JP2000333452A - Forward converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clamp reset pulse voltage of a main switching element. SOLUTION: A transformer 1 is provided with an auxiliary coil 28 and a reset pulse voltage clamping circuit 27. The reset pulse voltage clamping circuit 27 is for clamping the reset pulse voltage of the auxiliary coil 28 at a set value and forms a voltage multiplier rectifying circuit. An output voltage Vout output to a load 20 is controlled stably substantially to a set value. The sum of a charge voltage value of a capacitor 19 and that of a capacitor 33 is clamped to a set value by the load 20. With this method, even if the reset pulse voltage of the auxiliary coil 28 is clamped, the reset pulse voltage of the main switching element Q is also necessarily clamped. Accordingly, the reset pulse voltage of the main switching element Q can be clamped by a simple configuration, moreover without using expensive components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulation type forward converter such as a DC-DC converter having a transformer.

[0002]

2. Description of the Related Art FIG. 12 shows an example of a resonance reset type forward converter. As shown in FIG. 12, this forward converter has a transformer 1, a primary coil 2 of the transformer 1 is connected to a primary circuit 3, and a secondary coil 4 is connected to an output circuit (secondary circuit) 5. ing. The transformer 1 is provided with a tertiary coil 6, and a control power supply circuit 7 is connected to the tertiary coil 6.

The primary circuit 3 includes a main switch element Q (FIG. 1).
2, a MOS-FET), a capacitor 10, a resistor 11, and a switch element 12.
The input terminal 3a of the primary circuit 3 is connected to the positive terminal of a DC input power supply 8, and the input terminal 3b is connected to the negative terminal of the input power supply 8. Further, a control circuit 13 for controlling the on / off operation of the main switch element Q is connected to the gate of the main switch element Q.

The output circuit 5 comprises a MOS-FET 14 which is a commutation-side synchronous rectifier, a resistor 15 and diodes 16 and 1.
7, a choke coil 18, and a smoothing capacitor 19. Output terminals 5 a and 5 b of the output circuit 5 are connected to a load 20. The output circuit 5 has a function of rectifying and smoothing the energy of the transformer 1 based on the ON / OFF operation of the main switch element Q and outputting a DC voltage (current) to the load 20.

That is, as shown in FIG. 12, the choke coil 18 is provided on the path from one end 4a of the secondary coil 4 to the output end 5a of the output circuit 5, and the secondary coil 4
The diode 17 is interposed on the path from the other end 4b of the output circuit 5 to the output terminal 5b of the output circuit 5 with the cathode of the diode 17 facing the secondary coil 4. The smoothing capacitor 19 has one end connected to the output terminal 5a side of the choke coil 18 and the other end connected to the anode side of the diode 17.

Further, the drain side of the MOS-FET 14 is connected to the secondary coil 4 side of the choke coil 18 and the source side of the MOS-FET 14 is connected to the anode side of the diode 17.
The gate of 4 is connected to the cathode side of the diode 17 via the resistor 15. This MOS-FET 1
4 is connected to the cathode side of a diode 16, and the anode side of the diode 16 is connected to the MOS-
It is connected to the source side of FET14.

The output circuit 5 shown in FIG. 12 has the above-described circuit configuration. As described above, the energy of the secondary coil 4 is choke-input rectified, and the DC output voltage Vou
t Output the output current Iout to the load 20.

The control power supply circuit 7 includes a diode 2
1 and 22, a choke coil 23, and a capacitor 24. The energy of the tertiary coil 6 is choke-input rectified to charge the capacitor 24, and the control circuit 13 uses the charged voltage of the capacitor 24 as control power as control power. To supply. At startup, the capacitor 2
Since no charge is stored in the control circuit 4, the control power cannot be supplied from the control power supply circuit 7 to the control circuit 13. Therefore, a circuit (not shown) for turning on the switch element 12 of the primary circuit 3 at startup is provided. At startup, the switch element 12 is turned on, and the power of the input power supply 8 connects the resistor 11 and the switch element 12. As described above, the control power is supplied to the control circuit 13.

A detection circuit (not shown) for detecting the voltage Vout (or current Iout) output from the output circuit 5 to the load 20 is provided, and the control circuit 13 detects the voltage Vout (or the current Iout) by the detection circuit. Based on the detected output voltage (or detected output current), the output voltage Vout
A configuration is provided for controlling the ON / OFF operation of the main switch element Q so that (output current Iout) becomes a set value.
By the output stabilization control by the control circuit 13, the forward converter applies a stable output voltage Vou to the load 20.
t (or output current Iout).

[0010]

During the off period of the main switching element Q, the transformer 1 is reset by LC resonance between the exciting inductance L of the transformer 1 and the parasitic capacitance C of the main switching element Q. . In the resonance reset type forward converter as shown in FIG. 12, during the reset period, the following reset pulse voltage due to the LC resonance is applied to each of the coils 2, 4, 6 and the main switch element Q of the transformer 1. appear.

FIGS. 2 (e) and 2 (f) show waveform examples of the reset pulse voltage Pr generated on the drain side of the main switch element Q. FIG. FIG. 2F is a waveform example when the input voltage Vin supplied from is the minimum value of the predetermined standard, and FIG. 2F is a waveform example when the input voltage Vin is the maximum value of the standard.

As shown in FIGS. 2E and 2F, in the resonance reset type forward converter,
The pulse width H of the reset pulse voltage Pr is equal to the input voltage Vin.
Irrespective of the magnitude of the input voltage Vin, the peak value Vp of the reset pulse voltage Pr increases as the magnitude of the input voltage Vin increases.

As described above, in the resonance reset type forward converter, the peak value Vp of the reset pulse voltage Pr increases as the magnitude of the input voltage Vin increases. High withstand voltage MOS-FE that can withstand a large reset pulse voltage peak value Vp corresponding to the maximum input voltage.
There is a problem that T must be used as the main switching element Q.

As described above, when a high breakdown voltage MOS-FET is used as the main switch element Q, a high breakdown voltage MOS-FE
Since T is expensive, there arises a problem that the price of the forward converter rises, and a problem that the ON-resistance of the MOS-FET is very large, which causes a large conduction loss and lowers the circuit efficiency.

In the resonance reset type forward converter, as described above, the pulse width H of the reset pulse voltage Pr is constant regardless of the magnitude of the input voltage Vin. Therefore, there is a concern that a problem that conduction loss of the output circuit 5 shown in FIG.

