JP3451419B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention includes a snubber circuit.
It relates to a switching power supply device. A switching power supply device controls on / off of a switching element such as a field effect transistor so as to convert an input voltage into a desired voltage and further stabilizes it, and various configurations are already known. . In such a switching power supply device, a snubber circuit is provided in order to solve problems such as withstand voltage due to surge voltage when the switching element is turned off or when the rectifying diode is reversely recovered. Further, it is desired to improve the efficiency of the switching power supply device, and accordingly, it is necessary to reduce the loss in the snubber circuit or the like.

[0002]

2. Description of the Related Art FIG. 9 is an explanatory diagram of a conventional flyback converter configuration, in which an input voltage Vin having the illustrated polarity is
The main switch SW turns on and off the voltage applied to the primary winding N1 of the transformer T, and the voltage induced in the secondary winding N2 is rectified by a rectifying diode D and smoothed by a smoothing capacitor C2. Output voltage Vo
ut is detected by the control circuit CONT, and the ON period of the main switch SW is controlled by the drive signal P1 so that the error amount approaches zero as compared with the set reference voltage. The main switch SW is composed of a bipolar transistor, a field effect transistor, or the like.

FIG. 10 is a diagram for explaining the operation of the conventional example, P1.
Is a drive signal for the main switch SW, In2 is a transformer T
The current flowing in the secondary winding N2, Vd, indicates the voltage across the rectifying diode D. When the drive signal P1 is set to the high level, the main switch SW is turned on. This ON period is indicated by Ton. When the drive signal P1 is set to low level, the main switch SW is turned off. This off period is indicated by Toff.

When the main switch SW is turned on by the high level drive signal P1, a current due to the input voltage Vin flows through the primary winding N1 of the transformer T and is accumulated as excitation energy. At that time, in the rectifying diode D, A reverse voltage is applied as shown as Vd. Therefore,
During the on period Ton of the main switch SW, the secondary winding N
The current In2 of 2 becomes zero.

Next, when the main switch SW is turned off by the low level drive signal P1, the voltage induced in the secondary winding N2 of the transformer T becomes the forward direction of the rectifying diode D. As a result, the current In2 flows through the secondary winding N2 of the transformer T via the rectifying diode D. Therefore,
During the off period Toff of the main switch SW, the secondary winding N
2, the current In2 flows, the load current and the charging current for the smoothing capacitor C2 are generated, and when the main switch SW is turned on, the induced voltage in the secondary winding N2 of the transformer T is inverted, so that the reverse direction is applied to the rectifying diode D. Applied as a voltage, the current In2 becomes zero.

When the main switch SW is turned on, the voltage applied to the rectifying diode D changes from the forward voltage to the reverse voltage. At that time, a surge voltage Vs is generated in the voltage Vd applied to the rectifying diode D corresponding to the reverse recovery characteristic of the rectifying diode D. In particular,
In the case of a rectifying diode whose reverse recovery is slow, the reverse current becomes large and the surge voltage Vs becomes high.

FIG. 11 is an explanatory diagram of a conventional boost converter configuration and buck-boost converter configuration.
(A) shows a main part of a switching power supply device of a boost converter configuration, C1 is an input side capacitor, L is a reactor, SW is a main switch, D is a diode, C2
Is a smoothing capacitor, CONT is a control circuit, Vin is an input voltage, and Vout is an output voltage.

A reactor L and a diode D are connected in series between an input terminal and an output terminal, and a main switch SW is connected to the connection point thereof, which is a control circuit CON.
When the main switch SW is turned on by T, the input voltage Vin having the illustrated polarity is directly applied to the reactor L, a current flows, and the excitation energy is accumulated in the reactor L. Further, the charging voltage of the smoothing capacitor C2 is applied as a reverse voltage to the diode D to prevent the smoothing capacitor C2 from being discharged through the main switch SW in the ON state.

Next, when the main switch SW is turned off, the excitation energy accumulated in the reactor L generates a voltage in the direction of maintaining the continuity of the current, and this voltage is added to the input voltage Vin and the diode D Is applied to and charged by the smoothing capacitor C2. Therefore, the output voltage Vout having the illustrated polarity is equal to the input voltage Vin.
Is a value obtained by adding the voltage due to the reactor L. The output voltage Vout is detected by the control circuit CONT, and the ON period of the main switch SW is controlled so that the set constant output voltage Vout is obtained.

