JP2003037976A - Switching power device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power device in which a surge voltage to be generated in a reverse direction to an output rectifying diode is suppressed. SOLUTION: The switching power device is provided with a transformer 3, a switching circuit 1 provided on the input side of the transformer 3, a diode rectifying circuit provided on the output side of the transformer 3, an output smoothing circuit provided at the post stage of the diode rectifying circuit, a snubber circuit which contains at least serially connected snubber capacitor 59 and snubber diode 57 and suppresses the surge voltage to be generated in the reverse direction to the output rectifying diodes 7, 15 contained in the diode rectifying circuit, and clamp circuits which are connected in parallel between both ends of snubber capacitor 59 and clamp the voltage between the snubber capacitor 59. Thus, the voltage between both ends of the snubber capacitor 59 is clamped with the clamp circuit.

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, and more particularly, to switching including a snubber circuit.

[0002]

2. Description of the Related Art Conventionally, various types of switching power supply devices have been proposed, but the most common switching power supply device is a switching circuit that receives a DC input voltage and converts it into an alternating current, and a switching circuit. It is composed of a transformer that receives an output in an input winding, an output rectifying circuit that rectifies an AC voltage waveform that appears in the output winding of the transformer, and an output smoothing circuit that smoothes the output of the output rectifying circuit and converts the output to DC.

As an output rectifier circuit used in such a switching power supply device, a diode rectifier circuit using an output rectifier diode is most common. When a diode rectifier circuit is used as the output rectifier circuit, two important characteristics required for the output rectifier diode are that the forward voltage (Vf) is sufficiently low and that the reverse breakdown voltage is sufficiently high. To be However, it is known that a diode having a low forward voltage has a property that the reverse breakdown voltage is also low. For this reason, if an output rectifier diode having a sufficient reverse breakdown voltage is used, the forward voltage inevitably increases, and the loss generated in the output rectifier circuit increases.

Under such circumstances, various techniques have been proposed in the past for reducing the reverse voltage applied to the output rectifying diode, thereby making it possible to use the output rectifying diode having a low reverse withstand voltage. . A snubber circuit is one of such technologies. The snubber circuit is a circuit for suppressing a surge voltage generated in a reverse direction with respect to the output rectifying diode due to the switching operation of the switching circuit, and snubber circuits having various circuit configurations have been proposed.

As a conventional switching power supply device having a snubber circuit, for example, there is a switching power supply device described in WO00 / 79674A1.

FIG. 7 is a diagram showing FIG. 17 is a circuit diagram of the conventional switching power supply device described in FIG.

As shown in FIG. 7, FIG.
In the switching power supply device described in 17, the snubber circuit including the snubber inductor 23, the snubber diode 57, and the snubber capacitor 59 is added to the output rectifier circuit.
The surge voltage generated in the reverse direction of 5 is suppressed.

FIG. 8 shows FIG. 17 is an operation waveform diagram showing an operation of the conventional switching power supply device described in FIG.

As shown in FIG. 8, in the conventional switching power supply device, the peak voltage of the voltage Vc of the snubber capacitor 59 is 2 × Vin / n (n is the turns ratio of the transformer). The peak of the surge voltage generated in the reverse direction in the diode 15 is 4 × Vin /
It is suppressed by n. For example, Vin = 300V, n =
In the case of 10, the peak of the surge voltage generated in the output rectifying diode 15 in the reverse direction is 120V. Therefore, in this case, as the output rectifying diodes 7 and 15, diodes having a reverse breakdown voltage of about 120 V can be used.

[0010]

However, in order to further reduce the loss generated in the output rectifying circuit, a diode having a lower forward voltage, that is, a diode having a lower reverse breakdown voltage is used as the output rectifying diode. There is a need. Therefore, there is a demand for a switching power supply device in which the surge voltage is suppressed more than in the conventional switching power supply device.

Therefore, an object of the present invention is to provide a switching power supply device in which the surge voltage generated in the opposite direction to the output rectifying diode is further suppressed.

Another object of the present invention is to provide a switching power supply device having an improved snubber circuit.

[0013]

The object of the present invention is to:
A transformer, a switch circuit provided on the input side of the transformer, a diode rectifying circuit provided on the output side of the transformer, an output smoothing circuit provided at a subsequent stage of the diode rectifying circuit, and a snubber connected in series. A capacitor for snubber and at least a diode for snubber, a snubber circuit for suppressing a surge voltage generated in a reverse direction with respect to the output rectifying diode included in the diode rectifier circuit, and the snubber capacitor is connected in parallel across both ends, And a clamp circuit that clamps the voltage across the snubber capacitor.

According to the present invention, since the voltage between both ends of the snubber capacitor is clamped by the clamp circuit, the surge voltage generated in the opposite direction to the output rectifying diode is further suppressed. As a result, a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the output rectifying diode, so that a highly efficient switching power supply device can be provided.

In a preferred embodiment of the present invention, the clamp circuit has a voltage between the two ends of the snubber capacitor, which is twice the voltage obtained by dividing the input voltage to the switch circuit by the turns ratio of the transformer. Also clamp to a lower voltage.

In a further preferred aspect of the present invention, the clamp circuit clamps a voltage across the snubber capacitor to a voltage higher than a voltage obtained by dividing the input voltage by the turns ratio of the transformer.

In a further preferred aspect of the present invention, the clamp circuit clamps the voltage across the snubber capacitor to a voltage in the vicinity of a voltage obtained by dividing the input voltage by the turns ratio of the transformer.

[0018] In a further preferred aspect of the present invention, the clamp circuit includes a series circuit of a diode and a voltage source connected in parallel between both ends of the snubber capacitor.

