JPH08168244A - Switching power unit - Google Patents

Abstract

PURPOSE: To obtain an auxiliary power source circuit which does not use many parts and is not affected by noise and temperature. CONSTITUTION: A main transformer 12 is constituted of a forward transformer 3 and a flyback transformer 4. When a rectifying diode 6 is conducted, a DC output voltage Vout returns to the primary winding 3A of the forward transformer 3 as it is. Consequently, an operating current Vcc from an auxiliary power source circuit 41 is not affected by an input voltage Vin nor the duty ratio of a drive signal Vg1, but stabilized. Therefore, the circuit 41 can be constituted of only three parts. In addition, the circuit 41 is not affected by noise and temperature, because the circuit does not use any exclusively used IC nor switching element.

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 for improving an auxiliary power supply circuit.

[0002]

2. Description of the Related Art Generally, a switching power supply device of this type includes a main transformer and a main switching element for intermittently applying a DC input voltage to a primary winding of the main transformer. The control circuit that controls the operation of the main switching element as a feedback loop for stabilizing the DC output voltage by rectifying and smoothing the voltage induced in the output and outputting the specified DC output voltage to the load. Is provided. In such a switching power supply device, an auxiliary power supply circuit that supplies a predetermined operating voltage to a control circuit or the like is indispensable, and conventionally, a bias power supply including a dedicated IC and a switching element independently of the main inverter is used. The DC power supply is branched from the DC input voltage, and the bias power supply converts the DC input voltage into a predetermined operating voltage. An auxiliary winding is wound around the main transformer, and the voltage generated from this auxiliary winding is dropped to a predetermined operating voltage by a dropper composed of a transistor constant voltage circuit. The DC input voltage is converted into a predetermined operating voltage by the chopper circuit synchronized with the switching frequency of the main inverter. that's all,
The auxiliary power supply circuit is configured by using any one of the above methods.

[0003]

In the above prior art, the method (1) limits the operating temperature of the IC constituting the bias power supply. For example, the IC does not operate normally in the low temperature region of about -40 ° C. It causes problems such as. Further, since a bias power supply having a switching element is provided separately from the main inverter, not only the number of parts increases, but also these become noise sources independent of each other, and EMI (electromagnetic interference) increases. There are also drawbacks.

On the other hand, with the method (1), it seems that a desired operating voltage can be easily obtained simply by changing the number of turns of the auxiliary winding. However, as disclosed in Japanese Utility Model Publication No. 6-24985, a thin transformer in which a plurality of thin layer substrates having conductor patterns are stacked is used as a main transformer in order to reduce the thickness of the entire device. In this case, since the primary winding to which the DC input voltage is applied is composed of several turns, the operating voltage fluctuates greatly when the number of turns of the auxiliary winding is changed, and the adaptability of the operating voltage is poor. There is. Moreover, the dropper provided after the auxiliary winding is
Although the switching noise as described above does not occur, the efficiency is poor because the transistor is linearly used.

Further, in the method (1), the output voltage value from the chopper circuit depends on the duty of the drive signal from the control circuit and the DC input voltage. Therefore, in practice, a dropper for adjusting such variation is provided in the chopper circuit. It is necessary to provide it in the latter stage, which causes a significant increase in the number of parts. Also,
Similar to the above, since the chopper circuit having the switching element is provided in addition to the main inverter, each of them serves as a noise source, which has a drawback of increasing EMI.

In view of the above problems, the present invention does not generate noise, and the number of parts can be significantly reduced.
It is an object of the present invention to provide a switching power supply device including a highly efficient auxiliary power supply circuit that can easily obtain a desired operating voltage without being affected by a low temperature.