Further, FIG. 11B shows a main part of a switching power supply device having a buck-boost converter configuration.
The same reference numeral as (A) indicates the same name portion, and the main switch SW and the diode D are provided between the input terminal and the output terminal.
Is connected in series, and the reactor L is connected to the connection point, and the control circuit CONT detects the output voltage Vout having the polarity shown in the figure and sets the main switch SW so that the output voltage Vout becomes the set voltage. Controls on and off. When the main switch SW is turned on, the input voltage Vin having the illustrated polarity is applied to the reactor L, a current flows, and excitation energy is accumulated. At that time, a reverse voltage is applied to the diode D.

When the main switch SW is turned off, a voltage is induced to maintain the continuity of the current flowing in the reactor L, and a forward voltage is applied to the diode D. The smoothing capacitor C2 is charged by the current flowing through the reactor L via the diode D to the polarity shown in the figure (the opposite polarity to the case of FIG. 11A), and the voltage across the capacitor C2 becomes the output voltage Vout. The switching power supply device having this configuration can be either a step-up type or a step-down type.

FIG. 12 is an explanatory view of a conventional buck converter configuration and forward converter configuration. FIG. 12A shows a main part of a switching power supply device having a buck converter configuration, in which a capacitor C1 is connected between input terminals, A smoothing capacitor C2 is connected between the output terminals, a main switch SW and a reactor L are connected in series between the input terminal and the output terminal, and a diode D is connected to the connection point. The diode D is the main switch SW
When is turned on, the input voltage Vin having the illustrated polarity is connected so as to have a polarity applied as a reverse voltage.

The control circuit CONT detects the output voltage Vout having the polarity shown in the figure and controls the on / off of the main switch SW so that the voltage becomes a set voltage. When the main switch SW is turned on, the input voltage Vin is connected to the output terminal via the reactor L and the smoothing capacitor C is connected.
2 and the load. At this time, the voltage VL applied to the reactor L becomes VL = Vin-Vout, the reactor L is excited according to this voltage VL, and the smoothing capacitor C2 is charged.

When the main switch SW is turned off, the voltage induced by the characteristic of maintaining the continuity of the current flowing through the reactor L has a forward polarity with respect to the diode D. Therefore, the charging of the smoothing capacitor C2 and the supply of the load current are continued. In this structure, the excitation energy accumulated in the reactor L is equal to the input voltage Vi.
According to the difference between n and the output voltage Vout, a step-down switching power supply device is configured.

Further, FIG. 12B shows a main part of a switching power supply device having a forward converter configuration, and a transformer T
The main switch SW is connected to the primary winding N1, the capacitor C1 is connected to the input terminal, the main switch SW is turned on / off by the control circuit CONT, and the primary polarity N1 is applied to the primary winding N1 of the transformer T. The input voltage Vin is turned on and off.

The induced voltage in the secondary winding N2 caused by turning on the main switch SW has a forward polarity in the diode Da and a reverse polarity in the diode Db, and the current flowing in the secondary winding N2 is a diode. A charging current and a load current of the smoothing capacitor C2 are generated via Da and the reactor L, and excitation energy is accumulated in the reactor L. Further, the voltage having the illustrated polarity across the smoothing capacitor C2 becomes the output voltage Vout. The control circuit CONT detects the output voltage Vout, compares the output voltage Vout with the set reference voltage, and controls the ON period of the main switch SW by pulse width control or the like so that the error is zero.

When the main switch SW is turned off, the polarity of the induced voltage in the secondary winding N2 of the transformer T is inverted, so that the diode Da has a reverse voltage and the diode Db has a forward voltage. However, the applied voltage to the diode Db is blocked by the diode Da. Further, in the reactor L, in order to maintain the continuity of current, a forward voltage is induced in the diode Db by the accumulated excitation energy. Therefore, the charging current and the load current of the smoothing capacitor C2 are supplied.

Besides the switching power supply device shown in FIGS. 9, 11 and 12, various configurations such as a half-bridge type, a full-bridge type, a voltage resonance type, a current resonance type and a synchronous rectification type are known. There is.

