Switching power supply device

Abstract

To provide a switching power supply device which effectively uses energy accumulated in a transformer to decrease power consumption.SOLUTION: A switching power supply device 100 includes: a clamp circuit 106 provided with a clamp capacitor 106a and a clamp switching element 106b connected to an input winding wire 102a of a transformer 102 and serially connected; a drive circuit 107 driving the clamp switching element 106b; and a current-supply circuit 108 connected to the clamp capacitor 106a and the clamp switching element 106b. At least a part of electric charges the clamp capacitor 106a is charged with flow through the current-supply circuit 108 as current toward the drive circuit 107. The drive circuit 107 drives the clamp switching element 106b by at least a part of the electric charges the clamp capacitor 106a is charged with.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a switching power supply device that makes it possible to effectively utilize energy stored in a transformer and achieve low power consumption. [Background technology]

[0002] A switching power supply, particularly a flyback power converter, includes a transformer having an input winding and an output winding, a main switching element connected to the input winding, and an output circuit connected to the output winding. When the main switching element is turned on, the input voltage of the input power source is applied to the input winding, and energy is stored in the transformer. When the main switching element is turned off, the energy stored in the transformer is output as an output voltage and an output current by an output circuit that is a rectifying and smoothing circuit, utilizing the back electromotive force of the transformer. In such a flyback power converter, a clamp circuit connected to the input winding and the main switching element is adopted to process surge energy caused by leakage inductance of the input winding after the main switching element is turned off.

[0003] Patent Document 1 discloses a flyback power converter including a hybrid clamp circuit including a first parallel circuit and a second parallel circuit connected in series with each other, in which the first parallel circuit has a clamp switching element and a clamp diode connected in parallel, and the second parallel circuit has a clamp capacitor and a clamp resistor connected in parallel, the hybrid clamp circuit providing an active clamp circuit when the clamp switching element is periodically turned on and off, and providing a passive clamp circuit when the clamp switching element is turned off. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6964565 Summary of the Invention [Problem to be solved by the invention]

[0005] In the flyback power converter according to Patent Document 1, when the hybrid clamp circuit serves as a passive clamp circuit, the surge energy caused by the leakage inductance of the input winding is simply lost as heat by a clamp resistor connected in parallel to the clamp capacitor, and the surge energy cannot be effectively utilized. In addition, such a flyback power converter generally includes a drive circuit for driving the clamp switching element of the first parallel circuit, and a bootstrap circuit for supplying current to the drive circuit. However, even when the hybrid clamp circuit serves as a passive clamp circuit, the bootstrap circuit continues to operate, and furthermore, the drive circuit constantly consumes current, so that energy continues to be lost by the bootstrap circuit and the drive circuit. In addition, in the flyback power converter according to Patent Document 1, when the hybrid clamp circuit serves as an active clamp circuit, the clamp resistor is not necessary, but energy continues to be lost by the clamp resistor. Furthermore, in the flyback power converter disclosed in Patent Document 1, soft switching is performed on the main switching element using zero voltage switching (ZVS), thereby reducing switching loss and enabling the main switching element to be driven at high frequency. However, when a bootstrap circuit that supplies current to a drive circuit that drives a clamp switching element, which is common in such flyback power converters, is driven at high frequency, there is a problem in that the switching loss of the diode in the bootstrap circuit increases.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a switching power supply device which solves the above problems, effectively utilizes the energy stored in the transformer, and enables low power consumption to be achieved. [Means for solving the problem]

[0007] According to one aspect of the present invention, a switching power supply apparatus includes a transformer having an input winding and an output winding, a main switching element connected to the input winding, where when the main switching element is turned on, an input voltage of a first input power source is applied to the input winding, an output circuit connected to the output winding, where the output circuit generates an output current and an output voltage from energy transferred through the transformer, a clamp circuit including a clamp capacitor and a clamp switching element connected in series, the clamp circuit connected to the input winding, and a drive circuit for driving the clamp switching element, and the switching power supply apparatus further includes a current supply circuit connected to the clamp capacitor and the clamp switching element, where at least a portion of the charge charged in the clamp capacitor flows as a current through the current supply circuit toward the drive circuit, enabling the drive circuit to drive the clamp switching element with at least a portion of the charge charged in the clamp capacitor.

[0008] According to one embodiment of the present invention, in a switching power supply, a clamp switching element allows a current due to the inductance of the input winding to flow through the clamp switching element toward a clamp capacitor to charge the clamp capacitor.

