JPWO2007116481A1 - Power supply - Google Patents

Abstract

The power supply device includes a primary circuit 11 connected between the input terminal 1 and the primary winding N1 of the transformer 5, and a secondary circuit connected between the secondary winding N2 of the transformer 5 and the output terminal 2. The circuit 12, the auxiliary winding N 3 provided in the transformer 5, and a first voltage having a first polarity generated in the auxiliary winding N 3 due to the first current in the primary circuit 11 are detected. 1st voltage detection circuit (91, 63) and the 2nd voltage detection which detects the 2nd voltage which has the 2nd polarity which occurs in auxiliary winding N3 due to the 2nd current in primary circuit 11 The circuit (92, 64) and the comparison circuit 10 that compares the absolute values of the first and second voltages are provided.

Description

  The present invention relates to a power supply device, and more particularly to a large-capacity power supply device that prevents partial excitation in a transformer.

  For example, in a power supply device such as a full-bridge converter, as shown in FIG. 4, by connecting a capacitor 109 in series with the primary winding N <b> 1 of the transformer 105, the DC component is cut off, and the bias excitation of the transformer 105 is performed. Is preventing.

  In the circuit on the primary side of the full-bridge converter in FIG. 4, a solid line is applied in the positive half-wave application period (the period in which the pulse having the pulse width t1 in FIG. 3A is applied and the period before and after that). A current flows along a route a indicated by an arrow. That is, the current flows in the order of the power source 104 (+), the input terminal 101, the semiconductor switch 133, the transformer (main transformer) 105, the capacitor 109, the semiconductor switch 132, the input terminal 101, and the power source 104 (-). On the other hand, in the negative half-wave application period (the period in which the pulse having the pulse width t2 in FIG. 3B is applied and the period before and after that), current flows along the route b indicated by the dotted arrow. . That is, a current flows in the order of the power source 104 (+), the input terminal 101, the semiconductor switch 131, the capacitor 109, the transformer 105, the semiconductor switch 134, the input terminal 101, and the power source 104 (-). Accordingly, since the DC component is blocked by the capacitor 109, the partial excitation in the transformer 105 can be prevented.

  It should be noted that the inverter is controlled so that the DC component flowing to the AC output side of the inverter can be suppressed even if the partial excitation phenomenon occurs, using the correction amount that suppresses the DC component due to the partial excitation based on the output current of the inverter. It is known (see Patent Document 1 below).

  In addition, it is known to perform efficient conversion with a simple configuration by providing a series circuit of a primary winding of a transformer and a resonant capacitor between the middle points of two series of switching elements. See Patent Document 2 below).

Also, by providing the transformer with an auxiliary winding that generates a magnetic field that cancels the magnetic field generated by the transformer, the magnetic field is generated in the auxiliary winding only during the period when the primary winding current of the transformer is an overcurrent. It is known to cancel the magnetic field generated by the transformer, thereby preventing the partial excitation of the transformer (see Patent Document 3 below).
JP-A-8-223944 Japanese Patent Laid-Open No. 10-136653 JP-A-53-147223

  When the present inventor examined a power supply device (full-bridge converter) as shown in FIG. 4, it was found that there were the following problems.

  First, the current (primary current) flowing through the primary winding N1 of the transformer 105 all flows through the capacitor 109. For this reason, the current flowing through the capacitor 109 increases as the capacity of the power supply device increases. However, the capacitor 109 is limited in its current (allowable ripple current) and withstand voltage. It is impossible to use beyond the allowable ripple current and withstand voltage restrictions from the viewpoint of safety. Further, it is difficult to increase the allowable ripple current and the withstand voltage of the capacitor 109, and such a large improvement cannot be expected so much. In particular, the allowable ripple current of the capacitor 109 can hardly be increased. Therefore, the method of preventing the partial excitation of the transformer 105 by the capacitor 109 is not suitable for a large-capacity power supply device. Moreover, it cannot be said that the power supply device as shown in FIG. 4 is suitable for a large-capacity power supply device.

  Second, in the primary circuit 111 of the transformer 105, for example, a capacitor 109 must be added as an element for preventing partial excitation. However, since the primary circuit 111 is the main circuit of the power supply apparatus, it is desirable to avoid adding an element other than the switching element such as the capacitor 109 from the viewpoint of design and maintenance. Depending on the power supply device, there are restrictions on the mounting space and outer shape. However, when the capacitor 109 is added, there is a possibility that the restriction cannot be met.

