Power source device and method for controlling power source device

Abstract

To prevent a transformer from becoming magnetically biased in a switching power source device.SOLUTION: A power source device includes a first switching element, a first assisting switching element, a capacitor, a transformer including a first coil and a second coil, a second switching element, and a control circuit. The control circuit controls the timing to turn on the second switching element according to the magnitude of the load current flowing in the first coil, in a case where the first switching element and the second switching element are in the off-state, the first assisting switching element is in the on-state, and the second switching element is in the on-state.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a power supply device and a control method thereof.

Background Art

[0002] Patent Document 1 describes a switching power supply capable of realizing ZVS (Zero Voltage Switching) operation.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a switching power supply device in which a capacitor and an auxiliary transistor are connected to a winding of a transformer, the capacitor voltage changes due to the magnitude of the load current, the operating timing of the main transistor and the auxiliary transistor, and the leakage inductance of the transformer, and the exciting energy of the transformer may increase. As a result, the balance between the change amount of the exciting energy of the transformer during the period when the main transistor is on and the change amount of the exciting energy of the transformer during the period when the main transistor is off is lost, and the transformer may be magnetically biased.

[0005] An object of the present disclosure is to prevent a transformer from being magnetically biased in a switching power supply device.

Means for Solving the Problems

[0006] A power supply device according to one aspect of the present disclosure includes a first switching element having one end electrically connected to a first input terminal, a first auxiliary switching element having one end electrically connected to the other end of the first switching element, a capacitor having one end electrically connected to the other end of the first auxiliary switching element and the other end electrically connected to a second input terminal, a first winding having one end electrically connected to the other end of the first switching element and one end of the first auxiliary switching element and the other end electrically connected to the other end of the capacitor, a transformer including a second winding having one end electrically connected to a first output terminal and magnetically coupled to the first winding, a second switching element having one end electrically connected to a second output terminal and the other end connected to one end of the second winding, and a control circuit for controlling the first switching element, the first auxiliary switching element, and the second switching element. The control circuit controls the timing of turning on the second switching element according to the magnitude of the current flowing through the first winding when the first switching element and the second switching element are off and the first auxiliary switching element is on and the second switching element is turned on.

[0007] In the power supply device of the present disclosure, the control circuit advances the timing of turning on the second switching element as the peak value of the current flowing through the first winding increases, and delays the timing of turning on the second switching element as the peak value of the current flowing through the first winding decreases.

[0008] In the power supply device of the present disclosure, the control circuit delays the timing of turning on the second switching element as the input voltage input between the first input terminal and the second input terminal increases, and advances the timing of turning on the second switching element as the input voltage decreases.

[0009] In the power supply device of the present disclosure, the control circuit calculates the timing of turning on the second switching element based on a predetermined control formula.

[0010] In the power supply device of the present disclosure, a current detection unit is provided that detects information proportional to the magnitude of the current flowing through the first winding.

[0011] In the control method of the power supply device of the present disclosure, a first switching element having one end electrically connected to a first input terminal, a first auxiliary switching element having one end electrically connected to the other end of the first switching element, a capacitor having one end electrically connected to the other end of the first auxiliary switching element and the other end electrically connected to a second input terminal, a first winding having one end electrically connected to the other end of the first switching element and one end of the first auxiliary switching element and the other end electrically connected to the other end of the capacitor, a transformer including a second winding having one end electrically connected to a first output terminal and magnetically coupled to the first winding, and a second switching element having one end electrically connected to a second output terminal and the other end connected to one end of the second winding. A control method of a power supply device including: when the first switching element and the second switching element are off and the first auxiliary switching element is on, and when turning on the second switching element, controlling the timing of turning on the second switching element according to the magnitude of the current flowing through the first winding.

Advantages of the Invention

[0012] According to the present disclosure, in a switching power supply device, it is possible to prevent the transformer from being magnetically biased.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0014] Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. Note that the present disclosure is not limited by this embodiment, and in the following embodiments, the same parts are denoted by the same reference numerals, and redundant explanations are omitted.

