JPH099615A - Switching power supply apparatus - Google Patents

Abstract

PURPOSE: To provide a switching power-supply apparatus by which a switching loss and a noise are reduced by making use of both a voltage resonance and a current resonance and which is low-cost. CONSTITUTION: A first inductor 2 and a switch 3 are connected in series with a DC power supply. A series circuit which is composed of a first capacitor 4, of a first diode 5, of a second capacitor 6 and of a primary winding 12a at a transformer is connected in parallel with the switch. A series circuit which is composed of a third capacitor 6b and of a second diode 8 is connected to a secondary winding 12b at the transformer. Electric power is supplied to a load 10 from the second diode 8 via a smoothing circuit 9. When a switch is turned on, a resonance is generated by a resultant capacitance which is composed of the second and third capacitors and by a leakage inductance 121 at the transformer, and the current of the second diode is made nearly a half-wave resonance waveform. When the switch is turned off, a resonance is generated by a parallel resultant inductance which is composed of an exciting inductance at the transformer, of an inductance component 91 contained in the smoothing circuit and of the first inductor and by the first capacitor, and an applied voltage to the switch becomes nearly a half-wave resonance waveform.

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 device for supplying a DC voltage approximately proportional to an input DC voltage to a load in an electronic device for industrial use or consumer use, and particularly to utilizing both voltage resonance and current resonance. And a switching power supply device in which switching loss and switching noise are significantly reduced.

[0002]

2. Description of the Related Art In recent years, switching power supplies have been required to be smaller, more efficient, lower cost, and less noise due to cost reduction, miniaturization, high performance and energy saving of electronic equipment. There is.

As a switching power supply device in which switching loss and switching noise are reduced by utilizing both voltage resonance and current resonance, the description and drawings of Japanese Patent Application No. 5-268706 previously filed by the present applicant are described. There are things that have been done. Hereinafter, this conventional example will be described with reference to FIGS.

FIG. 5 shows a circuit configuration of a conventional switching power supply. In the figure, 1 is an input DC voltage source, and in the following description, the voltage is Vin. Reference numeral 13 is a first switching element, 14 is a first diode, and the first switching element 13 and the first diode 14 constitute a first switching means. 15 is a second switching element,
Reference numeral 16 denotes a second diode, which is the second switching element 1
5 and the second diode 16 constitute a second switching means. The first switching means and the second switching means are connected in series and connected to the input DC voltage source.

Reference numeral 17 denotes a first capacitor, which is connected to both ends of the first switching element 13 and suppresses a sharp change in the voltage applied to the first switching element 13 and the second switching element 15. A second capacitor 6a holds the DC voltage Vc1. A transformer 12 has a primary winding 12a and a secondary winding 12b, and the turn ratio between the primary winding 12a and the secondary winding 12b is n: 1. Primary winding 1
2a is connected to both ends of the second switching means 15 and 16 via the second capacitor 6a.

Reference numeral 6b is a third capacitor, which has a DC voltage V
Hold c2. Reference numeral 8 denotes a third diode, the anode of which is connected to one end of the secondary winding 12b of the transformer and the cathode of which is connected to the other end of the secondary winding 12b through the third capacitor 6b. 9 is a smoothing circuit composed of an inductor 9l and a capacitor 9c, the input side of which is connected to both ends of the third diode 8 and the output side of which is the load 10
It is connected to the. A control circuit 18 detects the output voltage of the smoothing circuit 9 and generates a control signal for changing the on / off ratio of the first switching element 13 and the second switching element 15 so that the output voltage becomes constant.

Reference numeral 12l is a leakage inductance or an inductor of the transformer 12, and the primary winding 1 of the transformer 12
2a is connected in series. Second switching element 1
In the ON period of 5, resonance occurs between the capacitance obtained by combining the second capacitor 6a and the third capacitor 6b and the inductance 12l, and the output current transmitted to the secondary winding 12b of the transformer 12 becomes a resonance current. The control circuit 18 is set so that there is a period in which the first switching element 13 and the second switching element 15 are simultaneously turned off.

