. Therefore, the voltage (V _IN / n−V _OUT ) is applied to the inductance element 16.
Is applied. Thereafter, this operation is repeated. The ON periods of the first switching unit 34 and the second switching unit 56 are set to P _ON having the same value. An off period from when the first switching unit 34 is turned off to when the second switching unit 56 is turned on, and an off period from when the second switching unit 56 is turned off to when the first switching unit 34 is turned on. Is equal to P _OFF . From the reset condition of the inductor 16, the period T ₂ ~T _3, T ₄
〜T ₅ , T ₆ ＴT _7, and T ₈ ＴT ₉ are short and, therefore, disregarding Expression (9).

[V _IN / n−V _OUT ] × P _ON = V _OUT × P _OFF (9)

Therefore, from equation (9), V _OUT is expressed as follows.

V _OUT = δV _IN / n

Here, δ is expressed as follows.

Δ = P _ON / (P _ON + P _OFF )

Therefore, the on / off ratio (P _ON / P 1) of the first switching element 3 and the second switching element 5
_OFF ), the output voltage V _OUT can be controlled. Considering the period _{T 2 ~T 3, T 4 ~T} 5, T 6 ~T 7, T 8 ~T 9, the output voltage V _OUT decreases. By increasing δ by that amount, a predetermined voltage can be obtained. In this configuration, the first to fourth switching elements 3, 5, 10
Immediately before the turn-on of the switching elements 3, 12, 10 and 12, the parasitic capacitances of the switching elements 3, 5, 10 and 12 and the distributed capacitance of the transformer 39 are discharged. Therefore, generation of surge current due to short-circuit can be reduced, efficiency can be improved, and generation of noise can be suppressed.

The surge voltage at the time of turning off the first and second switching elements 3 and 5 due to the leakage inductance of the transformer 39 is reduced by the third diode 11 and the fourth diode 13 in the bidirectional switching unit 25. By being turned on, it is effectively absorbed through the transformer 39. Therefore, generation of surge voltage is small. The surge voltage generated when the third switching element 10 and the fourth switching element 12 in the bidirectional switching unit 25 are turned off is also reduced by the first diode 4.
Then, the second diode 6 is turned on, and is absorbed by the input DC power supply 1 via the transformer 39. Therefore, no surge voltage is generated.

The charge / discharge energy of the parasitic capacitance depends on the energy stored in the exciting inductance and the leakage inductance of the transformer 39. An inductance element can be connected in series with the first secondary winding 39C and the second secondary winding 39D of the transformer 39, and the discharge energy can be further increased. Further, by reducing the inductance value of the transformer 39 and reversely exciting the transformer, the discharge of the parasitic capacitance of the first and second switching units 34 and 56 and the distributed capacitance of the transformer 39 can be assisted.

In the configuration of FIG. 11, the third switching element 10 and the fourth switching element
Is connected to the negative terminal 2B of the DC power supply 1. Therefore, the degree of freedom in setting the levels of the drive pulse signals _VG3 and _VG4 output from the control circuit 43 is increased. The connection point 45A may be connected to the positive terminal 2A of the DC power supply 1. Further, a desired voltage obtained by dividing the voltage V _IN may be applied to the connection point 45A. Thus, the connection point 45
Since the voltage setting of A has a degree of freedom, the design of the control circuit 43 becomes easy.

In the configuration shown in FIG. 11, a capacitor is externally connected in addition to the parasitic capacitors equivalently connected in parallel to the first switching unit 34, the second switching unit 56, the bidirectional switching unit 25, and the transformer 39. The addition does not affect the basic operation. The addition of the capacitor reduces the gradient of the change in the voltage applied when the first to fourth switching elements 3, 5, 10, and 12 are turned off, and thus has the effect of further reducing the loss that occurs during switching. As a result, a switching power supply device with high efficiency, low noise, and high frequency can be realized.

[0161]

According to the present invention, by turning on the bidirectional switching unit, from the turn-off of the first switching unit to immediately before the turn-on of the second switching unit, and from the turn-off of the second switching unit. The energy stored in the transformer can be retained until the first switching unit is turned on. Immediately before the first and second switching units are turned on, the charge of the parasitic capacitor equivalently connected in parallel to both switching units is discharged and then turned on, so that no surge current occurs.
In addition, the generation of a surge voltage due to the influence of the leakage inductance of the transformer when the first and second switching units are turned off is small due to the clamping action of the bidirectional switching unit. Further, there is no surge voltage generated when the bidirectional switching unit is turned on and when the bidirectional switching unit is turned off. Therefore, a small-sized switching power supply device that performs switching at high frequency with high efficiency and low noise can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a switching power supply according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of another example of the switching power supply device according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram of a switching power supply according to still another example of the first embodiment of the present invention.

FIG. 4 is a waveform chart showing the operation of the first embodiment.

FIG. 5 is a circuit diagram of a switching power supply according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram of a switching power supply according to another example of the second embodiment of the present invention.

FIG. 7 is a circuit diagram of a switching power supply according to still another example of the second embodiment of the present invention.

FIG. 8 is a waveform chart showing the operation of the second embodiment.

FIG. 9 is a circuit diagram of a switching power supply according to a third embodiment of the present invention.

FIG. 10 is a waveform chart showing the operation of the third embodiment.

FIG. 11 is a circuit diagram of a switching power supply according to a fourth embodiment of the present invention.

FIG. 12 is a waveform chart showing the operation of the fourth embodiment.

FIG. 13 is a circuit diagram of a first conventional switching power supply device.

