JPH0622548A - Switching power supply - Google Patents

Abstract

PURPOSE:To increase an efficiency and to reduce a noise and the cost by constituting a switching power supply of a self-excited DC-DC converter, etc., with automatic oscillation function-added simple circuits so that it may resonate only at the time of switching and by making a zero-volt switching possible. CONSTITUTION:When a FET5 is in an on-state, a magnetic flux of an iron core 23 of a saturable inductance 8 increases. When the saturable inductance 8 gets saturated, the FET5 gets turned off and a reactor 4 and a capacitor 10 resonate and a voltage between a drain and a source of the FET5 rises in the shape of a sine wave. Then, when a magnetic core 9 of a saturable transformer 2 is saturated, the reactor 4 and the capacitor 10 resonate and the voltage between the drain and the source of the FET5 drops in the shape of a sine wave. When the voltage becomes zero, the magnetic core 9 gets unsaturated and the FET5 gets turned off. Thus, the voltage of the FET5 at the time of a turn-on and a turn-off is made into the shape of a sine wave and a zero-volt switching is conducted for preventing a voltage peak.

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 such as a self-excited DC-DC converter.

[0002]

2. Description of the Related Art A separately-excited switching regulator in which a switching element is controlled by a PWM pulse is used in various fields.
However, since the turn-on and turn-off of the switching element for interrupting the DC voltage of the separately excited switching regulator are not performed in the state of zero current and zero voltage, a relatively large switching loss occurs. In addition, since a surge voltage is generated at turn-off, a snubber circuit is required to absorb the surge voltage.

As a solution to this type of drawback, a resonant converter operating with a sine wave has been proposed. According to this resonance type converter, zero current switching or zero voltage switching is possible, and switching loss and voltage surge / current surge can be reduced. However, since the resonance is used, the effective value of the high frequency current / voltage becomes very large, which increases the conduction loss of the switching element and the iron loss and copper loss of the magnetic component.

In order to solve the problems of the resonance type converter, a partial resonance type converter which resonates only at turn-off and / or turn-on has been proposed. However, in the conventional partial resonance type converter, a switching element for partial resonance is required, and the cost of the device becomes high.

Therefore, an object of the present invention is to improve the efficiency, noise, and cost of the switching power supply device.

[0006]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a saturable transformer having a saturable magnetic core, a primary winding, a secondary winding and a tertiary winding, and the primary winding. A DC power source connected to a wire, a switching element connected in series to the primary winding, and a capacitor and / or stray capacitance connected between one main terminal and the other main terminal of the switching element A series circuit of a saturable inductance and a diode connected in parallel to the primary winding, magnetic control means for magnetically controlling the saturable inductance, the primary winding and the saturable inductance And a starter circuit connected to a control terminal of the switching element, wherein the tertiary winding is provided between the control terminal of the switching element and the other main terminal. And a capacitance value and an inductance value at which the capacitor and / or the stray capacitance and the reactor resonate at a frequency higher than a repetition frequency of turning on / off of the switching element. The present invention relates to a switching power supply device.

As described in claim 2, it is desirable to provide a control winding and a control current source.

As described in claim 3, a rectifying / smoothing circuit for obtaining a DC output can be provided.

[0009]

When the saturable inductance is saturated, a resonance circuit of the reactor and the capacitor and / or the stray capacitance is formed, and the capacitor and / or the stray capacitance are charged. The saturable magnetic core of the transformer has a function of causing turn-on and turn-off of the switching element, and
It has a function of creating a state where the inductance value of the primary winding is large and a state where it is small. When the saturable magnetic core of the transformer is saturated and the inductance value of the primary winding becomes small, resonance occurs between the reactor and the capacitance of the capacitor and / or stray capacitance, and the capacitor and / or stray capacitance are discharged. Resonance is interrupted when the saturable magnetic core and the saturable inductance magnetic core are unsaturated. The tertiary winding controls the switching element in positive feedback. The control winding of claim 2 contributes to magnetic control of the saturable inductance.
The rectifying / smoothing circuit according to the third aspect is for obtaining a DC output.