The object of the present invention is also to provide a transformer having an input winding and an output winding, and a switch connected to the input winding of the transformer for switching a DC input voltage supplied to the input winding. A circuit and at least one output rectifying diode, one of the electrodes of the output rectifying diode being connected to one end of the output winding, and an output rectifying circuit connected on the input side to the other electrode of the output rectifying diode. An output smoothing circuit, and a snubber circuit, wherein the snubber circuit comprises a series-connected snubber capacitor and a snubber diode, wherein the series-connected snubber capacitor and snubber diode are the outputs. A snubber inductor is connected in parallel with the rectifier diode between the output winding and the other of the electrodes of the output rectifier diode, A switching power supply device connected to a connection point between the snubber capacitor and the snubber diode at an end, and to the output smoothing circuit at the other end, wherein the snubber inductor is at the other end. The snubber circuit is connected to the input side of the output smoothing circuit, and the snubber circuit further includes a clamp circuit connected in parallel between both ends of the snubber capacitor to clamp the voltage at the connection point. Achieved by a switching power supply.

Also in the present invention, since the clamp circuit is provided, a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the output rectifying diode, which results in high efficiency. It is possible to provide a simple switching power supply device.

The above object of the present invention is also directed to a transformer having an input winding, an output winding, and a center tap provided on the output winding, and connected to the input winding of the transformer,
A switch circuit for switching a DC input voltage supplied to the input winding, a first output rectifying diode whose one end is connected to one end of the transformer, and the same polarity as the one end of the first output rectifying diode. And a second output rectifying diode whose one end is connected to the other end of the transformer, wherein the other end of the first output rectifying diode and the other end of the second output rectifying diode having the same polarity are mutually A connected output rectifier circuit, an input side of which is connected to a connection point between the first output rectifier diode and the second output rectifier diode and the center tap of the transformer, and an output side of which is a pair of output terminals. A snubber circuit, the snubber circuit including a first snubber circuit, a second snubber circuit, and a snubber inductor, Of the snubber circuit includes a first snubber capacitor and a first snubber diode, and the first snubber capacitor and the first snubber diode are connected in series to each other to form a series circuit. ,
The series circuit is connected in parallel to the first output rectifying diode such that the first snubber diode has a reverse polarity relationship with the first output rectifying diode, and the second snubber circuit is , A second snubber capacitor,
A second snubber diode, wherein the second snubber capacitor and the second snubber diode are connected in series to each other to form a series circuit, and the series circuit includes the second snubber diode. Is connected in parallel with the second output rectifying diode so as to have a reverse polarity relationship with the second output rectifying diode, and one end of the snubber inductor is connected to the output side of the smoothing circuit,
The other end communicates with the first and second snubber circuits to form a unidirectional discharge path for the first and second snubber capacitors, and the snubber circuit further includes a unidirectional discharge path for the first snubber capacitor. A first clamp circuit, which is connected in parallel between both ends and clamps a voltage across the first snubber capacitor, and a second clamp circuit which is connected in parallel between both ends of the second snubber capacitor, And a second clamp circuit that clamps a voltage across the snubber capacitor.

Also in the present invention, since the clamp circuit is provided, a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the output rectifying diode, which results in high efficiency. It is possible to provide a simple switching power supply device.

The above object of the present invention is also directed to a transformer having an input winding, an output winding, and a center tap provided on the output winding, and connected to the input winding of the transformer,
A switch circuit for switching a DC input voltage supplied to the input winding, a first output rectifying diode whose one end is connected to one end of the transformer, and the same polarity as the one end of the first output rectifying diode. And a second output rectifying diode whose one end is connected to the other end of the transformer, wherein the other end of the first output rectifying diode and the other end of the second output rectifying diode having the same polarity are mutually A connected output rectifier circuit, an input side of which is connected to a connection point between the first output rectifier diode and the second output rectifier diode and the center tap of the transformer, and an output side of which is a pair of output terminals. And a snubber circuit, the snubber circuit including one snubber capacitor, one snubber diode, and
A snubber inductor, the snubber capacitor and the snubber diode are connected in series with each other, and are connected between the connection point of the first and second output rectifying diodes and the center tap. The snubber inductor has one end connected to the output side of the smoothing circuit and the other end connected to a connection point between the capacitor and the diode, and the snubber circuit further includes the snubber circuit. It is achieved by a switching power supply device characterized by comprising a clamp circuit connected in parallel between both ends of a capacitor for clamping to clamp the voltage at the connection point.

Also in the present invention, since the clamp circuit is provided, a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the output rectifying diode, which results in high efficiency. It is possible to provide a simple switching power supply device.

[0025]

DETAILED DESCRIPTION OF THE INVENTION Referring to the accompanying drawings,
A preferred embodiment of the present invention will be described in detail.

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

As shown in FIG. 1, the switching power supply device according to this embodiment has an input winding 2 and a transformer 3 composed of output windings 4 and 6 connected in series. The transformer 3 has a center tap 8 between the output windings 4 and 6,
The center tap 8 and both ends of the output windings 4 and 6 respectively form an output end. Number of turns n1 of input winding 2 and output winding 4
Of the input winding 2 and the number of turns n3 of the output winding 6 (n1 / n2).
In 3), both are n. Further, in the switching power supply device according to the present embodiment, the leakage inductance of the transformer 3 and the series inductance including the wiring are shown as L1.

The switching power supply device according to this embodiment further includes a switch circuit 1, an output rectifying circuit, an output smoothing circuit, and a snubber circuit.

The switch circuit 1 switches the DC input voltage Vin supplied through the input winding 2 of the transformer 3. This switch circuit 1 includes four switch elements S
This is a circuit configuration in which 1, S2, S3, and S4 are bridge-connected. As the switch elements S1, S2, S3, S4, various known elements or circuits can be used. The switch circuit 1 is controlled by the control circuit 39. Specifically, the control circuit 39 applies the control signals C1, C2, C3, and C4 to the switch circuit 1 to switch the switch circuit 1.
Control the switching operation of. Here, the control signal C
1, C2, C3, and C4 are switch elements S1 and S1, respectively.
This is a signal for controlling on / off of S2, S3, and S4. An input capacitor 27 is provided in the preceding stage of the switch circuit 1, and the switch circuit 1 has an input capacitor 27.
Is connected to the input terminals 31 and 33 via.

