JP2000092835A - Low loss circuit of partial resonance self-exciting type switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low loss circuit of a partial resonance self-exciting type switching power supply. SOLUTION: In a partial resonance self-exciting type switching power supply in which a first saturable inductor 15 is inserted serially between a positive feedback coil 13 and a control electrode of a main switch element 12, and a first snubber capacitor 14 is connected in parallel to the main switch element 12, this low loss circuit inserts an auxiliary switch element 1 between the main switch element 12 and the first snubber capacitor 14, winds an auxiliary winding 2 to a transformer to drive the auxiliary switch element in the inverse phase to the phase of the main switch element 12, inserts serially a second saturable inductor 3 between the control electrode of auxiliary switch element 1 and auxiliary winding 2, and moreover connects the second snubber capacitor 4 and a diode 5 in parallel to the auxiliary switch element 1.

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, and more particularly to a soft switch.

[0002]

2. Description of the Related Art Conventionally, as a soft switching technique of a self-excited switching power supply, there is a soft switching circuit of a self-excited switching power supply (Utility Model Registration Certificate No. 2560208) previously provided by the present applicant. FIG. 4 shows the circuit configuration, and FIG. 5 shows operation waveforms.

In the circuit shown in FIG. 4, the excitation energy stored in the transformer during the ON period of the switch element 112 is supplied to the load via the secondary winding 120 and the diode 121 during the OFF period of the switch element 112. . When the exciting energy of the transformer is completely released, the voltage of the winding of the transformer all drops to zero volts, but the voltage of the control electrode of the switch element 112 rises due to the charge of the capacitor 117 charged during the OFF period of the switch element 112, and the switch is switched again. The element 112 enters the ON state. Switch element 11
The voltage of the control electrode of the capacitor 2 is the charge of the
16, the saturable inductor 115 and the positive feedback winding 113. The current rises until the current saturates the saturable inductor 115 due to the high impedance of the saturable inductor 115. The rise of the voltage of the control electrode of the element 112 is delayed. (1) of the waveform diagram of FIG. 5 shows the waveform of the voltage of the control electrode of the switch element 112.

On the other hand, a DC power supply 119 is connected to a snubber capacitor 114 connected in parallel with the switch element 112.
If the switching element 112 is not immediately turned on after the transformer energy is completely discharged, the charge of the snubber capacitor 114 passes through the primary winding 111 to the DC power supply 119 because Flows.
At this time, resonance occurs due to the snubber capacitor 114 and the primary winding 111.

The resonance current reaches a peak when the voltage of the snubber capacitor 114 becomes equal to the voltage of the DC power supply 119, and continues to flow thereafter. Then, after a half cycle of the resonance, the voltage of the snubber capacitor 114 reaches the lowest point. FIG.
(2) of the waveform diagram of FIG. 7 shows the waveform of the voltage of the snubber capacitor 114.

Therefore, by appropriately selecting the delay of the rise of the voltage of the control electrode of the switch element 112 due to the saturable inductor 115, the snubber capacitor 114 and the primary winding are connected after the transformer element has completely discharged the switch element 112. It is turned on after a half cycle of the resonance by 111, whereby the loss caused by the electric charge of the snubber capacitor 114 flowing through the switch element 112 can be reduced.

[0007] Even if the capacitance of the snubber capacitor 114 is made larger than the conventional value, the switching loss due to the capacitance can be suppressed, so that the soft switching of the power supply can be realized.

[0008]

SUMMARY OF THE INVENTION Snubber capacitor 11
V3 is a value when the voltage of the DC power supply 4 reaches the lowest point, V3 is the voltage of the DC power supply 119, V2 is the voltage of the output voltage on the secondary side,
The numbers of turns of the primary winding 111 and the secondary winding 120 are n1 and n, respectively.
If it is set to 2, it can be represented by the following equation.

[0009]

(Equation 1)

However, this formula can be applied under the condition of V1 in which V3 becomes positive, and V3 in which V3 becomes negative.
Under the condition of 1, V3 becomes zero.

In recent years, as the number of portable electronic devices has increased, the demand for AC adapters that can be used for both AC 100 V and AC 240 V has been increasing. That is,
In the above equation, for a DC power supply in which the value of V1 varies from 100 V to 380 V, a method of reducing the loss due to the capacitance of the snubber capacitor 114 has been required. If V3 is designed to be zero when V1 is 100V, V3 is 280V when V1 is 380V.
And the effect of the delay by the saturable inductor 115 is not sufficiently exhibited. On the other hand, if V3 is designed to be zero when V1 is 380V, the snubber capacitor 114
Is theoretically zero, but the voltage applied between the drain and source of the switch element 112 increases,
Further, as n1 / n2 increases, the primary winding 1
The coupling between the secondary winding 11 and the secondary winding 120 is deteriorated, and the surge voltage at the time of turning off the switch element 112 is increased. As a result, a switch element with a higher withstand voltage is required, and the economic advantage is lost.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional method and to provide a circuit for reducing the loss of a partial resonance type self-excited switching power supply for a wide range of input voltage. .

