Switching power supply device and power conversion device

Abstract

To provide a switching power supply device capable of detecting an output short circuit before a large current flows at the time of an output short circuit.SOLUTION: A flyback switching power supply device includes: a transformer; a switching element connected to a primary winding of the transformer; a rectifier circuit including a diode connected to a secondary winding of the transformer; and a short-circuit detection circuit that detects an output short-circuit at a voltage output terminal connected to the secondary winding of the transformer. The short-circuit detection circuit determines that an output short-circuit of the voltage output terminal has occurred when a current flowing through the switching element exceeds a predetermined threshold value when the switching element is switched to a turn-on state during drive in a discontinuous current mode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a switching power supply device and a power conversion device. [Background technology]

[0002] There is known a switching power supply device that converts an input voltage into an output voltage of a different voltage value by driving a main switching element. Patent Document 1 describes a switching power supply device that turns off the main switching element when the drain current of the main switching element reaches a current detection value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-124573 A Summary of the Invention [Problem to be solved by the invention]

[0004] The switching power supply device described in Patent Document 1 has a problem in that the larger the current increase rate is, the larger the current continues to flow, causing a large current to flow through circuit elements including the main switching element, particularly when the output is short-circuited.

[0005] An object of the present invention is to provide a switching power supply device that can detect an output short circuit before a large current flows when the output short circuit occurs. [Means for solving the problem]

[0006] A switching power supply according to one embodiment of the present invention is a flyback-type switching power supply comprising a transformer, a switching element connected to a primary winding of the transformer, a rectifier circuit including a diode connected to a secondary winding of the transformer, and a short circuit detection circuit for detecting an output short circuit at a voltage output terminal connected to the secondary winding of the transformer, wherein the short circuit detection circuit determines that an output short circuit has occurred at the voltage output terminal when the switching element is switched to a turn-on state and the current flowing through the switching element exceeds a predetermined threshold during operation in a discontinuous current mode. Effect of the Invention

[0007] According to the present invention, when an output short circuit occurs, it is possible to detect the output short circuit before a large current flows. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a circuit diagram of a switching power supply device according to the first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating waveforms of a drain current and a diode current during normal operation. [Diagram 3] FIG. 3 is a diagram illustrating waveforms of a drain current and a diode current when the output is short-circuited. [Figure 4] FIG. 4 is a circuit diagram of a power conversion device using the switching power supply device of the first embodiment. [Diagram 5] FIG. 5 is a circuit diagram of a switching power supply device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] First Embodiment A switching power supply device 100 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4.

[0010] 1 is a circuit diagram of a switching power supply device 100 according to a first embodiment. The switching power supply device 100 is a switching power supply that functions as a so-called DC / DC converter that converts an input power supply voltage VIN into an output power supply voltage VOUT2. The switching power supply device 100 employs current-mode PWM control as a control method for the switching operation of the main switching element 11.

[0011] An input power supply voltage VIN is applied between input power supply terminal IN and input power supply terminal RETURN. The input power supply terminal IN is a terminal on the high potential side, and the input power supply terminal RETURN is a terminal on the low potential side. An output power supply voltage VOUT2 is applied between output power supply terminal OUT2 and output power supply terminal GND2. The output power supply terminal OUT2 is a terminal on the high potential side, and the output power supply terminal GND2 is a terminal on the low voltage side. A user of the switching power supply device 100 places a load 9 between the output power supply terminal OUT2 and the output power supply terminal GND2, and applies the output power supply voltage VOUT2 to the load 9.

[0012] The switching power supply device 100 includes an energy conversion circuit 10, a main switching element 11, a current detection resistor R1, a dividing resistor R2, a dividing resistor R3, a semiconductor device 23, and a short-circuit protection circuit 25.

[0013] The energy conversion circuit 10 converts an input power supply voltage VIN switched by a main switching element 11 into a feedback voltage VFB and an output power supply voltage VOUT2, each of which has a voltage value different from that of the input power supply voltage VIN. The feedback voltage VFB is applied between a feedback terminal FB and a feedback terminal GND1. The feedback terminal FB is a terminal on the high potential side, and the feedback terminal GND1 is a terminal on the low potential side. The feedback terminal FB is connected to a gate drive circuit 21, a regulator 22, and a dividing resistor 17 in a semiconductor device 23. The feedback terminal GND1 is connected to an input power supply terminal RETURN.