The output rectifying circuit includes a first output rectifying diode 7 and a second output rectifying diode 15. First
The anode of the output rectifier diode 7 is connected to one end of the output winding 4. Second output rectifying diode 15
Has an anode connected to one end of the output winding 6. The first and second output rectifying diodes 7 and 15 have cathodes of the same pole connected to each other. Therefore, the output rectifier circuit forms a center tap type rectifier circuit.

One of the input sides of the output smoothing circuit is the common cathode P of the first and second output rectifying diodes 7 and 15.
The center tap 8 is connected to
It is connected to the. The output side of the output smoothing circuit is led to the pair of output terminals 35 and 37. The output smoothing circuit smooths and outputs the rectified output of the output rectifying circuit.

More specifically, the output smoothing circuit is
Output choke coil 2 including output choke coil 25
5 is connected in series between one end on the input side and one end on the output side. Specifically, both ends of the output choke coil 25 are connected between the connection point P1 of the first and second output rectifying diodes 7 and 15 and the output terminal 35. Furthermore, the output smoothing circuit includes an output smoothing capacitor 29, and both ends of the output smoothing capacitor 29 are connected to the center tap 8 and an output terminal 37 and the output choke coil 2.
5 is connected to the output terminal 35.
The terminal voltage of the output smoothing capacitor 29 is the DC output voltage V
It is output as 0.

The snubber circuit includes a snubber capacitor 59.
A first snubber diode 57, a snubber inductor 23, a second snubber diode 100, and a snubber voltage source 101. The first snubber diode 57 and the snubber capacitor 59 are connected in series between the connection point P1 of the first and second output rectifying diodes 7 and 15 and the center tap 8. Specifically, the anode of the first snubber diode 57 is connected to the connection point P1 of the first and second output rectifying diodes 7 and 15, and the cathode of the first snubber diode 57 is the snubber capacitor 59. Snubber capacitor 59 connected to one end
The other end of is connected to the center tap 8. The snubber inductor 23 includes a connection point P1 between the first and second output rectifying diodes 7 and 15 and the first snubber diode 5
7 and the snubber capacitor 59 and a connection point P3. The second snubber diode 100 and the snubber voltage source 101 are connected in series between both ends of the snubber capacitor 59. Specifically, the anode of the second snubber diode 100 is the snubber capacitor 59.
Of the first snubber diode 57 and the snubber capacitor 59 and the second snubber diode 100 has a cathode connected to the snubber voltage source 101.
Of the snubber voltage source 101 is connected to the other end (center tap 8) of the snubber capacitor 59.

Here, the second snubber diode 100
The snubber voltage source 101 constitutes a clamp circuit, and the terminal voltage Vc of the snubber capacitor 59 is the voltage Vs1 of the snubber voltage source 101 and the forward voltage (falling voltage) of the second snubber diode 100. Sum with Vs2 (V
Clamp to s1 + Vs2).

The voltage Vs1 of the snubber voltage source 101 is (Vin [max] / n) -Vs2 <Vs1 when the maximum value of the DC input voltage Vin is Vin [max].
It is necessary to set it in the range of <(2Vin [max] / n) -Vs2, and it is preferable to set it as low as possible within the above range. The voltage V of the snubber voltage source 101
When s1 is set to (Vin [max] / n) -Vs2 or less, the terminal voltage Vc of the snubber capacitor 59 is Vin.
Since it is clamped below [max] / n, normal rectification operation is hindered. On the other hand, since the terminal voltage Vc of the snubber capacitor 59 does not exceed 2Vin [max] / n, the voltage Vc of the snubber voltage source 101.
When s1 is set to (2Vin [max] / n) -Vs2 or more, it is useless as a clamp circuit.

Next, the operation of the switching power supply device according to this embodiment will be described. The switch circuit 1 switches the DC input voltage Vin supplied from the input terminals 31, 33 to the input winding 2 of the transformer 3 based on the control signals C1, C2, C3, C4 from the control circuit 39,
Performs phase shift control. Switching output is transformer 3
Output to the output windings 4 and 6 side.

Due to the switching operation of the switch circuit 1, the voltages V01 and V02 appearing on the output windings 4 and 6 side are
It is rectified by the first and second output rectifying diodes 7 and 15, and a rectified output is generated between the center tap 8 and the connection point P1 of the first and second output rectifying diodes 7 and 15. The rectified output generated between the center tap 8 and the connection point P1 of the first and second output rectifying diodes 7, 15 is smoothed by the output smoothing circuit, and a pair of output terminals 35,
The DC output voltage V0 is taken out from 37.

Next, the operation of the switching power supply device according to this embodiment will be described in more detail.

FIG. 2 is an operation waveform diagram showing the operation of the switching power supply device according to this embodiment. In FIG. 2, the low level and the high level of the control signals C1, C2, C3, C4 correspond to the off state and the on state of the switch elements S1, S2, S3, S4, respectively.

As shown in FIG. 2, in the phase shift control, a control signal C1 for controlling the switch element S1 and a control signal C4 for controlling the switch element S4.
Becomes a high level alternately with a predetermined dead time, and a control signal C2 for controlling the switch element S2.
Is phase-shifted with respect to the control signal C1, and the control signal C3 for controlling the switch element S3 is the control signal C4.
Is phase-shifted with respect to. Here, the waveform of the output voltage Vuv of the switch circuit 1 is determined by the phase shift amount of the control signal C2 with respect to the control signal C1 and the phase shift amount of the control signal C3 with respect to the control signal C4. Specifically, as shown in FIG. 2, the control signal C1 and the control signal C
During the period when 2 is high level,
Since both the switch elements S1 and S2 are turned on, the waveform of the output voltage Vuv of the switch circuit 1 becomes Vin, while the control signal C3 and the control signal C4 are both at the high level, the switch Element S3
And S4 are both turned on, the switch circuit 1
The output voltage Vuv has a waveform of -Vin. In other periods, the output voltage Vuv of the switch circuit 1 is zero.