This is for the following reason. FIG.
In the configuration shown in FIG. 2, during the off period of the main switch element Q,
MOS-FET 14 using reset pulse voltage Pr
Are turned on. Further, as the input voltage Vin increases, the period T during which the main switch element Q is turned off is reduced.
off is longer. As shown in FIG. 2E, the off period Toff of the main switch element Q when the standard minimum input voltage Vin is supplied and the pulse width H of the reset pulse voltage Pr generated in the main switch element Q are different. When the circuit is configured so as to be substantially equal to each other, when the minimum input voltage Vin is supplied, the MOS is almost completely turned off during the off period of the main switch element Q.
While the FET 14 can be turned on, when the standard maximum input voltage Vin is supplied, as compared to when the minimum input voltage Vin is supplied, as shown in FIG. Although the off-period Toff of the switch element Q becomes longer, the pulse width H of the reset pulse voltage Pr does not change, so that the MOS-FET 14 is turned off regardless of the off-period of the main switch element Q. The time will be quite long.

During the off period of the main switch element Q, the MOS
-When the FET 14 is turned off, the current is
6 and the diode 16 is MOS
Since the forward voltage drop is larger than that of the FET 14, when the current flows through the diode 16, the MOS-FET 1
4, the conduction loss in the output circuit 5 increases.

As described above, in the forward reset converter of the resonance reset type, there is a concern that the conduction loss of the output circuit 5 during the off period of the main switching element Q increases as the input voltage Vin increases.

In order to prevent the problem of increased conduction loss, the off-period Toff of the main switch element Q when the standard maximum input voltage Vin is supplied is substantially equal to the pulse width H of the reset pulse voltage Pr. It is conceivable to configure the circuit so that However, as such,
When the circuit is configured, when the input voltage Vin is smaller than the maximum value of the standard, the main switch element Q is turned on during the generation of the reset pulse voltage Pr, that is, before the reset of the transformer 1 is completed. In this case, short-circuit loss of the parasitic capacitance of the main switch element Q occurs, and the main switch element Q is turned on while the MOS-FET 14 is on.
There is a problem that a short-circuit current flows through the S-FET 14.

In the resonant reset type forward converter, as described above, the pulse width H of the reset pulse voltage Pr is constant irrespective of the magnitude of the input voltage Vin of the input power supply 8, and the reset pulse voltage Pr Since the peak value Vp increases as the input voltage Vin increases, various problems may occur.

An active reset type forward converter as shown in FIG. 10 capable of preventing occurrence of these problems has been proposed. In FIG. 10, the same components as those of the resonance reset type forward converter shown in FIG. 12 are denoted by the same reference numerals, and redundant description of the common portions will be omitted.

A characteristic of the active reset type forward converter shown in FIG. 10 is that a MOS-FET 25 is provided in the primary circuit 3. M above
The source of the OS-FET 25 is connected to the drain of the main switch element Q, the drain of the MOS-FET 25 is connected to the capacitor 10, and the gate of the MOS-FET 25 is connected to the control circuit 13.

The MOS-FET 25 is connected to the control circuit 13
The switching operation is controlled so that the main switch element Q is turned on during the off-period, and the MOS-FET 25 controls the main switch element Q as shown in FIGS. 2C and 2D. The reset pulse voltage Pr generated in Q can be clamped to a set value. The waveform of the reset pulse voltage Pr shown in FIG. 2C is an example of a waveform when the standard minimum input voltage Vin is supplied, and the waveform of the reset pulse voltage Pr shown in FIG. 5 is a waveform example when the maximum input voltage Vin is supplied.

In the active reset type forward converter shown in FIG. 10, since the reset pulse voltage Pr of the main switch element Q is clamped to the set value as described above, the reset is performed regardless of the magnitude of the input voltage Vin. The peak value Vp of the pulse voltage Pr can be made substantially constant. From this, it is possible to suppress the peak value of the voltage applied to the main switching element Q during the OFF period of the main switching element Q, and to provide the high withstand voltage MO to the main switching element Q.
The effect of not using an S-FET can be obtained.

Also, as shown in FIGS. 2C and 2D, by clamping the reset pulse voltage Pr to a set value, the pulse width H of the reset pulse voltage Pr becomes larger than the input voltage Vin. Therefore, the main switching element Q can be changed regardless of the magnitude of the input voltage Vin.
And the pulse width H of the reset pulse voltage Pr can be made substantially the same.

The reset pulse voltage P of the main switch element Q
r, a reset pulse voltage having a waveform similar to that of r is generated in the secondary coil 4. As described above, the reset pulse voltage Pr of the main switch element Q is clamped to a set value, so that the MOS-FET 14 Turns on over almost the entire area of the period when the main switch element Q is off, regardless of the magnitude of the input voltage Vin, and the MOS-F is turned on during the off period of the main switch element Q as described above.
It is possible to prevent an increase in conduction loss caused by the ET 14 being turned off, and to prevent the main switch element Q from being turned on before the reset of the transformer 1 ends. It is possible to avoid the problem of short-circuit loss due to parasitic capacitance and the problem of short-circuit current flowing through the MOS-FET 14.

However, in the active reset type forward converter shown in FIG. 10, since the source potential of the main switch element Q is different from the source potential of the MOS-FET 25, it is not shown.
A drive transformer must be provided to drive the MOS-FET 25, which causes a problem that the size of the forward converter is increased.

The main switching element Q and the MOS-FET
Dead time Td shown in FIG.
The circuit configuration for providing the dead time Td and controlling the switching of the MOS-FET 25 is very complicated.
There is a problem that the circuit configuration of No. 3 becomes very complicated, which hinders the cost reduction of the forward converter.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a forward converter capable of clamping a reset pulse voltage of a main switch element to a set value with a simple circuit configuration. To provide.