[0007]

According to a first aspect of the present invention, there is provided a switching power supply device comprising a main transformer and a main switching element for intermittently applying a DC input voltage to a primary winding of the main transformer. And a control circuit for controlling the operation of the main switching element in order to stabilize the DC output voltage by rectifying and smoothing the voltage induced in the secondary winding by the rectifying and smoothing circuit to output a DC output voltage. In the switching power supply device, a first transformer and a second transformer each having an energy storage means are connected in series to form the main transformer, and one end of a secondary winding of each of the first and second transformers. To one end of each of the rectifying elements, and a smoothing capacitor is connected between the other end of each of the rectifying elements connected in common and the other ends of the secondary windings of the first and second transformers. The auxiliary transformer primary winding is connected to the primary winding of the first transformer, and the peak rectifying circuit including a diode and a capacitor is connected to the secondary winding of the auxiliary transformer. Then, the auxiliary power supply circuit is configured.

According to a second aspect of the switching power supply device, between the primary windings of the first and second transformers,
A series circuit of a voltage clamping capacitor for clamping the flyback voltage of the primary winding and a second switching element is connected, and the main switching element is connected in parallel with the first capacitor and the first diode. A second capacitor and a second diode are connected in parallel to the second switching element, and the main switching element and the second diode are connected.
The control means is configured to alternately supply drive signals having a dead time to the switching element.

[0009]

Since the first and second transformers also have the function of the smoothing choke coil inserted and connected to the output voltage line, the rectifying / smoothing circuit includes the pair of rectifying diodes and the smoothing diode. It can consist of only a capacitor. In this case, when the rectifying diode connected to one end of the secondary winding of the first transformer becomes conductive, the DC output voltage stabilized by the control circuit is directly returned to the primary winding of the first transformer. . The voltage between the primary winding of this first transformer is converted by an auxiliary transformer,
If this is rectified by a peak rectification circuit composed of a diode and a capacitor, a stable operating voltage can be supplied from the auxiliary power supply circuit with only three parts.

According to the second aspect of the invention, the first capacitor and the first capacitor connected in parallel with the main switching element are provided.
, And the second capacitor and the second diode connected in parallel to the second switching element can be used to achieve zero voltage switching of the main switching element and the second switching element. It can be easily incorporated into such a partial resonance type converter having two transformers.

[0011]

An embodiment of the present invention will be described below with reference to the accompanying drawings. In FIG. 1 showing the circuit configuration, 1 is a DC power supply, and 2 and 2 A are input terminals connected to both ends of the DC power supply 1, respectively. Between the input terminals 2 and 2A, the primary winding 3A of the forward transformer 3 which insulates the primary side and the secondary side from each other.
Similarly, the primary winding 4A of the flyback transformer 4, which also insulates the primary side and the secondary side, and the first MOS type FET 5 are sequentially connected in series. Then, by the switching operation of the first FET 5, the DC input voltage Vin from the DC power supply 1 is intermittently applied to the primary windings 3A and 4A of the forward transformer 3 and the flyback transformer 4.

In the forward transformer 3 and the flyback transformer 4, the secondary windings 3B and 4B are also connected in series, and one end of the secondary winding 3B, that is, the dot side terminal,
The anodes, which are one ends of the rectifying diodes 6 and 7, are connected to one end of the secondary winding 4B, that is, the non-dot side terminal. The cathodes, which are the other ends of the rectifier diodes 6 and 7, are commonly connected to one output terminal 8, and the other end of the secondary winding 3B, that is, the non-dot side terminal and the other end of the secondary winding 4B, that is, The connection point with the dot side terminal is connected to the other output terminal 8A. A smoothing capacitor 9 is connected between the output terminals 8 and 8A, and a rectifying and smoothing circuit 10 composed of this smoothing capacitor 9 and rectifying diodes 6 and 7 allows each secondary winding 3
The voltage induced in B and 4B is output to the load 11 as the DC output voltage Vout.

The forward transformer 3 and the flyback transformer 4 are main transformers of a partial resonance type converter.
12 comprises the forward transformer 3,
First to store energy when the rectifier diode 6 is not conducting
The energy storage means 13 is provided, and the flyback transformer 4 is provided with a second energy storage means 14 that stores energy when the rectifier diode 7 is not conducting. Although not shown, these energy storage means 13 and 14 can be easily achieved by providing a gap in the cores of the forward transformer 3 and the flyback transformer 4, for example. The energy stored in the first energy storage means 13 is sent to the output side when the rectifier diode 6 is conducting, and the energy stored in the second energy storage means 14 is output to the output side when the rectifying diode 7 is conducted. Sent out.