FIG. 6 shows operation waveforms of respective parts of the conventional switching power supply device configured as described above. In FIG. 6, (a) shows the drive pulse waveform v _G1 of the first switching element 13 which is one of the outputs of the control circuit 18, and (b) shows the second switching which is one of the outputs of the control circuit 18. The driving pulse waveform v _G2 of the element 15 is shown, (c) shows the primary winding current waveform i _TP of the transformer 12, and (d) shows the voltage waveform v _TP applied to the first switching means. (E) shows the third diode 8
Shows the current waveform i _SD that flows through, and (f) shows the voltage waveform v _SD applied to the third diode 8,
(G) shows the input current waveform i _FL of the smoothing circuit 9.

The basic operation is as follows.

At time t ₀ , the ON signal v _G1 of the control circuit 18 is output while the second switching element 15 is OFF.
Thus, when the first switching element 13 is turned on, the voltage Vin-Vc1 is applied to the primary winding 12a of the transformer 12. At this time, the voltage (V
in-Vc1) / n is generated, and the third diode 8 remains off. In the inductor 9l in the smoothing circuit 9,
Voltage (Vin-Vc1) / n + Vc2-Vo (however, V
(o is an output voltage), and the current flowing through the inductor 9l increases linearly. Primary winding 12a of transformer 12
Current i _TP is the exciting current of the transformer 12 and the secondary winding 12b
Since it is the sum of the primary side converted currents of the currents flowing through, the currents linearly increase and the excitation energy is accumulated in the transformer 12 and the inductor 9l.

At time t ₁ , the first switching element 13 is turned off by the off signal v _G1 of the control circuit 18,
Both the switching element 13 and the second switching element 15 are turned off, but since the third capacitor 17 is connected to both ends of the first switching element 13,
The transformer 12, its leakage inductance or the inductor 12l when the switching element 13 is turned off.
Also, the steep rise of the voltage waveform due to the excitation energy accumulated in the inductor 9l is relaxed, and a voltage resonance state occurs. Then, v _TP rises until it is clamped to the input DC voltage source 1 by the second diode 16.

At time t ₂ , the second switching element 15 is turned on by the ON signal v _G2 of the control circuit 18, but the operation is large regardless of whether the ON current flows through the second diode 16 or the second switching element 15. There is no change. When the second diode 16 or the second switching element 15 is turned on, the first capacitor 6a is attached to the primary winding 12a of the transformer 12.
Is applied to the DC voltage Vc1 held by the transformer 12, a voltage Vc1 / n is generated in the secondary winding 12b of the transformer 12,
The diode 8 is forward-biased to be in a conductive state.

First capacitor 6a and second capacitor 6b
Resonance occurs due to the combination of the above and the leakage inductance or the inductor 12l, but the resonance frequency is set sufficiently low. The current i _SD of the third diode 8 becomes a current resonance state and rises from zero to t ₃
It becomes zero again. Therefore, the third diode 10 becomes zero current switching, and recovery does not occur.

Since the exciting inductance value of the transformer 12 is set to be sufficiently small so that the exciting current becomes negative, when the second switching means is turned off,
Since the electric current is set to flow in the opposite direction so that the electric power is regenerated in the input DC voltage source 1, the charges of the parasitic capacitances of the first switching element 13 and the second switching element 15 and the distributed capacitance of the transformer 12 are discharged. It becomes possible to do.

At time t ₄ , when the second switching element 15 is turned off by the output signal v _G2 of the control circuit 18 when a negative current is flowing through the second switching element 15, the leakage inductance of the transformer 12 or the action of the inductor 12l. In order to continue the negative current, the voltage v _{TP at} the connection point of the first and second switching elements tries to fall sharply. However, since the third capacitor 17 is connected to both ends of the first switching element 13, the sharp fall of the voltage v _TP when the second switching element 15 is turned off is mitigated. Then, after the charge of the third capacitor 17 is regenerated to the input DC voltage source 1, the first diode 14 is turned on.