[0010]

First Embodiment Next, a switching power supply device according to an embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, a primary winding 3 of a saturable transformer 2, a resonance reactor 4, and a switching element are provided between one end and the other end of a DC power source 1 including a rectifying circuit, a smoothing circuit, and a storage battery. A series circuit with an insulated gate FET (field effect transistor) 5 is connected. The saturable transformer 2 has a secondary winding 6, a tertiary winding 7, and a square saturable magnetic core 9 in addition to the primary winding 3. A saturable inductance 8 is connected in parallel to the primary winding 3 via a diode D1.

The resonance reactor 4 is connected in series with the primary winding 3. The resonance capacitor 10 is an FET
5 is connected between the drain (first main terminal) and the source (second main terminal). The FET 5 has a stray capacitance Cs between the drain and the source as shown by a broken line, and further incorporates a diode Ds. If the inductance value of the resonance reactor 4 is L1, and the inductance values of the primary winding 3 and the saturable inductance 8 and the capacitance of the FET 5 are ignored, a series resonance circuit of C1 and L1 is formed. L1
The values of C1 and C1 are set so that the resonance frequency thereby becomes higher than the on / off repetition frequency of the FET5. The constants of each part are as follows. FET5 is 2SK
577, the capacitance C1 of the capacitor 10 is about 1 nF,
The inductance value L1 of the reactor 4 is about 3.8 μF. The power supply voltage Va is 140V, the output voltage is 5V,
The output current is 0 to 20A.

In order to form an output circuit, the secondary winding 6 has diodes 11, 12 and a smoothing reactor 13 in the secondary winding 6.
And a smoothing capacitor 14 for rectifying and smoothing circuit 15
Are connected to the output terminals 16 and 1 of the rectifying / smoothing circuit 15.
A load 18 is connected between the seven.

The tertiary winding 7 is connected between the gate (control terminal) and the source of the FET 5 via a coupling capacitor 19 in order to enable self-excited operation by feedback. FE
It is parallel to the gate and source of T5 and 3
A series circuit of a Zener diode 20 and a diode 21 is connected to the next winding 7 and the coupling capacitor 19 in parallel. The capacitor 19 and the zener diode 20 have the function of shifting down the maximum amplitude value of the gate-source voltage in the positive direction to the zener voltage Vz and lowering the gate-source voltage between t1 and t4 below the gate threshold Vth.

The starting resistor 22 is connected between the DC power supply 1 and the gate of the FET 5. The starting resistor 22 can be replaced with a circuit that gives a starting pulse.

The saturable inductance 8 comprises a rectangular saturable magnetic core 23 and a winding 24. A control winding 25 for magnetic control is wound around a magnetic core 23 of the saturable inductance 28, and a variable current source 26 is connected to the control winding 25. When the current flowing from the variable current source 26 to the control winding 25 is changed, the time width until the saturable inductance 8 reaches saturation and the time width until the saturable transformer 2 is saturated change, and the output voltage changes. .

[0017]