A clamp circuit 21 for clamping the flyback voltage of the primary windings 3A and 4A is connected between the primary windings 3A and 4A of the forward transformer 3 and the flyback transformer 4. The clamp circuit 21 is composed of a series circuit of a voltage clamping capacitor 22 and a second MOS type FET 23. Specifically, one end of the capacitor 22 is connected to the dot side terminal of the primary winding 3A of the forward transformer 3. , A second MOS type FET on the other end of the capacitor 22
The drain of 23 is connected, and the source of the second FET 23 is connected to the non-dot side terminal of the primary winding 4A of the flyback transformer 4. In addition, the first FET5
Equivalently between the drain and source of the first capacitor
24 and the first diode 25 are connected in parallel, and also between the drain and source of the second FET 23 equivalently to the second diode
The capacitor 26 and the second diode 27 are connected in parallel. These first and second capacitors 24 and 26 utilize the parasitic capacitance existing between the drain and source of the first and second FETs 5 and 23, but external capacitors may be connected. . Also, the first and second diodes
Although 25 and 27 are composed of body diodes existing in the first and second FETs 5 and 23, they may be connected to external diodes. The capacitance of the capacitor 22 that constitutes the clamp circuit 21 is the same as that of the first and second capacitors 24,
It is set to a value much larger than the capacity of 26.

On the other hand, this DC output voltage Vout is used as a feedback loop for stabilizing the DC output voltage Vout.
The first and second FETs based on the voltage detection signal from the connection point of the voltage dividing resistors 31 and 32 for monitoring the voltage and the resistors 31 and 32.
A pulse width control circuit 33 which is a control circuit for variably controlling the pulse conduction widths of the drive signals Vg1 and Vg2 supplied to 5 and 23, respectively.
Is provided. The drive signals Vg1 and Vg from the pulse width control circuit 33 are applied to the gates of the first and second FETs 5 and 23, respectively.
2 is alternately applied with a suitable dead time, ie the time when the first and second FETs 5, 23 are both off.

Reference numeral 41 is an auxiliary power supply circuit for supplying a predetermined operating voltage Vcc to the pulse width control circuit 33 and the like. The auxiliary power supply circuit 41 includes an auxiliary transformer 42 that is provided independently of the forward transformer 3 and the flyback transformer 4, and further, a diode 43 whose anode is connected to a dot side terminal of a secondary winding 42B of the auxiliary transformer 42. And a smoothing capacitor 44 connected between the cathode of the diode 43 and the non-dot side terminal of the secondary winding 42B.
It is configured by connecting 45 to the auxiliary transformer 42. Further, the primary winding 42A of the auxiliary transformer 42 is connected between the primary windings 3A of the forward transformer 3, the dot side terminal of the primary winding 42A is connected to the dot side terminal of the primary winding 3A, and The non-dot side terminal of the wire 42A is connected to the non-dot side terminal of the primary winding 3A.

In the above structure, the first embodiment of the present invention is used.
The FET 5 corresponds to the main switching element in the claims, and the second FET 23 corresponds to the second switching element. The forward transformer 3 of the present embodiment corresponds to the first transformer in the claims, and the flyback transformer 4 corresponds to the second transformer in the claims.
The rectifying element in the claims uses the rectifying diodes 6 and 7 having a simple configuration in this embodiment, but when the forward voltage drop of the rectifying diodes 6 and 7 poses a problem,
MOS type FET is used instead of the rectifier diodes 6 and 7,
A synchronous rectification method may be adopted.

Next, the operation of the above structure will be described with reference to the waveform diagram of FIG. In FIG. 2, the upper part shows the drive signal Vg1 supplied from the pulse width control circuit 33 to the gate of the first FET 5, and hereinafter, the drive signal Vg2 supplied to the gate of the second FET 23 and the primary winding of the forward transformer 3. The voltage Vp1 across the line 3A is shown.