[0014] The energy conversion circuit 10 includes a switching transformer 1, a primary rectifier diode 5, a primary smoothing capacitor 6, a secondary rectifier diode 7, and a secondary smoothing capacitor 8. The switching transformer 1 includes a primary winding 2, an auxiliary winding 3, and a secondary winding 4. The polarity of the primary winding 2 is opposite to the polarities of the auxiliary winding 3 and the secondary winding 4, and the switching power supply device 100 is of a flyback type.

[0015] The primary winding 2 has one end connected to the input power supply terminal IN and the other end connected to the input terminal of the main switching element 11. The auxiliary winding 3 has one end connected to the feedback terminal FB and the other end connected to the feedback terminal GND1. The primary rectifier diode 5 is disposed between the auxiliary winding 3 and the feedback terminal FB such that the auxiliary winding 3 side serves as the anode. The secondary winding 4 has one end connected to the output power supply terminal OUT2 and the other end connected to the output power supply terminal GND2. The secondary rectifier diode 7 is disposed between the secondary winding 4 and the output power supply terminal OUT2 such that the secondary winding 4 side serves as the anode. The primary smoothing capacitor 6 is disposed between the cathode of the primary rectifier diode 5 and the other end of the auxiliary winding 3. The secondary smoothing capacitor 8 is disposed between the cathode of the secondary rectifier diode 7 and the other end of the secondary winding 4.

[0016] The energy conversion circuit 10 having the above configuration rectifies and smoothes the AC voltage induced in the auxiliary winding 3 and the secondary winding 4 by the switching operation of the main switching element 11, and generates the feedback voltage VFB and the output power supply voltage VOUT2.

[0017] The main switching element 11 is, for example, a MOSFET with high voltage resistance. The main switching element 11 has an input terminal (corresponding to the drain terminal of the FET), an output terminal (corresponding to the source terminal of the FET), and a control terminal (corresponding to the gate terminal of the FET). The output terminal of the main switching element 11 is connected to the input power terminal RETURN. A current detection resistor R1 is installed between the output terminal of the main switching element 11 and the input power terminal RETURN. The current detection resistor 12 converts the current returning from the input power terminal IN through the main switching element 11 to the input power terminal RETURN into a voltage, and inputs it to the PWM latch circuit 20 in the semiconductor device 23. The control terminal of the main switching element 11 is connected to a gate drive circuit 21 of the semiconductor device 23. The gate drive circuit 21 generates a drive signal and outputs it to the control terminal of the main switching element 11. The main switching element 11 performs a switching operation in accordance with this drive signal. This switching operation switches the input power voltage VIN.

[0018] The dividing resistors R2 and R3 detect the voltage level of the feedback voltage VFB, and feed back a feedback signal FB_S indicating the detected voltage level to the negative input terminal of the error amplifier 24 in the semiconductor device 23. The high potential side terminal of the dividing resistor R2 is connected to the feedback terminal FB. The low potential side terminal of the dividing resistor R2, the high potential side terminal of the dividing resistor R3, and the negative input terminal of the error amplifier 24 in the semiconductor device 23 are connected to each other. The low potential side terminal of the dividing resistor R3 is connected to the feedback terminal GND1.

[0019] The semiconductor device 23 includes an oscillator 19, a PWM latch circuit 20, a gate drive circuit 21, a regulator 22, an error amplifier 24, resistors R4 and R5. The oscillator 19 supplies a clock signal for PWM control to the PWM latch circuit 20. The input terminal of the regulator 22 is connected to a feedback terminal FB. A reference signal generated by dividing the output of the regulator 22 by resistors R4 and R5 is input to the + input terminal of the error amplifier 24. The PWM latch circuit 20 is connected to the output terminal of the error amplifier 24. The output terminal of the PWM latch circuit 20 is connected to the input terminal of the gate drive circuit 21. The PWM latch circuit 20 changes the duty ratio of the output signal output to the gate drive circuit 21 according to the input voltage from the error amplifier 24, and controls the on-time and off-time of the main switching element 11.