At time t ₅ , the first switching element 13 is again turned on.
Is turned on, and the operation after time t ₀ is repeated.

[0017]

In the above conventional structure, although the current resonance is fully utilized, the voltage resonance is only partially used in the range from 0 to the input voltage Vin. Absent. Further, two switching elements are required, and the driving circuit for the high-side switching element (15 in FIG. 5) among them becomes complicated. Therefore, it cannot be said that the noise and the price are sufficiently low, and there is room for improvement.

Therefore, an object of the present invention is to set the switching element to the low side in order to solve the above conventional problems.
It is an object of the present invention to provide a switching power supply device in which the cost is reduced by using only one unit and the switching loss and the switching noise are significantly reduced by fully utilizing both the voltage resonance and the current resonance.

[0019]

According to a first characteristic configuration of a switching power supply device of the present invention for achieving the above object, a first inductor and a switching element are connected in series to an input DC voltage source, and A first capacitor and a first unidirectional conducting element are respectively connected in parallel to the switching element, and the first unidirectional conducting element is conducted by the DC voltage source and the first inductor in the uncharged state. And a second capacitor, a second inductor, and a second unidirectional conductive element connected in series are connected in parallel with the switching element, and the second unidirectional conductive element is connected in parallel. The element includes an input DC voltage source, the first inductor in an uncharged state, the second capacitor in an uncharged state, and the second inductor in an uncharged state when the switching element is off. The second unidirectional conducting element is connected to the input side of the smoothing circuit at both ends of the second unidirectional conducting element, and power is supplied to the load from the output side of the smoothing circuit. When the switching element is on, the current that resonates in the closed circuit composed of the second capacitor, the second inductor, the second unidirectional conducting element, and the switching element, and flows through the closed circuit is a half-wave current. On the other hand, when the switching element is off, the voltage across the switching element has a substantially half-wave voltage resonance waveform.

According to the second characteristic configuration, the input DC voltage source is connected in series with the first inductor and the switching element, and the switching element is connected in parallel with the first capacitor and the first unidirectional conducting element. The first unidirectional conducting element is arranged in a direction in which the DC voltage source and the first inductor in the uncharged state are not electrically connected, and further, the second capacitor, the primary winding, and the second winding. A secondary winding and a primary winding of a transformer having a leakage inductance, which are connected in series, are connected in parallel with the switching element, and a secondary winding of the transformer has a third capacitor and a second unidirectional conducting element. Connected in series are connected,
The second unidirectional conducting element includes the input DC voltage source, the uncharged first inductor, and the uncharged second capacitor via the uncharged transformer when the switching element is off. And the third capacitor in the non-charged state are arranged so as not to conduct electricity, the input side of the smoothing circuit is connected to both ends of the second unidirectional conducting element, and the output side of the smoothing circuit is connected to the load Power is supplied to the switching element, and when the switching element is on, the second capacitor, the third capacitor, the second unidirectional conducting element, and the switching element are connected in series via the transformer. The current flowing through the closed circuit resonates in a closed circuit and becomes a substantially half-wave current resonance waveform. The voltage across the child is a schematic half-wave voltage resonance waveform.

[0021]

With the above characteristic configuration, half-wave voltage resonance can be realized when the switching element is off, and half-wave current resonance can be realized when the switching element is on. When the switching element is turned on, it is stored not only in the capacitor in parallel with the switching element but also in the parasitic capacitance of the switching element and the unidirectional conductive element equivalently existing in parallel with the switching element and the distributed capacitance of the transformer. Since the energy is discharged and then turned on, no spike current is generated, and when the switching means is turned off, no spike voltage is generated due to the influence of the leakage inductance of the transformer. Due to the leakage inductance of the transformer or the resonance between the inductor and the capacitor, zero current switching of the second unidirectional conducting element (for example, diode) can be achieved, and the occurrence of turn-off recovery of the diode can be eliminated, resulting in low noise and high efficiency. It is possible to realize a switching power supply.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In FIG. 1, circuit elements having the same functions as those of the circuit element of FIG. 5 used in the description of the conventional example are given the same numbers as the circuit elements of FIG.