[0013]

According to the present invention, a first saturable inductor is inserted in series between a positive feedback winding and a control electrode of a main switch element, and a main switch is provided. In a partial resonance type self-excited switching power supply characterized in that a first snubber capacitor is connected in parallel with the element, an auxiliary switch element is inserted in series between the main switch element and the first snubber capacitor to assist the transformer. The auxiliary winding is connected such that the auxiliary switching element is turned off when the main switching element is on and is turned on when the main switching element is off. A second saturable inductor is inserted in series between the control electrodes of
And a diode was connected in parallel with the auxiliary switch element. The relationship between the ON and OFF timings of the main switch element and the auxiliary switch element is determined by turning off the auxiliary switch element shortly before the main switch element is turned on, and turning on the auxiliary switch element a short time after the main switch element is turned off. Characteristics of the first saturable inductor and the second saturable inductor.

1 immediately after the main switch element is turned off
The surge voltage due to the secondary winding is absorbed by the first snubber capacitor, the second snubber capacitor, and the diode connected in parallel to the auxiliary switch element. After a short time, the auxiliary switch element is turned on, the voltage across the second snubber capacitor becomes zero, and the first snubber capacitor is charged with a voltage having the same value as the voltage applied to the main switch element. Next, when the main switch element is turned on, the auxiliary switch element is in the off state, so that the electric charge of the first snubber capacitor flows through the main switch element through the second snubber capacitor. If the capacity of the second snubber capacitor is selected to be smaller than the capacity of the first snubber capacitor, it is possible to suppress the loss caused by the charge of the first snubber capacitor flowing through the main switch element.

Also, during the ON state of the main switch element,
Since the voltages of the first snubber capacitor and the second snubber capacitor become equal, the series combined voltage of the two snubber capacitors immediately after the main switch element is turned off becomes zero, and the voltage across the main switch element becomes zero. Since it rises from the point, the effect of the soft switch can be maintained. Since the loss does not increase even if the capacity of the first snubber capacitor is increased, the voltage applied to the main switch element at the time of turn-off can be suppressed to a low voltage without lowering the efficiency.

[0016]

FIG. 1 is a circuit diagram showing a low-loss circuit of a partial resonance type self-excited switching power supply according to an embodiment of the present invention. FIG. 2 is a waveform diagram showing a voltage / current waveform of a main part of the circuit diagram of FIG.

In FIG. 1, when the main switch element 12 is turned on, the auxiliary switch element 1 is turned off, and the first snubber capacitor 14 and the second snubber capacitor 4 are charged with electric charge proportional to their respective capacities. However, the voltage between both ends of the series connection is almost zero like the voltage of the main switch element 12. When the main switch element 12 is turned off from the on state, a positive voltage is generated in each winding of the transformer on the side marked with a dot mark. Primary winding 1
Since a large current flows through 1 just before turning off, a surge voltage is generated at the time of turning off. On the other hand, a voltage is generated in the auxiliary winding 2 with the dot mark side being positive,
The auxiliary switch element 1 is turned on by raising the voltage of the control electrode of the auxiliary switch element 1, but is turned on later than the main switch element 12 is turned off by the second saturable inductor 3. During the delay period, the primary winding 11
Is absorbed by the second snubber capacitor 4 and the first snubber capacitor 14, and when the voltage of the second snubber capacitor 4 reaches the forward drop voltage of the diode 5, this diode 5 and the first snubber capacitor The absorption is continued by the capacitor 14. By increasing the capacity of the first snubber capacitor 14, the surge voltage can be suppressed low.

The excitation energy of the transformer is supplied to the load side through the secondary winding 20 and the diode 21, and eventually becomes zero. At this time, the voltage charged in the capacitor 17 connected to the control electrode of the main switch element 12 turns on the main switch element 12 again, but the first saturable inductor connected in series to the capacitor 17 15 delays a rise in the voltage of the control electrode and delays the turn-on.

