JPH10248254A - Resonance snubber circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a resonance snubber circuit which eliminates a loss generated by the discharge of a snubber capacitor. SOLUTION: In a switching power-supply apparatus, a switching element 12 is connected in series with the primary winding 11a of a main transformer 11, and a snubber capacitor 13 is connected in parallel with the switching element 12. In the switching power-supply apparatus, a first diode 1 is inserted in series with the snubber capacitor 13, a current flows to the first diode 1 when the snubber capacitor 13 is charged, a series circuit which comprises an inductor 3 and the primary winding 2a of a current transformer 2 is connected in parallel with the first diode 1, a current flows to the inductor 3 and to the current transformer 2 when the snubber capacitor 13 is discharged, and current energy in its discharge is supplied to the secondary side via the current transformer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial resonance type switching power supply, and more particularly, to a switching circuit thereof.

[0002]

2. Description of the Related Art As a conventional partial resonance type power supply technology, FIG.
As shown in FIG. 3, there has been provided a general switching power supply in which a resonance switch circuit and a delay circuit are added (FIG. 3 of Japanese Patent Application Laid-Open No. 4-210775). In the circuit shown in FIG. 3, the control electrode of the main switch element 101 includes the inductor 103 and the snubber capacitor 10 of the resonance switch circuit.
There is a delay circuit that delays turn-on by one-fourth of the resonance period determined by F.4. Main switch element 101
Before the device turns on, the resonance switch element 102 turns on early, and the voltage of the snubber capacitor 104 is reduced. The voltage of the snubber capacitor is one quarter of the resonance period
Becomes zero after elapse of the main switch element 1
01 would turn on when the voltage across it was zero, thereby allowing a zero volt switch.

[0003]

In such a conventional partial resonance type power supply, a resonance switch element is used separately from a main switch element, and a logic circuit or a timer circuit is provided for a control electrode of the main switch element. The applied delay circuit is attached.

Since the peak value of the current applied to the resonant switching element and the peak value of the applied voltage are not different from those of the main switching element, the cost of the switching element required for one power supply is nearly doubled and the cost burden is large. .

Further, since the pulse signal applied to the control electrode of the main switch element affects the efficiency of the power supply device, the delay circuit is required to have a high time accuracy and a large slew rate. Becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a resonant snubber circuit capable of realizing a zero volt switch with a simple circuit configuration, which eliminates a cost increase and a complicated circuit.

[0007]

SUMMARY OF THE INVENTION The present invention provides an inductor which forms a resonance circuit in series with a snubber capacitor when a snubber capacitor is charged and discharges when a snubber capacitor is charged, and a current flowing through the resonance circuit as energy. By flowing the current transformer for taking out, the loss due to the discharge of the snubber capacitor was eliminated.

Thus, even if a large-capacity snubber capacitor is used, the loss when the switch element is turned on does not increase. Rather, the rise of the voltage applied to the switch element at the time of turn-off is delayed, so that the soft switching is realized. This made it possible to reduce the loss at turn-off.

According to the first aspect of the present invention, the current obtained on the secondary side of the current transformer charges the smoothing capacitor on the output side.

According to the second aspect of the present invention, the input side smoothing capacitor is charged by the current obtained on the secondary side of the current transformer.

[0011]

When the switch element is turned off, the snubber capacitor is charged with a current equal to the peak value of the exciting current flowing through the primary winding of the main transformer. Therefore, the larger the capacitance of the snubber capacitor, the more slowly the voltage across the snubber capacitor increases. This voltage is substantially equal to the voltage across the switch element. On the other hand, the time required for the current of the switch element to become zero depends on the characteristics of the switch element and the control circuit regardless of the capacitance of the snubber capacitor. Turn off to reach zero. Switching loss is the value obtained by integrating the product of the voltage across the switch element and the current flowing through the switch element.However, the voltage across the switch element only slightly increases from zero while the current flows through the switch element. It will be a small value.

The first diode has a function of flowing a current for charging the snubber capacitor when the switch element is turned off, and flowing a current for discharging the snubber capacitor to the inductor and the current transformer when the switch element is turned on.

If the turns ratio of the current transformer is selected so as to be larger on the secondary side, the voltage dropped in the primary winding of the current transformer due to the current discharged from the snubber capacitor can be suppressed.

The resonance current generated by the snubber capacitor and the inductor rises in a sine wave, and the voltage of the snubber capacitor decreases in a cosine wave. When the voltage of the falling snubber capacitor reaches almost zero, the resonance stops. On the other hand, in the phase where the voltage of the snubber capacitor becomes zero, the resonance current reaches a peak, so that the energy stored in the inductor becomes an annular current flowing through the current transformer and the first diode, and reaches a zero with a constant gradient. Go down. The first diode also functions as a flywheel diode.

[0015]

FIG. 1 is a circuit diagram showing an embodiment in which the invention of claim 1 of the present invention is applied to a forward converter.

FIG. 2 is a circuit diagram showing an embodiment in which the invention of claim 2 is applied to a step-up chopper.