[0019]

In the diode D in the above-mentioned conventional example, when a forward voltage is applied, a voltage drop of about 0.6 V occurs in the case of a normal pn junction type diode. Resulting in power loss. Therefore, a configuration in which a switch is connected in parallel with the diode D to make it a synchronous type is known. That is, by turning on the switch at the timing when the forward voltage is applied to the diode D and turning off the switch at the timing when the reverse voltage is applied, it is possible to obtain a diode characteristic in a nearly lossless state. You can However, there is a problem of loss due to the inability to switch on and off the switch in the zero voltage state. Further, the influence of the surge voltage due to the reverse recovery of the diode on the breakdown voltage becomes a problem. The present invention is a snubber capable of suppressing the above-mentioned surge voltage and ignoring switching loss.
An object of the present invention is to provide a switching power supply device including a circuit .

[0020]

A switching power supply device of the present invention is a main switch for turning on and off a DC input voltage.
Switch SW1 and on / off of this main switch SW1
Through a transformer to apply a pulsed voltage due to
Or, by connecting directly, turning on the main switch SW1,
Synchronous rectification switch S for on / off control in opposite phase to off
And W2, connected in parallel with the synchronous rectification switch SW2
The diode D2 and the snubber capacitor C3 are connected between the output terminal and the synchronous rectification switch SW2 .
ON / OFF of the smoothing capacitor C2 connected so as to apply a voltage depending on the ON / OFF state and the main switch SW1 so as to make the output voltage between the output terminals constant, and when the main switch SW1 is turned on. , When the synchronous rectification switch SW2 is turned off and the main switch SW1 is turned off, the delay time after the discharge current flows through the snubber capacitor C3 and the current flows through the diode D2 is set , and the synchronous rectification is performed in the zero voltage state. Switch SW2 is turned on
And a control circuit 1 having a controlled configuration. As a result, the synchronous rectification switch SW2 is switching-controlled at zero voltage , and the switching loss is reduced so that it can be ignored.

(2) The control circuit 1 includes the main switch S
An inversion circuit that inverts an on drive signal that turns on W1 and an off drive signal that turns off, and an on drive signal of the main switch SW1 that is inverted by this inversion circuit is used as an off drive signal that turns off the synchronous rectification switch SW2. A configuration can be provided in which the OFF drive signal of the main switch SW1 inverted by the inversion circuit is used as an ON drive signal for turning on the synchronous rectification switch SW2 via the delay circuit.

(3) The main switch SW1 is connected to the primary winding N1 of the transformer 2, and the synchronous rectifying switch SW2 having a configuration in which the diode D2 is connected in parallel is connected to the secondary winding N2 of the transformer 2, and the output terminals are connected to each other. Smoothing capacitor C2
In the switching power supply device of the flyback converter configuration in which the main switch SW1 is turned on and off so as to make the output voltage between the snubber capacitor C3 connected in parallel to the synchronous rectification switch SW1 and the output terminal constant. When the main switch SW1 is turned on, the synchronous rectification switch SW2 is turned off, and when the main switch SW1 is turned off, the delay time after the discharge current flows through the snubber capacitor C3 and the current flows through the diode D2. The control circuit 1 configured to turn on the synchronous rectification switch SW1 by setting it.

(4) The main switch is connected to the primary winding of the transformer, and the secondary winding of the transformer is connected to the first and second synchronous rectifying switches in parallel with the diode. Connect in series so as to have polarity,
A forward converter-type switching power supply device in which a series circuit of a smoothing reactor and a smoothing capacitor is connected to both ends of a second synchronous rectification switch, and both ends of the smoothing capacitor are connected between output terminals. Of the snubber capacitor connected in parallel with the synchronous rectification switch of the main switch and the on / off control of the main switch so as to keep the output voltage between the output terminals constant, and when the main switch is turned on, the first synchronous rectification switch Is turned on, the second synchronous rectification switch is turned off, and the main switch is turned off, the first synchronous rectification switch is turned off, and a delay occurs after the discharge current flows through the snubber capacitor and the current flows through the diode. And a control circuit configured to turn on the second synchronous rectification switch by setting time.