A first inductor 2 and a switching element 3 are connected in series to an input DC voltage source 1, and the switching element 3 includes a first capacitor 4 and a first diode as a first unidirectional conducting element. 5 and 5 are connected in parallel. The first diode 5 is connected in the reverse direction to the DC voltage source 1, and is not forward biased by the DC voltage source 1 and the first inductor 2 in the uncharged state.

Further, a series connection of the second capacitor 6, the second inductor 7, and the second diode 8 as the second unidirectional conducting element is connected in parallel with the switching element 3. The second diode 8 is also connected in the opposite direction to the DC voltage source. That is, when the switching element 3 is off, the DC voltage source 1, the first inductor 2 in the uncharged state, and the second capacitor 6 in the uncharged state.
And the second inductor 7 in the uncharged state is not biased in the forward direction.

An input side of a smoothing circuit 9 composed of a third inductor 9l and a third capacitor 9c is connected to both ends of the second diode 8, and a load 10 is connected to its output side. When the switching element 3 is on,
Resonance occurs in a closed circuit including the second capacitor 6, the second inductor 7, the second diode 8 and the switching element 3. The current flowing through this closed circuit has a roughly half-wave current resonance waveform. On the other hand, when the switching element 3 is off, the voltage across the switching element 3 has a substantially half-wave voltage resonance waveform.

Reference numeral 11 is a control circuit, which generates a control signal for controlling ON / OFF of the switching element 3 so as to maintain the current resonance and the voltage resonance.

The operation of the switching power supply device configured as described above will be described with reference to the operation waveforms of the respective parts shown in FIG. In the following description, the first capacitor 4
Switching element 3 or diode 5 existing in parallel with
The distributed capacitance and the like of the first inductor 2 that is equivalently paralleled will be described as being included in the first capacitor 4 for simplification of the description.

In FIG. 2, (a) shows the drive pulse v _PG of the switching element 3 which is the output of the control circuit 11, and (b) shows the current i _IN flowing through the first inductor 2,
(C) shows the voltage v _PS applied to the switching element 3,
(D) is the sum i of currents flowing through the switching element 3, the first diode 5, and the first capacitor 4 connected in parallel.
_PS , (e) is the voltage v _SD applied to the second diode 8
(F) is the current i _SD flowing through the second diode 8,
(G) shows the input current i _FL of the smoothing circuit 9, respectively.

The basic operation is as follows.

First, at time t ₀ , the switching element 3 is turned off by the output v _PG of the control circuit 11, and the first diode 5 and the second diode 8 are both turned off. In this state, the capacitance value of the first capacitor 4 is set sufficiently smaller than the equivalent capacitance value of the input DC voltage source or the capacitance values of the second capacitor 6 and the third capacitor 9c, and the inductance value of the third inductor 9l. Is set to be sufficiently larger than the inductance value of the second inductor 7, the input DC voltage source 1, the second capacitor 6, the third capacitor 9c, and the second inductor 7 can all be ignored. Therefore, the parallel inductance of the first inductor 2 and the third inductor 9l and the first capacitor 4
And form a resonance circuit.

Comparing the current i _IN flowing through the first inductor 2 and the current i _FL flowing through the third inductor 9l at time t ₀ , i _IN is larger, so that the potential difference v _PS across the first capacitor 4 starts to rise. After reaching the peak, the resonance state starts to fall. The time point t ₁ is the time point when the potential difference v _PS across the first capacitor 4 decreases and reaches almost zero, and the first diode 5 starts to conduct. From time t ₀ to t ₁ , v _PS, which is the potential difference across the first capacitor 4, has a roughly half-wave voltage resonance waveform, and there is no abrupt voltage change, so there is little noise. The sum i _PS of the currents flowing through the switching element 3, the first diode 5, and the first capacitor 4 connected in parallel becomes negative at time t ₁ .