FIG. 14 is a waveform chart showing the operation of the first conventional switching power supply device.

FIG. 15 is a circuit diagram of a second conventional switching power supply device.

FIG. 16 is a waveform chart showing the operation of the second conventional example.

[Explanation of symbols]

Reference Signs List 1 DC power supply 2A, 2B input terminal 3 first switching element 4 first diode 5 second switching element 6 second diode 9, 21, 27, 39 transformer 9A, 21A, 27A, 27B, 39A, 39B
Primary winding 9B, 9C, 21B, 21C, 27C, 27D, 39
C, 39D Secondary winding 7, 8 Capacitor 10 Third switching element 11 Third diode 12 Fourth switching element 13 Fourth diode 14 First rectifier diode 15 Second rectifier diode 16 Inductance element 17 Smoothing Capacitor 18A, 18B output terminal 19 Load 21D, 39E Auxiliary winding 25, 45 Bidirectional switching unit 34 First switching unit 40, 41, 42, 43 Control circuit 56 Second switching unit

Continuation of the front page (56) References JP-A-4-299066 (JP, A) JP-A-7-87740 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3 / 335 H02M 3/28

Claims (4)

(57) [Claims] 1. A series connection of first switching means and second switching means connected between terminals of a DC power supply and alternately turned on and off, a first capacitor connected between terminals of the DC power supply, and a A DC connection of two capacitors, comprising a primary winding and at least one secondary winding, wherein one end of the primary winding is connected to a connection point of the first and second capacitors; The other end of the next winding is connected to a connection point of a series connection of the first and second switching means,
A transformer for storing energy when the second switching means is on; a bidirectional switching means connected in parallel to a primary winding of the transformer; a rectifying and smoothing means connected to a secondary winding of the transformer; When the output of the rectifying / smoothing means is applied, and the first and second switching means are both off, the bidirectional switching means passes a predetermined period after the first or second switching means is turned off. Is turned on, the primary winding of the transformer is short-circuited, the current of the primary winding is made to flow continuously, the energy stored in the transformer is held, and the first or second switching is performed. The bidirectional switching means is turned off before the means is turned on, and the first and second switching means, the bidirectional switching means, and the Parasitic capacitors connected equivalently parallel with the scan so as to charge and discharge control means for controlling the said first and second switching means bidirectional switching means, the switching power supply apparatus having a. 2. A series connection of a first switching means and a second switching means connected between terminals of a DC power supply and alternately turning on and off alternately, a first capacitor connected between terminals of the DC power supply, A DC connection of a second capacitor, comprising a primary winding, an auxiliary winding and at least one secondary winding, one end of the primary winding being connected to a connection point of the first and second capacitors; A transformer for connecting the other end of the primary winding to a connection point of a series connection of the first and second switching means, and storing energy when the first and second switching means are on. Bidirectional switching means connected in parallel to the auxiliary winding of the transformer, rectifying / smoothing means connected to the secondary winding of the transformer, and the output of the rectifying / smoothing means is applied, and the first and second
During a period in which both of the switching means are off, the bidirectional switching means is turned on after a predetermined period after the first or second switching means is turned off to short-circuit the primary winding of the transformer. Holding the energy stored in the transformer by allowing the current of the primary winding to flow continuously, and turning off the bidirectional switching means before the first or second switching means is turned on. Controlling the first and second switching means and the bidirectional switching means such that the first and second switching means and a parasitic capacitor equivalently connected in parallel to the transformer are charged and discharged. A switching power supply having control means. 3. A DC power supply having a first primary winding and a second primary winding each having one end connected to one terminal thereof, and at least one secondary winding. A first transformer that is connected in series to the first primary winding and has an end connected to the other terminal of the DC power supply and that repeats on and off
A second switching means connected in series to the second primary winding and having an end connected to the other terminal of the DC power supply to alternately turn on and off with the first switching means. Bidirectional switching means connected between a connection point between the first primary winding and the first switching means and a connection point between the second primary winding and the second switching means Rectifying / smoothing means for rectifying / smoothing the current of the secondary winding, and the output of the rectifying / smoothing means is applied,
After turning on the bidirectional switching means for a predetermined period after the first or second switching means is turned off while both of the switching means are off, the stored energy of the transformer is maintained continuously. Holding the energy stored in the transformer, turning off the bidirectional switching means before turning on the first or second switching means, and equivalent to the first and second switching means and the transformer. And a control means for controlling the first and second switching means and the bidirectional switching means such that a parasitic capacitor connected in parallel is charged and discharged. And a first primary winding and a second primary winding each having one end connected to one terminal of the DC power supply, at least one secondary winding and an auxiliary winding. A transformer for storing energy, the first being connected in series to the first primary winding, and the other end being connected to the other terminal of the DC power supply to repeatedly turn on and off.
A second switching means connected in series to the second primary winding, an end connected to the other terminal of the DC power supply, and alternately turning on and off with the first switching means; Bidirectional switching means connected in parallel to the auxiliary winding; rectifying / smoothing means for rectifying / smoothing the current of the secondary winding;
After turning on the bidirectional switching means for a predetermined period after the first or second switching means is turned off while both of the switching means are off, the stored energy of the transformer is maintained continuously. Holding the energy stored in the transformer, turning off the bidirectional switching means before turning on the first or second switching means, and equivalent to the first and second switching means and the transformer. A switching power supply device having control means for controlling the first and second switching means and the bidirectional switching means such that a parasitic capacitor connected in parallel is charged and discharged.