(5) A smoothing capacitor is connected between the output terminals, and a synchronous rectification switch having a structure in which a reactor and a diode are connected in parallel is connected in series between the input terminal of the power supply and the output terminal, and the reactor is connected in series. In a switching power supply device with a boost converter configuration in which a main switch is connected to the connection point between a diode and a diode, a snubber capacitor connected in parallel with the synchronous rectification switch and the main switch to keep the output voltage between the output terminals constant. ON / OFF is controlled, and when this main switch is turned on, the synchronous rectification switch is turned off, and when the main switch is turned off, the delay time after the discharge current flows in the snubber capacitor and the current flows in the diode is set. And a control circuit configured to turn on the synchronous rectification switch by setting.

(6) A smoothing capacitor is connected between the output terminals, and a main switch and a synchronous rectification switch having a diode connected in parallel are connected in series between the input terminal of the power source and the output terminal. In a switching power supply device with a buck-boost converter configuration in which a reactor is connected to the connection point between a main switch and a diode, a snubber capacitor connected in parallel with a synchronous rectification switch and an output voltage between the output terminals are made constant. Controlling on / off of the main switch, when the main switch is turned on, the synchronous rectification switch is turned off, and when the main switch is turned off, a discharge current flows through the snubber capacitor and a current flows through the diode. And a control circuit configured to turn on the synchronous rectification switch by setting a delay time later. That.

(7) A smoothing capacitor is connected between the output terminals, a main switch and a reactor are connected in series between the input terminal of the power source and the output terminal, and the main switch and the reactor are connected to each other. , In a switching power supply device of a buck converter configuration in which a synchronous rectification switch of a configuration in which diodes are connected in parallel is connected, a snubber capacitor connected in parallel to the synchronous rectification switch and an output voltage between the output terminals are made constant. Main switch on,
When the main switch is turned on, the synchronous rectification switch is turned off when this main switch is turned on, and when the main switch is turned off, the delay time after the discharge current flows through the snubber capacitor and the current flows through the diode is set. And a control circuit configured to turn on the synchronous rectification switch.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of a first embodiment of the present invention, showing a case where it is applied to a switching power supply device having a flyback converter configuration, and 1 is a control circuit,
2 is a transformer, N1 is a primary winding, N2 is a secondary winding, C1
Is an input side capacitor, C2 is a smoothing capacitor, C3
Is a snubber capacitor, SW1 is a main switch, SW
2 is a synchronous rectification switch, D2 is a diode, Vin is an input voltage, Vout is an output voltage, and P1 and P2 are drive signals.

The snubber capacitor C3 is connected in parallel to the synchronous rectification switch SW2 having a structure in which the diode D2 is connected in parallel.
Connect. Further, the control circuit 1 uses the output voltage V having the polarity shown in the drawing.
Out is detected and compared with the set reference voltage, and the ON period of the main switch SW1 is controlled by the drive signal P1 so that the error becomes zero. The basic configuration for controlling the main switch SW1 is similar to that of the conventional example, and various configurations known as pulse width modulation (PWM) control can be applied, for example. Further, the operation of making the output voltage Vout constant as the flyback converter configuration is the same as the configuration shown in FIG. 9 described above, and thus the duplicated description will be omitted. In the present invention, the main switch S
When W1 is turned on, the synchronous rectification switch SW2 is turned off,
On the contrary, when the main switch SW1 is turned off, the discharge current flows through the snubber capacitor C3 and the diode D
After the current flows through the switch 2, the synchronous rectification switch SW2 is turned on. Such a configuration can be easily configured by applying a delay circuit.

FIG. 2 is an operation explanatory diagram of the first embodiment of the present invention, in which P1 is a drive signal of the main switch SW1,
P2 is a drive signal for the synchronous rectification switch SW2, In2 is a current flowing through the secondary winding N2 of the transformer 2, Id2 is a current flowing through the diode D2 and the synchronous rectification switch SW2, and I2.
sw2 is a current flowing through the synchronous rectification switch SW2, Vsw
2 shows an example of each waveform of the voltage applied to the synchronous rectification switch SW2.

The period when the drive signal P1 is set to the high level and the main switch SW1 is turned on is Ton1, the period when the drive signal P1 is set to the low level and the main switch SW1 is turned off is Toff1, and the drive signal P2 is set to the high level. The period when the synchronous rectification switch SW2 is turned on is Ton2, and the low level is set to the synchronous rectification switch S.
The period when W2 is turned off is shown as Toff2.