The operation will be described below with reference to the circuit diagram shown in FIG. When the switch element 12 is turned off, the primary winding 11a of the main transformer 11 causes the main transformer 11 to turn off.
The excitation energy stored in the first diode 1
And is discharged as a current for charging the snubber capacitor 13. Since the value of this current is the same as the peak value of the exciting current flowing immediately before the switch element 12 is turned off, the snubber capacitor 13 is charged with a current almost equal to a constant current, and the voltage at both ends is a linear function. Ascend on a curve close to. The voltage applied to the switch element 12 is a value obtained by adding the forward voltage of the first diode 1 to the voltage across the snubber capacitor 13. The change of the voltage and the current of the switch element 12 before and after the turn-off has the waveform shown in FIG. 4, and it can be seen that the integrated value of the product of the voltage and the current is small.

Next, when the switch element 12 is turned on, the energy charged in the snubber capacitor 13 is released as a current flowing through the inductor 3 and the current transformer 2. This current is supplied to the snubber capacitor 13
Is a resonance current having a resonance cycle determined by the capacitance of the inductor 3 and the inductance of the inductor 3, but since the current always rises from zero, the switch element 12 is turned on,
The value of the resonance current when the voltage becomes zero is still small. The change of the voltage and the current of the switch element 12 before and after the turn-on has the waveform shown in FIG. 5, and it can be seen that the integrated value of the product of the voltage and the current is small.

Although the voltage of the snubber capacitor drops in a cosine wave, when the voltage is near zero, the voltage of the switch element 12 is almost zero, so that the voltage of the first diode 1 cannot be further reduced. That is, it is clamped by the forward voltage of the first diode 1. On the other hand, since the current of the inductor 3 has reached the peak at this time, the energy of the inductor 3 becomes a flywheel current flowing in the annular circuit formed by the primary winding 2a of the current transformer 2 and the first diode 1. Released.

The primary winding 2a of the current transformer 2 has
The resonance current flows and subsequently the flywheel current also flows, and charges the smoothing capacitor 16 via the secondary winding 2b and the second diode 4. The charging current has the waveform shown in FIG.

In this way, most of the energy charged in the snubber capacitor 13 is regenerated except for the loss due to each component.

In the embodiment of the present invention shown in FIG. 2, a method is used in which the current generated in the secondary winding 2b of the current transformer 2 is regenerated to the smoothing capacitor on the input side.
Except for this point, the operation is the same as that of the embodiment of FIG.

In the embodiment of the first aspect of the present invention, a circuit diagram applied to a forward converter, and in the embodiment of the second aspect of the invention, a circuit diagram applied to a boost chopper is shown. It can be applied to converters and step-down choppers.

[0024]

According to the present invention, the loss consumed by the snubber capacitor at the time of turn-on can be eliminated by adding three components of the diode, the inductor and the current transformer. In addition, the capacity of the snubber capacitor can be increased thereby, and as a result, the loss consumed at turn-off can be reduced, and the efficiency of the power supply device can be increased. Also, by increasing the capacitance of the snubber capacitor, the occurrence of noise could be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the invention described in claim 2;

FIG. 3 is a circuit example showing a configuration of a conventional example.

FIG. 4 is a waveform diagram of a voltage and a current when the switch element of the circuit diagram shown in FIG. 1 is turned off.

5 is a waveform diagram of a voltage and a current when the switch element of the circuit diagram shown in FIG. 1 is turned on.

FIG. 6 is a waveform diagram of a current flowing through a secondary winding of a current transformer in the circuit diagram shown in FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 first diode 2 current transformer 2a primary winding of current transformer 2b secondary winding of current transformer 3 inductor 4 second diode 11 main transformer 11a primary winding of main transformer 11b secondary winding of main transformer DESCRIPTION OF SYMBOLS 12 Switch element 13 Snubber capacitor 14, 15 Rectifier diode 16, 17 Smoothing capacitor 101 Main switch element 102 Resonant switch element 103 Inductor 104 Snubber capacitor 107, 108 Diode 109 Pulse width control circuit 110 Delay circuit

Claims (2)

[Claims] 1. A main transformer having a primary winding and a secondary winding, a switch element connected in series to a primary winding of the main transformer, and a snubber capacitor connected in parallel to the switch element. A rectifier diode connected in series to the secondary winding of the main transformer, and a smoothing capacitor for absorbing a ripple component of a switching current flowing in a series circuit including the secondary winding of the main transformer and the rectifier diode. In the switching power supply, a first diode which is inserted in series with the snubber capacitor and becomes non-conductive when a voltage across the switch element becomes lower than a voltage across the snubber capacitor, and a primary winding of the first diode is connected to the first diode. A current transformer having a secondary winding connected in parallel to the first diode and having a secondary winding connected in parallel to the smoothing capacitor; An inductor inserted in series with the primary winding of the current transformer, and an inductor inserted in series with the secondary winding of the current transformer when the voltage of the smoothing capacitor is higher than the voltage across the secondary winding of the current transformer. A resonance snubber circuit, wherein a second diode that becomes conductive is added. 2. A switch element connected in series to a primary winding of a main transformer, a snubber capacitor connected in parallel to the switch element, and a primary winding of the main transformer and the switch element. In a switching power supply having a smoothing capacitor that absorbs a ripple component of a switching current flowing in a series circuit, the switching power supply device is inserted in series with the snubber capacitor and becomes non-conductive when a voltage across the switch element becomes lower than a voltage across the snubber capacitor. And the primary winding of the first diode is
A current transformer whose secondary winding is connected in parallel to the smoothing capacitor, an inductor inserted in series with the primary winding of the current transformer, and a secondary winding of the current transformer And a second diode inserted in series with the line and becoming nonconductive when the voltage of the smoothing capacitor is higher than the voltage across the secondary winding of the current transformer.