[0030]

In order to achieve the above-mentioned object, the present invention provides means for solving the above-mentioned problems with the following constitution. That is, the first invention has an output circuit that rectifies and smoothes the energy of the transformer based on the ON / OFF operation of the main switch element and outputs the rectified energy. In a forward converter configured to generate a reset pulse voltage, an auxiliary winding portion including an auxiliary coil provided in a transformer; and a reset pulse voltage for clamping the reset pulse voltage generated in the auxiliary coil to a set value. The auxiliary winding unit has a first auxiliary coil and a second auxiliary coil, and the reset pulse voltage clamp circuit is configured to switch the first pulse when the main switch element is turned on. An on-on rectification charging circuit for rectifying the energy of the auxiliary coil and charging the first charging capacitor unit, and a main switch element turned off And an on-off rectification charging circuit for rectifying the energy of the second auxiliary coil and charging the second charging capacitor unit when the first and second auxiliary coils are in operation. Is provided with a connection portion connected to a charging voltage clamp portion. The charging voltage clamp portion provides a voltage value obtained by adding the charging voltage value of the first charging capacitor portion and the charging voltage value of the second charging capacitor portion. Is clamped to a set value, and the reset pulse voltage clamp circuit includes a charge voltage value of the first charge capacitor unit and a second voltage value.
The reset pulse voltage generated in the second auxiliary coil is clamped by clamping the sum of the charge voltage value of the charge capacitor unit and the reset pulse voltage of the main switch element. It is characterized by having.

According to a second aspect of the present invention, there is provided an output circuit for rectifying and smoothing the energy of a transformer based on the on / off operation of the main switch element, and outputting the rectified energy. An auxiliary winding portion comprising an auxiliary coil provided in a transformer, and a reset pulse for clamping the reset pulse voltage generated in the auxiliary coil to a set value. A voltage clamp circuit, the auxiliary winding section has an auxiliary coil, the reset pulse voltage clamp circuit is a multiple voltage rectifier circuit, and the multiple voltage rectifier circuit has an energy of the auxiliary coil. Is configured to charge the capacitor section by multiplying the voltage by multiple times, and the capacitor section is connected to the charging voltage clamp section. A connection portion is provided, and the charging voltage of the capacitor portion is clamped to a set value by the charging voltage clamp portion.The reset pulse voltage clamp circuit is configured such that the charging voltage of the capacitor portion is clamped, The reset pulse voltage of the auxiliary coil is clamped, and the reset pulse voltage of the main switch element is clamped.

A third aspect of the present invention has the configuration of the first or second aspect, wherein the forward converter has a circuit configuration for stabilizing an output voltage output to a load, and causes the load to function as a charging voltage clamping unit. It is configured as a feature.

According to a fourth aspect of the present invention, there is provided the control circuit according to the second aspect of the present invention, wherein the control circuit controls the on / off operation of the main switch element in a direction to stabilize the output voltage output from the forward converter to the load. The capacitor portion of the multiple voltage rectifier circuit, which is a reset pulse voltage clamp circuit, is provided between terminals to which the load is connected, and the transformer is provided with a control power supply auxiliary coil. A control power supply multiple voltage rectifier circuit for rectifying the energy of the power supply auxiliary coil and charging the control power supply capacitor unit is provided. The control circuit supplies the charging voltage of the power supply capacitor section as control power to the control circuit, and forwards a voltage corresponding to the charging voltage of the control power supply capacitor section. Forms as a detection output voltage of de converter and configured to apply to the control circuit, the control circuit,
The stabilization control of the output voltage of the forward converter is performed based on the detected output voltage of the forward converter added from the control power supply multiple voltage rectifier circuit.

According to a fifth aspect of the present invention, there is provided the configuration of any one of the first to fourth aspects of the present invention, wherein the output circuit includes a commutation-side synchronous rectifier that is turned on based on a reset pulse voltage. The feature is that it is.

In the invention having the above configuration, the reset pulse voltage clamp circuit clamps a reset pulse voltage generated in the auxiliary coil of the auxiliary winding unit to a set value. Since a reset pulse voltage having the same voltage waveform as the reset pulse voltage of the auxiliary coil is generated in the main switch element, the reset pulse voltage of the auxiliary coil is clamped to the set value by the reset pulse voltage clamp circuit as described above. Thereby, the reset pulse voltage of the main switch element can be clamped.

The reset pulse voltage clamp circuit for clamping the reset pulse voltage of the auxiliary coil can be constructed with a simple circuit configuration and without using expensive parts, so that the circuit configuration of the forward converter is complicated. The excellent effect obtained by clamping the reset pulse voltage of the main switch element as described above can be obtained while suppressing the increase in cost, and the above-mentioned problem can be solved.

[0037]

Embodiments of the present invention will be described below with reference to the drawings.

A characteristic of the first embodiment is that, as shown in FIG. 1A and FIG. 1B, the auxiliary winding portion 26 and the reset That is, a pulse voltage clamp circuit 27 is provided.

The forward converters shown in FIGS. 1 (a) and 1 (b) both use the on / off operation of the main switch element Q as in the case of the resonance reset type forward converter shown in FIG. The output circuit 5 has a configuration in which the output circuit 5 performs choke input rectification and smoothing based on the input energy of the input power source 8 and outputs the energy to the load 20. The circuit shown in FIG. The difference between the circuits shown in FIG.
-Whether or not the FET 14 is provided. In FIGS. 1A and 1B, the same components as those in the circuit shown in FIG. 12 are denoted by the same reference numerals, and in the description of the first embodiment, the circuit shown in FIG. The duplicate description of the common part is omitted. Although not shown in FIGS. 1A and 1B, the forward converters shown in FIGS. 1A and 1B are also similar to the primary circuit shown in FIG. 3, a resistor 11 and a switch element 12 are provided, and a circuit for supplying control power to the control circuit 13 and a detection circuit for detecting an output voltage Vout (or an output current Iout) output to the load 20 are provided. ing.

In the first embodiment, as described above, the auxiliary winding unit 2 which is characteristic in the first embodiment is used.
6 and a reset pulse voltage clamp circuit 27 are provided. The auxiliary winding section 26 has an auxiliary coil 28 provided in the transformer 1 and a reset pulse voltage clamp circuit 27.
Has a configuration in which the reset pulse voltage generated in the auxiliary coil 28 is clamped to a set value.

Since the reset pulse voltage Pr generated in the main switch element Q has a voltage waveform substantially similar to the reset pulse voltage of the auxiliary coil 28, the reset pulse voltage clamp circuit 27 generates the reset pulse voltage Pr of the auxiliary coil 28. Is clamped, the reset pulse voltage Pr of the main switching element Q can be clamped as shown in FIGS.