Time t₁And the first diode 5 turns on.
Current i_PSIs negative while time t₂At
Output v of circuit 11_PGSwitching element 3 turns on
Become. The capacitance value of the second capacitor 6 is equal to that of the first capacitor 4.
Second capacitor because it is set sufficiently larger than the capacitance value
The fluctuation of the potential difference between both ends of 6 is larger than that of the first capacitor 4.
Very small. Also, it is applied to the switching element 3.
Voltage v_PSThe minimum value of is clamped by the first diode 5
Therefore, it is approximately 0, and similarly applied to the second diode 8.
Voltage v_SDSince the minimum value of is approximately 0, the second capacity
The potential difference between both ends of the shutter 6 is maintained at almost zero. others
Therefore, time t₁The first diode 5 turns on at
Before and after the current i of the second diode 8_SDBegins to flow. Ma
At time t ₁To t₂While the first diode 5 is ON,
Since it continues, the voltage v applied to the switching element
_PSIs approximately 0. Time t₂At switching element
3 turns on, but at this time it is not applied to the switching element.
Voltage v_PSIs approximately 0, the switching element 3
The switching noise associated with turning on is very small.

When the switching element 3 is turned on at time t ₂ , the switching element 3, the second diode 8,
A series resonance circuit is formed by the second inductor 7 and the second capacitor 6. The voltage held in the second capacitor 6 is approximately 0 as described above, but strictly speaking, it is charged so that v _PS > v _SD during the OFF period of the switching element 3. As a result, the second diode 8 is forward biased and the resonance current starts to flow. The resonance frequency is set sufficiently small. Resonant current becomes zero again at time t _3, since the second diode 8 is reverse biased, the resonance current is half-wave. The second diode 8 has zero current switching, and the recovery noise at turn-off is very small.

After the second diode 8 is turned off at time t ₃ , the charging of each inductor and the capacitor is continued until the switching element 3 is turned off at time t ₄ . When the switching element 3 is turned off by the output v _PG of the control circuit 11 at time t ₄ , the same operation state as at time t ₀ is entered, and thereafter, the same operation is repeated.

Next, a second embodiment of the present invention will be described with reference to FIGS. This embodiment is greatly different from the first embodiment in that it has a transformer as shown in the circuit diagram of FIG. By inserting the transformer, the insulation between the primary and the secondary can be secured, and the output voltage can be appropriately set by changing the winding ratio. In the circuit diagram of the second embodiment shown in FIG. 3, those having the same function as the circuit elements in the circuit diagram of FIG. 1 or 5 are as follows.
The same number is attached.

As shown in FIG. 3, a first inductor 2 and a switching element 3 are connected in series to an input DC voltage source 1, and the switching element 3 has a first capacitor 4 connected thereto.
And a first diode 5 as a first unidirectional conducting element are connected in parallel. First diode 5
Is connected in the reverse direction to the DC voltage source 1 and is not forward biased by the DC voltage source 1 and the first inductor 2 in the uncharged state.

Further, the series connection of the second capacitor 6a and the primary winding 12a of the transformer 12 is connected in parallel with the switching element 3. The primary winding 12
Reference numeral 12l connected in series with a is an inductance obtained by converting the leakage inductance of the transformer 12 or a combined inductance of the leakage inductance and an additional second inductor connected to the primary side or the secondary side into the primary side. Is.

The secondary winding 12b of the transformer 12 is connected with a third capacitor 6b and a second diode 8 as a second unidirectional conducting element connected in series. The second diode 8 is connected in the direction shown in FIG.
When the switching element 3 is off, the input DC voltage source 1, the uncharged first inductor 2, the uncharged second capacitor 6a, and the uncharged third capacitor 6b are connected via the uncharged transformer 12. It is not forward biased. The input side of the smoothing circuit 9 composed of the third inductor 9l and the fourth capacitor 9c is connected to both ends of the second diode 8, and the load 10 is connected to the output side thereof.