[0015] [Embodiment] (Power Supply Device) A configuration example of the power supply device according to the embodiment will be described with reference to FIG. 1. FIG. 1 is a diagram showing a configuration example of the power supply device according to the embodiment.

[0016] As shown in FIG. 1, the power supply device 1 includes a first input terminal 1a, a second input terminal 1b, a first output terminal 1c, and a second output terminal 1d. The power supply device 1 is an active clamp type switching power supply device.

[0017] The first input terminal 1a is electrically connected to the high potential side of the power supply 11. The second input terminal 1b is electrically connected to the low potential side of the power supply 11. The first output terminal 1c is electrically connected to one end of the load 12. The second output terminal 1d is electrically connected to the other end of the load 12.

[0018] The power supply device 1 steps down the input voltage Vin input between the first input terminal 1a and the second input terminal 1b, and outputs the output voltage Vout to the load 12 electrically connected to the first output terminal 1c and the second output terminal 1d.

[0019] As shown in FIG. 1, the power supply device 1 includes a first switching element Q1, a second switching element Q2, a first auxiliary switching element Q3, a second auxiliary switching element Q4, a capacitor 21, a current transformer 31, a capacitor 51, a control circuit 61, an inductor Lr, a transformer T, and a choke Lo.

[0020] The first switching element Q1, the second switching element Q2, the first auxiliary switching element Q3, and the second auxiliary switching element Q4 are MOSFETs. In the embodiment, each switching element and each auxiliary switching element is a MOSFET, but the present disclosure is not limited to this. Each switching element and each auxiliary switching element may be a silicon power device, a GaN power device, a SiC power device (e.g., an IGBT (Insulated Gate Bipolar Transistor)), or the like.

[0021] Each switching element and each auxiliary switching element has a parasitic diode (body diode) that can actively conduct current, or has a diode connected in antiparallel to it, which is a pn junction between the back gate and the source and drain of the MOSFET.

[0022] The source of the first switching element Q1 is electrically connected to the second input terminal 1b. The drain of the first switching element Q1 is electrically connected to the source of the first auxiliary switching element Q3. The drain of the first auxiliary switching element Q3 is electrically connected to one end of a capacitor 21. The other end of the capacitor 21 is electrically connected to the first input terminal 1a.

[0023] The transformer T includes a first winding 41, a second winding 42, and a core 43. The first winding 41 and the second winding 42 are wound around the core 43. In this embodiment, the number of turns of the first winding 41 is set to N p , the number of turns of the second winding 42 is N s Let's say.

[0024] The drain of the first switching element Q1 and the source of the first auxiliary switching element Q3 are electrically connected to one end of the current transformer 31. The other end of the current transformer 31 is electrically connected to one end of the first winding 41. The current transformer 31 detects the transformer current I p flowing through the first winding 41. The transformer current I p is proportional to the load current I out .

[0025] The other end of the capacitor 21 is electrically connected to one end of the inductor Lr. The other end of the inductor Lr is electrically connected to the other end of the first winding 41. The inductor Lr is the leakage inductance of the transformer T. The inductor Lr may be a winding component or a wiring inductance.

[0026] The source of the second switching element Q2 is electrically connected to the source of the second auxiliary switching element Q4. The drain of the second switching element Q2 is electrically connected to one end of the second winding 42. The other end of the second winding 42 is electrically connected to the drain of the second auxiliary switching element Q4. Note that the second auxiliary switching element Q4 may be a diode whose cathode is electrically connected to the other end of the second winding 42 and whose anode is electrically connected to the source of the second switching element Q2.

[0027] One end of the choke Lo is electrically connected to the drain of the second auxiliary switching element Q4 and the other end of the second winding 42. The other end of the choke Lo is electrically connected to the high potential side of the capacitor 51. The low potential side of the capacitor 51 is electrically connected to the source of the second switching element Q2 and the source of the second auxiliary switching element Q4.