The voltage waveform shown in FIG.
FIG. 2 is a waveform example of a reset pulse voltage Pr generated on the drain side of the main switching element Q when the input voltage Vin is the minimum value of the standard in the forward converter having the circuit configuration shown in the embodiment of FIG. The voltage waveform shown in (b) is a waveform example of the reset pulse voltage Pr generated on the drain side of the main switch element Q when the input voltage Vin is the maximum value of the standard. As shown in FIGS. 2 (a) and 2 (b), by clamping the reset pulse voltage Pr of the main switch element Q, the input power source 8 is switched in the same manner as in the active reset type forward converter shown in FIG. Irrespective of the magnitude of the input voltage Vin, the peak value of the reset pulse voltage Pr can be suppressed to a substantially constant value, and the off period Toff of the main switch element Q, which varies according to the magnitude of the input voltage Vin, Similarly, the pulse width H of the reset pulse voltage Pr can be varied.

As will be described later, the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 can be formed with a very simple circuit configuration and without using expensive components. The reset pulse voltage P of the main switch element Q is reduced while suppressing complication and price increase.
The above-described excellent effects obtained by clamping r can be obtained.

Hereinafter, four examples of the circuit configuration of the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 will be described. Of course, the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 clamp the reset pulse voltage generated in the auxiliary coil 28 of the auxiliary winding section 26 to a set value to clamp the reset pulse voltage Pr of the main switch element Q. What is necessary is to have a circuit configuration that can
The present invention is not limited to the circuit configuration shown below.

FIG. 3 shows a first circuit configuration example of the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27. The auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 shown in FIG.
Is a circuit incorporated in the circuit shown in FIG.
Can be incorporated in the circuit shown in FIG.

The auxiliary winding section 26 shown in FIG. 3 includes a first auxiliary coil 28a and a second auxiliary coil 28b, and the reset pulse voltage clamp circuit 27 includes a first diode 30 and a second auxiliary coil 28a. It has two diodes 31, a first charging capacitor unit 32, and a second charging capacitor unit 33.

That is, the anode of the first diode 30 is connected to one end of the first auxiliary coil 28a, and the cathode of the first diode 30 is connected to one end of the first charging capacitor 32. The other end of the first charging capacitor section 32 is connected to the other end of the first auxiliary coil 28a.

The anode of the second diode 31 is connected to one end of the second auxiliary coil 28b, and the cathode of the second diode 31 is connected to one end of the second charging capacitor unit 33. The other end of the second charging capacitor section 33 is connected to the other end of the second auxiliary coil 28b. The first charging capacitor section 32 and the second charging capacitor section 33 are connected in series, and both ends of a series connection of the first charging capacitor section 32 and the second charging capacitor section 33 Each is connected to the charging voltage clamp section 34 via the connection sections 27a and 27b.

In the example shown in FIG. 3, the charging voltage clamp section 34 is constituted by a series connection of a resistor 35 and a Zener diode 36, and this series connection is formed by connecting the charging capacitor sections 32, 33 in series. Connected in parallel to the connector.

In the first circuit configuration example, the auxiliary winding unit 2
6 and the reset pulse voltage clamp circuit 27 are configured as described above. When the main switch element Q is on, the energy of the first auxiliary coil 28a
Is supplied through a path that passes through the diode 30 and the first charging capacitor unit 32 in this order. That is, the first diode 3
By 0, the energy of the first auxiliary coil 28a is rectified and charged in the first charging capacitor unit 32. The first diode 30 and the first charging capacitor unit 32 constitute an on-on rectification charging circuit.

When the main switch element Q is off, the energy of the second auxiliary coil 28b is conducted through a path that passes through the second diode 31 and the second charging capacitor section 33 in that order. The energy rectified by 31 charges the second charging capacitor unit 33. The second diode 31 and the second charging capacitor unit 33 constitute an on-off rectification charging circuit.

As described above, the charging capacitor section 32,
33 are connected in series with the resistor 3 of the charging voltage clamp unit 34.
5 and the Zener diode 36 are connected in parallel, so that the charging voltage of the series connection of the charging capacitor units 32 and 33, that is, the charging voltage value of the first charging capacitor unit 32 and the second The voltage value obtained by adding the charging voltage values of the charging capacitor unit 33 is clamped to a set value based on the Zener voltage of the Zener diode 36. In this way, the reset voltage generated in the second auxiliary coil 28b is generated by clamping the voltage value obtained by adding the charging voltage value of the first charging capacitor unit 32 and the charging voltage value of the second charging capacitor unit 33. The voltage is clamped.

As described above, when the reset pulse voltage of the second auxiliary coil 28b is clamped when the main switch element Q is off, as described above,
The reset pulse voltage Pr of the main switch element Q is also clamped.

In FIG. 3, the Zener diode 36
The resistor 35 is connected in series to the resistor 3.
Numeral 5 is for preventing the Zener diode 36 from being damaged by an overcurrent flowing through the Zener diode 36. For example, when the Zener diode 36 has excellent current resistance, the resistor 35 is omitted. You may.

The number of windings of the first auxiliary coil 28a and the number of windings of the second auxiliary coil 28b may be equal or different, and are set as appropriate.

FIG. 4 shows a second circuit configuration example of the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27. The auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 shown in FIG. 4 are incorporated in the circuit shown in FIG.
The auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 shown in FIG. 1 can also be incorporated in the circuit shown in FIG.

The auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 shown in FIG.
3 is omitted, the reset pulse voltage clamp circuit 27 is a multiple voltage rectifier circuit, and the second auxiliary coil 28b shown in FIG. 3 is omitted. This is what constitutes a certain voltage doubler rectifier circuit.

That is, the anode of the first diode 30 and the second diode 3 are connected to one end of the auxiliary coil 28.
1 is connected to the cathode side of the first diode 30, and the first charging capacitor section 32 is connected to the cathode side of the first diode 30.
Of the first charging capacitor unit 32
Is connected to one end of a second charging capacitor section 33, and the other end of the second charging capacitor section 33 is connected to the anode side of the second diode 31,
The connection between the charging capacitor units 32 and 33 is connected to the other end of the auxiliary coil 28. The series connection of the charging capacitor units 32 and 33 is connected to the connection units 27a and 27
7b is connected to the charging voltage clamp unit 34.

The second example of the circuit configuration of the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 shown in FIG. 4 is configured as described above, and when the main switch element Q is on, the auxiliary coil When the main switch element Q is turned off, the energy of the auxiliary coil 28 is transferred to the second charge capacitor unit 33 when the energy of the first charge capacitor unit 32 is charged through the first diode 30.
Then, current is supplied through a path passing through the second diode 31 to charge the second charging capacitor unit 33. That is, in the circuit shown in FIG. 4, the first charging capacitor unit 32 and the second
The charging capacitor section 33 constitutes the capacitor section of the voltage doubler rectifier circuit, and the energy of the auxiliary coil 28 is double-voltage rectified and charged in the capacitor section.