[0009] According to one embodiment of the present invention, a switching power supply is configured to apply a predetermined voltage to a drive circuit using at least a portion of the charge stored in a clamp capacitor.

[0010] According to one embodiment of the present invention, in a switching power supply device, no resistor is connected in parallel to the clamp capacitor.

[0011] According to one embodiment of the present invention, a switching power supply device has a first period in which a main switching element is turned on and a clamp switching element is turned off, a second period in which the main switching element is turned off after the first period, a third period in which the clamp switching element is turned on after the second period, and a fourth period in which the clamp switching element is turned off after the third period, and during the first period, a current supply circuit enables at least a portion of the charge stored in the clamp capacitor to flow as a current through the current supply circuit toward a drive circuit.

[0012] According to one embodiment of the present invention, in a switching power supply, a clamp switching element includes a transistor and a diode connected in parallel, and a drive circuit drives the transistor.

[0013] According to one embodiment of the present invention, in a switching power supply, a diode allows a current due to the inductance of the input winding to flow through the diode toward the clamp capacitor during the second period.

[0014] According to one embodiment of the present invention, in a switching power supply, a transistor allows a current due to an inductance of an input winding to flow through the transistor toward a clamp capacitor during a third period.

[0015] According to one embodiment of the present invention, the switching power supply device is configured to reduce the voltage applied to the main switching element in the fourth period.

[0016] According to one embodiment of the present invention, a switching power supply device is configured to apply an input voltage of a second input power supply to a drive circuit during a first time period. Effect of the Invention

[0017] According to the present invention, at least a portion of the charge stored in the clamp capacitor can be effectively utilized as a current flowing through a drive circuit that drives a clamp switching element, thereby realizing low power consumption.

[0018] Other objects, features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic diagram of a switching power supply device according to an embodiment of the present invention; [Diagram 2] 1 is a schematic diagram of a switching power supply device including a current supply circuit according to an embodiment of the present invention; [Diagram 3] 1 is a schematic diagram of a switching power supply device including a current supply circuit according to another embodiment of the present invention. [Figure 4] 1 is a schematic diagram of a switching power supply device including a current supply circuit according to another embodiment of the present invention. [Diagram 5] 2 is a timing chart for operating a main switching element and a clamp switching element of the switching power supply device of the embodiment in FIG. 1. [Figure 6] 2 is a schematic diagram showing the direction of current flowing in a bootstrap circuit of the switching power supply device of the embodiment in FIG. 1. [Figure 7] FIG. 1 is a schematic diagram of a switching power supply device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

[0021] 1 to 7, a switching power supply device 100 according to some embodiments of the present invention will be described. The switching power supply device 100 includes a transformer 102 having an input winding 102a and an output winding 102b, a main switching element 103 connected to the input winding 102a, an output circuit 104 connected to the output winding 102b, a clamp circuit 106 including a clamp capacitor 106a and a clamp switching element 106b connected in series with each other, and a drive circuit 107 for driving the clamp switching element 106b. When the main switching element 103 is turned on, the input voltage V 11is applied to the input winding 102a, and energy is stored in the transformer 102. When the main switching element 103 is turned off, the energy stored in the transformer 102 is released using the back electromotive force of the transformer 102, and the energy is transferred from the input side to the output side via the transformer 102. The output circuit 104 functions as a rectifying and smoothing circuit, and may include a rectifying element 104a and a smoothing capacitor 104b. The released energy is output as an output voltage V0 and an output current I0 by the output circuit 104, and the output voltage V0 is applied to the output load 105. In FIGS. 1 to 4, the rectifying element 104a is a diode, but may be another rectifying element such as an NMOS transistor. In FIGS. 1 to 4, the main switching element 103 is an NMOS transistor, but may include a diode connected in anti-parallel to the NMOS transistor, and the diode may be a parasitic diode of the NMOS transistor. The NMOS transistor may be a transistor based on a wide band gap semiconductor, for example, a SiC-based transistor or a GaN-based transistor. Furthermore, the main switching element 103 may be another transistor such as an NPN transistor, and may include a diode connected in anti-parallel to the transistor. The switching power supply device 100 may be a flyback converter as shown in Figures 1 to 4, or may be another converter such as a forward converter including an output circuit 104 further including a freewheeling element 104c and a choke coil 104d as shown in Figure 7.