On the other hand, the auxiliary switch element 1 in the ON state
Turns off because the voltage of the auxiliary winding 2 decreases, but the discharge of the control electrode of the auxiliary switch element 1
By the saturable inductor 3 of FIG. However, the characteristics of the second saturable inductor 3 are selected so that this delay is slightly shorter than the turn-on delay of the main switch element 12.

While the turn-on of the main switch element 12 is delayed, the electric charge of the first snubber capacitor 14 passes through the auxiliary switch element 1 in the ON state and the primary winding 11, and the DC power supply 1
Flow to 9. Since this current becomes a resonance current, the current continues even if the voltage of the first snubber capacitor 14 becomes lower than the voltage of the DC power supply 19 and becomes the lowest when a half cycle of resonance has occurred. At this time, the main switch element 12 is turned on. Therefore, the characteristics of the first saturable inductor 15 are selected. The voltages of the control electrodes of the main switch element 12 and the auxiliary switch element 1 and the respective ON periods are as shown in (1) and (2) of the waveform diagram of FIG.

Although the auxiliary switch element 1 is turned off shortly before the main switch element 12 is turned on, the auxiliary switch element 1 is turned off after the auxiliary switch element 1 is turned off until the main switch element 12 is turned on. The resonance changes due to the series combined capacitance of the first snubber capacitor 14 and the second snubber capacitor 4 and the primary winding 11, and a part of the electric charge of the first snubber capacitor 14 is transferred to the second snubber capacitor 4. Thus, the voltage of the main switch element 12 further decreases as shown in (3) of the waveform diagram of FIG.

When the main switch element 12 is turned on,
The charge on the first snubber capacitor 14 is further transferred to the second snubber capacitor 4 so that the voltage across each of the two capacitors is equal. At this time, the voltage across the second snubber capacitor 4 keeps a value equal to the voltage of the first snubber capacitor 14 while the main switch element 12 is in the ON state as shown in (4) of the waveform diagram of FIG. .

As shown in (3) of the waveform diagram of FIG. 2, the voltage immediately after the turn-off of both ends of the main switch element 12 has a rising line like a broken line. The first rise is due to the current flowing through the second snubber capacitor 4, and the next broken line is due to the current flowing through the diode 5. Further, in the falling portion immediately before the turn-on, the first drop due to the resonance is due to the electric current of the charge of the first snubber capacitor 14 flowing through the auxiliary switch element 1, and the next drop in the broken line is the second snubber capacitor 4. Due to the current flowing through it.

FIG. 3 is a circuit diagram showing a low-loss circuit of a partial resonance type self-excited switching power supply according to another embodiment of the present invention. N-channel MOSFE for main switch element 12
T, and a P-channel MOSF
By using the ET, the positive feedback winding 13 can also serve as the auxiliary winding 2 that supplies a signal to the auxiliary switch element 1.

In the circuit diagrams of FIGS. 1 and 3, when the body diode of the auxiliary switch element 1 can also function as the diode 5, the diode 5 can be eliminated.

[0026]

As compared with the conventional system shown in FIG. 4, the loss due to the first snubber capacitor 14 can be prevented by adding the auxiliary switch element 1 and other small parts. Further, since the current flowing through the auxiliary switching element 1 is smaller than the current flowing through the main switching element 12, the cost increase due to the addition of the auxiliary switching element 1 is not so large.
Further, since the capacity of the first snubber capacitor 14 can be considerably increased, the surge voltage applied to both the main switch element 12 and the auxiliary switch element 1 decreases, and an element whose withstand voltage is reduced by one rank can be used. If included, the cost increase will be even smaller. On the other hand, when the input voltage range is wide, the merit is very large.
It is expected to be applied to a power supply that is also used for 20 V.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a low-loss circuit of a partial resonance type self-excited switching power supply according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing voltage and current waveforms of a main part of FIG.

FIG. 3 is a circuit diagram showing a low-loss circuit of a partial resonance type self-excited switching power supply according to another embodiment of the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional system.