Therefore, the power transmitted to the output side of the transformer 3 is determined by the phase shift amount of the control signal C2 with respect to the control signal C1 and the phase shift amount of the control signal C3 with respect to the control signal C4, and the voltage Vin of the DC input power source is When it becomes smaller, the control circuit 39 reduces the phase shift amount of the control signal C2 with respect to the control signal C1 and the phase shift amount of the control signal C3 with respect to the control signal C4, whereby both the control signal C1 and the control signal C2 are at a high level. And the control signal C3 and the control signal C4
Prolongs the period when both are high level. On the other hand, when the voltage Vin of the DC input power source increases, the control circuit 39
Increases the phase shift amount of the control signal C2 with respect to the control signal C1 and the phase shift amount of the control signal C3 with respect to the control signal C4, whereby both the control signal C1 and the control signal C2 are at a high level, and The period in which both the control signal C3 and the control signal C4 are at the high level is shortened. Therefore, when the load connected to the output terminals 35 and 37 is in the light load state or the no load state, the control signal C1 and the control signal C2 are both at the high level, and the control signal C3 and the control signal C4 are In both cases, the high level period is zero, and no power is transmitted to the output side of the transformer 3.

Thus, when both the switch elements S1 and S2 are turned on, the DC voltage Vuv (= Vin) appears on the output side of the switch circuit 1, and when both the switch elements S3 and S4 are turned on. A DC voltage Vuv (= −Vin) appears on the output side of the switch circuit 1, and this DC voltage Vuv is supplied to the input winding 2 of the transformer 3. Here, between the switch circuit 1 and the input winding 2 of the transformer 3, there is a series inductance L1 including the leakage inductance of the transformer 3 and wiring. Therefore, the voltage Vt1 generated in the input winding 2 of the transformer 3
Shows an LC resonance voltage waveform as shown in FIG.
This voltage Vt1 is transmitted to the output side of the transformer 3 by the transformer coupling between the input winding 2 and the output windings 4 and 6.

More specifically, the switch elements S1 and S2
When both are turned on, the output winding 4 of the transformer 3,
The voltages V01 and V02 appearing at 6 are in the reverse direction with respect to the second output rectifying diode 15 and are in the forward direction with respect to the first output rectifying diode 7 and the first snubber diode 57. Therefore, as shown in FIG. 1, the first output rectifying diode 7 and the first snubber diode 5 are provided.
7, the snubber capacitor 59 and the charging loop Ic1 that surrounds the output winding 4 of the transformer 3 are formed. Charging loop I
At c1, an LC resonance circuit is formed by the leakage inductance L1 of the transformer 3 and the snubber capacitor 59, and the terminal voltage Vc of the snubber capacitor 59 is formed.
Rises according to the LC resonance voltage waveform.

However, in the switching power supply device according to this embodiment, the clamp circuit composed of the second snubber diode 100 and the snubber voltage source 101 is connected between both ends of the snubber capacitor 59. As shown in FIG. 2, the terminal voltage Vc of the snubber capacitor 59 is equal to the voltage V of the snubber voltage source 101.
It is clamped to the sum (Vs1 + Vs2) of s1 and the forward voltage (drop voltage) Vs2 of the second snubber diode 100. Therefore, the reverse voltage Vd2 applied to the second output rectifying diode 15 is 2 × (Vs1 in the period in which both the switch elements S1 and S2 are in the ON state.
It is clamped to + Vs2).

As described above, in the switch circuit 1,
During the period in which both the switch elements S1 and S2 are in the ON state, the voltage V0 that appears in the output winding 4 of the transformer 3
1 is in the forward direction with respect to the first output rectifying diode 7. Therefore, as shown in FIG. 1, the current Ix2 flows from the output winding 4 through the first output rectifying diode 7 to the input side of the output smoothing circuit.

Next, when the switch element S1 is turned off, the snubber inductor 23 becomes the snubber capacitor 5
A unidirectional discharge path Id for 9 is formed. Therefore, when the switch element S1 is turned off, the energy stored in the snubber capacitor 59 is regenerated to the load side through the unidirectional discharge path Id, and the efficiency can be improved.

Similarly, when both the switch elements S3 and S4 are turned on, the voltages V01 and V02 appearing at the output windings 4 and 6 of the transformer 3 are in the opposite directions with respect to the first output rectifying diode 7, Second output rectifier diode 1
5 and the first snubber diode 57. Therefore, as shown in FIG. 1, the charging loop Ic2 that surrounds the second output rectifying diode 15, the first snubber diode 57, the snubber capacitor 59, and the output winding 6 of the transformer 3 is formed. Also in the charging loop Ic2, the leakage inductance L1 of the transformer 3
And a snubber capacitor 59 constitute an LC resonance circuit, and the terminal voltage Vc of the snubber capacitor 59 is L
It rises according to the C resonance voltage waveform.

However, in the switching power supply device according to the present embodiment, as described above, the clamp circuit including the second snubber diode 100 and the snubber voltage source 101 is connected between both ends of the snubber capacitor 59. Therefore, the terminal voltage Vc of the snubber capacitor 59 is clamped to the sum (Vs1 + Vs2) of the voltage Vs1 of the snubber voltage source 101 and the forward voltage (falling voltage) Vs2 of the second snubber diode 100. . Therefore, the reverse voltage Vd1 applied to the first output rectifying diode 7 is 2 × (Vs1 + Vs) in the period in which both the switch elements S3 and S4 are in the ON state.
It is clamped to 2).

Therefore, in the switching power supply device according to this embodiment, the reverse voltages Vd1 and Vd2 applied to the first and second output rectifying diodes 7 and 15 can be suppressed, and the first and second output rectifier diodes 7 and 15 can be suppressed. As the output rectifying diodes 7 and 15, diodes having a low forward voltage drop can be used. Therefore, it is possible to reduce the loss due to the first and second output rectifying diodes 7 and 15 and obtain a switching power supply device including a highly efficient center tap type rectifier circuit with low energy consumption.

Further, as described above, the reverse voltages Vd1 and Vd applied to the first and second output rectifying diodes 7 and 15 are used.
Since 2 is clamped to 2 × (Vs1 + Vs2), the voltage Vs1 of the snubber voltage source 101 is (Vin [max] / n) −Vs2 <Vs1 <(2Vi
If it is set as low as possible within the range of n [max] / n) -Vs2, that is, within the above range, (Vin [max] / n) -V
If it is set near s2, the reverse voltage Vd applied to the first and second output rectifying diodes 7 and 15 accordingly.
1, Vd2 also becomes low. Therefore, the snubber voltage source 10
By setting the voltage Vs1 of 1 as low as possible within the above range, it becomes possible to use diodes having a lower forward voltage drop as the first and second output rectifying diodes 7, 15.

As a concrete example, Vin [ma
x] = 300V and n = 10, Vs1 = 30
If V and Vs2 = 0.6V are set, the reverse voltage Vd1 applied to the first and second output rectifying diodes 7 and 15 is
The peak of the surge voltage generated in the opposite direction to Vd2 is 61.
It is 2 V, which is significantly lower than the conventional peak voltage of 120 V.

As described above, in the switching power supply device according to this embodiment, the clamp circuit composed of the second snubber diode 100 and the snubber voltage source 101 is provided between both ends of the snubber capacitor 59. To set the terminal voltage Vc of the snubber capacitor 59 to Vs
Since it is clamped to 1 + Vs2, the first and second
Reverse voltage Vd applied to the output rectifying diodes 7, 15 of
It is possible to clamp 1 and Vd2 to 2 × (Vs1 + Vs2). As a result, a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the first and second output rectifying diodes 7 and 15, and thus a highly efficient switching power supply device is provided. You can

The clamp circuit can be applied to a switching power supply device having a circuit configuration different from that of the switching power supply device shown in FIG. Various switching power supply devices to which such a clamp circuit is applied will be described below with reference to the drawings.

FIG. 3 is a circuit diagram of a switching power supply device according to another preferred embodiment of the present invention. In the figure, the same components as those of the switching power supply device shown in FIG. 1 are designated by the same reference numerals.

As shown in FIG. 1, the switching power supply device according to this embodiment includes an input winding 2 and an output winding 4.
It has a transformer 3. In this embodiment,
The transformer 3 has one output winding 4, and both ends of the output winding 4 form an output end. The winding number ratio (n1 / n2) between the winding number n1 of the input winding 2 and the winding number n2 of the output winding 4 is n. Also in the switching power supply device according to the present embodiment, the leakage inductance of the transformer 3 and the series inductance including the wiring are shown as L1.

The switching power supply device according to this embodiment further includes a switch circuit 1, an output rectifying circuit, an output smoothing circuit, and a snubber circuit.

The switch circuit 1 switches the DC input voltage Vin supplied through the input winding 2 of the transformer 3. In this embodiment, the switch circuit 1 is
It is composed of only one switch element. The switch circuit 1 is connected in series with the input winding 2 of the transformer 3 to form a series circuit, and the series circuit has the input terminals 31, 33.
Connected between. Between the input terminals 31 and 33,
The input capacitor 27 is connected.

The output rectifying circuit includes a first output rectifying diode 7 and a second output rectifying diode 10. First
The anode of the output rectifier diode 7 is connected to one end of the output winding 4. The first output rectifying diode 7 is
The voltage V01 generated in the output winding 4 is rectified and output. The output rectifier circuit further includes a second output rectifier diode 10. The cathode of the second output rectifier diode 10 is connected to the cathode of the first output rectifier diode 7, and the anode of the second output rectifier diode 10 is connected to the other end of the output winding 4.

The output smoothing circuit has the same structure as the output smoothing circuit of the switching power supply device shown in FIG.

The snubber circuit includes a snubber capacitor 17
A first snubber diode 19, a snubber inductor 23, a second snubber diode 100, and a snubber voltage source 101. The first snubber diode 17 and the snubber capacitor 19 are connected in series between both ends of the first output rectifying diode 7. Specifically, the anode of the first snubber diode 19 is connected to the connection point P1 of the first and second output rectifying diodes 7 and 15, and the cathode of the first snubber diode 19 is the snubber capacitor 17. It is connected to one end and the other end of the snubber capacitor 17 is connected to the anode of the first output rectifying diode 7. The snubber inductor 23 has a connection point P1 between the first and second output rectifying diodes 7 and 15.
And the connection point P3 between the first snubber diode 19 and the snubber capacitor 17 are connected. The second snubber diode 100 and the snubber voltage source 101 are
It is connected in series between both ends of the snubber capacitor 17. Specifically, the anode of the second snubber diode 100 is connected to one end of the snubber capacitor 17 (the connection point P3 between the first snubber diode 19 and the snubber capacitor 17), and the second snubber diode 17 is connected. The cathode of 100 is connected to the high-side terminal of the snubber voltage source 101, and the low-side terminal of the snubber voltage source 101 is connected to the other end of the snubber capacitor 17 (one end of the output winding 4 of the transformer 3). .

Here, the second snubber diode 100
The snubber voltage source 101 constitutes a clamp circuit, and the terminal voltage Vc of the snubber capacitor 17 is set to the voltage Vs1 of the snubber voltage source 101 and the forward voltage (falling voltage) of the second snubber diode 100. Sum with Vs2 (V
Clamp to s1 + Vs2).