[0022] The switching power supply device 100 includes a clamp circuit 106 connected to the input winding 102a, and the clamp circuit 106 includes a clamp capacitor 106a and a clamp switching element 106b connected in series to each other. After the main switching element 103 is turned off, the clamp switching element 106b is turned on to enable at least a portion of the energy stored in the transformer, including the energy stored in the leakage inductance of the input winding 102a, to be transferred to the clamp capacitor 106a. The switching power supply device 100 also includes a drive circuit 107 that drives the clamp switching element 106b. One end of the clamp switching element 106b is connected to a connection point n1 at which the input winding 102a and the main switching element 103 are connected, and the clamp circuit 106 may be connected in parallel to the input winding 102a or may be connected in parallel to the main switching element 103.

[0023] The switching power supply device 100 further includes a current supply circuit 108 connected to the clamp capacitor 106a and the clamp switching element 106b. The current supply circuit 108 may be connected to a connection point n0 at which the clamp capacitor 106a and the clamp switching element 106b are connected. The current supply circuit 108 may also be connected to the drive circuit 107 at a connection point n2. The current supply circuit 108 allows at least a portion of the charge stored in the clamp capacitor 106a to flow as a current through the current supply circuit 108 toward the drive circuit 107, and allows the drive circuit 107 to drive the clamp switching element 106b with at least a portion of the charge stored in the clamp capacitor 106a. Specifically, when clamp capacitor 106a is charged and the potential of node n0 becomes higher than the potential of node n2, current supply circuit 108 allows current to flow from node n0 to node n2 as shown in current direction 112 in Fig. 1, and the current from clamp capacitor 106a flows through current supply circuit 108 and then flows through drive circuit 107 and is used to drive clamp switching element 106b. Note that the current from clamp capacitor 106a may flow through current supply circuit 108 and then flows through drive circuit 107 even when drive circuit 107 is not driving clamp switching element 106b. In addition, in order to prevent current from flowing from current supply circuit 108 toward clamp circuit 106, a backflow prevention diode may be provided between current supply circuit 108 and clamp circuit 106, and in order to prevent current from flowing from drive circuit 107 toward current supply circuit 108, a backflow prevention diode may be provided between drive circuit 107 and current supply circuit 108.

[0024] After the main switching element 103 is turned off, the clamp switching element 106b is turned on to allow at least a portion of the energy stored in the transformer 102 to be transferred to the clamp capacitor 106a, and the current due to the inductance of the input winding 102a is allowed to flow through the clamp switching element 106b toward the clamp capacitor 106a to charge the clamp capacitor 106a. Specifically, after the main switching element 103 is turned off, the input voltage V 11 A potential obtained by adding the voltage applied to the input winding 102a to the potential of the connection point n1 is generated at the connection point n1. When the potential of the connection point n1 becomes higher than the potential of the connection point n0, the clamp switching element 106b allows a current to flow from the connection point n1 to the connection point n0, and the current due to the potential of the connection point n1 flows through the clamp switching element 106b and is used to charge the clamp capacitor 106a. In this way, at least a part of the energy stored in the transformer 102 is transferred to the clamp capacitor 106a and can be effectively utilized as a current flowing in the drive circuit 107 that drives the clamp switching element 106b, and further, low power consumption of the switching power supply device 100 can be realized.

[0025] No resistor is connected in parallel to the clamp capacitor 106a. If a resistor were connected in parallel to the clamp capacitor 106a, the energy would simply be lost as heat, and it would be difficult to effectively use at least a portion of the energy stored in the transformer 102. Even if a resistor is connected in parallel to the clamp capacitor 106a, there are cases where a current from the clamp capacitor 106a flows through the current supply circuit 108 toward the drive circuit 107, but it is not possible to effectively use at least a portion of the energy stored in the transformer 102, so it is preferable not to connect a resistor in parallel to the clamp capacitor 106a.

[0026] A predetermined voltage may be applied to the drive circuit 107 using at least a part of the charge stored in the clamp capacitor 106a. As shown in FIG. 2, the current supply circuit 108 may include a voltage adjustment switching element 108a. For example, when the voltage applied to the drive circuit 107 becomes equal to or lower than a predetermined voltage, the voltage adjustment switching element 108a is turned on by the drive circuit 107 to allow a current to flow from the connection point n0 to the connection point n2. In this way, the drive circuit 107 can be adjusted using the current from the clamp capacitor 106a so that a predetermined voltage is applied to the drive circuit 107. The current supply circuit 108 may also include an inductor 108b and a diode 108c to suppress the voltage applied to the drive circuit 107.