On period Ton1 of main switch SW1
At this time, the excitation energy is accumulated in the transformer 2.
Further, the synchronous rectification switch SW2 is off, and the induced voltage of the secondary winding N2 of the transformer 2 and the smoothing capacitor C
A voltage of opposite polarity is applied to the diode D2 by the charging voltage of 2 and the snubber capacitor C3 is charged by this voltage.

The control circuit 1 detects the output voltage Vout and controls the main switch SW1.
When 1 is set to low level and the main switch SW1 is turned off, after a period of Td1, the drive signal P2 is set to high level and the synchronous rectification switch SW2 is turned on,
On the contrary, when the drive signal P1 is set to high level to turn on the main switch SW1, the drive signal P2 is set to low level to turn on the synchronous rectification switch SW2.

When the main switch SW1 is on,
Due to the induced voltage of the secondary winding N2 of the transformer 2 and the charging voltage (output voltage Vout) of the smoothing capacitor C2, a reverse voltage is applied to the diode D2 and the snubber capacitor C3 is charged. Therefore, the synchronous rectification switch SW2, the diode D2, and the snubber capacitor C3
The voltage indicated by Vsw2 is applied to the parallel circuit of and.

When the drive signal P1 is set to low level and the main switch SW1 is turned off, the voltage induced in the secondary winding N2 of the transformer 2 has the forward polarity of the diode D2, but the diode D2 has a snubber. The charging voltage of the capacitor C3 is applied as a reverse voltage, and the diode D2 continues to be off. Then, the charge of the snubber capacitor C3 is discharged to the smoothing capacitor C2 side through the secondary winding N2 of the transformer 2, and the current In2 corresponds to this discharge current. Then, the voltage Vsw2 applied to the synchronous rectification switch SW2 rapidly decreases as the snubber capacitor C3 discharges.

Then, after the period of Td2, when the voltage Vsw2 becomes zero, the current Id2 flowing through the diode D2.
Suddenly rises, and the current In2 flowing through the secondary winding N2 becomes almost this current Id2. And the synchronous rectification switch SW
During a period in which the voltage Vsw2 at both ends of 2 is zero, that is, during a period of Td3, the drive signal P2 is set to the high level and the synchronous rectification switch SW2 is turned on. As a result, the current Isw2 flows through the synchronous rectification switch SW2, and the current Isw2 can flow with almost no loss. Further, since the switching can be performed in the zero voltage state, the switching loss can be zero.

When the drive signal P1 is set to the high level to turn on the main switch SW1 and the drive signal P2 is set to the low level to turn off the synchronous rectification switch SW2, the diode D is connected to the secondary winding N2 of the transformer 2.
The voltage of the opposite polarity of 2 is induced, the diode D2 is turned off, the charging current flows through the snubber capacitor C3, and this current flows during the period of Td4. Therefore, the voltage Vsw2 applied to the synchronous rectification switch SW2 rises with a slope corresponding to the charging characteristic of the snubber capacitor C3. Therefore, the synchronous rectification switch S
W2 can be switched in the zero voltage state.
The surge voltage due to the reverse recovery of the diode D2 can be absorbed by the snubber capacitor C3.

FIG. 3 is an explanatory view of the synchronous rectification switch,
(A) shows the synchronous rectification switch SW2 and the diode D2 shown in FIG. 1, and the ON / OFF of the synchronous rectification switch SW2 is controlled by the drive signal P2. This structure has the field effect transistor shown in (B). 3 can be realized. In this case, since the n-channel field effect transistor includes the parasitic diode 4, the parasitic diode 4 can be used as the diode D2. Further, the main switch SW1 can also be composed of such a field effect transistor 3.

FIG. 4 is an explanatory view of the second embodiment of the present invention, showing a case in which the configuration shown in FIG. 1 is further embodied.
The same reference numerals as in FIG. 1 denote the same parts, 3 is a synchronous rectification switch composed of an n-channel field effect transistor having a configuration in which a diode 4 is connected in parallel, 5 is a main switch also composed of an n-channel field effect transistor, and 6 is A pulse width control circuit (PWMC), 7 is an inverter (inversion circuit), 8 is a delay circuit (DL), and 9 and 10 are diodes.