[0028] The control circuit 61 controls the on and off states of the first switching element Q1, the second switching element Q2, the first auxiliary switching element Q3, and the second auxiliary switching element Q4. The control circuit 61 outputs a drive signal Vg1 to the first switching element Q1 to control the on and off states of the first switching element Q1. The control circuit 61 outputs a drive signal Vg2 to the second switching element Q2 to control the on and off states of the second switching element Q2. The control circuit 61 outputs a drive signal Vg3 to the first auxiliary switching element Q3 to control the on and off states of the first auxiliary switching element Q3. The control circuit 61 outputs a drive signal Vg4 to the second auxiliary switching element Q4 to control the on and off states of the second auxiliary switching element Q4. Each switching element and each auxiliary switching element are controlled to turn on when a high-level drive signal is input and to turn off when a low-level drive signal is input.

[0029] [Operation of Comparative Example] With reference to FIGS. 2 and 3, the operation of the power supply device according to the comparative example will be described. FIGS. 2 and 3 are diagrams showing the operation timing of the power supply device according to the comparative example.

[0030] FIG. 2 shows waveform 101, waveform 102, waveform 103, waveform 104, and waveform 105. Waveform 101 represents the operating state of the first switching element Q1. Waveform 102 represents the operating state of the second switching element Q2. Waveform 103 represents the operating state of the first auxiliary switching element Q3. Waveform 104 represents the voltage V ds between the drain and source of the first switching element Q1. Waveform 105 represents the current Ic flowing through the capacitor 21. In the example shown in FIG. 2, the operation with periods T1 to T8 as one cycle is repeated.

[0031] In period T1, the first switching element Q1 is on, the second switching element Q2 is on, and the first auxiliary switching element Q3 is off. In period T1, in the power supply device 1, current flows through the first switching element Q1, the inductor Lr, the transformer T, the second switching element Q2, the choke Lo, and the capacitor 51, and the load current I outOutput to load 12. During period T1, exciting energy is stored in choke Lo.

[0032] During period T2, the first switching element Q1 is off, the second switching element Q2 is off, and the first auxiliary switching element Q3 is off. During period T2, the second switching element Q2 is controlled from on to off. During period T2, in the power supply device 1, current flows through the parasitic capacitor of the first switching element Q1, inductor Lr, transformer T, the second switching element Q2 (after turning off, the parasitic capacitor of the second switching element Q2), choke Lo, and capacitor 51, and the load current I out is output to load 12. The voltage V ds between the drain and source of the first switching element Q1 increases.

[0033] During period T3, the first switching element Q1 is off, the second switching element Q2 is off, and the first auxiliary switching element Q3 is off. During period T3, current flows through inductor Lr, transformer T, the parasitic diode of the first auxiliary switching element Q3, and capacitor 21, and at the same time, the exciting energy stored in choke Lo during period T1 is released. As a result, current flows through the second auxiliary switching element Q4 (before turning on, the parasitic diode of the second auxiliary switching element Q4) and capacitor 51, and the load current I out is output to load 12.

[0034] During period T4, the first switching element Q1 is off, the second switching element Q2 is off, and the first auxiliary switching element Q3 is on. During period T4, continuing from period T3, current flows through inductor Lr, transformer T, the first auxiliary switching element Q3, and capacitor 21, and at the same time, current flows through choke Lo, the second auxiliary switching element Q4, and capacitor 51, and the load current I out is output to load 12.

[0035] During period T5, the first switching element Q1 is off, the second switching element Q2 is off, and the first auxiliary switching element Q3 is on. During period T5, continuing from period T4, current flows through the inductor Lr, the transformer T, the first auxiliary switching element Q3, and the capacitor 21, and current also flows through the choke Lo, the second auxiliary switching element Q4, and the capacitor 51, and the load current I out is output to the load 12.