The switching element 3 is in the ON state
The second capacitor connected in series via the transformer 12.
Switch 6a, third capacitor 6b, second diode 8, switch
It resonates in a closed circuit composed of the switching element 3. And the second
2 Current flowing through diode 8 i _SDIs a half-wave resonant current wave
Be in shape. On the other hand, the switching element 3 is turned off.
The voltage across the switching element is approximately a half-wave voltage.
It becomes a resonance waveform.

The operation of the switching power supply device configured as described above will be described with reference to the operation waveforms of the respective parts shown in FIG. In the following description, the first capacitor 4
Switching element 3 or diode 5 existing in parallel with
The parasitic capacitance, the distributed capacitance of the transformer that is equivalently paralleled, the distributed capacitance of the first inductance, and the like will be described as being included in the first capacitor 4 for the sake of simplification of the description.

In FIG. 4, (a) shows the output of the control circuit 11.
Drive pulse v of the switching element 3 which is force_PGShowing
(B) shows the current i flowing through the first inductor 2._INTo
(C) is the voltage v applied to the switching element 3._PSTo
(D) is a switching element 3 and a first die connected in parallel
The sum i of the currents flowing through the ode 5 and the first capacitor 4 _PS
(E) is the voltage v applied to the second diode 8.
_SD(F) is the current i flowing through the second diode 8._SDTo
(G) is the input current i of the smoothing circuit 9_FLAre shown respectively
You.

The basic operation is as follows.

First, time t₀In the control circuit 11,
Output v_PGCauses the switching element 3 to turn off and the first die
Both the ode 5 and the second diode 8 are not turned off.
You. In this state, the capacitance value of the first capacitor 4 is
DC voltage source equivalent capacitance value or second capacitor
6a, the third capacitor 6b and the fourth key.
Set the capacity of the capacitor 9c sufficiently smaller than the converted value on the primary side.
And the inductance of the inductance 12l
Primary conversion of the inductance value of the third inductor 9l
Calculated value or primary side exciting inductance of transformer 12
Value or the inductance value of the first inductor 2
If the setting is small, the input DC voltage source and the second
Passer 6a, third capacitor 6b, and inductor
All 12l can be ignored. Therefore, the transformer 12
Primary side exciting inductance, first inductor 2, and
Parallel inductor of primary side equivalent inductance of 3 inductor 9l
It is determined by the inductance value and the capacitance value of the first capacitor 4.
A resonance circuit having a resonance frequency of Time t
₀Current i flowing through the first inductor 2 at_INAnd third a
Current i flowing through inductor 9l_FLCompare with the primary conversion value of
And i_INIs larger, both ends of the first capacitor 4
Potential difference v_PSBegins to rise, peaks and then falls.
It becomes a resonance state in which it shifts. First capacitor 4
Potential difference v across_PSDropped to almost 0, and the first Dio
The time when the card 5 starts conducting is time t₁It is. Time t₀Or
Et t₁Up to, the potential difference v across the first capacitor 4_PSIs
Approximately half-wave voltage resonance waveform, no sharp voltage change
Therefore, there is little noise. Time t ₁Are connected in parallel in
Switching element 3, first diode 5, first capacitor
Sum of currents flowing through the shutter 4 i_PSIs negative because of resonance
You.