The control circuit 1 has a pulse width control circuit 6, an inverter 7, a delay circuit 8, and diodes 9 and 10. The pulse width control circuit 6 has an output voltage V
out is detected, and compared with the set reference voltage, the high level period of the drive signal P1 is shortened so that the ON period Ton1 is shortened when the output voltage Vout is high, and the ON period Ton1 is turned on when the output voltage Vout is low. There is a configuration in which the high-level period of the drive signal P1 is extended so as to extend the period Ton1, and various known configurations can be applied.

The drive signal P from the pulse width control circuit 6
1 is inverted by the inverter 7 to turn on the main switch 5 (ON level drive signal (high level drive signal P1))
Is inverted by the inverter 7 and becomes low level,
An OFF drive signal (low-level drive signal P2) is applied to the gate of the synchronous rectification switch 3 via the diode 10. Therefore, the main switch 5 is turned on and the synchronous rectification switch 3 is turned off.

The off drive signal (low level drive signal P1) for turning off the main switch 5 is inverted by the inverter 7 to a high level and passes through the diode 9 and the delay circuit 8 to the gate of the synchronous rectification switch 3. To the ON drive signal (high level drive signal P2). The delay time of the delay circuit 8 is set so as to correspond to the period of Td1 described above.

Therefore, only the signal obtained by inverting the off drive signal for turning off the main switch 5 by the inverter 7 is delayed by the delay circuit 8 to become the on drive signal for the synchronous rectification switch 3, and after the main switch 5 is turned off. , Td1, the synchronous rectification switch 3 is turned on to allow zero voltage switching.

FIG. 5 is an explanatory view of the third embodiment of the present invention, showing a main part of a switching power supply device having a boost converter configuration, where Vin is an input voltage, Vout is an output voltage, and C1 is a capacitor on the input side. , C2 is a smoothing capacitor, C3 is a snubber capacitor, SW1 is a main switch, SW2 is a synchronous rectification switch, D2 is a diode, L
Is a reactor, 1 is a control circuit, and P1 and P2 are drive signals.

A synchronous rectification switch having a structure in which a smoothing capacitor C2 is connected between output terminals, a capacitor C1 is connected between input terminals, and a reactor L and a diode D2 are connected in parallel between an input terminal and an output terminal. The switch SW2 is connected in series, the main switch SW1 is connected to the connection point, the snubber capacitor C3 is connected in parallel to the synchronous rectification switch SW2, and the control circuit 1 detects the output voltage Vout having the illustrated polarity. Then, the ON period of the main switch SW1 is controlled so as to compare with the set reference voltage and the error amount approaches zero.

By the drive signal P1 from the control circuit 1,
When the main switch SW1 is on, the drive signal P2 causes the synchronous rectification switch SW2 to be off, a current due to the input voltage Vin flows through the reactor L to accumulate excitation energy, and the snubber capacitor C3 is connected to the smoothing capacitor C2. It is charged by the charging voltage, and its terminal voltage has a reverse polarity with respect to the diode D2.

Next, when the main switch SW1 is turned off by the drive signal P1, the synchronous rectification switch SW2 continues to be off, and the voltage due to the accumulated excitation energy of the reactor L is added to the input voltage Vin, It is applied to the snubber capacitor C3 and the smoothing capacitor C2. At that time, the reverse voltage is applied to the diode D2, and the snubber capacitor C3 is discharged, and the voltage across its terminals is rapidly lowered to zero, and the forward voltage is applied to the diode D2. Will be done. Thereby, a current flows through the diode D2. At this time, since the voltage across the synchronous rectification switch SW2 is 0 V, the synchronous rectification switch SW2 is turned on at this point, that is, after the main switch SW1 is turned off and after a predetermined delay time. Thereby, the diode D2
It is possible to realize zero voltage switching without causing a loss due to.

FIG. 6 is an explanatory view of the fourth embodiment of the present invention, in which a main switch SW1 and a diode are provided between an input terminal connected with a capacitor C1 and an output terminal connected with a smoothing capacitor C2. The main part of a switching power supply device of a buck-boost converter configuration in which a synchronous rectification switch SW2 having a configuration in which D2 is connected in parallel is connected in series, and a reactor L is connected to the connection point is shown. The main capacitor SW1 is turned on / off by the drive signal P1 from the control circuit 1, and the synchronous rectification switch SW2 is turned on / off by the drive signal P2 having a phase opposite to this.