[Operation] First, without connecting the load 18, the output terminal 16,
It is in a no-load state in which 17 is opened, and the control current source 2
The operation of the control coil 6 in the control state in which a constant current Ic is passed through the control winding 25 will be described with reference to FIGS. However,
The stray capacitance Cs, the inductances of the primary winding 3 and the winding 24 are neglected, and these are described as being included in the capacitor 10 and the reactor 4. Further, it is assumed that the number of windings of the saturable inductance 8 and the number of windings of the control winding 25 are N ₂₄ and N ₂₅ , respectively, and the two magnetic cores 9 and 23 are in a non-saturated state. The DC power supply 1 passes through the starting resistor 22 and FE
The gate and source of T5 are charged, and FET5 is turned on. The voltage Vi of the DC power supply 1 is the saturable transformer 2
Is applied to the primary winding 3 of the FET, a voltage is induced in the tertiary winding 7, and the voltage is applied between the gate and the source of the FET 5 through the coupling capacitor 19 to keep the FET 5 ON. When FET5 is on, before t1 and t in FIG.
As shown in section 4 to t5, FET5 and capacitor 1
The voltage Vc between both terminals of 0 is substantially 0 volt, the primary winding 3
The voltage Vb applied to the DC voltage becomes the voltage Vi of the DC power supply 1.
During the ON period of the FET 5, the magnetic flux φ of the magnetic core 9 of the transformer 2 is the Ψ-mmf curve (linkage magnetic flux Ψ vs. magnetomotive force mm in FIG. 3A).
It is a characteristic line of f, and linearly increases according to the ab section of the characteristic line obtained by performing the coordinate conversion based on the BH curve. On the other hand, in the case of the saturable inductance 8, the voltage Vi of the DC power supply 1 is determined by turning on the diode D1 and the FET5.
The magnetic flux applied to the winding 24 and the magnetic flux of the magnetic core 23 is a− in FIG.
It increases according to section b. The primary winding 3 of the saturable transformer 2 has an exciting current I2 and the saturable inductance 8 has a winding 2
An exciting current I3 flows in each of the four. The magnetomotive force of the magnetic core 23 is mmf = N ₂₅ Ic + N _{24 I} 3. In the case of a square magnetic core, the magnetomotive force is sufficiently small and the exciting current can be ignored. If the current I2 of the saturable transformer 2 and the current 13 of the saturable inductance 8 are ignored, no load is applied, so before t1 and t4 in FIG. As shown in section ~ t5,
The current I1 flowing through the reactor 4 becomes zero. Figure 4 is FE
An equivalent circuit of the ON period of T5, that is, before t1 and in the period from t4 to t5 is shown.

When the magnetized state of the magnetic core 23 of the saturable inductance 8 reaches the point b, the magnetic core 23 is saturated and the magnetic core 23
3B, the interlinkage magnetic flux is kept substantially constant, the voltage induced in the winding 24 is reduced, and the diode D1 is turned on. Therefore, the saturable transformer 2 The voltage Vb applied to the primary winding 3 of the
The interlinkage magnetic flux of is held at approximately point b as shown in FIG.
The voltage induced in the tertiary winding 7 also decreases, the gate-source voltage Vgs of the FET 5 becomes lower than the threshold voltage, and the FET 5 is turned off. Due to the saturation of the magnetic core 23, the impedance of the saturable inductance 8 becomes small, and the inductance L1 of the reactor 4, the capacitance C1 of the capacitor 10 and series resonance occur in the equivalent circuit shown in FIG. 5, a current Il flows, and the capacitor 10 is charged. As a result, the voltage Vc rises toward the value 2Vi which is twice the power supply voltage Vi as shown in the section t1 to t2 in FIG. Therefore, t1
During the turn-off period of ~ t2, the voltage Vc across FET5
Is gradually increased in a sinusoidal manner as shown in FIG. After the magnetic core 23 is magnetized to the point d of the Ψ-mmf curve of FIG. 3 (B), the interlinkage magnetic flux Ψ decreases, and the state transitions to the unsaturated state again at the point b.

In the next section, since the magnetic cores 9 and 23 are in a non-saturated state, the primary winding 3 and the saturable inductance 28
The inductance value of the capacitor becomes very large, the resonance operation is interrupted, and if the exciting currents I2 and I3 are ignored, the capacitor 10
Voltage Vc is 2Vi as shown in the section from t2 to t3 in FIG.
Held in. As a result, the primary winding 3 has Vi -2Vi
A voltage of = -Vi is continuously applied, the magnetic core 9 is excited in the opposite direction, and the interlinkage magnetic flux [Psi] changes toward the point a as shown in section b-a of FIG. 3 (A). During that time, a negative voltage is induced in the winding 7, and the FET 5 remains off. on the other hand,
In the saturable inductance 8, even after the interlinking magnetic flux returns from the saturated state to the point b, the magnetomotive force mmf = N ₂₅ Ic + N ₂₄ I3 is more than N ₂₅ Ic as shown in the section b-a of FIG. 3 (B). Is also large, the current I3 is continuously flowing through the winding 24,
Diode D1 remains on. As a result, the voltage of Vi−2Vi = −Vi is continuously applied to the winding 24, the magnetic core 23 is excited in the opposite direction, and the interlinkage magnetic flux Ψ shown in FIG.
As shown in (B), it changes toward point a. Note that t
An equivalent circuit in the section 2 to t3 can be shown in FIG.