At time t ₁ , the time during which the first diode 5 is turned on and the sum i _{PS of the} currents flowing through the switching element 3, the first diode 5 and the first capacitor 4 connected in parallel remains negative. At t ₂ , the switching element 3 is turned on by the output v _PG of the control circuit 11. Second capacitor 6
Since the capacitance value of a and the primary-side converted capacitance value of the third capacitor 6b are set to be sufficiently larger than the capacitance value of the first capacitor 4, the second capacitor 6a and the third capacitor 6b connected in series via a transformer. The fluctuation of the potential difference between both ends of the combined capacitance of is smaller than that of the first capacitor 4.
The minimum value of the voltage v _PS applied to the switching element 3 is approximately 0 because it is clamped by the first diode 5, and the minimum value of the voltage v _SD applied to the second diode 8 is also approximately 0. Therefore, the potential difference between both ends of the combined capacitance of the second capacitor 6a and the third capacitor 6b connected in series via the transformer 12 is maintained at almost zero. Therefore, the current i _SD of the second diode 8 starts to flow before and after the first diode 5 is turned on at time t ₁ . Further, since the first diode 5 continues to be turned on from the time t ₁ to the time t ₂ , the voltage v applied to the switching element is
_PS is roughly 0. At time t ₂ , the switching element 3 is turned on, but since the voltage v _PS applied to the switching element at this time is approximately 0, the switching element 3 is turned on.
The switching noise associated with turning on is very small.

When the switching element 3 is turned on at time t ₂ , a series resonance circuit is formed by the switching element 3, the second diode 8, the second capacitor 6a, the third capacitor 6b, and the inductance 12l via the transformer 12. . The voltage held in the combined capacitance of the second capacitor 6a and the third capacitor 6b connected in series via the transformer is approximately 0 as described above, but strictly speaking, during the off period of the switching element 3, It is charged so that v _PS > v _SD . As a result, the second diode 8 is forward biased and the resonance current starts to flow. The resonance frequency is set sufficiently small. At t ₃ , the resonance current becomes zero again and the second diode 8 is reverse biased, so that the resonance current becomes a half wave. The second diode 8 has zero current switching, and the recovery noise at turn-off is very small.

The second diode 8 at time t ₃ is after turned off, the switching element 3 at time t ₄ until the off, charging of the inductors and capacitors is continued. When the switching element 3 is turned off by the output v _PG of the control circuit 11 at time t ₄ , the same operation state as at time t ₀ is entered, and thereafter, the same operation is repeated.

In the description of the first and second embodiments, the DC voltage source is used as the power source, but it is clear that there is no particular problem even if the voltage source obtained by rectifying and smoothing the AC power source is used. is there. Although not specifically limited as the switching element 3, a power transistor, a power MOSFET, or the like can be used. Power MO
When the SFET is used, the parasitic diode of the power MOSFET can be used as the first unidirectional conducting element 5. When a power transistor is used, the diode is added between the base terminal and the emitter terminal of the power transistor in the direction in which the diode between the base and collector of the power transistor is forward biased. It is used as a reverse transistor, so that the first unidirectional conducting element 5
Can be omitted. In this case, the added diode may have a low breakdown voltage because the reverse voltage is limited by V _BE of the power transistor.

[0049]

As described above, according to the present invention, zero current switching of the second unidirectional conducting element is achieved by making the current flowing through the second unidirectional conducting element a substantially half-wave current resonance waveform. However, this makes it possible to eliminate the occurrence of turn-off recovery of the diode used as the unidirectional conducting element. In addition, the voltage applied to the switching element has a substantially half-wave voltage resonance waveform, which can minimize switching noise. Further, when the switching element is turned on, the energy stored in the parasitic capacitance of the switching element and the distributed capacitance of the transformer is discharged before turning on, so that no spike current is generated, and when the switching element is turned off, the leakage inductance of the transformer is reduced. There is no generation of spike voltage due to the influence of. Efficiency is good because there is little noise.
Furthermore, since only one low-side switching element is required, the drive circuit can be simplified and a low-cost switching power supply device can be realized as compared with the conventional device that requires two switching elements.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing operation waveforms of the switching power supply device of FIG.

FIG. 3 is a circuit configuration diagram showing a switching power supply device according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing operation waveforms of the switching power supply device of FIG.

FIG. 5 is a circuit configuration diagram of a switching power supply device according to a conventional example.