In the second circuit configuration example shown in FIG. 4, similarly to the first circuit configuration example shown in FIG. 3, the charging voltage of the capacitor section of the voltage doubler rectifier circuit 27, that is,
The sum of the charging voltage value of the first charging capacitor unit 32 and the charging voltage value of the second charging capacitor unit 33 is clamped by the charging voltage clamp unit 34 to a set value based on the Zener voltage of the Zener diode 36. .

As described above, the first charging capacitor unit 32
Is clamped to a set value, and the reset pulse voltage of the auxiliary coil 28 is clamped,
As described above, the reset pulse voltage Pr of the main switch element Q is necessarily clamped.

In the second circuit configuration example shown in FIG. 4, the resistor 35 of the charging voltage clamp section 34 may be omitted as in the circuit configuration example of FIG.

FIG. 5 shows a third circuit configuration example of the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27. The auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 shown in FIG.
However, it is needless to say that the circuit can be incorporated in the circuit shown in FIG. 1B.

In the third circuit configuration example, the control circuit 13
The third circuit configuration example is characterized in that the reset pulse voltage clamp circuit 27 is connected to the load 20 via the connection portions 27a and 27b. It is connected. The other configuration is shown in FIG.
Is the same as that of the second circuit configuration example shown in FIG.

In the third circuit configuration example shown in FIG. 5, the series connection of the first charging capacitor section 32 and the second charging capacitor section 33 in the reset pulse voltage clamp circuit 27 is connected via the connection sections 27a and 27b. And connected in parallel to the load 20.

As described above, the output voltage Vout output from the forward converter to the load 20 is subjected to the stabilization control and is substantially constant, so that the output voltage Vout of the first charging capacitor unit 32 and the output voltage Vout are substantially constant. The sum of the charging voltage values of the second charging capacitor unit 33 is clamped to a set value based on the output voltage Vout to the load 20.
That is, the load 20 can perform the same function as the charging voltage clamp unit 34 shown in FIGS.

As described above, the load 20 causes the first
Similarly to the second circuit configuration example, the sum of the charging voltage value of the first charging capacitor unit 32 and the charging voltage value of the second charging capacitor unit 33 is clamped to a set value,
The reset pulse voltage of the auxiliary coil 28 is clamped, and the reset pulse voltage Pr of the main switch element Q is also clamped.

In FIG. 5, the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 have substantially the same circuit configuration as in FIG. 3 is substantially the same as the circuit shown in FIG. 3, and the reset pulse voltage clamp circuit 27 may be connected to the load 20 via the connection portions 27a and 27b instead of the charging voltage clamp portion 34.

FIGS. 6 and 7 show a fourth circuit configuration example of the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27. FIG. The auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 shown in FIG. 6 are incorporated in the circuit shown in FIG. 1A, and the auxiliary winding section 26 and the reset pulse voltage shown in FIG. The clamp circuit 27 is incorporated in the circuit shown in FIG. 1B, and includes an auxiliary winding unit 26 and a reset pulse voltage clamp circuit 27 shown in FIG. 6 and an auxiliary winding unit 26 and a reset pulse unit shown in FIG. The voltage clamp circuit 27 has the same circuit configuration.

A characteristic of the fourth circuit configuration example shown in FIGS. 6 and 7 is that the reset pulse voltage clamp circuit 2
7 is omitted, the smoothing capacitor 19 of the output circuit 5 functions in the same manner as the first charging capacitor unit 32, and the reset pulse voltage clamp circuit 27 is a voltage doubler rectifier circuit. And
The rest of the configuration is almost the same as the circuit shown in FIG.
Here, the duplicate description of the common part is omitted.

In the fourth circuit configuration example shown in FIGS. 6 and 7, the sum of the charging voltage value of the smoothing capacitor 19 and the charging voltage value of the second charging capacitor unit 33 is clamped to a set value by the load 20. As a result, the reset pulse voltage of the auxiliary coil 28 is clamped, and the reset pulse voltage Pr of the main switch element Q is also clamped.

According to the first embodiment, the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 are provided, and the reset pulse voltage clamp circuit 27 controls the reset pulse of the auxiliary coil 28 of the auxiliary winding section 26. By clamping the voltage and thus the reset pulse voltage of the auxiliary coil 28, the reset pulse voltage Pr of the main switch element Q is inevitably clamped. The voltage clamp circuit 27 has a simple circuit configuration,
Since it can be formed without using expensive components, the above-described excellent effects obtained by clamping the reset pulse voltage Pr of the main switch element Q while suppressing the complexity and cost of the circuit are suppressed. Can be played.

In other words, the peak value of the reset pulse voltage Pr of the main switch element Q can be clamped to a substantially constant value regardless of the magnitude of the input voltage Vin of the input power supply 8, so that the reset pulse voltage Pr causes the reset pulse voltage Pr. It is possible to prevent a large voltage from being applied to the main switch element Q. Thus, it is not necessary to use a high breakdown voltage MOS-FET as the main switch element Q. As described above, it is not necessary to use a high-breakdown-voltage MOS-FET as the main switch element Q, so that it is possible to obtain an effect that the conduction loss in the main switch element Q can be reduced.

Further, by clamping the reset pulse voltage Pr of the main switch element Q, the reset pulse voltage P is set in accordance with the magnitude of the input voltage Vin of the input power supply 8.
The pulse width H of r can be varied. As a result, the pulse width H of the reset pulse voltage Pr can be varied similarly to the off-period Toff of the main switch element Q which varies according to the magnitude of the input voltage Vin, regardless of the magnitude of the input voltage Vin. Instead, the off period Toff of the main switch element Q and the pulse width H of the reset pulse voltage Pr can be made substantially the same.

The reset pulse voltage generated in the secondary coil 4 has the same waveform as the reset pulse voltage Pr of the main switch element Q, and as described above, the input voltage Vin
Of the main switch element Q regardless of the magnitude of
And the pulse width H of the reset pulse voltage Pr, the output circuit 5 can turn on the MOS-FET 14 using the reset pulse voltage, as shown in FIG. , The MO is applied over almost the entire off-period Toff of the main switch element Q irrespective of the magnitude of the input voltage Vin.
Since the S-FET 14 can be turned on, current flows through the MOS-FET 14 and hardly flows through the diode 16, so that as the magnitude of the input power source Vin increases as in the related art, The problem that the conduction loss of the output circuit 5 increases during the off period of the switch element Q can be prevented.