Next, when the interlinking magnetic flux Ψ of the magnetic core 23 reaches the point a, as shown by the point a in FIG. 3B, the magnetomotive force mmf =
N ₂₅ Ic + N ₂₄ I3 becomes equal to N ₂₅ Ic and winding 24
Current I3 becomes zero, diode D1 turns off,
The interlinkage magnetic flux Ψ is held at the point a. On the other hand, the magnetic core 9 is continuously excited by the voltage -Vi until the saturation magnetic flux in the negative direction is reached. When the interlinking magnetic flux of the magnetic core 9 reaches the point a, the magnetic core 9
Is saturated and the inductance of the primary winding 3 is reduced, so that the resonance circuit shown in FIG. 7 is formed. As a result, the voltage Vc of the capacitor 10, that is, the drain-source voltage of the FET 5 gradually decreases in accordance with the sine wave as shown in FIG. 2, and returns to zero. The interlinkage magnetic flux of the magnetic core 9 is a-c in FIG.
-Vary along a. When returning to the point a through the point c, the magnetic core 9 becomes unsaturated, the voltage Vi of the DC power supply 1 is applied to the primary winding of the saturable transformer 2, the voltage is induced in the tertiary winding 7, and the FET 5 Is turned on. In the next operation, the voltage Vi of the DC power supply 1 is applied to the primary winding of the saturable transformer 2, and the magnetic core 9 is excited along the section ab in FIG. 3 (A). At the same time, the voltage Vi of the DC power supply 1 is
Saturable inductance 8 from switching on D1 and FET5
Is also applied to the winding 24 of the magnetic core 23, and the magnetic core 23 is ab in FIG.
It is excited as shown in the section. Then, the operation of a-b-a-c-a of the Ψ-mmf curve of FIG.
The operation a-b-d-b-a in (B) occurs repeatedly.
Therefore, in the steady state, both magnetic cores 9 and 23 are excited at the same voltage Vi at the same time from the point a, and the change in the positive direction of the interlinking magnetic flux of both magnetic cores becomes equal. The next negative excitation is also performed at the same voltage -Vi from the point b at the same time, and the change in the negative direction of the interlinking magnetic flux of both magnetic cores becomes equal.
At the same time that the interlinking magnetic flux of 3 reaches the point a, the interlinking magnetic flux of the magnetic core 9 also reaches the point a of the saturation magnetic flux. As a result, the period t2 to t
3 and the lengths of the periods t4 to t5 are both ΔΨ / Vi.
On the other hand, the periods t2 to t2 and the periods t3 to t4 are determined by the resonance frequencies of L1 and C1.

FIG. 8 shows the state of each part under load. Figure 8
The current Il flowing through the primary winding 3 under the above load condition is a combination of the current Is flowing through the FET 5 shown in FIG. 8 and the resonance current Il shown in FIG. The change in the state of each part other than the current is almost the same as that in FIG. As is apparent from the relationship between the voltage Vc across the FET 5 and the current Is in FIG. 8, zero volt switching is achieved during the turn-off period from t1 to t2 and the turn-on period from t3 to t4.

In the circuit of FIG. 1, the off period of the FET 5 is t1.
It is t4, the ON period is t4 to t5, and by changing ΔΨ, the ON time ratio of the FET 5 is changed and the output is changed. This is the reason for the current Ic flowing from the variable current source 26 to the control winding 25. FIGS. 9 and 10 explain this. When the control current Ic is large in the negative direction, the ab section becomes long as shown in FIG. 9, and the change amount ΔΨ of the interlinkage magnetic flux also becomes large. t2-t3 and t4-t
5 becomes longer, and therefore the lengths of the off periods t1 to t4 and the on periods t4 to t5 approach each other. As a result, the on-time ratio approaches 0.5. On the other hand, when the control current Ic is increased in the positive direction, as shown in FIG. Becomes shorter, and the periods t2 to t3 and t4 to t5 become shorter, so that the on period t4 to t5 becomes much shorter than the off period t1 to t4. As a result, the on-time ratio approaches 0. This converter has the same characteristics as the PWM converter, and the output voltage is determined by the on-time ratio. Therefore, the output voltage can be controlled to be constant by changing the control current. Although not shown, means for detecting the output voltage and controlling the variable current source 26 is provided.