6 is an explanatory diagram showing operation waveforms of the switching power supply device of FIG.

[Explanation of symbols]

1 Input DC voltage source 2, 7, 9l Inductor 3, 13, 15 Switching element 4, 6, 6a, 6b, 9c, 17 Capacitor 5, 8, 14, 16 Diode (unidirectional conduction element) 9 Smoothing circuit 10 Load 11, 18 Control circuit 12 Transformer 12a Primary winding of transformer 12b Secondary winding of transformer 12l Inductance obtained by converting leakage inductance of the transformer into the primary side

Claims (5)

[Claims] 1. A first inductor and a switching element are connected in series to an input DC voltage source, and a first capacitor and a first unidirectional conducting element are connected in parallel to the switching element, respectively, and the first unidirectional The conductive element is arranged in a direction in which the DC voltage source is not electrically connected to the uncharged first inductor, and further, the second capacitor, the second inductor, and the second unidirectional conductive element. Are connected in parallel with the switching element, and the second unidirectional conducting element is connected to the input DC voltage source and the first inductor in the uncharged state when the switching element is off. The second capacitor in a charged state and the second inductor in a non-charged state are arranged so as not to be electrically connected, and a smoothing circuit input is provided at both ends of the second unidirectional conducting element. There are connected, the power is supplied to the load from the output side of the smoothing circuit in the switching element is turned on, the second
A closed circuit composed of a capacitor, the second inductor, the second unidirectional conducting element, and the switching element resonates, and a current flowing through the closed circuit has a substantially half-wave current resonance waveform, while the switching element is turned off. In the state, the switching power supply device is characterized in that the voltage across the switching element has a substantially half-wave voltage resonance waveform. 2. A first inductor and a switching element are connected in series to an input DC voltage source, and a first capacitor and a first unidirectional conducting element are connected in parallel to the switching element, respectively, and the first unidirectional element is connected. The conductive element is arranged in a direction in which the DC voltage source and the first inductor in an uncharged state are not electrically connected, and further, the second capacitor, the primary winding and the secondary winding, and the leakage inductance are arranged. A transformer having a primary winding connected in series is connected in parallel with the switching element, and a transformer having a secondary winding connected in series with a third capacitor and a second unidirectional conducting element. The second unidirectional conducting element is connected to the input DC voltage source through the transformer in the uncharged state and the first inductor in the uncharged state when the switching element is off. And the second capacitor in the uncharged state and the third capacitor in the uncharged state are arranged so as not to be electrically connected, and the input side of the smoothing circuit is connected to both ends of the second unidirectional conducting element. Power is supplied to the load from the output side of the smoothing circuit, and the second capacitor, the third capacitor, and the second unidirectionality that are connected in series via the transformer in a state where the switching element is on. Resonance occurs in a closed circuit composed of a conducting element and the switching element, and the current flowing through the closed circuit has a substantially half-wave current resonance waveform. On the other hand, when the switching element is off, the voltage across the switching element is approximately A switching power supply device having a half-wave voltage resonance waveform. 3. The second capacitor, wherein a second inductor is added in series to a primary winding or a secondary winding of the transformer, and the switching element is turned on, the second capacitor is connected in series through the transformer. 3. The resonant circuit according to claim 2, wherein the current flowing through the closed circuit resonates in a closed circuit including the third capacitor, the second inductor, the second unidirectional conducting element, and the switching element, and is a substantially half-wave resonant current. Switching power supply. 4. A power MOSF as a switching element.
4. The switching power supply device according to claim 1, 2 or 3, wherein ET is used and a parasitic diode of the power MOSFET is used as the first unidirectional conducting element. 5. A power transistor is used as a switching element, and a small capacity diode for forward biasing the diode between the base and collector of the power transistor is added between the base terminal and the emitter terminal. 4. The switching power supply device according to claim 1, 2 or 3, wherein a power transistor is used as a reverse transistor, whereby the first unidirectional conducting element is omitted.