[0020] When the feedback voltage VFB rises, the voltage of the feedback signal FB_S, i.e., the voltage at the negative input terminal of the error amplifier 24, rises, and the output voltage of the error amplifier 24 decreases. When the output voltage of the error amplifier 24 decreases, the PWM latch circuit 20 controls the PWM on-duty of the output signal to be smaller. As a result, the on-time of the main switching element 11 becomes shorter, and the feedback voltage VFB decreases. In this way, the feedback voltage VFB is kept at a constant value. The voltage across the secondary winding 4 of the switching transformer 1 is proportional to the voltage across the auxiliary winding 3 and the turns ratio. For example, if the number of turns of the auxiliary winding 3 and the number of turns of the secondary winding 4 are made the same, the voltage across the auxiliary winding 3 and the voltage across the secondary winding 4 will be the same. In this way, the voltage of the output power supply voltage VOUT2 is controlled to a constant value.

[0021] The short-circuit protection circuit 25 includes a high-pass filter 13, an AND circuit 14, a latch circuit 15, and a switching element 16. An input terminal of the high-pass filter 13 is connected to a control terminal of the main switching element 11. An output terminal of the high-pass filter 13 is connected to one of two input terminals of the AND circuit 14. The other of the two input terminals of the AND circuit 14 is connected to the output terminal of the main switching element 11, i.e., the high potential side terminal of the current detection resistor R1.

[0022] The high-pass filter 13 is a so-called high-pass filter that generates a positive spike voltage when the main switching element 11 is turned on and a negative spike voltage when the main switching element 11 is turned off. The positive spike voltage generated by the high-pass filter 13 exceeds the input High threshold of the AND circuit 14, so a High signal is input to one of the input terminals of the AND circuit 14.

[0023] Here, the input High threshold of the AND circuit 14 for detecting the spike voltage is set in advance based on the recovery characteristics of the secondary rectifier diode 7. The peak value of the reverse recovery current by the secondary rectifier diode 7 is determined by the diode characteristics (forward current characteristics, temperature characteristics, di / dt characteristics, etc.). Specifically, the larger the forward current (If), the higher the temperature, and the higher the di / dt, the larger the peak value of the reverse recovery current. Therefore, the input High threshold of the AND circuit 14 is set in consideration of these characteristics. Note that even when the output is not short-circuited, a minute spike current flows when the main switching element 11 is turned on, so the threshold must be sufficiently larger than the current value of this minute spike current.

[0024] Since the high potential terminal of the current detection resistor R1 is connected to the other input terminal of the AND circuit 14, when the voltage of the current detection resistor R1 exceeds the input High threshold of the AND circuit 14, a High signal is input to the other input terminal of the AND circuit 14. When High signals are input to both of the two input terminals of the AND circuit 14, the output of the AND circuit 14 becomes High. In other words, if a certain amount or more of drain current flows through the main switching element 11 when the main switching element 11 is turned on, the output of the AND circuit 14 becomes High.

[0025] The output signal of the AND circuit 14 is input to the latch circuit 15. The latch circuit 15 is, for example, a D flip-flop. The output of the latch circuit 15 is Low in the initial state. This can be realized, for example, by connecting a circuit such as a CR charging circuit that becomes Low only for a certain period after power is turned on to the clear terminal of the D flip-flop. When the output signal of the AND circuit 14 is High, the output of the latch circuit 15 also becomes High, and the latch circuit 15 maintains the output of High thereafter. The control terminal of the switching element 16 is connected to the output terminal of the latch circuit 15. The switching element 16 is, for example, a MOSFET. The switching element 16 has an input terminal (corresponding to the drain terminal of the FET), an output terminal (corresponding to the source terminal of the FET), and a control terminal (corresponding to the gate terminal of the FET). The input terminal of the switching element 16 is connected to the output terminal of the error amplifier 24 in the semiconductor device 23. The output terminal of the switching element 16 is connected to the feedback terminal GND1.

[0026] When the output of the latch circuit 15 becomes high, the switching element 16 turns on, and the input voltage to the PWM latch circuit 20 in the semiconductor device 23 becomes almost zero. The lower the input voltage of the PWM latch circuit 20, the smaller the PWM on-duty of the output signal becomes. Therefore, at this time, the PWM on-duty becomes 0%, and the output of the gate drive circuit 21 is always low. As a result, the main switching element 11 turns off. Since the high output of the latch circuit 15 is maintained, the main switching element 11, once turned off, maintains its off state.

[0027] FIG. 2 is a diagram showing a schematic diagram of the waveforms of the drain current IDS and the diode current ID during normal operation. The drain current IDS is a current flowing through the drain terminal of the main switching element 11. The diode current ID is a current flowing through the secondary rectifier diode 7. In FIG. 2, the period during which the main switching element 11 is on is represented as Ton, the period during which it is off is represented as Toff, the period during which a current flows through the secondary rectifier diode 7 is represented as Td, and the switching period is represented as T. The switching power supply device 100 according to the first embodiment operates in a current discontinuous operation mode during normal operation. That is, there is a current discontinuous period during which no current flows through both the main switching element 11 and the secondary rectifier diode 7. In FIG. 2, this current discontinuous period is represented as Δt.

[0028] During the period Ton when the main switching element 11 is on, the drain current IDS increases linearly with time. During this period, the secondary rectifier diode 7 is reverse biased, so that the diode current ID does not flow through the secondary rectifier diode 7.

[0029] When the main switching element 11 is turned off, the drain current IDS becomes zero, and the energy stored in the primary winding 2 flows through the secondary winding 4 as a diode current ID to the load 9. During the period Td when current flows through the secondary rectifier diode 7, the diode current ID decreases linearly over time. When all the energy stored in the primary winding 2 is released, the diode current ID becomes zero, and a current discontinuous period Δt begins during which no current flows through either the main switching element 11 or the secondary rectifier diode 7. When a switching period T has elapsed since the main switching element 11 was turned on, the main switching element 11 turns on again and the drain current IDS begins to flow.

[0030] FIG. 3 is a diagram showing the waveforms of the drain current IDS and the diode current ID when the output is short-circuited. The current discontinuous period Δt that exists during normal operation shown in FIG. 2 does not exist when the output is short-circuited as shown in FIG. 3. This is because the current flowing through the load 9 increases when the output is short-circuited. That is, when the output is short-circuited, a current always flows through either the main switching element 11 or the secondary rectifier diode 7. In other words, when the output is short-circuited, the switching power supply device 100 operates in a so-called current continuous mode. When the main switching element 11 is turned on, a reverse bias is applied to the secondary rectifier diode 7. At this time, a current flows in the forward direction in the secondary rectifier diode 7, so that after the reverse bias is applied, a so-called reverse recovery current Irr flows from the cathode to the anode of the secondary rectifier diode 7, and a corresponding spike current Isp flows in the main switching element 11. The short-circuit protection circuit 25 detects a short circuit in the load 9 by observing the presence or absence of this spike current Isp.

[0031] As described above, an output short circuit is detected in response to the reverse recovery current Irr and spike current Isp that flow when a reverse bias is applied (when the main switching element 11 is turned on). Therefore, compared to conventional overcurrent protection methods such as the pulse-by-pulse method, an output short circuit can be detected at an earlier timing, before a large current flows.

[0032] FIG. 4 is a circuit diagram of a power conversion device 101 using the switching power supply device 100 of the first embodiment. The power conversion device 101 functions as a so-called AC / DC converter. The power conversion device 101 is composed of a bridge circuit 102 and a switching power supply device 100. The bridge circuit 102 is a so-called diode bridge circuit (full-wave rectifier circuit) composed of four diodes 103, 104, 105, and 106. An AC voltage of a predetermined voltage value is applied to the power conversion device 101 from an external AC power supply 107. The bridge circuit 102 converts this AC voltage into a DC voltage. The converted DC voltage is input to the switching power supply device 100, and is converted into a DC voltage of a desired voltage value by the switching power supply device 100. If so-called power semiconductor elements are selected as the diodes 103, 104, 105, and 106, the power conversion device 101 can be used for applications requiring high voltage and large current.

[0033] According to the above-described first embodiment, the following advantageous effects are achieved.

[0034] (1) The switching power supply device 100 includes a switching transformer 1 (transformer), a main switching element 11 (switching element) connected to a primary winding 2 of the switching transformer 1 (transformer), an energy conversion circuit 10 (rectifier circuit) including a secondary rectifier diode 7 (diode) connected to a secondary winding 4 of the switching transformer 1 (transformer), and a short-circuit protection circuit 25 (short-circuit detection circuit) that detects an output short circuit at an output power terminal OUT2 (voltage output terminal) connected to the secondary winding 4 of the switching transformer 1 (transformer). The short-circuit protection circuit 25 (short-circuit detection circuit) determines that an output short circuit has occurred at the output power terminal OUT2 (voltage output terminal) when the drain current flowing through the main switching element 11 (switching element) exceeds a predetermined threshold value when the main switching element 11 (switching element) is switched to a turn-on state during driving in a discontinuous current mode. As a result, an output short circuit can be detected before a large current flows, that is, at an earlier timing than in the past. In addition, because the current can be interrupted before a large current flows during a short circuit, it is possible to prevent a large current from flowing through the circuit elements, and there is no need to use expensive circuit elements with a higher resistance than the rated resistance on the assumption that a large current will flow. In other words, the cost of the circuit elements can be reduced without compromising safety.

[0035] (2) The short circuit protection circuit 25 (short circuit detection circuit) detects an output short circuit based on a predetermined threshold value that is set in advance based on the recovery characteristics of the secondary rectifier diode 7 (diode). As a result of this configuration, the threshold value can be set using the data sheet of the secondary rectifier diode 7 or the results of actual measurement.

[0036] (3) The short circuit protection circuit 25 (short circuit detection circuit) includes a latch circuit 15 that continuously stops switching by the main switching element 11 (switching element) when an output short circuit is detected. As a result, once protection is activated, switching by the main switching element 11 can be continuously stopped, and the circuit can be protected more reliably.

[0037] (4) The short-circuit detection and short-circuit protection by the switching power supply 100 utilizes a phenomenon that occurs in a diode (i.e., when a reverse voltage is applied while a forward current is flowing through a diode, a reverse recovery current flows in the opposite direction for the recovery time), and therefore can be applied to a wide variety of DC / DC converters, including chopper type and isolated type.

[0038] <Second embodiment> A switching power supply device 200 according to a second embodiment of the present invention will be described with reference to Fig. 5. Configurations that are the same as or equivalent to those described in the first embodiment are given the same reference symbols, and differences will be mainly described.

[0039] Fig. 5 is a circuit diagram of a switching power supply device 200 according to a second embodiment, which is similar to Fig. 1. The switching power supply device 200 shown in Fig. 5 is different from the switching power supply device 100 shown in Fig. 1 in the configuration of the energy conversion circuit 10.

[0040] The switching transformer 1 according to the second embodiment includes secondary windings 4a and 4b connected in series, instead of the secondary winding 4. Moreover, the energy conversion circuit 10 according to the second embodiment includes secondary rectifier diodes 7a and 7b, instead of the secondary rectifier diode 7, and secondary smoothing capacitors 8a and 8b, instead of the secondary smoothing capacitor 8. The switching power supply device 200 includes an output power supply terminal OUT3 in addition to the output power supply terminal OUT2.

[0041] The anode of the secondary rectifier diode 7a is connected to one end of the secondary winding 4a, and the cathode is connected to the output power supply terminal OUT2. The anode of the secondary rectifier diode 7b is connected to the other end of the secondary winding 4a and one end of the secondary winding 4b, and the cathode is connected to the output power supply terminal OUT3. The secondary smoothing capacitor 8a is connected between the cathode of the secondary rectifier diode 7a and the other end of the secondary winding 4b. The secondary smoothing capacitor 8b is connected between the cathode of the secondary rectifier diode 7b and the other end of the secondary winding 4b. The other end of the secondary winding 4b is connected to the output power supply terminal GND2.

[0042] The energy conversion circuit 10 having the above configuration rectifies and smoothes the AC voltage induced in the auxiliary winding 3, the secondary winding 4a, and the secondary winding 4b by the switching operation of the main switching element 11, to generate a feedback voltage VFB, an output power supply voltage VOUT2, and an output power supply voltage VOUT3. The output power supply voltage VOUT2 is applied between the output power supply terminal OUT2 and the output power supply terminal GND2. The output power supply voltage VOUT3 is applied between the output power supply terminal OUT3 and the output power supply terminal GND2. As in the first embodiment, a user of the switching power supply device 200 can connect a load between the output power supply terminal OUT2 and the output power supply terminal GND2, as well as another load between the output power supply terminal OUT3 and the output power supply terminal GND2.

[0043] As described above, the switching power supply device 200 according to the second embodiment outputs a plurality of output power supply voltages. A user can apply voltages to a plurality of loads individually using a single switching power supply device 200. The configuration other than the energy conversion circuit 10 is the same as that of the first embodiment. That is, the switching power supply device 200 can detect short circuits in both the load connected between the output power supply terminal OUT2 and the output power supply terminal GND2 and the load connected between the output power supply terminal OUT3 and the output power supply terminal GND2, and protect the circuit. No matter which output is short-circuited, a spike current flows on the primary side, so that output short circuits in a plurality of outputs can be detected collectively by detecting this spike current in the same manner as in the first embodiment. That is, when at least one of the loads is short-circuited, the short-circuit protection circuit 25 detects the short circuit and causes the semiconductor device 23 to maintain the main switching element 11 in the off state.

[0044] It is also possible to make the energy conversion circuit 10 compatible with three or more output voltages. In other words, it is possible to provide a greater number of output voltages to the user by preparing a greater number of combinations of output power supply terminals, secondary windings, secondary rectifier diodes, and secondary smoothing capacitors.

[0045] According to the above-described second embodiment, the following advantageous effects are achieved.

[0046] (1) The switching transformer 1 (transformer) has multiple secondary windings 4a, 4b. The short-circuit protection circuit 25 (short-circuit detection circuit) is connected to the main switching element 11 (switching element) and collectively detects output short circuits at multiple output power supply terminals OUT2, OUT3 (voltage output terminals) connected to the multiple secondary windings 4a, 4b, respectively. In this way, fewer circuits are required for short-circuit detection and short-circuit protection compared to when an output short circuit is detected on the secondary side, and the costs required for short-circuit detection and short-circuit protection are reduced.

[0047] The following modified examples are also within the scope of the present invention, and it is possible to combine the configurations shown in the modified examples with the configurations described in the above-mentioned embodiments, to combine the configurations described in the different embodiments above, or to combine the configurations described in the different modified examples below.

[0048] <Variation 1> The short-circuit protection circuit 25 may be provided on the secondary side instead of the primary side. In this case, the spike current Isp that flows when the load is short-circuited may be detected on the secondary side.

[0049] <Variation 2> The latch circuit 15 may be omitted. When the latch circuit 15 is provided, the latching by the latch circuit 15 may be released at regular intervals.

[0050] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments. [Explanation of symbols]

[0051] 1...switching transformer, 2...primary winding, 3...auxiliary winding, 4, 4a, 4b...secondary winding, 5...primary rectifier diode, 6...primary smoothing capacitor, 7, 7a, 7b...secondary rectifier diode, 8, 8a, 8b...secondary smoothing capacitor, 10...energy conversion circuit, 11...main switching element, 13...high-pass filter, 14...AND circuit, 15...latch circuit, 16...switching element, 19...oscillator, 20...PWM latch circuit, 21...gate drive circuit, 22...regulator, 24...error amplifier, 25...short-circuit protection circuit, 100, 200...switching power supply device, 101...power conversion device, 102...bridge circuit, 103, 104, 105, 106...diode

Claims

1. Transformer and A switching element connected to a primary winding of the transformer; a rectifier circuit including a diode connected to a secondary winding of the transformer; a short circuit detection circuit for detecting an output short circuit at a voltage output terminal connected to a secondary winding of the transformer; A flyback switching power supply device comprising: the short circuit detection circuit determines that an output short circuit has occurred at the voltage output terminal when a current flowing through the switching element exceeds a predetermined threshold value when the switching element is switched to a turn-on state during operation in a discontinuous current mode. Switching power supply.

2. 2. The switching power supply device according to claim 1, The transformer has a plurality of secondary windings, the short circuit detection circuit is connected to the switching element and detects output short circuits in a single operation at each of the voltage output terminals connected to the secondary windings, respectively. Switching power supply.

3. 2. The switching power supply device according to claim 1, the short circuit detection circuit detects an output short circuit based on the predetermined threshold value that is set in advance based on a recovery characteristic of the diode. Switching power supply.

4. 2. The switching power supply device according to claim 1, the short circuit detection circuit includes a latch circuit that continuously stops switching by the switching element when an output short circuit is detected. Switching power supply.

5. The switching power supply device according to claim 1 ; a drive circuit that drives a power semiconductor element based on an output voltage of the switching power supply device; a bridge circuit constituted by the power semiconductor elements; A power conversion device comprising:

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