Further, it is possible to prevent a situation in which the main switch element Q is turned on before the reset of the transformer 1 is completed, thereby causing a problem of short-circuit loss of the parasitic capacitance of the main switch element Q. Further, it is possible to prevent a problem that a short-circuit current flows through the ON-state MOS-FET 14 when the main switch element Q is turned on.

As described above, by clamping the reset pulse voltage Pr of the main switch element Q, the input voltage V
Since the pulse width H of the reset pulse voltage Pr can be automatically and variably controlled in substantially the same manner as the off-period Toff of the main switch element Q in accordance with the magnitude of in, the conduction of the output circuit 5 during the off-period of the main switch element Q Both the loss increase problem and the short-circuit loss occurrence problem of the parasitic capacitance of the main switching element Q can be avoided, and thereby the circuit efficiency of the forward converter can be improved.

As described above, in the configuration shown in the first embodiment, an excellent configuration obtained by clamping the reset pulse voltage Pr of the main switch element Q while suppressing the complexity and cost of the circuit. The effect can be obtained.

As shown in the second circuit configuration example of the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27, when the reset pulse voltage clamp circuit 27 is configured by a voltage doubler rectifier circuit, Only one coil 28 needs to be provided, and it is possible to avoid an increase in the size of the transformer 1.

Further, as shown in the third circuit configuration example of the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27, when the load 20 is configured to function as a charging voltage clamp section, the circuit configuration Can be further simplified, and the reset pulse voltage generated in the auxiliary coil 28 is not lost and is regenerated to the load 20, so that the circuit efficiency can be further improved.

Hereinafter, a second embodiment will be described.

In the second embodiment, the reset pulse voltage clamp circuit 27 is a voltage doubler rectifier circuit as shown in the first embodiment, and the reset pulse voltage clamp circuit 27 is connected to the load 20. When connected in parallel, a control power supply auxiliary coil 37 and a control power supply circuit 38 as shown in FIG. 8 are provided. The other configuration is the same as that of the first embodiment. The same components as those of the first embodiment are denoted by the same reference numerals, and the description of the common portions will not be repeated.

As shown in FIG. 8, in the second embodiment, a transformer 1 is provided with a control power supply auxiliary coil 37, and a control power supply circuit 38 is connected to the control power supply auxiliary coil 37. Have been. The control power supply circuit 38 is a voltage doubler rectifier circuit which is a multiple voltage rectifier circuit for control power supply, and has a circuit configuration substantially similar to that of the reset pulse voltage clamp circuit 27.

That is, as shown in FIG. 8, one end of the control power supply auxiliary coil 37 is connected to the anode side of the diode 39, and the cathode side of the diode 39 is connected to one end side of the capacitor 41. 41
Is connected to the other end of the control power supply auxiliary coil 37.

The anode side of the diode 39 is connected to the cathode side of the diode 40, the anode side of the diode 40 is connected to one end of a capacitor 42, and the other end of the capacitor 42 is connected to the control power supply. It is connected to the auxiliary coil 37. The above capacitor 4
1, 42 are connected in series.

The series connection of the capacitors 41 and 42 constitutes a capacitor section of a control power supply circuit 38 which is a voltage doubler rectifier circuit.
a, 43b in parallel. The series connection of the capacitors 41 and 42 is connected to the control circuit 13, and the connection between the resistors 43 a and 43 b is connected to the control circuit 13.

The control power supply auxiliary coil 37 and the control power supply circuit 3 which are characteristic in the second embodiment
8 is configured as described above. The charge voltage value of the capacitor portion of the control power supply circuit 38 (that is, the sum of the charge voltage value of the capacitor 41 and the charge voltage value of the capacitor 42) is determined by the charge voltage value of the capacitor portion of the reset pulse voltage clamp circuit 27 ( In the example shown in FIG. 8, the voltage value is proportional to the charging voltage value of the second charging capacitor unit 33). As described in the first embodiment, since the charging voltage value of the capacitor section of the reset pulse voltage clamping circuit 27 is clamped to be substantially constant, the charging voltage value of the capacitor section of the control power supply circuit 38 is also substantially It will be stabilized at a constant value.

In the second embodiment, the charging voltage of the capacitor section of the control power supply circuit 38, which is stabilized at a substantially constant value, is supplied to the control circuit 13 as control power.

The reset pulse voltage clamp circuit 27 is connected to the load 20, and the charge voltage value of the capacitor section of the reset pulse voltage clamp circuit 27 is clamped to a voltage value corresponding to the output voltage Vout to the load 20. Therefore, the charging voltage value of the capacitor section of the control power supply circuit 38 also becomes a voltage value corresponding to the output voltage Vout.

In the second embodiment, the charging voltage of the capacitor of the control power supply circuit 38 is
a, 43b and the output voltage Vou to the load 20
It is supplied to the control circuit 13 as a detection output voltage corresponding to t.

The control circuit 13 includes the control power supply circuit 38
, And based on the detected value of the output voltage Vout applied from the control power supply circuit 38, the output voltage Vout supplied to the load 20 is stabilized.

According to the second embodiment, the first
Since the auxiliary winding section 26 and the reset pulse voltage clamp circuit 27 are provided in the same manner as in the second embodiment, the effect as described in the first embodiment, that is, the circuit is complicated and the price is high. While suppressing, the reset pulse voltage Pr of the main switch element Q can be clamped, and the excellent effect obtained by clamping the reset pulse voltage Pr of the main switch element Q can be obtained.

In addition, in the second embodiment, the control power supply circuit 38 having the same circuit configuration as the reset pulse voltage clamp circuit 27 is provided, so that stable control power can be supplied to the control circuit 13. Can be.

Since the control power supply circuit 38 supplies the control power supply voltage obtained by rectifying the energy of the control power supply auxiliary coil 37 by double voltage to the control circuit 13 as shown in FIGS. The number of turns of the control power supply auxiliary coil 37 is reduced to one third to one fourth of the number of turns of the tertiary coil 6 shown in FIG. Thus, the size of the transformer 1 can be reduced.

Further, the control power supply circuit 38 shown in the second embodiment has a function of supplying control power to the control circuit 13 as described above, as well as an output voltage Vout to the load 20.
Is provided with a function of outputting a detection output voltage corresponding to the control voltage supply circuit, so that the detection circuit is omitted as compared with a case where a detection circuit for detecting the output voltage Vout is separately provided in addition to the control power supply circuit. Therefore, the circuit configuration can be further simplified.