First, in the section from t1 to t2, the first FE
The drive signal Vg1 to T5 is at the H level, and in response to this, the first FET 5 becomes conductive and the second FET
23 becomes non-conductive. In this case, the primary windings 3A, 4A of the forward transformer 3 and the flyback transformer 4
A DC input voltage Vin is applied between the primary windings 3A, 4 and
The inductor current of A increases with time due to the inductance present in each primary winding 3A, 4A. Also,
Since a positive voltage is generated at the dot side terminals in each of the secondary windings 3B and 4B, one rectifying diode 6 is in a conducting state and the other rectifying diode 7 is in a non-conducting state. Therefore, from the secondary winding 3B of the forward transformer 3,
Smoothing capacitor 9 and load via rectifier diode 6
While the energy is sent to the 11 side, the energy storage means 14 of the flyback transformer 4 stores energy based on the inductor current of the primary winding 4A.

In the next section from t2 to t3, the first FET is
5 and the second FET 23 are both non-conductive. At this time, the first capacitor 24 is connected in series with each primary winding 3A, 4A, and resonance occurs due to the inductance of the primary windings 3A, 4A and the first capacitor 24. And the first
The drain-source voltage of FET5 is
The voltage rises gently by charging the first capacitor 24 from A, 4A, and at the time of this rise, the current flowing into the first FET 5 becomes zero due to the charging current to the first capacitor 24, and the first FET 5 The loss at turn-off is significantly reduced.

In the section from t2 to t3, the second capacitor 26 is discharged due to the inductance of the primary windings 3A and 4A, but when the second capacitor 26 is completely discharged, the second diode 27 is discharged. Because of conduction, reverse charging of the second capacitor 26 is blocked. Therefore, the drain-source voltage of the second FET 23 is maintained at zero volt when the second capacitor 26 is completely discharged. Further, the inductor current of each primary winding 3A, 4A decreases with time.

In the period from t3 to t4, the drive signal Vg
Corresponding to 2, the second FET 23 becomes conductive. At this point, the second capacitor 26 has already been completely discharged, and no large loss or noise is generated when the second FET 23 is turned on. On the other hand, the flyback voltage generated in each of the primary windings 3A and 4A is charged in the low-impedance capacitor 22. The voltage across the capacitor 22 actually changes due to charging and discharging of the capacitor 22, but the capacity of the capacitor 22 itself is large and the amount of fluctuation thereof is extremely small. As a result, the drain-source voltage of the first FET 5 is clamped to a substantially constant value by the voltage across the capacitor 22 during the conduction period of the second diode 27.

In this way, when the charging of the capacitor 22 is completed and the inductor currents from the primary windings 3A and 4A become zero, the next section from t4 to t5 is entered. In this section, the discharge current of the capacitor 22 flows to the primary windings 3A and 4A via the second FET 23, so that an inductor current in the opposite direction to the section from t1 to t4 increases with time. Therefore, a positive voltage is generated at the non-dot side terminals of the respective primary windings 3A and 4A, and one rectifying diode 6
Becomes non-conductive, and the other rectifying diode 7 becomes conductive. Energy is sent out from the secondary winding 4B of the flyback transformer 4 via the rectifier diode 7, while energy based on the inductor current of the primary winding 3A is stored in the energy storage means 13 of the forward transformer 3. .

Then, in the section from t5 to t6, the second
When the FET 23 of turns off, the primary windings 3A, 4 again
The inductance of A resonates with the first capacitor 24.
In this case, the inductor current of each primary winding 3A, 4A is
It is in the opposite direction to that at the time of resonance in the section from t2 to t3,
The first capacitor 24 is discharged and the drain-source voltage of the first FET 5 gradually decreases. Also, the second F
The drain-source voltage of ET23 is the second capacitor
Since it slowly rises due to charging to 26, the second FET
The turn-off loss of 23 is significantly reduced. First
When the capacitor 24 of the
25 becomes conductive and reverse charging of the first capacitor 24 is blocked. Therefore, the drain-source voltage of the first FET 5 is maintained at zero volt when the first capacitor 24 is completely discharged.