[0036] During period T6, the first switching element Q1 is off, the second switching element Q2 is on, and the first auxiliary switching element Q3 is on. During period T6, continuing from period T5, current flows through the choke Lo, the second auxiliary switching element Q4, and the capacitor 51, and the load current I out is output to the load 12. Also, a current proportional to the current flowing through the transformer T, the second switching element Q2, and the second auxiliary switching element Q4 is added to the current flowing through the inductor Lr, the transformer T, the first auxiliary switching element Q3, and the capacitor 21.

[0037] During period T7, the first switching element Q1 is off, the second switching element Q2 is on, and the first auxiliary switching element Q3 is off. During period T7, continuing from period T6, current flows through the choke Lo, the second auxiliary switching element Q4, and the capacitor 51, and the load current I out is output to the load 12. Also, current flows through the inductor Lr, the transformer T, and the parasitic capacitor of the first switching element Q1, and the drain-source voltage V ds of the first switching element Q1 decreases.

[0038] During period T8, the first switching element Q1 is off, the second switching element Q2 is on, and the first auxiliary switching element Q3 is off. During period T8, continuing from period T7, current flows through the choke Lo, the second auxiliary switching element Q4, and the capacitor 51, and the load current I out is output to the load 12. Also, current flows through the inductor Lr, the transformer T, and the parasitic diode of the first switching element Q1.

[0039] During period T9 (T1), the first switching element Q1 is on, the second switching element Q2 is on, and the first auxiliary switching element Q3 is off. Since the first switching element Q1 turns on from a state where current is flowing through the parasitic diode, ZVS operation becomes possible.

[0040] As shown in FIG. 2, in the comparative example, during period T6, the second switching element Q2 is on before the first auxiliary switching element Q3 turns off. In this case, during period T6, since the current flowing through the capacitor 21 increases, the capacitor voltage changes and the exciting energy of the transformer T increases. For this reason, the balance between the change amount of the transformer exciting energy during the period when the first switching element Q1 is on and the change amount of the transformer exciting energy during the period when the first switching element Q1 is off is disrupted, and there is a possibility that the transformer T may be magnetically biased.

[0041] FIG. 3 shows waveform 101, waveform 102, waveform 103, waveform 104, and waveform 106. Waveform 106 represents the current I out flowing through the capacitor 21 when the inductor Lr is large and the load current I c is large.

[0042] As shown by waveform 106, during period T3, a current corresponding to the load current I out is added to the current Ic flowing through the capacitor, so the capacitor voltage changes, and there is a possibility that the balance of the change amount of the exciting energy of the transformer T may be disrupted. Therefore, even when a large inductor Lr occurs, there is a possibility that the transformer T may be magnetically biased.

[0043] Therefore, the present disclosure controls the first switching element Q1, the second switching element Q2, and the first auxiliary switching element Q3 so as to prevent the transformer T from being magnetically biased.

[0044] [Operation of Embodiment] With reference to FIGS. 4 and 5, the operation of the power supply device according to the embodiment will be described. FIGS. 4 and 5 are diagrams showing the operation timing of the power supply device according to the embodiment.

[0045] FIG. 4 shows the operation timing of the power supply device when the load current is relatively large. In FIG. 4, waveform 201, waveform 202, waveform 203, waveform 204, waveform 205, and waveform 206 are shown. Waveform 201 represents the operating state of the first switching element Q1. Waveform 202 represents the operating state of the second switching element Q2. Waveform 203 represents the operating state of the first auxiliary switching element Q3. Waveform 204 represents the voltage V ds between the drain and source of the first switching element Q1. Waveform 205 represents the transformer current Ip flowing through the first winding 41. Waveform 206 represents the magnetic flux density of the transformer T. In FIG. 4, since the operating states of the first switching element Q1, the second switching element Q2, and the first auxiliary switching element Q3 from period T1 to period T8 are the same as those in the comparative example shown in FIGS. 3 and 4, the description thereof will be omitted.