Further, the output voltage V output to the load 20
When detecting out directly, a detection circuit including a photocoupler and a shunt regulator is provided.However, since the photocoupler has a short life, the forward converter has a short life. Occurs. On the other hand, as shown in the second embodiment, the output voltage Vout is detected by the control power supply circuit 38 that does not use a photocoupler. The problem of shortening the life of the device can be prevented. Furthermore, while the photocoupler and the shunt regulator are expensive, the control power supply circuit 38 shown in the second embodiment can be configured without using such expensive components. As a result, the increase in the price of the forward converter can be suppressed.

[0097] The present invention is not limited to the above embodiments, but may take various embodiments. For example, as shown in FIG.
-The FET 14 has been incorporated in the circuit so as to be turned on using the reset pulse voltage of the secondary coil 4,
For example, as shown in FIG. 9, a dedicated auxiliary coil 45 for driving the MOS-FET 14 is provided in the transformer 1, and the energy of the auxiliary coil 45
-It may be configured to drive the FET 14 on.

Further, in each of the above embodiments, the reset pulse voltage clamp circuit 27 is provided with the diodes 30 and 31 for rectifying the energy of the auxiliary coil 28, but one of the diodes 30 and 31 is provided. Alternatively, a synchronous rectifier such as a MOS-FET may be provided instead of both. When a synchronous rectifier is provided in place of the diode 30, a circuit for controlling the synchronous rectifier is provided. The circuit allows the synchronous rectifier to conduct when the diode 17 of the output circuit 5 becomes conductive. ON drive control is performed so as to be in the state.

When a synchronous rectifier is provided instead of the diode 31, a circuit for controlling the drive of the synchronous rectifier is provided.
On-drive control is performed so that the diode 16 of the output circuit 5 becomes conductive when the diode 16 becomes conductive.

Further, in the first embodiment, an example of a circuit configuration in which the reset pulse voltage clamp circuit 27 is formed as a voltage doubler rectifier circuit has been described. It may be constituted by a voltage rectifier circuit.

Further, in each of the circuit configuration examples shown in FIGS. 6 to 8, an example in which the first charging capacitor section 32 shown in FIG. 3 is omitted is shown, but the first charging capacitor section 32 is omitted. Instead, the configuration may be such that the second charging capacitor unit 33 is omitted. In this case, the smoothing capacitor 19 performs the function of the second charging capacitor unit 33.

The reset pulse voltage clamp circuit 27 shown in FIG. 8 in the second embodiment has the same circuit configuration as the voltage doubler rectifier circuit shown in FIGS. 6 and 7. The reset pulse voltage clamp circuit 27 shown in the second embodiment may have the same circuit configuration as the voltage doubler rectifier circuit as shown in FIG. It may be. Further, in the second embodiment, the control power supply circuit 38 is a voltage doubler rectifier circuit. However, the control power supply circuit 38 may be a triple or more multiple voltage rectifier circuit.

Further, in each of the above embodiments, a single output type forward converter has been described as an example, but the present invention can be applied to a multiple output type forward converter.

[0104]

According to the present invention, an auxiliary winding section and a reset pulse voltage clamp circuit are provided, and the reset pulse voltage clamp circuit clamps the reset pulse of the auxiliary coil of the auxiliary winding section to thereby reset the main switch element. Since the configuration is such that the reset pulse voltage is clamped, the reset pulse voltage of the main switch element can be clamped with a simple circuit configuration and without using expensive components.

Conventionally, the provision of a circuit for clamping the reset pulse voltage of the main switch element causes a problem that the circuit of the forward converter becomes complicated and large, and increases the price. However, according to the present invention, the reset pulse voltage of the main switch element can be clamped with a simple circuit configuration as described above and without using expensive components. It is possible to prevent problems such as an increase in the size of the forward converter, complexity of the circuit, and an increase in price.

As described above, since the reset pulse voltage of the main switch element can be clamped, application of a large reset pulse voltage to the main switch element can be avoided. It is not necessary to use a component with a high breakdown voltage as an element. The high-withstand voltage main switch element is expensive and has a large conduction loss. However, in the present invention, such a high-withstand voltage main switch element does not have to be used. In addition, conduction loss in the main switch element can be suppressed.

Further, by clamping the reset pulse voltage of the main switch element, the pulse width of the reset pulse voltage automatically changes according to the magnitude of the input voltage supplied to the forward converter. This makes it possible to vary the pulse width of the reset pulse voltage substantially in the same manner as the off period of the main switch element that varies according to the input voltage. For this reason, it is possible to prevent a problem that the main switching element is turned on before the reset of the transformer is completed, thereby causing a short-circuit loss of the parasitic capacitance of the main switching element.

In the case where the output circuit has a commutation-side synchronous rectifier that is turned on based on the reset pulse voltage, the reset pulse voltage of the main switch element is clamped as described above to reset. Since the pulse width of the pulse voltage can be varied almost in the same manner as the OFF period of the main switch element which varies according to the input voltage, over almost the entire period during which the main switch element is OFF, The commutation-side synchronous rectifier can be turned on, and the above-described problem of an increase in conduction loss of the output circuit can be prevented. Further, since the commutation-side synchronous rectifier is in the ON state when the main switch element is turned on, it is possible to avoid a problem that a short-circuit current flows through the commutation-side synchronous rectifier.

The auxiliary winding section has a first auxiliary coil and a second auxiliary coil, and the reset pulse voltage clamp circuit has an on-on rectification charging circuit and an on-off rectification charging circuit. Therefore, the reset pulse voltage of the main switch element can be clamped with a very simple circuit configuration, and the same effect as described above can be obtained.

When the reset pulse voltage clamp circuit is a multiple voltage rectifier circuit, the reset pulse voltage of the main switch element can be reduced by a simpler circuit configuration while preventing the transformer from becoming large. Clamping can be performed, and the above-described effects can be obtained.

In the configuration in which the load to which the output voltage is stably supplied from the forward converter functions as the charging voltage clamp unit, further simplification of the circuit configuration can be promoted. Since the energy of the auxiliary coil of the unit can be regenerated as the output of the forward converter without loss, the circuit efficiency of the forward converter can be significantly improved.