In the next section from t6 to t1, the first FET 5 becomes conductive in response to the drive signal Vg1. At this point, the first capacitor 24 has already been completely discharged, and no large loss or noise is generated when the first FET 5 is turned on. The inductor current in each of the primary windings 3A and 4A gradually decreases, and when the inductor current becomes zero, one cycle of operation ends.

Since the rectifying / smoothing circuit 10 of the partial resonance type converter according to the present embodiment is configured so that the output smoothing choke coil is not connected to the output voltage line on the secondary side, the forward transformer when the rectifying diode 6 is conducting. Three
The voltage generated between the secondary winding 3B of the
When ignoring the forward voltage drop of, the DC output voltage V
It will be the same as out. Here, the number of turns of the primary winding 3A of the forward transformer 3 is Np1, and the number of turns of the secondary winding 3B is Np.
If s1 is set, the voltage Vp1 generated at the dot side terminal of the primary winding 3A can be expressed by the following formula.

[0027]

[Equation 1]

Since the voltage Vp1 across the primary winding 3A is directly applied to the primary winding 42A of the auxiliary winding 42, a voltage of the positive electrode is generated at the dot side terminal of the secondary winding 42B.
The voltage of the secondary winding 42B is peak rectified by the diode 43 and the capacitor 44 and supplied to the pulse width control circuit 33 and the like as the operating voltage Vcc. In this case, ignoring the forward voltage drop of the diode 43, the operating voltage Vcc from the auxiliary winding circuit 41 can be expressed by the following formula.

[0029]

[Equation 2]

However, in the above equation 2, n1 = Np1
/ Ns1, n2 = Np2 / Ns2. As is clear from Equation 2, the operating voltage Vcc of the auxiliary winding circuit 41 does not depend on the duty of the drive signal Vg1 for the first FET 5, the input voltage Vin, the load 11, etc., and is proportional to the DC output voltage Vout. It can be seen that the output is always stable. In this case, the auxiliary transformer 42 has a high magnetizing inductance, and the operating voltage Vcc is increased from the secondary winding 42B.
If the output taken out as is (1.5 W or less),
The auxiliary power supply circuit 41 has almost no influence on the operation of the power conversion circuit such as the main transformer 12.

As described above, in the above embodiment, the forward transformer 3 and the flyback transformer 4 are connected in series to form the main transformer 12, and the forward transformer 3 and the flyback transformer 4 have energy storage means 13 respectively. , 14 are provided so that the main transformer 12 can simultaneously store and send out energy, and the forward transformer 3 and the flyback transformer 4 are provided.
Also has the function of a smoothing choke coil that is inserted and connected to the output voltage line. Therefore, the rectifying / smoothing circuit 10 can be composed of only the rectifying diodes 6 and 7 and the smoothing capacitor 9. However, in such a rectifying / smoothing circuit 10 without a choke coil, when the rectifying diode 6 is in conduction, The voltage across the secondary winding 3B becomes equal to the DC output voltage Vout stabilized by the pulse width control circuit 33. Focusing on this point, the present invention is one in which the auxiliary power supply circuit 41 is connected to the primary winding 3A side of the forward transformer 3, and the voltage between the primary windings 3A of the forward transformer 3 generated when the rectifying diode 6 is conducting. Is converted by an auxiliary transformer 42, and this is converted to a diode 43.
By performing peak rectification by the peak rectification circuit 45 including the capacitor 44 and the capacitor 44, it is possible to obtain a stable operating voltage Vcc with only three parts, regardless of the duty ratio of the drive signal Vg1 or the input voltage Vin. Becomes

Further, the auxiliary power supply circuit 41 does not have a dedicated IC or a separate switching element as in the conventional example, so that there is no influence due to temperature or generation of noise in synchronization with the switching cycle. In addition, the internal loss of the auxiliary power supply circuit 41 is extremely small as compared with the conventional dropper that linearly uses transistors, and high efficiency (90% or more) can be easily achieved. Furthermore, since the auxiliary transformer 42 is provided separately from the main transformer 12, even if the primary winding 3A of the forward transformer 3 has a number of turns of several times, By appropriately adjusting the winding ratio with the secondary winding 42B, the operating voltage Vcc can be changed little by little, and the desired operating voltage Vcc can be easily obtained. In fact, the primary winding of this auxiliary transformer 42
By adjusting the turn ratio between the secondary winding 42A and the secondary winding 42B, the operating voltage Vcc from the auxiliary power supply circuit 41 can be changed by about + 1V to -1V.

That is, the main transformer 12 and the first FET 5 for intermittently applying the DC input voltage Vin to the primary windings 3A and 4A of the main transformer 12 are provided, and the secondary winding 3B of the main transformer 12 is provided. Rectifying and smoothing circuit 10 for the voltage induced in 4B.
In order to stabilize the DC output voltage Vout while the DC output voltage Vout is output after being rectified and smoothed by the first
In the switching power supply device including the pulse width control circuit 33 for controlling the operation of the FET 5,
A forward transformer 3 and a flyback transformer 4 each having energy storage means 13 and 14 are connected in series to form a main transformer 12, and one end of each of the secondary windings 3B and 4B of the forward transformer 3 and the flyback transformer 4. To the rectifying / smoothing circuit 10 by connecting one ends of the rectifying diodes 6 and 7, respectively, and connecting a smoothing capacitor 9 between the other ends of the rectifying diodes 6 and 7 commonly connected and the other ends of the secondary windings 3B and 4B. And the primary winding 3 of the forward transformer 3
The primary winding 42A of the auxiliary transformer 42 is connected to A, and the diode 43 and the capacitor are connected to the secondary winding 42B of this auxiliary transformer 42.
Auxiliary power circuit by connecting the peak rectification circuit 45 consisting of 44
By configuring 41, it is possible to provide a switching power supply device including a highly efficient auxiliary power supply circuit 41 that can significantly reduce the number of components and can easily obtain a desired operating voltage Vcc without being affected by low temperature. This is applicable to any circuit configuration in which the DC output voltage Vout stabilized by at least the control circuit such as the pulse width control circuit 33 is returned to the primary winding 3A of the forward transformer 3 as it is.

Further, in this embodiment, the primary windings 3A and 4A of the forward transformer 3 and the flyback transformer 4 are used.
A series circuit of a voltage clamping capacitor 22 and a second FET 23 is connected between the pulse width control circuit 33 and driving signals Vg1 and Vg2 having dead times alternately with respect to the first and second FETs 5 and 23. By supplying, by using the first and second capacitors 24 and 26, which are built in or externally attached to the first and second FETs 5 and 23, and the first and second diodes 25 and 27, , The zero-voltage switching of the first and second FETs 5, 23 can be achieved, and the auxiliary power supply circuit 41 has a partial resonance with, in particular, two such transformers, a forward transformer 3 and a flyback transformer 4. It can be easily incorporated into a type converter. In this case, various advantages of the auxiliary power supply circuit 41 can be added to the function of the partial resonance type converter.

That is, between the primary windings 3A and 4A of the forward transformer 3 and the flyback transformer 4, a voltage clamping capacitor 22 for clamping the flyback voltage of the primary windings 3A and 4A and a second switching element.
23 is connected in series, the first FET 5 is connected in parallel with the first capacitor 24 and the first diode 25, and the second FET 23 is connected in parallel with the second capacitor 26 and the second diode 27. However, by configuring the pulse width control means 33 so as to alternately supply the drive signal having the dead time to the first FET 5 and the second FET 23, noise is not generated and the auxiliary power supply circuit 41 is provided. The number of parts can be significantly reduced, and without being affected by low temperature,
Highly efficient auxiliary power supply circuit that can easily obtain the desired operating voltage
It becomes possible to easily incorporate 41 into a partial resonance type converter capable of achieving zero voltage switching of both the first and second FETs 5 and 23.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

[0037]

According to the first aspect of the present invention, there is provided a switching power supply device comprising: a main transformer; and a main switching element for intermittently applying a DC input voltage to a primary winding of the main transformer. A switching power supply device including a control circuit that rectifies and smoothes a voltage induced in a line by a rectifying and smoothing circuit to output a DC output voltage, and controls the operation of the main switching element to stabilize the DC output voltage. In, a first transformer and a second transformer each having an energy storage means are connected in series to form the main transformer, and rectifying elements are respectively provided at one ends of secondary windings of the first and second transformers. Connect one end of
A smoothing capacitor is connected between the other end of each of the rectifying elements that are commonly connected and the other ends of the secondary windings of the first and second transformers to form the rectifying and smoothing circuit, and The primary winding of the auxiliary transformer is connected to the primary winding of the transformer, and the peak rectification circuit consisting of a diode and a capacitor is connected to the secondary winding of the auxiliary transformer to form an auxiliary power supply circuit. It is possible to provide a switching power supply device having a high-efficiency auxiliary power supply circuit that can generate a desired operating voltage easily without being generated, the number of parts can be significantly reduced, and without being affected by low temperature.

According to a second aspect of the switching power supply device, between the primary windings of the first and second transformers,
A series circuit of a voltage clamping capacitor for clamping the flyback voltage of the primary winding and a second switching element is connected, and the main switching element is connected in parallel with the first capacitor and the first diode. A second capacitor and a second diode are connected in parallel to the second switching element, and the main switching element and the second diode are connected.
The control means is configured to alternately supply a drive signal having a dead time to the switching element, and noise is not generated, and the number of parts can be significantly reduced, which is affected by low temperature. Without this, a highly efficient auxiliary power supply circuit that can easily obtain a desired operating voltage can be easily incorporated in a partial resonance converter that can achieve zero voltage switching of the main switching element and the second switching element.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing a state of each part of the above.

[Explanation of symbols]

 3 forward transformer (first transformer) 4 flyback transformer (second transformer) 5 first FET (main switching element) 6, 7 rectifier diode (rectifier element) 9 smoothing capacitor 10 rectifying and smoothing circuit 12 main transformer 13, 14 Energy Storage Means 22 Capacitor (Voltage Clamp Capacitor) 23 Second FET (Second Switching Element) 24 First Capacitor 25 First Diode 26 Second Capacitor 27 Second Diode 33 Pulse Width Control Circuit ( Control circuit) 41 Auxiliary power supply circuit 42 Auxiliary transformer 43 Diode 44 Capacitor 45 Peak rectifier circuit

Claims (2)

[Claims] 1. A main transformer and a main switching element for intermittently applying a DC input voltage to a primary winding of the main transformer, and a rectifying / smoothing circuit for rectifying a voltage induced in a secondary winding of the main transformer. A switching power supply device including a control circuit for controlling the operation of the main switching element to stabilize the DC output voltage by rectifying and smoothing the DC output voltage by rectifying and smoothing the DC output voltage. One transformer and a second transformer are connected in series to form the main transformer, one end of each rectifying element is connected to one end of the secondary winding of each of the first and second transformers, and they are commonly connected. A smoothing capacitor is connected between the other end of each of the rectifying elements and the other ends of the secondary windings of the first and second transformers to configure the rectifying and smoothing circuit, and A primary winding of an auxiliary transformer is connected to the primary winding of the transformer, and a secondary rectifying circuit of the auxiliary transformer is connected to a peak rectifying circuit composed of a diode and a capacitor to form an auxiliary power supply circuit. Power supply. 2. A series circuit of a voltage clamping capacitor for clamping a flyback voltage of the primary winding and a second switching element is connected between the primary windings of the first and second transformers, and First to main switching element
Of the first switching element and the first diode are connected in parallel, the second switching element is connected in parallel with the second capacitor and the second diode, and are alternately connected to the main switching element and the second switching element. The switching power supply device according to claim 1, wherein the control means is configured to supply a drive signal having a dead time.