[0046] The control circuit 61 controls the timing of turning on the second switching element Q2 according to the magnitude of the transformer current I p flowing through the first winding 41 of the transformer T, which changes in proportion to the load current, in period T6. The current flowing through the first winding of the transformer T is detected by the current transformer 31.

[0047] As shown in waveform 205, the transformer current I p proportional to the load current flowing in the negative direction increases in period T1 and reaches a peak value I P1 when the first switching element Q1 is turned off. The peak value I P1 is represented by the following formula (1).

[0048]

Equation

[0049] In formula (1), I out is the magnitude of the load current, Np is the number of turns of the first winding 41, N s is the number of turns of the second winding 42. As shown in the waveform 205, the transformer current I proportional to the load current flowing in the positive direction p increases during the period T6 and reaches the peak value I when the first auxiliary switching element Q3 is turned off P2 . The peak value I P2 is expressed by the following formula (2). When the exciting inductance of the transformer T and the inductance of the choke Lo are small, a current proportional to the ripple current of the exciting current and the choke current is added to the peak value I P1 , so the added amount may be considered

[0050]

Equation

[0051] In formula (2), V C is the capacitor voltage of the capacitor 21, ΔT6 is the length of the period T6, and L r is the inductance of the inductor L r . In the active clamp type power supply device, the capacitor voltage V C is generally expressed by the following formula (3).

[0052]

Equation

[0053] Vin is the magnitude of the input voltage, and D on and D off are the on and off time ratios of the first switching element Q1 determined by the control circuit 61. Therefore, the control circuit 61 can calculate the value of the capacitor voltage V C by receiving the input voltage Vin from the power supply 11. Generally, the on time ratio D on of the first switching element Q1 is inversely proportional to the input voltage Vin in order to control the output voltage Vout to be constant. Therefore, the value of the capacitor voltage V C is inversely proportional to the input voltage Vin

[0054] The control circuit 61 controls the timing of turning on the second switching element Q2 so as to balance the absolute value of the peak value I P1 and the absolute value of the peak value I P2 . When balancing the absolute value of the peak value I P1 and the absolute value of the peak value I P2 , the following formula (4) holds.

[0055]

Equation

[0056] That is, ΔT6 can be expressed by the following formula (5).

[0057]

Equation

[0058] In this embodiment, when the magnitude of the transformer current I out of the first winding 41 of the transformer T proportional to the load current I is relatively large, the control circuit 61 makes the timing of turning on the second switching element Q2 earlier than the reference timing. That is, in this case, the period T6 during which both the second switching element Q2 and the first auxiliary switching element Q3 are on becomes relatively long. Specifically, the control circuit 61 controls the timing of turning on the second switching element Q2 according to the control formula based on the length T6 of the period T6. As a result, since the peak value I p of the positive current from the period T6 to the period T7 increases, the absolute value of the peak value I P2 of the negative current from the period T1 to the period T2 and the absolute value of the peak value I P1 of the positive current from the period T6 to the period T7 can be balanced. Thereby, the bias excitation of the transformer T can be suppressed. The control formula can be expressed as the following formula (6). P12

[0059]

Equation

[0060] In other words, the control circuit 61 controls the interval of the period T6 according to the control formula shown in Formula (6). In Formula (6), T 6_0A is the interval of the period T6 when the load current I out is 0 A. T 6_0A may be 0 seconds.

[0061] For example, since the capacitor voltage V C is inversely proportional to the input voltage Vin, T6 becomes longer as the input voltage Vin increases. Therefore, the control circuit 61 advances the timing of turning on the second switching element Q2 as the input voltage Vin input between the first input terminal 1a and the second input terminal 1b is larger, and delays the timing of turning on the second switching element Q2 as the input voltage Vin is smaller. As a result, as shown in the waveform 205, the control circuit 61 changes the peak value I P2 from the period T6 to the period T7, so the absolute value of the peak value I P1 and the absolute value of the peak value I P2 can be balanced. Thereby, the DC bias of the transformer T can be suppressed.

[0062] FIG. 5 shows the operation timing of the power supply device when the load current is relatively small. In FIG. 5, a waveform 211, a waveform 212, a waveform 213, a waveform 214, a waveform 215, and a waveform 216 are shown. The waveform 211 represents the operating state of the first switching element Q1. The waveform 212 represents the operating state of the second switching element Q2. The waveform 213 represents the operating state of the first auxiliary switching element Q3. The waveform 214 represents the voltage V ds between the drain and source of the first switching element Q1. The waveform 215 represents the transformer current I pIt represents. Waveform 216 represents the magnetic flux density of transformer T. In FIG. 5, since the operating states of the first switching element Q1, the second switching element Q2, and the first auxiliary switching element Q3 from period T1 to period T8 are the same as those in the comparative example shown in FIGS. 3 and 4, the description thereof is omitted.

[0063] When the magnitude of the current in the first winding 41 of transformer T is relatively small, control circuit 61 delays the timing of turning on the second switching element Q2 with respect to the reference timing. That is, the period T6 during which both the second switching element Q2 and the first auxiliary switching element Q3 are on becomes relatively short. As a result, the peak value I of the positive current from period T6 to period T7 P12 is suppressed from increasing, so that the peak value I of the negative current from period T1 to period T2 P11 and the peak value I of the positive current from period T6 to period T7 P12 can be balanced in absolute value. Thereby, the DC bias of transformer T can be suppressed.

[0064] [Comparison of DC bias] (Comparative example) FIG. 6 is a diagram for explaining the DC bias of the transformer according to the comparative example. In FIG. 6, waveform 301, waveform 302, waveform 303, waveform 304, waveform 305, waveform 306, and waveform 307 are shown. Waveform 301 represents the operating state of the first switching element Q1. Waveform 302 represents the operating state of the second switching element Q2. Waveform 303 represents the operating state of the first auxiliary switching element Q3. Waveform 304 represents the voltage V between the drain and source of the first switching element Q1 ds . Waveform 305 represents the load current I out . Waveform 306 represents the transformer current I flowing through the first winding 41 of transformer T p . Waveform 307 represents the magnetic flux density of transformer T.

[0065] As shown by waveform 305, the load current I outIt decreases as time passes. In the comparative example, the interval between the timing t1 when the second switching element Q2 turns on and the timing t2 when the first auxiliary switching element Q3 turns off is always constant.

[0066] Line 308 represents the upper limit of the allowable magnetic flux density. Line 309 represents the lower limit of the allowable magnetic flux density. As shown by waveform 307, when the load current I out becomes smaller than a predetermined value, the difference between the peak value of the negative current and the peak value of the positive current of the transformer T becomes larger, and the magnetic flux density exceeds the upper limit. That is, in the comparative example, the transformer T becomes magnetically unbalanced when the load current I out becomes smaller.

[0067] (Embodiment) FIG. 7 is a diagram for explaining the magnetic unbalance of the transformer according to the embodiment. In FIG. 7, waveform 401, waveform 402, waveform 403, waveform 404, waveform 405, waveform 406, and waveform 407 are shown. Waveform 401 represents the operating state of the first switching element Q1. Waveform 402 represents the operating state of the second switching element Q2. Waveform 403 represents the operating state of the first auxiliary switching element Q3. Waveform 404 represents the voltage V ds between the drain and source of the first switching element Q1. Waveform 405 represents the load current I out . Waveform 406 represents the transformer current I p flowing through the first winding 41 of the transformer T. Waveform 407 represents the magnetic flux density of the transformer T.

[0068] As shown by waveform 405, the load current I out decreases as time passes. In the embodiment, the interval between the timing t11 when the second switching element Q2 turns on and the timing t12 when the first auxiliary switching element Q3 turns off changes so that the peak value of the negative current and the peak value of the positive current of the transformer T are balanced according to the magnitude of the load current I out .

[0069] Line 408 represents the upper limit of the allowable magnetic flux density. Line 409 represents the lower limit of the allowable magnetic flux density. As shown by waveform 407, regardless of the magnitude of the load current I out , the magnetic flux density always remains between line 408 and line 409. That is, the embodiment can prevent the transformer T from being magnetized asymmetrically.

[0070] [Modifications of the Embodiment] (Modification) With reference to FIG. 8, a configuration example of a power supply device according to a modification of the embodiment will be described. FIG. 8 is a diagram showing a configuration example of a power supply device according to a modification of the embodiment.

[0071] As shown in FIG. 8, the power supply device 1A differs from the power supply device 1 shown in FIG. 1 in that it includes a current sensor 71 instead of the current transformer 31.

[0072] The current sensor 71 detects the transformer current I p flowing through the first winding 41 of the transformer T. That is, in the present disclosure, there is no limitation on the method of detecting the transformer current I p flowing through the first winding 41.

[0073] As described above, the embodiments of the present disclosure have been described, but the present disclosure is not limited by the contents of these embodiments. In addition, the above-described components include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or changes of the components can be made without departing from the gist of the above-described embodiments.

Description of Reference Numerals

[0074] 11 Power supply 12 Load 21, 51 Capacitor 31 Current transformer 41 First winding 42 Second winding 43 Core 61 Control circuit 71 Current sensor Lo choke Lr inductor Q1 First switching element Q2 Second switching element Q3 First auxiliary switching element Q4 Second auxiliary switching element T transformer

Claims

1. A first switching element having one end electrically connected to a first input terminal; A first auxiliary switching element having one end electrically connected to the other end of the first switching element; A capacitor having one end electrically connected to the other end of the first auxiliary switching element and the other end electrically connected to a second input terminal; A first winding having one end electrically connected to the other end of the first switching element and one end of the first auxiliary switching element and the other end electrically connected to the other end of the capacitor, and a transformer including a second winding having one end electrically connected to a first output terminal and magnetically coupled to the first winding; A second switching element having one end electrically connected to a second output terminal and the other end connected to one end of the second winding; A control circuit for controlling the first switching element, the first auxiliary switching element, and the second switching element; When the control circuit turns on the second switching element in a state where the first switching element and the second switching element are off and the first auxiliary switching element is on, the control circuit controls the timing of turning on the second switching element according to the magnitude of the current flowing through the first winding. A power supply device.

2. The control circuit advances the timing of turning on the second switching element as the peak value of the current flowing through the first winding increases, and delays the timing of turning on the second switching element as the peak value of the current flowing through the first winding decreases. The power supply device according to Claim 1.

3. The control circuit delays the timing of turning on the second switching element as the input voltage input between the first input terminal and the second input terminal increases, and advances the timing of turning on the second switching element as the input voltage decreases. The power supply device according to Claim 2.

4. The control circuit calculates the timing of turning on the second switching element based on a predetermined control formula. The power supply device according to Claim 2 or 3.

5. Comprising a current detection unit for detecting information proportional to the magnitude of the current flowing through the first winding. The power supply device according to Claim 1.

6. A first switching element having one end electrically connected to a first input terminal, a first auxiliary switching element having one end electrically connected to the other end of the first switching element, a capacitor having one end electrically connected to the other end of the first auxiliary switching element and the other end electrically connected to a second input terminal, a first winding having one end electrically connected to the other end of the first switching element and one end of the first auxiliary switching element and the other end electrically connected to the other end of the capacitor, a transformer including a second winding having one end electrically connected to a first output terminal and magnetically coupled to the first winding, and a second switching element having one end electrically connected to a second output terminal and the other end connected to one end of the second winding, and a control method for a power supply device, When the first switching element and the second switching element are off and the first auxiliary switching element is on, and when turning on the second switching element, the timing of turning on the second switching element is controlled according to the magnitude of the current flowing through the first winding. A control method for a power supply device.

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