In the case where the control power supply auxiliary coil and the control power supply multi-voltage rectifier circuit are provided, the energy of the control power supply auxiliary coil is multi-voltage rectified and used. A large amount of power can be obtained with the auxiliary coil having the number of windings, which is smaller than the conventional case where the energy of the auxiliary coil is choke-input rectified and supplied to the control circuit as control power. The number can be significantly reduced,
It is easy to reduce the size of the transformer.

Further, since the multiplying voltage rectifier circuit for supplying control power also has a function of detecting a voltage corresponding to the output voltage output from the forward converter to the load, the detection for detecting the output voltage is performed. There is no need to provide a separate circuit, and the circuit configuration can be further simplified as compared with a case where a detection circuit must be provided separately from the control power supply circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a characteristic circuit configuration in a first embodiment.

FIG. 2 shows a waveform example of a reset pulse voltage of a main switch element shown in the first embodiment together with an example of a reset pulse voltage waveform of a main switch element of each forward converter of an active reset type and a conventional resonance reset type. FIG.

FIG. 3 is a circuit diagram showing a first example of a circuit configuration of a characteristic auxiliary winding unit and a reset pulse voltage clamp circuit in the first embodiment;

FIG. 4 is a circuit diagram illustrating a second example of a circuit configuration of a characteristic auxiliary winding unit and a reset pulse voltage clamp circuit in the first embodiment;

FIG. 5 is a circuit diagram showing a third example of a circuit configuration of a characteristic auxiliary winding unit and a reset pulse voltage clamp circuit in the first embodiment;

FIG. 6 is a circuit diagram showing a fourth example of a circuit configuration of a characteristic auxiliary winding unit and a reset pulse voltage clamp circuit in the first embodiment;

FIG. 7 is a diagram showing a fourth embodiment of the auxiliary winding unit and the reset pulse voltage clamp circuit which are characteristic in the first embodiment.
FIG. 3 is a circuit diagram showing an example of the circuit configuration of FIG.

FIG. 8 is a circuit diagram showing a characteristic circuit configuration example in the second embodiment.

FIG. 9 is a circuit diagram showing another embodiment.

FIG. 10 is a circuit diagram showing an example of a circuit configuration of an active reset type forward converter.

FIG. 11 is an explanatory diagram showing a problem of an active reset type forward converter.

FIG. 12 is a circuit diagram showing a circuit configuration example of a conventional resonance reset type forward converter.

[Explanation of symbols]

 Reference Signs List 1 transformer 5 output circuit 13 control circuit 14 MOS-FET 20 load 26 auxiliary winding part 27 reset pulse voltage clamp circuit 27a, 27b connection part 28 auxiliary coil 28a first auxiliary coil 28b second auxiliary coil 32 first charging Capacitor unit 33 Second charging capacitor unit 34 Charging voltage clamp unit 37 Control power supply auxiliary coil 38 Control power supply circuit 41, 42 Capacitor Q Main switch element

Claims (5)

[Claims] An output circuit for rectifying and smoothing the energy of a transformer based on the on / off operation of a main switch element and outputting the rectified energy, wherein a reset pulse voltage is applied to the main switch element and the transformer during an off period of the main switch element. An auxiliary winding portion comprising an auxiliary coil provided in a transformer in a forward converter configured to generate
A reset pulse voltage clamp circuit that clamps the reset pulse voltage generated in the auxiliary coil to a set value, wherein the auxiliary winding unit includes a first auxiliary coil and a second auxiliary coil.
The reset pulse voltage clamp circuit rectifies the energy of the first auxiliary coil and charges the first charging capacitor unit when the main switch element is turned on. And an on-off rectification charging circuit for rectifying the energy of the second auxiliary coil and charging the second charging capacitor when the main switch element is off, wherein the first charging is performed. The capacitor unit and the second charge capacitor unit are provided with a connection unit connected to a charge voltage clamp unit. The charge voltage clamp unit allows the charge voltage value of the first charge capacitor unit and the charge voltage of the second charge capacitor unit to be connected. A voltage value obtained by adding the charging voltage value is clamped to a set value, and the reset pulse voltage clamping circuit includes a charging voltage of the first charging capacitor unit. A configuration in which the reset pulse voltage generated in the second auxiliary coil is clamped and the reset pulse voltage of the main switch element is clamped by clamping the sum of the reset voltage and the charging voltage value of the second charging capacitor unit And a forward converter. 2. An output circuit for rectifying and smoothing the energy of a transformer based on the on / off operation of a main switch element, and outputting a reset pulse voltage to the main switch element and the transformer during an off period of the main switch element. An auxiliary winding portion comprising an auxiliary coil provided in a transformer in a forward converter configured to generate
A reset pulse voltage clamp circuit for clamping the reset pulse voltage generated in the auxiliary coil to a set value; the auxiliary winding unit has an auxiliary coil; and the reset pulse voltage clamp circuit is a multiple voltage rectifier circuit. The multiple voltage rectifier circuit has a configuration in which the energy of the auxiliary coil is multiply rectified and charged to the capacitor unit, and the capacitor unit is provided with a connection unit connected to a charging voltage clamp unit. The charging voltage of the capacitor unit is clamped to a set value by the charging voltage clamping unit.
A forward converter characterized in that the charging voltage of the capacitor section is clamped to clamp a reset pulse voltage of an auxiliary coil and a reset pulse voltage of a main switch element. 3. The forward converter according to claim 1, wherein the forward converter has a circuit configuration for stabilizing an output voltage output to a load, and causes the load to function as a charging voltage clamp unit. 4. An on / off operation of a main switch element in a direction to stabilize an output voltage output from a forward converter to a load.
A control circuit for controlling the OFF operation is provided, and a capacitor portion of the multiple voltage rectifier circuit which is a reset pulse voltage clamp circuit is provided between terminals to which the load is connected,
The transformer is provided with a control power supply auxiliary coil, and a control power supply multiple voltage rectifier circuit is provided for rectifying the energy of the control power supply auxiliary coil and charging the control power supply capacitor unit. The control power supply multiplying voltage rectifier circuit supplies the charging voltage of the control power supply capacitor unit as control power to the control circuit, and responds to the charging voltage of the control power supply capacitor unit. A voltage that is applied to the control circuit as a detected output voltage of the forward converter. The control circuit is configured to apply a forward converter based on the detected output voltage of the forward converter applied from the control power supply multiple voltage rectifier circuit. 3. The forward converter according to claim 2, wherein the output voltage is stabilized. 5. The forward converter according to claim 1, wherein the output circuit has a commutation-side synchronous rectifier that is turned on based on a reset pulse voltage. .