[0027] 3, the current supply circuit 108 may include an NPN transistor 108d, a resistor 108e, and a Zener diode 108f. The NPN transistor 108d is turned on when the voltage between the connection point n0 and the connection point n2 becomes larger than the base-emitter threshold voltage of the NPN transistor 108d, allowing a current to flow from the connection point n0 to the connection point n2. When the voltage between the connection point n0 and the connection point n1 becomes larger than the Zener voltage of the Zener diode 108f, the Zener diode 108f is turned on, and the voltage between the cathode and the anode of the Zener diode 108f is clamped to the Zener voltage. When the voltage applied to the drive circuit 107 becomes smaller than the voltage obtained by subtracting the base-emitter threshold voltage of the NPN transistor 108d from the Zener voltage of the Zener diode 108f, the NPN transistor 108d is turned on, allowing a current to flow from the connection point n0 to the connection point n2. In this manner, using the current from the clamp capacitor 106a, the drive circuit 107 can be adjusted so that a predetermined voltage based on the Zener voltage of the Zener diode 108f is applied to the drive circuit 107.

[0028] 4, the current supply circuit 108 may include a current supply resistor 108g and a Zener diode 108h. The current supply resistor 108g allows a current to flow from the connection point n0 to the connection point n2 when the voltage of the connection point n0 becomes higher than the voltage of the connection point n2. The current supply resistor 108g allows a current to flow from the connection point n2 to the connection point n0 even when the voltage of the connection point n2 becomes higher than the voltage of the connection point n0. However, the resistance value of the current supply resistor 108g is set so that, when the current flowing from the connection point n0 to the connection point n2 is positive, the average value of the current flowing from the connection point n0 to the connection point n2 while the switching power supply device 100 is operating is always positive (i.e., 0 A or more). When the voltage applied to the drive circuit 107 becomes higher than the Zener voltage of the Zener diode 108h, the Zener diode 108h is turned on, allowing the voltage between the connection point n2 and the connection point n1 to be clamped to the Zener voltage. In this manner, using the current from the clamp capacitor 106a, the drive circuit 107 can be adjusted so that a predetermined voltage based on the Zener voltage of the Zener diode 108h is applied to the drive circuit 107. The current supply resistor 108g may be replaced with a constant current circuit, for example, a constant current diode, that allows a current to flow from the node n0 to the node n2.

[0029] The switching power supply device 100 includes a control circuit 110, which controls the main switching element 103 and also controls the clamp switching element 106b via a drive circuit 107. When the main switching element 103 and the clamp switching element 106b are NMOS transistors as shown in FIGS. 1 to 4, the gate-source voltage V gsThe control circuit 110 controls the main switching element 103 and the clamp switching element 106b so that in a first period, the main switching element 103 is turned on and the clamp switching element 106b is turned off, in a second period after the first period, the main switching element 103 is turned off and the clamp switching element 106b continues to be turned off, in a third period after the second period, the main switching element 103 continues to be turned off and the clamp switching element 106b is turned on, and in a fourth period after the third period, the main switching element 103 continues to be turned off and the clamp switching element 106b is turned off, and the first to fourth periods are repeated sequentially.

[0030] In the first period, the control circuit 110 controls the main switching element 103 to be turned on, thereby controlling the input voltage V of the first input power source 101. 11 is applied to the input winding 102a, and energy is stored in the transformer 102. The switching power supply device 100 may include a bootstrap circuit 111 to supplement the current for the drive circuit 107 to drive the clamp switching element 106b. The bootstrap circuit 111 includes a diode 111a and a capacitor 111b. Since the anode of the diode 111a is connected to the second input power source 109, the cathode of the diode 111a is connected to the connection point n2, and the main switching element 103 is turned on, a current is allowed to flow from the connection point n2 to the connection point n1 as shown in the current direction 113 in FIG. 6, and the input voltage V of the second input power source 109 is supplied to the input winding 102a. 12to the capacitor 111b, the capacitor 111b is charged, and the capacitor 111b may be used as a power source for the drive circuit 107, or a current from the capacitor 111b may flow through the drive circuit 107 and be used to drive the clamp switching element 106b. If the capacitor 111b is sufficiently charged by the current from the clamp capacitor 106a to drive the clamp switching element 106b, the switching power supply device 100 may not include the bootstrap circuit 111, and the diode 111a may be omitted. In this way, the current flowing through the diode 111a can be reduced by the current from the clamp capacitor 106a, so that even when the bootstrap circuit 111 is driven at a high frequency, the switching loss of the diode 111a can be reduced, and further, low power consumption of the switching power supply device 100 can be achieved. The second input power source 109 may be used as a power source for the control circuit 110.

[0031] In the second period, the control circuit 110 controls the main switching element 103 so that the main switching element 103 is turned off, and the energy stored in the transformer 102 is released using the back electromotive force of the transformer 102, and the energy is transferred from the input side to the output side via the transformer 102. The clamp switching element 106b may include a clamp transistor and a clamp diode connected in parallel, and the drive circuit 107 may drive the clamp transistor. In FIGS. 1 to 4, the clamp switching element 106b is an NMOS transistor, but the NMOS transistor may be the clamp transistor and the clamp diode may be a diode connected in anti-parallel to the NMOS transistor, or may be a parasitic diode of the NMOS transistor. The NMOS transistor may be a transistor based on a wide bandgap semiconductor, for example, a SiC-based transistor or a GaN-based transistor. The clamp switching element 106b may also include an NPN transistor and a clamp diode connected in anti-parallel to the NPN transistor.

[0032] In the second period, the clamp diode allows a current due to the inductance of the input winding 102a to flow through the clamp diode toward the clamp capacitor 106a, thereby charging the clamp capacitor 106a. Specifically, in the second period, when the input voltage V 11A potential obtained by adding the voltage applied to the input winding 102a to the potential of the connection point n1 is generated at the connection point n1. When the potential of the connection point n1 becomes higher than the potential of the connection point n0, the clamp diode only allows a current to flow from the connection point n1 to the connection point n0, and the current due to the potential of the connection point n1 flows through the clamp diode and is used to charge the clamp capacitor 106a. The current flowing through the clamp diode reduces the voltage between the connection point n1 and the connection point n0. In a third period after the second period, the clamp transistor is allowed to be turned on while keeping the voltage between the connection point n1 and the connection point n0 reduced. By performing soft switching by zero voltage switching (ZVS) on the clamp switching element 106b, the switching loss of the clamp switching element 106b can be reduced, and further, the power consumption of the switching power supply device 100 can be reduced.

[0033] The control circuit 110 controls the clamp switching element 106b so that the clamp switching element 106b is turned on in the third period. When the clamp switching element 106b includes a clamp transistor, the control circuit 110 controls the clamp transistor via the drive circuit 107 so that the clamp transistor is turned on. In the third period, the clamp transistor allows a current due to the inductance of the input winding 102a to flow through the clamp transistor toward the clamp capacitor 106a, as in the second period, to charge the clamp capacitor 106a. Then, in the third period, the direction of the current due to the inductance of the input winding 102a may be reversed, and the clamp transistor may allow a current from the clamp capacitor 106a to flow through the clamp transistor toward the input winding 102a. Note that, when the clamp switching element 106b includes a clamp diode, the clamp transistor may remain off rather than turned on depending on the method of using the switching power supply device 100 in the third period.

[0034] In the fourth period, the control circuit 110 controls the clamp switching element 106b so that the clamp switching element 106b is turned off. In the third period, the direction of the current due to the inductance of the input winding 102a is reversed, and the current continues to flow toward the input winding 102a even in the fourth period, and the current due to the inductance of the input winding 102a enables the voltage applied to the main switching element 103 to be reduced. Specifically, a parasitic capacitor connected to the connection point n1 is charged with an electric charge due to the electric potential of the connection point n1, but the electric charge charged in the parasitic capacitor is drawn by the current due to the inductance of the input winding 102a, and the electric potential of the connection point n1 is reduced. In the first period after the fourth period, the voltage applied to the main switching element 103 remains reduced, and the main switching element 103 is enabled to be turned on. In this way, by performing soft switching by zero voltage switching (ZVS) on the main switching element 103, the switching loss of the main switching element 103 can be reduced, and further, low power consumption of the switching power supply device 100 can be achieved.

[0035] The control circuit 110 controls the main switching element 103 so that the main switching element 103 is turned on during the first period, and the switching power supply device 100 operates as described above. Furthermore, the current supply circuit 108 allows at least a part of the charge stored in the clamp capacitor 106a to flow as a current through the current supply circuit 108 toward the drive circuit 107 during the first period, and allows the current to flow through the drive circuit 107. Specifically, after the clamp capacitor 106a is charged during the second and third periods, and the clamp switching element 106b is turned off during the fourth period to electrically separate the connection point n0 from the connection point n1, when the potential of the connection point n0 becomes higher than the potential of the connection point n2 during the first period, the current supply circuit 108 allows the current to flow from the connection point n0 to the connection point n2, as in the current direction 112 shown in FIG. 1, and the current from the clamp capacitor 106a may be charged to the capacitor 111b or may flow through the drive circuit 107. The charge stored in capacitor 111b is used to drive clamp switching element 106b in the third period. When the current flowing from node n0 to node n2 is positive, current supply circuit 108 is configured so that the average value of the current flowing from node n0 to node n2 during the first to fourth periods is always positive (i.e., 0 A or more). When the fourth period is set long and the potential of node n0 is higher than the potential of node n2 during the fourth period, current supply circuit 108 allows the current to flow from node n0 to node n2, and the current from clamp capacitor 106a may be charged into capacitor 111b or may flow through drive circuit 107.

[0036] As described above, the current due to the inductance of input winding 102a is charged to clamp capacitor 106a, and at least a portion of the charge charged in clamp capacitor 106a flows as a current through drive circuit 107 and is used to drive clamp switching element 106b. As a result, the current flowing through diode 111a of the bootstrap circuit can be reduced, and the switching loss of diode 111a can be reduced. In particular, the no-load loss (standby power) when switching power supply device 100 is operated with output load 105 in an unloaded state can be reduced, and low power consumption of switching power supply device 100 can be achieved.

[0037] Although the above description has been given with respect to a particular embodiment, it will be apparent to those skilled in the art that the present invention is not limited thereto, and that various changes and modifications can be made within the principles of the present invention and the scope of the appended claims. [Explanation of symbols]

[0038] 100 Switching power supply 101 First input power supply 102 Trans 102a Input winding 102b Output winding 103 Main switching element 104 Output circuit 104a Rectifying element 104b Smoothing capacitor 104c Current collector 104d Choke coil 105 Output Load 106 Clamp Circuit 106a Clamp Capacitor 106b Clamp switching element 107 Drive Circuit 108 Current supply circuit 108a Voltage regulation switching element 108b inductor 108c Diode 108d NPN transistor 108e resistor 108f Zener Diode 108g current supply resistance 108h Zener Diode 109 Second input power supply 110 Control circuit 111 Bootstrap Circuit 111a Diode 111b Capacitor 112 Current direction 113 Current direction

Claims

1. a transformer having an input winding and an output winding; a main switching element connected to the input winding, the main switching element applying an input voltage of a first input power source to the input winding when the main switching element is turned on; an output circuit connected to the output winding for generating an output current and an output voltage from the energy transferred through the transformer; a clamp circuit comprising a clamp capacitor and a clamp switching element connected in series, the clamp circuit being connected to the input winding; a drive circuit for driving the clamp switching element; A switching power supply device comprising: The switching power supply device further comprises a current supply circuit connected to the clamp capacitor and the clamp switching element, wherein at least a portion of the charge stored in the clamp capacitor flows as a current through the current supply circuit toward the drive circuit, enabling the drive circuit to drive the clamp switching element with at least a portion of the charge stored in the clamp capacitor.

2. 2. The switching power supply according to claim 1, wherein the clamp switching element allows a current due to an inductance of the input winding to flow through the clamp switching element toward the clamp capacitor to charge the clamp capacitor.

3. 2. The switching power supply device according to claim 1, wherein the switching power supply device is configured to apply a predetermined voltage to the drive circuit by using at least a portion of the charge stored in the clamp capacitor.

4. 2. The switching power supply device according to claim 1, wherein no resistor is connected in parallel to said clamp capacitor.

5. 5. The switching power supply device according to claim 1, further comprising: a first period in which the main switching element is turned on and the clamp switching element is turned off; a second period in which the main switching element is turned off after the first period; a third period in which the clamp switching element is turned on after the second period; and a fourth period in which the clamp switching element is turned off after the third period, and during the first period, the current supply circuit allows at least a portion of the charge stored in the clamp capacitor to flow as a current through the current supply circuit toward the drive circuit.

6. 6. The switching power supply according to claim 5, wherein the clamp switching element comprises a transistor and a diode connected in parallel, and the drive circuit drives the transistor.

7. 7. The switching power supply of claim 6, wherein the diode allows a current due to an inductance of the input winding to flow through the diode toward the clamp capacitor during the second period.

8. 7. The switching power supply of claim 6, wherein the transistor allows a current due to an inductance of the input winding to flow through the transistor toward the clamp capacitor during the third period.

9. 6. The switching power supply device according to claim 5, wherein the switching power supply device is configured to reduce a voltage applied to the main switching element in the fourth period.

10. 6. The switching power supply device according to claim 5, wherein the switching power supply device is configured to apply an input voltage of a second input power supply to the drive circuit during the first period.

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