When the main switch SW1 is turned off, the synchronous rectification switch SW2 continues to be in the off state as in the above-described respective embodiments, during which the snubber capacitor C3 is discharged by the induced voltage in the reactor L. In addition, the smoothing capacitor C2 is charged to the polarity shown. The snubber capacitor C3 is discharged and the voltage across its terminals is zero V
Then, a current due to the induced voltage of the reactor L flows through the diode D2, and the smoothing capacitor C2 is continuously charged. At this time, the voltage across the synchronous rectifying switch SW2 becomes 0 V, so the synchronous rectifying switch SW2 is turned on by the drive signal P2. That is, zero voltage switching can be performed.

FIG. 7 is an explanatory view of the fifth embodiment of the present invention, in which a main switch SW1 and a reactor L are provided between an input terminal connected with a capacitor C1 and an output terminal connected with a smoothing capacitor C2. Is connected in series, and a main part of a switching power supply device of a buck converter configuration in which a synchronous rectification switch SW2 is connected to the connection point is shown. A snubber capacitor C3 is connected in parallel with the synchronous rectification switch SW2, and the control circuit 1 The main switch SW1 is ON / OFF controlled by the drive signal P1 from the above, and the synchronous rectification switch SW2 is ON / OFF controlled by the drive signal P2 having a phase relationship opposite to this.

The control circuit 1 is similar to each of the above-described embodiments in that the drive signal P is controlled so as to keep the output voltage Vout constant.
1 controls ON / OFF of the main switch SW1,
When the main switch SW1 is turned on, the synchronous rectification switch SW2 is turned off, and when the main switch SW1 is turned off, a discharge current flows through the snubber capacitor C3,
Next, after the current flows through the diode D2, the synchronous rectification switch SW2 is turned on.

For example, when the main switch SW1 is on, the synchronous rectification switch SW2 is off, a current flows through the reactor L and is accumulated as excitation energy, and the snubber capacitor C3 is charged with a reverse polarity to the diode D2. To be done. Next, when the main switch SW2 is turned off, the synchronous rectification switch SW2 continues to be turned off, the voltage due to the excitation energy is induced in the reactor L, the snubber capacitor C3 is discharged, and the smoothing capacitor C2 is charged.

When the terminal voltage becomes zero due to the discharge of the snubber capacitor C3, a current then flows into the reactor L via the diode D2. At this time, the synchronous rectification switch S
Turn on W2. That is, zero voltage switching is performed.

FIG. 8 is an explanatory view of the sixth embodiment of the present invention, in which the main switch SW1 is connected to the primary winding N1 of the transformer 12 and the secondary winding N2 of this transformer 12 is
The first synchronous rectification switch SW2 having a configuration in which the diode D2 is connected in parallel and the second synchronous rectification switch SW3 having a configuration in which the diode D3 is connected in parallel are connected to the diode D2.
D3 are connected in series so that they have opposite polarities, a series circuit of a smoothing reactor L and a smoothing capacitor C2 is connected to both ends of the first synchronous rectification switch SW2, and both ends of the smoothing capacitor C2 are output terminals. The principal part of the switching power supply device of the connected forward converter structure is shown.

A snubber capacitor C3 is connected in parallel to the first synchronous rectification switch SW2 of this switching power supply device, and the control circuit 11 keeps the output voltage constant.
When the main switch SW1 is turned on and off, the second synchronous rectification switch SW3 is turned on and off in synchronization with the turning on and off of the main switch SW1, and when the main switch SW1 is turned on, the first switch Synchronous rectification switch SW
When the second switch is turned off and the main switch SW1 is turned off, a discharge current flows through the snubber capacitor C3, a current flows through the diode D2, and then the first synchronous rectification switch SW2 is turned on. There is.

Therefore, when the main switch SW1 is on, the first synchronous rectification switch SW2 is off, the second synchronous rectification switch SW3 is on, and the induced voltage in the secondary winding N2 of the transformer 12 is the third. Synchronous rectification switch SW3
And the reactor L, and is applied to the smoothing capacitor C2. Also, the snubber capacitor C3 is a diode D2.
It is charged with the opposite polarity.