As for the voltage Vs1 of the snubber voltage source 101, when the maximum value of the DC input voltage Vin is Vin [max], (Vin [max] / n) -Vs2 <Vs1 <(2Vi
It is necessary to set in the range of n [max] / n) -Vs2, and it is preferable to set it as low as possible within the above range. Let the voltage Vs1 of the snubber voltage source 101 be (Vin [max] / n) -Vs
If the value is set to 2 or less, the terminal voltage Vc of the snubber capacitor 17 is clamped to Vin [max] / n or less, which hinders normal rectification operation. on the other hand,
The terminal voltage Vc of the snubber capacitor 17 is 2 Vin
Since it does not exceed [max] / n, the voltage Vs1 of the snubber voltage source 101 is (2Vin [max] / n)-
If it is set to Vs2 or more, it is useless as a clamp circuit.

Also in the switching power supply device having such a configuration, between the both ends of the snubber capacitor 17,
Second snubber diode 100 and snubber voltage source 1
Since the clamp circuit consisting of 01 is connected,
The reverse voltage applied to the first output rectifying diode 7 is 2
It is clamped to × (Vs1 + Vs2). This allows
Since a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the first output rectifying diode 7, a highly efficient switching power supply device can be provided.

FIG. 4 is a circuit diagram of a switching power supply device according to still another preferred embodiment of the present invention. In the figure, the same components as those of the switching power supply device shown in FIGS. 1 and 3 are designated by the same reference numerals.

As shown in FIG. 4, the switching power supply device according to the present embodiment has four switch elements S1, S2, S as in the switching power supply device shown in FIG.
3, a switch circuit 1 having a circuit configuration in which S4 is bridge-connected, a transformer 3 including an input winding 2 and output windings 4 and 6, and first and second output rectifying diodes 7 and 15
And an output smoothing circuit including an output choke coil 25 and an output smoothing capacitor 29, and a snubber circuit. The circuit configurations of the switch circuit 1, the transformer 3, the output rectifying circuit, and the output smoothing capacitor are the same as those of the switching power supply device shown in FIG. Note that the control circuit 39 for controlling the switch circuit 1 is not shown in FIG.

The snubber circuit includes a first snubber circuit and a second snubber circuit. The first snubber circuit includes a first snubber capacitor 17 and a first snubber diode 19
, The second snubber diode 21, the first snubber inductor 232, and the third snubber diode 100.
-1 and the first snubber voltage source 101-1. In addition, the second snubber circuit includes a second snubber capacitor 9, a fourth snubber diode 11, a fifth snubber diode 13, and a second snubber inductor 2
31, the sixth snubber diode 100-2, and the second snubber diode 100-2.
And the snubber voltage source 101-2.

Here, the third snubber circuit includes the third snubber circuit.
The snubber diode 100-1 and the first snubber voltage source 101-1 constitute a first clamp circuit, and the terminal voltage Vc of the first snubber capacitor 17 is
The voltage is clamped to the sum (Vs1 + Vs2) of the voltage Vs1 of the first snubber voltage source 101-1 and the forward voltage (drop voltage) Vs2 of the third snubber diode 100-1.
Similarly, a sixth snubber diode 100-2 and a second snubber voltage source 101- included in the second snubber circuit.
2 constitutes a second clamp circuit, and the terminal voltage Vc of the second snubber capacitor 9 is set to the voltage Vs1 of the second snubber voltage source 101-2 and the sixth snubber diode 100-2. Clamps to the sum (Vs1 + Vs2) of the forward voltage (falling voltage) of Vs2.

The voltage V of the first snubber voltage source 101-1
s1 and the voltage Vs1 of the second snubber voltage source 101-2 are set to be substantially equal, and the voltage Vs1 of the first and second snubber voltage sources 101-1 and 101-2 is: The maximum value of the DC input voltage Vin is Vin [max]
In the case of, (2Vin [max] / n) -Vs2 <Vs1 <(4V
It is necessary to set in the range of in [max] / n) -Vs2, and it is preferable to set as low as possible within the above range. When the voltage Vs1 of the first and second snubber voltage sources 101-1 and 101-2 is set to (2Vin [max] / n) -Vs2 or less, the terminals of the first and second snubber capacitors 17 and 9 are set. Since the voltage Vc is clamped to 2 Vin [max] / n or less, normal rectification operation is hindered. On the other hand, since the terminal voltage Vc of the first and second snubber capacitors 17 and 9 does not exceed 4 Vin [max] / n, the first and second snubber voltage sources 101-1 and 1
The voltage Vs1 of 01-2 is (4 Vin [max] / n)-
If it is set to Vs2 or more, it is useless as a clamp circuit.

Also in the switching power supply device having such a configuration, the third snubber diode 100-1 and the first snubber voltage source 101-1 are provided between the both ends of the first snubber capacitor 17. The first clamp circuit is connected, and the second clamp circuit including the sixth snubber diode 100-2 and the second snubber voltage source 101-2 is connected between both ends of the second snubber capacitor 9. Since they are connected, the reverse voltage applied to the first and second output rectifying diodes 7, 15 is 2 × (Vs1
It is clamped to + Vs2). As a result, a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the first and second output rectifying diodes 7 and 15, and thus a highly efficient switching power supply device is provided. You can

FIG. 5 is a circuit diagram of a switching power supply device according to still another preferred embodiment of the present invention. In the figure, the same components as those of the switching power supply device shown in FIGS. 1, 3 and 4 are designated by the same reference numerals.

The switching power supply device shown in FIG.
The first snubber inductor 232 and the second snubber inductor 231 included in the switching power supply device shown in FIG. 4 are combined into one snubber inductor 23. Other parts have the same configuration as the switching power supply device shown in FIG.

Also in this embodiment, the voltage Vs1 of the first snubber voltage source 101-1 and the second snubber voltage source 1
The voltage Vs1 of 01-2 is set to be substantially equal, and the first and second snubber voltage sources 101-1 and 10-1 are connected.
As the voltage Vs1 of 1-2, when the maximum value of the DC input voltage Vin is Vin [max], (2Vin [max] / n) -Vs2 <Vs1 <(4V
It is necessary to set in the range of in [max] / n) -Vs2, and it is preferable to set as low as possible within the above range. When the voltage Vs1 of the first and second snubber voltage sources 101-1 and 101-2 is set to (2Vin [max] / n) -Vs2 or less, the terminals of the first and second snubber capacitors 17 and 9 are set. Since the voltage Vc is clamped to 2 Vin [max] / n or less, normal rectification operation is hindered. On the other hand, since the terminal voltage Vc of the first and second snubber capacitors 17 and 9 does not exceed 4 Vin [max] / n, the first and second snubber voltage sources 101-1 and 1
The voltage Vs1 of 01-2 is (4 Vin [max] / n)-
If it is set to Vs2 or more, it is useless as a clamp circuit.

Also in the switching power supply device having such a configuration, the third snubber diode 100-1 and the first snubber voltage source 101-1 are provided between the both ends of the first snubber capacitor 17. The first clamp circuit is connected, and the second clamp circuit including the sixth snubber diode 100-2 and the second snubber voltage source 101-2 is connected between both ends of the second snubber capacitor 9. Since they are connected, the reverse voltage applied to the first and second output rectifying diodes 7, 15 is 2 × (Vs1
It is clamped to + Vs2). As a result, a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the first and second output rectifying diodes 7 and 15, and thus a highly efficient switching power supply device is provided. You can

FIG. 6 is a circuit diagram of a switching power supply device according to still another preferred embodiment of the present invention. In the figure, the same components as those of the switching power supply device shown in FIG. 5 are designated by the same reference numerals.

The switching power supply device shown in FIG.
Although it has substantially the same circuit configuration as the switching power supply device shown in FIG. 5, the snubber inductor 23 is provided on the output side of the output smoothing circuit, that is, the choke coil 25, the output smoothing capacitor 29 and the output terminal 35 in the output smoothing circuit. Is connected to the connection point between and. Other configurations are similar to those of the switching power supply device shown in FIG.

Therefore, also in this embodiment, the first
The voltage Vs1 of the snubber voltage source 101-1 and the voltage Vs1 of the second snubber voltage source 101-2 are set to be substantially equal to each other, and the first and second snubber voltage sources 10
As the voltage Vs1 of 1-1 and 101-2, when the maximum value of the DC input voltage Vin is Vin [max], (2Vin [max] / n) -Vs2 <Vs1 <(4V
It is necessary to set in the range of in [max] / n) -Vs2, and it is preferable to set as low as possible within the above range. When the voltage Vs1 of the first and second snubber voltage sources 101-1 and 101-2 is set to (2Vin [max] / n) -Vs2 or less, the terminals of the first and second snubber capacitors 17 and 9 are set. Since the voltage Vc is clamped to 2 Vin [max] / n or less, normal rectification operation is hindered. On the other hand, since the terminal voltage Vc of the first and second snubber capacitors 17 and 9 does not exceed 4 Vin [max] / n, the first and second snubber voltage sources 101-1 and 1
The voltage Vs1 of 01-2 is (4 Vin [max] / n)-
If it is set to Vs2 or more, it is useless as a clamp circuit.

Also in the switching power supply device having such a configuration, the third snubber diode 100-1 and the first snubber voltage source 101-1 are provided between the both ends of the first snubber capacitor 17. The first clamp circuit is connected, and the second clamp circuit including the sixth snubber diode 100-2 and the second snubber voltage source 101-2 is connected between both ends of the second snubber capacitor 9. Since they are connected, the reverse voltage applied to the first and second output rectifying diodes 7, 15 is 2 × (Vs1
It is clamped to + Vs2). As a result, a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop can be used as the first and second output rectifying diodes 7 and 15, and thus a highly efficient switching power supply device is provided. You can

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. It goes without saying that it is a thing.

For example, in the present invention, the circuit configuration of the input side circuit of the transformer 3 is not limited to the circuit configuration shown in each of the above-described embodiments, and the input side circuit of the transformer 3 has a forward winding structure. Any circuit configuration may be used as long as it is provided.

[0080]

As described above, in the present invention, since the terminal voltage of the snubber capacitor is clamped by using the snubber voltage source, the reverse voltage applied to the output rectifying diode is set to a predetermined value. It becomes possible to clamp to the voltage. As a result, it is possible to use a diode having a low reverse breakdown voltage, that is, a diode having a low forward voltage drop, as the output rectifying diode.
A highly efficient switching power supply device can be provided.

[Brief description of drawings]

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

FIG. 2 is an operation waveform diagram showing an operation of the switching power supply device according to the preferred embodiment of the present invention.

FIG. 3 is a circuit diagram of a switching power supply device according to another preferred embodiment of the present invention.

FIG. 4 is a circuit diagram of a switching power supply device according to another preferred embodiment of the present invention.

FIG. 5 is a circuit diagram of a switching power supply device according to another preferred embodiment of the present invention.

FIG. 6 is a circuit diagram of a switching power supply device according to another preferred embodiment of the present invention.

FIG. 7 is a circuit diagram of a conventional switching power supply device.

FIG. 8 is an operation waveform diagram showing an operation of the conventional switching power supply device.

[Explanation of symbols]

1 switch circuit 2 input winding 3 transformers 4, 6 output winding 7 First output rectifier diode 8 center tap 10,15 Second output rectifier diode 11 Fourth snubber diode 13 Fifth snubber diode 17 Snubber capacitors 19 First snubber diode 21 Second snubber diode 23 Snubber inductor 25 output choke coil 27 Input capacitor 29 Output smoothing capacitor 31, 33 Input terminals 35, 37 output terminals 39 Control circuit 57 First Snubber Diode 59 Snubber capacitors 100 Second snubber diode 101 Snubber voltage source 100-1 Third snubber diode 100-2 Sixth snubber diode 101-1 First voltage source for snubber 101-2 Second snubber voltage source 231 Second inductor for snubber 232 First snubber inductor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomoyuki Kondo             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. F-term (reference) 5H730 AA02 AA20 AS01 BB27 BB57                       DD01 DD41 EE03 EE08 EE59                       FD01

Claims (8)

[Claims] 1. A transformer, a switch circuit provided on the input side of the transformer, a diode rectifier circuit provided on the output side of the transformer, and an output smoothing circuit provided after the diode rectifier circuit. A snubber circuit, which includes at least a snubber capacitor and a snubber diode connected in series, suppresses a surge voltage generated in a reverse direction with respect to an output rectifying diode included in the diode rectifying circuit, and is parallel between both ends of the snubber capacitor. A switching power supply device comprising: a clamp circuit that is connected and clamps a voltage across the snubber capacitor. 2. The clamp circuit clamps the voltage across the snubber capacitor to a voltage lower than twice the voltage obtained by dividing the input voltage to the switch circuit by the turns ratio of the transformer. The switching power supply device according to claim 1. 3. The clamp circuit clamps a voltage across the snubber capacitor to a voltage higher than a voltage obtained by dividing the input voltage by a turns ratio of the transformer. The switching power supply described. 4. The clamp circuit clamps the voltage across the snubber capacitor to a voltage in the vicinity of a voltage obtained by dividing the input voltage by the turns ratio of the transformer. The switching power supply described. 5. The switching according to claim 1, wherein the clamp circuit comprises a series circuit of a diode and a voltage source connected in parallel between both ends of the snubber capacitor. Power supply. 6. A transformer having an input winding and an output winding; a switch circuit connected to the input winding of the transformer for switching a DC input voltage supplied to the input winding; An output rectifying circuit including an output rectifying diode, one of electrodes of the output rectifying diode being connected to one end of the output winding, and an output smoothing circuit being connected to the other electrode of the output rectifying diode on the input side, A snubber circuit, wherein the snubber circuit comprises a series-connected snubber capacitor and a snubber diode, wherein the series-connected snubber capacitor and the snubber diode are parallel to the output rectifying diode. A snubber inductor, which is connected between the output winding and the other of the electrodes of the output rectifying diode, has a snubber inductor at one end. A switching power supply device connected to the output smoothing circuit at the other end at the connection point between the capacitor for snubber and the snubber diode, wherein the snubber inductor is at the other end of the output smoothing circuit. The switching power supply device is connected to an input side, and the snubber circuit further includes a clamp circuit connected in parallel between both ends of the snubber capacitor to clamp a voltage at the connection point. 7. A transformer having an input winding, an output winding, and a center tap provided on the output winding, and a DC input voltage connected to the input winding of the transformer and supplied to the input winding. A switch circuit for switching the first output rectifying diode having one end connected to one end of the transformer and one end having the same polarity as the one end of the first output rectifying diode connected to the other end of the transformer. And a second output rectifying diode, wherein the other end of the first output rectifying diode having the same polarity and the other end of the second output rectifying diode are connected to each other, and An output connected to a connection point between the first output rectifying diode and the second output rectifying diode and the center tap of the transformer, the output side of which is connected to a pair of output terminals. And a snubber circuit, wherein the snubber circuit includes a first snubber circuit, a second snubber circuit, and a snubber inductor, and the first snubber circuit includes a first snubber circuit. Capacitor and a first snubber diode, wherein the first snubber capacitor and the first snubber diode are connected in series to each other to form a series circuit, and the series circuit is the first circuit. The snubber diode is connected in parallel to the first output rectifier diode so as to have a reverse polarity relationship with the first output rectifier diode, and the second snubber circuit includes a second snubber capacitor And a second snubber diode, wherein the second snubber capacitor and the second snubber diode are connected in series to each other to form a series circuit, and the series circuit includes: The second snubber diode is connected in parallel with the second output rectifier diode so as to have a reverse polarity relationship with the second output rectifier diode, and one end of the snubber inductor is connected to the smoothing circuit. The one end is connected to the output side and the other end communicates with the first and second snubber circuits to form a unidirectional discharge path for the first and second snubber capacitors. Further, the snubber circuit includes the first and second snubber circuits. A first clamp circuit, which is connected in parallel across both ends of the first snubber capacitor and clamps a voltage across the first snubber capacitor, and is connected in parallel across both ends of the second snubber capacitor. And a second clamp circuit that clamps a voltage across the second snubber capacitor. 8. A transformer having an input winding, an output winding, and a center tap provided on the output winding, and a DC input voltage connected to the input winding of the transformer and supplied to the input winding. A switch circuit for switching the first output rectifying diode having one end connected to one end of the transformer and one end having the same polarity as the one end of the first output rectifying diode connected to the other end of the transformer. And a second output rectifying diode, wherein the other end of the first output rectifying diode having the same polarity and the other end of the second output rectifying diode are connected to each other, and An output connected to a connection point between the first output rectifying diode and the second output rectifying diode and the center tap of the transformer, the output side of which is connected to a pair of output terminals. And a snubber circuit, wherein the snubber circuit includes one snubber capacitor, one snubber diode, and one snubber inductor, and the snubber capacitor and the snubber diode. Are connected in series with each other, and are connected between a connection point of the first and second output rectifying diodes and the center tap, and one end of the snubber inductor is connected to the output side of the smoothing circuit. The other end is connected to a connection point between the capacitor and the diode, and the snubber circuit is connected in parallel between both ends of the snubber capacitor to clamp the voltage at the connection point. A switching power supply device comprising a circuit.