According to this embodiment, a switching power supply device capable of zero-volt switching operation and capable of self-oscillation can be constructed by an extremely simple circuit. In addition, the snubber circuit becomes unnecessary. As a result,
The efficiency of the switching power supply device can be increased and noise can be reduced.

[0024]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible. (1) If the stray capacitance Cs is large, the capacitor 10
Can be omitted. (2) Leakage inductance existing on the primary winding 3 side of the saturable transformer 2 and the winding 24 of the saturable inductance 8
When the leakage inductance existing on the side is large, the reactor 4 can be omitted. (3) Instead of the FET, another switching element such as a bipolar transistor can be used. (4) The secondary winding 6 of the saturable transformer 2 is omitted, and the primary winding of the linear transformer (unsaturated transformer) is newly connected in parallel with the primary winding 3, and the secondary winding of the linear transformer is connected. The voltage can be rectified and smoothed to obtain the output. (5) The rectifying / smoothing circuit 15 of FIG. 1 can be omitted to form an inverter circuit.

[0025]

As is apparent from the above, according to the invention of each claim, it becomes possible to cause self-excited oscillation with a simple circuit, and the voltage of the switching element during the turn-on period and the turn-off period is sinusoidal by resonance operation. It becomes possible to achieve zero volt switching by making waves and suppress the voltage peak of the switching element. Therefore, a highly efficient switching power supply device can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a switching power supply device according to a first embodiment.

2 is a circuit diagram of FIG. 1 with no load, Vc, Il, Vb, V
It is a wave form diagram which shows gs and (phi).

FIG. 3 is a Ψ-mmf characteristic diagram of two saturable magnetic cores and a diagram showing a change in interlinkage magnetic flux during operation.

FIG. 4 is an equivalent circuit diagram of an ON period of the FET of FIG.

5 is an equivalent circuit diagram of a turn-off period of the FET of FIG.

FIG. 6 is an equivalent circuit diagram of the FET of FIG. 1 in an off period.

FIG. 7 is an equivalent circuit diagram of the FET of FIG. 1 during a turn-on period.

8 is a circuit diagram of FIG. 1 with load Vc, Il, Vb, Vg.
It is a waveform diagram which shows s, (phi), and Is.

9 is a waveform diagram showing the voltage of the FET when a large control current is applied to the control winding in FIG. 1 in the negative direction.

10 is a waveform diagram showing the voltage of the FET when a large control current is applied to the control winding in FIG. 1 in the positive direction.

[Explanation of symbols]

 1 Power Supply 2 Saturable Transformer 3 Primary Winding 4 Reactor 5 FET 6 Secondary Winding 7 Third Winding 8 Saturable Inductance 9 Saturable Magnetic Core 10 Capacitor

Claims (3)

[Claims] 1. A saturable transformer having a saturable magnetic core, a primary winding, a secondary winding, and a tertiary winding; a DC power source connected to the primary winding; and a primary winding connected to the primary winding. A switching element connected in series, a capacitor and / or a stray capacitance connected between one main terminal and the other main terminal of the switching element, and a saturable element connected in parallel to the primary winding. A series circuit of an inductance and a diode; magnetic control means for magnetically controlling the saturable inductance; a reactor connected in series with the primary winding and the saturable inductance; A starting circuit connected to a control terminal, wherein the tertiary winding is connected between the control terminal of the switching element and the other main terminal,
Moreover, the switching power supply device is characterized in that the capacitor and / or the stray capacitance and the reactor have a capacitance value and an inductance value that resonate at a frequency higher than a repetition frequency of ON / OFF of the switching element. 2. The switching according to claim 1, wherein the magnetic control means is a control winding wound around a saturable magnetic core of the saturable inductance and a variable current source connected to the control winding. Power supply. 3. The switching power supply device according to claim 1, further comprising a rectifying / smoothing circuit connected to the secondary winding.