  An object of the present invention is to provide a large-capacity power supply device that enables stable operation by preventing partial excitation in the transformer without changing the primary circuit of the transformer.

  A power supply apparatus according to the present invention includes an input terminal, an output terminal, a transformer including a primary winding and a secondary winding, and a primary circuit connected between the input terminal and the primary winding of the transformer. And a secondary circuit connected between the secondary winding of the transformer and the output terminal, an auxiliary winding provided in the transformer, and the first current in the primary circuit The first voltage detection circuit that detects the absolute value of the first voltage having the first polarity, which is a voltage generated in the auxiliary winding, and the first current in the primary circuit are in the opposite direction A second voltage that is generated in the auxiliary winding due to the flowing second current and that detects an absolute value of the second voltage having a second polarity opposite to the first polarity. A detection circuit; and a comparison circuit that compares absolute values of the first and second voltages.

  Preferably, according to one embodiment of the power supply device of the present invention, the power supply device further eliminates the difference between the absolute values of the first and second voltages based on the result of the comparison. A control unit for controlling the primary circuit is provided.

  Preferably, according to one embodiment of the power supply device of the present invention, the first voltage detection circuit comprises a first capacitor connected between a positive side and a middle point of the auxiliary winding. The second voltage detection circuit includes a second capacitor connected between the midpoint and the negative side of the auxiliary winding.

  Preferably, according to one embodiment of the power supply device of the present invention, the first voltage detection circuit is further connected between a positive side of the auxiliary winding and the first capacitor. And the second voltage detection circuit further includes a second diode connected between the negative side of the auxiliary winding and the second capacitor.

  Preferably, according to one embodiment of the power supply device of the present invention, the comparison circuit includes a terminal voltage appearing at a terminal connected to a positive side of the auxiliary winding of the first capacitor, and the second And a comparator that compares a terminal voltage appearing at a terminal connected to the negative side of the auxiliary winding of the capacitor.

  According to the power supply device of the present invention, the auxiliary winding is provided in the transformer, and the first voltage generated in the auxiliary winding due to the first current in the primary circuit and the second current in the primary circuit are provided. This is compared with the second voltage generated in the auxiliary winding. As a result, since the partial excitation generated in the transformer can be directly detected and controlled, it is possible to prevent the partial excitation of the transformer without using a capacitor with restrictions on allowable ripple current and withstand voltage. Moreover, the partial excitation of the transformer can be prevented without adding an element other than a switching element such as a capacitor in the primary circuit which is the main circuit of the power supply apparatus.

  According to an embodiment of the present invention, the primary circuit is controlled based on the result of the comparison so that the difference between the absolute values of the first and second voltages is eliminated. As a result, the operation of the primary circuit can be directly controlled based on the voltage generated in the auxiliary winding so as to cancel the partial excitation generated in the transformer, so that the partial excitation of the transformer is prevented without using a capacitor. be able to.

  According to one embodiment of the present invention, the first voltage detection circuit is composed of a first capacitor, and the second voltage detection circuit is composed of a second capacitor. Thereby, the first and second voltages can be detected with a relatively simple configuration, and as a result, the partial excitation of the transformer can be prevented.

  Further, according to one embodiment of the present invention, the first voltage detection circuit includes a first capacitor and a first diode, and the second voltage detection circuit includes a second capacitor and a second diode. Thereby, it is possible to prevent the current from flowing backward in the first and second voltage detection circuits and to accurately detect the first and second voltages, and as a result, to prevent the partial excitation of the transformer. Can do.

  According to one embodiment of the present invention, the first and second voltages are compared using a comparator. As a result, the first and second voltages can be detected by a circuit having a relatively simple configuration, and as a result, partial excitation of the transformer can be prevented.

It is a figure which shows an example of a structure of the power supply device of this invention. It is explanatory drawing of operation | movement of the power supply device of FIG. The waveform of the power supply device of FIG. 1 is shown. It is explanatory drawing of the conventional power supply device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input terminal 2 Output terminal 5 Transformer 11 Primary circuit 12 Secondary circuit 13 Partial excitation detection circuit 14 Control part 31-34 Semiconductor switch

  FIG. 1 is a configuration diagram of a power supply device and shows a configuration of a power supply device according to an embodiment of the present invention. The power supply device includes an input terminal 1, an output terminal 2, a transformer 5, a primary circuit 11, a secondary circuit 12, a partial excitation detection circuit 13, and a control unit 14. The transformer 5 includes an auxiliary winding N3 in addition to the primary winding N1 and the secondary winding N2. N1 also represents the number of turns of the primary winding N1. The same applies to N2 and N3. As will be described later, the secondary winding N2 is equally divided into a first portion N2-1 and a second portion N2-2 of the secondary winding N2 at its midpoint. To correspond to the secondary winding N2, the auxiliary winding N3 is also divided into two equal parts at the midpoint between the first portion N3-1 and the second portion N3-2 of the auxiliary winding N3.

  A plurality (that is, two) of input terminals 1 are provided. A power supply 4 is connected between the input terminals 1. The power supply 4 supplies the power supply device with a power supply, for example, a power supply having a waveform as shown in the uppermost stage of FIG. The power source 4 is not limited to this, and may be other various power sources.

  The primary circuit (input circuit) 11 is connected between the input terminal 1 and the primary winding N <b> 1 of the transformer 5. The primary circuit 11 includes a bridge circuit including first to fourth switching elements, for example, semiconductor switches 31 to 34. The first and second semiconductor switches 31 and 32 are connected in series in this order to constitute a first series circuit. The third and fourth semiconductor switches 33 and 34 are connected in series in this order to form a second series circuit. The first and second series circuits are connected in parallel and inserted between the input terminals 1. One terminal of the primary winding N1 of the transformer 5 is connected to a connection point (middle point) of the first and second semiconductor switches 31 and 32 connected in series. The other terminal of the primary winding N1 of the transformer 5 is connected to a connection point (middle point) of the third and fourth semiconductor switches 33 and 34 connected in series.

  As is well known, the semiconductor switches 31 to 34 are made of, for example, a semiconductor element such as a power MOSFET, IGBT, BJT, SIT, thyristor, or GTO. A predetermined control signal is supplied from the control unit 14 to the control electrodes (gate electrode or base electrode) of the semiconductor switches 31 to 34. Thereby, the semiconductor switches 31 to 34 are basically controlled to be turned on / off so as to correspond to the change in the amplitude of the output of the power supply 4.

  The secondary circuit (output circuit) 12 is connected between the secondary winding N <b> 2 of the transformer 5 and the output terminal 2. A plurality of (that is, two) output terminals 2 are provided. Between the output terminals 2, a DC voltage that is the output of the power supply device is output. The secondary circuit 12 includes diodes 61 and 62, an inductance 7, and a capacitor 8. As is well known, the diodes 61 and 62 may be constituted by MOSFET, IGBT, SIT or the like instead of the diode. The output voltage of the transformer 5 is output to one of the output terminals 2 via the diodes 61 and 62 connected to both terminals of the secondary winding N2 of the transformer 5. The other of the output terminals 2 is connected to the midpoint of the secondary winding N2 of the transformer 5. That is, the secondary winding N2 of the transformer 5 is divided into two by the midpoint so that the turns ratio of the first part N2-1 and the second part N2-2 is equal. The inductance 7 and the capacitor 8 constitute a smoothing circuit, and this smoothing circuit is inserted between the output terminals 2. Thereby, the output voltage of the transformer 5 is rectified and smoothed.

  The partial excitation detection circuit 13 includes a first voltage detection circuit, a second voltage detection circuit, and a comparison circuit 10. The auxiliary winding N3 of the transformer 5 can be considered to constitute a part of the partial excitation detection circuit 13. Further, it can be considered that the partial excitation detection circuit 13 is provided in the secondary circuit 12.

  The first voltage detection circuit is a voltage generated in the auxiliary winding N3 due to the first current in the primary circuit 11, and detects the absolute value of the first voltage having the first polarity. The first current is a current of route a (indicated by a dotted line in FIG. 2 described later), and is a current in a positive half-wave period. The first voltage detection circuit includes a first capacitor 91 and a first diode 63. The first diode 63 is a diode for preventing reverse current flow (return). Therefore, the first voltage detection circuit only needs to include at least the first capacitor 91. The first capacitor 91 is connected between the positive terminal of the auxiliary winding N3 and the midpoint. The first diode 63 is connected between the positive terminal of the auxiliary winding N3 and the first capacitor 91. The midpoint of the auxiliary winding N3 is connected to the ground potential.

  The second voltage detection circuit is a voltage generated in the auxiliary winding N3 due to the second current in the primary circuit 11, and has a second polarity opposite to the first polarity. Detect the absolute value of voltage. The second current is a current of route b (indicated by a one-dot chain line in FIG. 2), and is a current in a negative half-wave period. The second voltage detection circuit includes a second capacitor 92 and a second diode 64. The second diode 64 is a diode for preventing reverse current flow (return). Therefore, the second voltage detection circuit may include at least the second capacitor 92. The second capacitor 92 is connected between the midpoint of the auxiliary winding N3 and the negative terminal. The second diode 64 is connected between the negative terminal of the auxiliary winding N 3 and the second capacitor 92.

  The comparison circuit 10 includes, for example, a comparator 10 and compares the absolute values of the first and second voltages to obtain the difference. That is, the output of the first capacitor 91 that is the first voltage detection circuit is input to one input terminal of the comparator 10. The output of the second capacitor 92 that is the second voltage detection circuit is input to the other input terminal of the comparator 10. Thereby, the comparison circuit 10 has a terminal voltage appearing at a terminal connected to the positive side of the auxiliary winding N3 of the first capacitor 91 and a terminal connected to the negative side of the auxiliary winding N3 of the second capacitor 92. Is compared with the terminal voltage appearing at, and the difference is obtained. The output of the comparison circuit 10 is input (feedback) to the control unit 14.

  As is well known, the control unit 14 supplies predetermined control signals to the control electrodes of the semiconductor switches 31 to 34 constituting the primary circuit 11 and controls ON / OFF thereof. That is, in one positive half-wave period, the semiconductor switches 32 and 33 are turned on (ON), and at the same time, the semiconductor switches 31 and 34 are turned off (OFF). Next, in the negative half-wave period, the semiconductor switches 31 and 34 are turned on (ON), and at the same time, the semiconductor switches 32 and 33 are turned off (OFF). Further, as will be described later, the control unit 14 controls the primary circuit 11 based on the comparison result (the obtained difference, the same applies hereinafter) in the comparison circuit 10. That is, the primary circuit 11 is feedback-controlled.

  FIG. 2 is an explanatory diagram of the operation of the power supply device of FIG. In FIG. 2, illustration of the control unit 14 and reference numerals 11 to 13 is omitted.

  First, the operation of the positive half wave in the power supply device of FIG. In this case, as described above, the semiconductor switches 32 and 33 are turned on (ON) by the control signal from the control unit 14. Thereby, a route indicated by a dotted line a in FIG. 2 is formed, and a current flows through this route.

  That is, the current (first current) is from the power source 4 (+) to the input terminal 1, the semiconductor switch 33, the primary winding N1 of the transformer 5, the semiconductor switch 32, the input terminal 1, and the power source 4 (-). Flowing (positive loop of primary winding N1). As a result, the power supply voltage Vin is applied to the primary winding N1 of the transformer 5. At the same time, a voltage corresponding to the winding direction is induced in the auxiliary winding N3 (N3-1), current flows (positive loop of the auxiliary winding N3), and the capacitor 91 is charged through the diode 63. To do.

  Next, the operation of the negative half wave in the power supply device of FIG. In this case, as described above, the semiconductor switches 31 and 34 are turned on (ON) by the control signal from the control unit 14. As a result, a route indicated by an alternate long and short dash line b in FIG. 2 is formed, and a current flows through this route.

  That is, the current (second current) is supplied from the power source 4 (+) to the input terminal 1, the semiconductor switch 31, the primary winding N1 of the transformer 5, the semiconductor switch 34, the input terminal 1, and the power source 4 (-). Flow (negative loop of primary winding N1). As a result, the power supply voltage Vin is applied to the primary winding N1 of the transformer 5 in the opposite direction to that of the positive loop. At the same time, in the auxiliary winding N3 (N3-2), a corresponding voltage is induced in the direction opposite to the winding direction, and a current flows (negative loop of the auxiliary winding N3) via the diode 64. To charge the capacitor 92.

  As described above, the partial excitation detection circuit 13 detects the first and second voltages generated in the auxiliary winding N <b> 3 provided in the transformer 5. Thereby, the partial excitation detection circuit 13 detects the voltage of the primary winding N1 (and consequently the secondary winding N2) of the transformer 5. That is, the partial excitation generated in the transformer 5 is detected.

  The first voltage is a voltage appearing at a terminal connected to the positive side of the auxiliary winding N3 of the first capacitor 91, and is detected by the first capacitor 91 which is a first voltage detection circuit. The first voltage is a voltage generated by the voltage Vin applied to the transformer 5 when a current flows in the first circuit 11 in the first direction (route a in FIG. 2). This is equivalent to the voltage generated on the positive side of the line N1. The value of the first voltage is a value proportional to the pulse width of the current in the primary circuit 11. That is, the voltage Vin applied to the transformer 5 causes a current to flow in a route (master side route) represented by a dotted line similar to the route a in the auxiliary winding N3, and the first capacitor 91 is charged. The first capacitor 91 is charged to the value of the first voltage.

  The second voltage is a voltage that appears at a terminal connected to the negative side of the auxiliary winding N3 of the second capacitor 92, and is detected by the second capacitor 92, which is a second voltage detection circuit. The second voltage is a voltage generated by the voltage Vin applied to the transformer 5 when a current flows in the second direction (route b in FIG. 2) in the primary circuit 11. This is equivalent to the voltage generated on the negative side of the line N1. The value of the second voltage is a value proportional to the pulse width of the current in the primary circuit 11. In other words, the voltage Vin applied to the transformer 5 causes a current to flow in a route (slave side route) represented by a dashed line similar to the route b in the auxiliary winding N3, and the second capacitor 92 is charged. The second capacitor 92 is charged to the value of the second voltage.

  The control unit 14 controls the primary circuit 11 based on the comparison result in the comparison circuit 10 so that the difference between the absolute values of the first and second voltages is eliminated. That is, in the primary circuit 11, the control unit 14 turns on the semiconductor switches 32 and 33 in the ON time (ON time in the positive half wave, pulse width t1 in FIG. 3A), and the semiconductor switch Control is performed so that the ON time in the switching of 31 and 34 (ON time in the negative half wave, pulse width t2 in FIG. 3A) is longer or shorter than the value at that time. To do.

  For example, when the first voltage is higher than the second voltage, the conduction time (ON time) t1 of the semiconductor switches 32 and 33 is shortened by a predetermined time, for example, than the conduction time at that time. The range of shortening is determined empirically (the same applies hereinafter). Alternatively, the conduction time t2 of the semiconductor switches 31 and 34 is made longer by a predetermined time than the conduction time at that time, for example. Conversely, when the second voltage is greater than the first voltage, the conduction time t2 of the semiconductor switches 31 and 34 is shortened by a predetermined time, for example, from the conduction time at that time. Alternatively, the conduction time t1 of the semiconductor switches 32 and 33 is set longer by a predetermined time than the conduction time at that time, for example. By sequentially performing this control, t1 = t2 is finally obtained. Thereby, partial excitation in the transformer 5 can be prevented.

  FIG. 3 shows waveforms of the power supply device of FIG. 3A shows a waveform when the power supply device of FIG. 1 is normal, and FIG. 3B shows a waveform when the power supply device of FIG. 1 is abnormal.

In FIG. 3A, the partial excitation of the transformer 5 is prevented by the partial excitation detection circuit 13 (and the control unit 4). As a result, in the input waveform from the power supply 4, the pulse width t1 on the positive side (positive half-wave application period) and the pulse width t2 on the negative side (negative half-wave application period) are equal. As a result, the current I _T1-N1 in the primary circuit 11 becomes a normal waveform corresponding to the input waveform, and the current I _T1N3-1 flowing in the auxiliary winding N3-1 and the current I _T1N3- flowing in the auxiliary winding _{N3-2. 2} also has a normal waveform. As a result, the first voltage V _C1 generated in the capacitor 91 and the second voltage V _C2 generated in the capacitor 92 are equal, and the difference is “0”. In this case, the control unit 14 maintains the pulse width t1 and the pulse width t2 as they are. Therefore, this waveform indicates that the partial excitation detection of the transformer 5 can be prevented by the partial excitation detection circuit 13.

On the other hand, in FIG. 3B, for some reason, in the input waveform from the power supply 4, the pulse width t1 on the positive side and the pulse width t2 on the negative side are not equal. That is, t1> t2. As a result, the first voltage V _C1 generated in the capacitor 91 is larger than the second voltage V _C2 generated in the capacitor 92. That is, V _C1 > V _C2 . In this state, the transformer 5 is saturated due to the partial excitation, and eventually is destroyed by the overcurrent. The same applies to the case of t1 <t2.

  Note that the waveform in FIG. 3B is almost the same as the example in which the capacitor 109 is omitted in the power supply device in FIG. That is, in a power supply device that performs large-capacity power conversion, the capacitor 109 cannot be applied (connected) due to restrictions on the withstand voltage of the capacitor 109 and allowable ripple current. For this reason, the transformer 105 is saturated by the bias excitation, and eventually destroyed by the overcurrent, and the bias excitation of the transformer 105 cannot be prevented.

Therefore, in the present invention, the comparison circuit 10 compares the first voltage V _C1 generated in the capacitor 91 with the second voltage V _C2 generated in the capacitor 92, and the difference V _CS = V _C1 −V which is the comparison result. _{Based on C2} > 0 (or V _CS = V _C2 −V _C1 > 0), the primary circuit 11 is controlled so that the difference V _CS becomes “0” (in a direction toward “0”). The As a result, as shown in FIG. 3A again, in the input waveform from the power supply 4, the pulse width t1 on the positive side and the pulse width t2 on the negative side are equal. Therefore, this waveform indicates that the partial excitation of the transformer 5 is prevented by the partial excitation detection circuit 13 of the present invention.

  As can be seen from the above, the partial excitation detection of the transformer 5 can be prevented by the partial excitation detection circuit 13. Thereby, it is possible to realize a large-capacity power supply device (that performs large-capacity power conversion) in which the partial excitation of the transformer 5 is prevented.

  As mentioned above, although this invention was demonstrated according to the embodiment, this invention can be variously deformed within the scope of the gist.

  For example, the present invention is not limited to the full-bridge converter shown in FIG. 1, but can be applied to various switching converters such as a push-pull converter, and a DC component is cut off using a capacitor. It can be applied to various power supply devices.

As described above, according to the present invention, in the power supply device, it is possible to prevent the partial excitation of the transformer without using a capacitor that is limited in allowable ripple current and withstand voltage. Therefore, since no capacitor is used, even if a large current flows in the primary winding of the transformer, it is possible to prevent the partial excitation of the transformer. As a result, it is possible to realize a power supply device that performs large-capacity power conversion while preventing the partial excitation of the transformer. Moreover, the partial excitation of the transformer can be prevented without adding any elements other than the switching elements in the primary circuit which is the main circuit of the power supply apparatus. Therefore, the design and maintenance of the power supply device can be facilitated, and restrictions on the mounting space and the outer shape of the power supply device can be dealt with.

Claims (7)

An input terminal;
An output terminal;
A transformer comprising a primary winding and a secondary winding;
A primary circuit connected between the input terminal and a primary winding of the transformer;
A secondary circuit connected between the secondary winding of the transformer and the output terminal;
An auxiliary winding provided in the transformer;
A first voltage detection circuit for detecting an absolute value of a first voltage having a first polarity, which is a voltage generated in the auxiliary winding due to a first current in the primary circuit;
A voltage generated in the auxiliary winding due to a second current flowing in a direction opposite to the first current in the primary circuit, wherein the second polarity is opposite to the first polarity. A second voltage detection circuit for detecting an absolute value of the second voltage having;
A power supply apparatus comprising: a comparison circuit that compares absolute values of the first and second voltages. The power supply device according to claim 1, further comprising:
A power supply apparatus comprising: a control unit that controls the primary circuit so that a difference between absolute values of the first and second voltages is eliminated based on a result of the comparison. The power supply device according to claim 2,
The primary circuit comprises a bridge circuit comprising a semiconductor switch;
The power supply device, wherein the control unit controls switching of the semiconductor switch based on a result of the comparison so that a difference between absolute values of the first and second voltages is eliminated. The power supply device according to claim 3,
The primary circuit includes a first series circuit in which first and second semiconductor switches are connected in series in this order, and a second series circuit in which third and fourth semiconductor switches are connected in series in this order. It consists of a bridge circuit connected in parallel,
Based on the result of the comparison, the control unit switches the first and fourth semiconductor switches and eliminates the difference between the absolute values of the first and second voltages. A power supply device that controls switching of the semiconductor switch. The power supply device according to claim 1,
The first voltage detection circuit comprises a first capacitor connected between a positive side and a middle point of the auxiliary winding;
The power supply apparatus, wherein the second voltage detection circuit includes a second capacitor connected between a midpoint and a negative side of the auxiliary winding. The power supply device according to claim 5,
The first voltage detection circuit further comprises a first diode connected between a positive side of the auxiliary winding and the first capacitor;
The power supply apparatus, wherein the second voltage detection circuit further includes a second diode connected between a negative side of the auxiliary winding and the second capacitor. The power supply device according to claim 5,
The comparison circuit has a terminal voltage appearing at a terminal connected to the positive side of the auxiliary winding of the first capacitor, and a terminal appearing at a terminal connected to the negative side of the auxiliary winding of the second capacitor A power supply device comprising a comparator for comparing voltage.

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