FIG. 5 is a waveform diagram showing waveforms of a voltage and a current of a main part of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 auxiliary switch element 2 auxiliary winding 3 second saturable inductor 4 second snubber capacitor 5 diode 11 primary winding 12 main switch element 13 positive feedback winding 14 first snubber capacitor 15 first saturable inductor 16 Resistor 17 Capacitor 18 ON period control circuit 19 DC power supply 20 Secondary winding 21 Diode 22 Capacitor 23 Load 111 Primary winding 112 Switching element 113 Positive feedback winding 114 Snubber capacitor 115 Saturable inductor 116 Resistance 117 Capacitor 118 ON period Control circuit 119 DC power supply 120 Secondary winding 121 Diode 122 Capacitor 123 Load

[Procedure amendment]

[Submission date] December 9, 1998 (1998.12.
9)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

[0013]

According to a first aspect of the present invention, a first saturable inductor is inserted in series between a positive feedback winding and a control electrode of a main switch element. And a first snubber capacitor connected in parallel with the main switch element, wherein an auxiliary switch element is inserted in series between the main switch element and the first snubber capacitor. The auxiliary winding is connected to the transformer so that the auxiliary switching element is turned off when the main switching element is turned on and is turned on when the main switching element is turned off. Between the control electrode of the auxiliary switch element and the
Saturable inductors were connected in series, a second snubber capacitor was connected in parallel with the auxiliary switch element, and a diode was connected in parallel with the auxiliary switch element. The relationship between the ON and OFF timings of the main switch element and the auxiliary switch element is determined by turning off the auxiliary switch element shortly before the main switch element is turned on, and turning on the auxiliary switch element a short time after the main switch element is turned off. Characteristics of the first saturable inductor and the second saturable inductor. According to a second aspect of the present invention, a MOSFET is used as the auxiliary switch element, and the second saturable inductor is replaced with a resistor, and
Select the resistance value of the resistor according to the capacitance between the gate and source of the MOSFET so that the FET turns off shortly before the main switch element turns on, and turns on a little after the main switch element turns off. It is.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

[0016]

FIG. 1 is a circuit diagram showing a low loss circuit of a partial resonance type self-excited switching power supply according to an embodiment of the present invention. FIG. 2 is a waveform diagram showing a voltage / current waveform of a main part of the circuit diagram of FIG.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0025

[Correction method] Change

[Correction contents]

FIG. 6 is a circuit diagram showing a low-loss circuit of a partial resonance type self-excited switching power supply according to an embodiment of the present invention. The operation of the circuit is the same as the operation of the circuit of FIG. 1 shown above. When the auxiliary switch element 1 in the circuit diagrams of FIGS. 1 and 3 and the body diode of the MOSFET in FIG. 6 can also function as the diode 5, the diode 5 can be eliminated.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a loss reduction circuit of a partial resonance type self-excited switching power supply according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing voltage and current waveforms of a main part of FIG.

FIG. 3 is a circuit diagram showing a low-loss circuit of a partial resonance type self-excited switching power supply according to another embodiment of the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional system.

FIG. 5 is a waveform diagram showing waveforms of a voltage and a current of a main part of FIG.

FIG. 6 is a circuit diagram showing a low-loss circuit of the partial resonance type self-excited switching power supply according to the second embodiment.

[Description of Signs] 1 auxiliary switching element 2 auxiliary winding 3 second saturable inductor 4 second snubber capacitor 5 diode 11 primary winding 12 main switching element 13 positive feedback winding 14 first snubber capacitor 15th 1 saturable inductor 16 resistor 17 capacitor 18 ON period control circuit 19 DC power supply 20 secondary winding 21 diode 22 capacitor 23 load 24 MOSFET 25 resistance 111 primary winding 112 switch element 113 positive feedback winding 114 snubber capacitor 115 possible Saturation inductor 116 Resistance 117 Capacitor 118 ON period control circuit 119 DC power supply 120 Secondary winding 121 Diode 122 Capacitor 123 Load

[Procedure amendment 6]

[Document name to be amended] Drawing

[Correction target item name] Fig. 6

[Correction method] Added

[Correction contents]

FIG. 6

Claims (1)

[Claims] 1. A transformer for a self-excited switching power supply.
A secondary winding, a main switch element connected in series to the primary winding, a positive feedback winding wound on the transformer for self-oscillating the main switch element, the positive feedback winding, and the main switch. A first saturable inductor inserted in series between control electrodes of the element, a first snubber capacitor connected in parallel to the main switch element, and an on-period control circuit for controlling an on-period of the main switch element. In the partial resonance type self-excited switching power supply provided, an auxiliary switch element is inserted in series between the main switch element and the first snubber capacitor, an auxiliary winding is wound around the transformer, and the signal is output to the auxiliary switch element. Are connected so that they are turned off while the main switch element is on and turned on while the main switch element is off, and the control electrode of the auxiliary switch element is connected to the control electrode. A second saturable inductor inserted in series between the auxiliary winding, second in parallel with the auxiliary switching device
Wherein the switching loss due to the first snubber capacitor is improved by connecting a diode in parallel with the auxiliary switching element, thereby reducing a loss in the partial resonance type self-excited switching power supply. .