Next, when the main switch SW1 is turned off, the second synchronous rectification switch SW3 is also turned off, and the first synchronous rectification switch SW2 is kept off. As a result, the snubber capacitor C3 is discharged to the smoothing capacitor C2 side by the induced voltage of the reactor L, and when the terminal voltage becomes zero, the reactor L passes through the diode D2.
Current flows through. At that time, the first synchronous rectification switch SW2 is turned on. Therefore, zero voltage switching can be performed.

The present invention is not limited to the above-mentioned embodiments, but can be variously modified and added.
The first to third synchronous rectifying switches SW1 to SW3 and the diodes D2 and D3 can be realized by field effect transistors each including a parasitic diode. The delay time for turning on the synchronous rectification switch SW2 after the main switch SW1 is turned off is obtained by the delay circuit shown in FIG. 4, or the discharge current of the snubber capacitor C3 is detected. , Using the timing of detecting the discharge current, synchronous rectification switch SW
It is also possible to adopt a configuration in which the turn-on control of 2 is performed.

[0058]

As described above, according to the present invention, there are provided a main switch SW1 including a field effect transistor and the like, a synchronous rectification switch SW2 including a field effect transistor and the like in which a diode D2 is connected in parallel, and the synchronous rectification switch SW2. A control circuit including a snubber capacitor C3 connected in parallel controls ON / OFF of the main switch SW1 so as to keep the output voltage Vout constant, and when the main switch SW1 is turned ON, a synchronous rectification switch is provided. When SW2 is turned off and the main switch SW1 is turned off, a discharge current flows through the snubber capacitor and a current flows through the diode D2.
Since it is turned on when the applied voltage to W2 becomes zero, there is an advantage that the loss due to the diode D2 for rectification can be reduced and the switching loss can be reduced by the zero voltage switching.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a synchronous rectification switch.

FIG. 4 is an explanatory diagram of a second embodiment of the present invention.

FIG. 5 is an explanatory diagram of a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a fifth embodiment of the present invention.

FIG. 8 is an explanatory diagram of a sixth embodiment of the present invention.

FIG. 9 is an explanatory diagram of a conventional flyback converter configuration.

FIG. 10 is an operation explanatory diagram of a conventional example.

FIG. 11 is an explanatory diagram of a boost converter configuration and a buck-boost converter configuration of a conventional example.

FIG. 12 is an explanatory diagram of a conventional buck converter configuration and forward converter configuration.

[Explanation of symbols]

1 control circuit 2 transformers SW1 main switch SW2 Synchronous rectification switch D2 diode C1 input side capacitor C2 smoothing capacitor C3 snubber capacitor Drive signal for P1 main switch Drive signal for P2 synchronous rectification switch

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H02M 3/28 H02M 3/28 RT (56) References JP-A-4-42776 (JP, A) JP-A-8-168239 (JP, A) JP-A-6-311443 (JP, A)

Claims (2)

(57) [Claims] 1. A main for turning on and off a DC input voltage
The pulse voltage generated by turning on and off the switch and the main switch
ON / OFF control in opposite phase to ON / OFF of the main switch by connecting directly or through a transformer
A synchronous rectification switch, a diode and scan <br/> snubber capacitor connected in parallel to the synchronous rectifier switch, as well as connected between the output terminal of said synchronous rectifier switch
A smoothing capacitor connected to apply a voltage depending on ON and OFF, and ON / OFF of the main switch is controlled so as to make the output voltage between the output terminals constant, and the main switch is turned on when the main switch is turned ON. When the synchronous rectification switch is turned off and the main switch is turned off, the delay time after the discharge current flows through the snubber capacitor and the current flows through the diode is set, and the synchronous rectification switch is turned on in the zero voltage state. And a control circuit configured to control the switching power supply device. 2. The control circuit includes an inversion circuit that inverts an on-drive signal that turns on the main switch and an off-drive signal that turns off the main switch, and an on-drive signal for the main switch that is inverted by the inversion circuit. An off drive signal for turning off the synchronous rectification switch is provided, and an off drive signal for the main switch inverted by the inversion circuit is made an on drive signal for turning on the synchronous rectification switch through a delay circuit. The switching power supply device according to claim 1, wherein: