JP7143754B2 - Power supply protection circuit and power supply - Google Patents

Description

The present disclosure relates to a protection circuit for a power supply and a power supply.

Conventionally, as a power supply device, for example, a power supply device has been proposed in which an output voltage is obtained from an input voltage by controlling the on/off of a normally-on transistor (see, for example, Patent Document 1).

JP 2015-65776 A

By the way, when trying to adjust the output voltage, a control circuit for controlling the on/off of the transistor is required. However, in the case of a normally-on transistor, the transistor becomes conductive when the power supply to the control circuit is stopped. Here, when a current flows from the output side to the input side in the inductor on the output side, the current flows to the conductive transistor. As a result, depending on the amount of current drawn from the inductor, the transistor may fail.

An object of the present disclosure is to provide a protection circuit for a power supply device and a power supply device that can suppress transistor failures.

A power supply device protection circuit according to one embodiment of the present disclosure is a protection circuit for protecting the transistor in a power supply device having a normally-on transistor and a first inductor connected to the transistor, The transistor is turned off based on a second inductor electrically insulated from the first inductor and magnetically coupled with the first inductor, and a second current induced in the second inductor by the first current of the first inductor. a gate voltage generation circuit for generating a gate voltage to

According to this configuration, when current flows from the first inductor to the transistor, a negative voltage is applied to the gate terminal of the transistor based on the second current induced in the second inductor magnetically coupled with the first inductor. . A normally-on transistor is cut off by a negative voltage applied to its gate terminal. Therefore, since the flow of current from the first inductor to the first transistor is suppressed, failure of the transistor can be suppressed.

According to the protection circuit of the power supply device and the power supply device according to one embodiment of the present disclosure, failure of the transistor can be suppressed.

1 is a circuit diagram of a power supply device including a protection circuit according to the first embodiment; FIG. The circuit diagram of the power supply device provided with the protection circuit of 2nd Embodiment. The circuit diagram of the power supply device provided with the protection circuit of 3rd Embodiment. The circuit diagram of the power supply device provided with the protection circuit of 4th Embodiment. The circuit diagram of the power supply device provided with the protection circuit of a modification. The circuit diagram of the power supply device provided with the protection circuit of a modification. The circuit diagram of the power supply device provided with the protection circuit of a modification. The circuit diagram of the power supply device provided with the protection circuit of a modification.

Hereinafter, each embodiment will be described with reference to the drawings.
(First embodiment)
As shown in FIG. 1, a step-down DC-DC converter 10, which is an example of a power supply device, includes a pair of first power supply terminals 11a and 11b, a pair of second power supply terminals 12a and 12b, a first smoothing capacitor 13, a chopper It has a circuit 14 , a second smoothing capacitor 15 , a control circuit 20 and a protection circuit 30 . In this embodiment, the pair of first power supply terminals 11a and 11b form the input terminals of the step-down DC-DC converter 10, and the pair of second power supply terminals 12a and 12b form the output terminals of the step-down DC-DC converter. is doing.

The first electric wire 10A is connected to the positive terminal of the power supply CS through the first power supply terminal 11a and to the first terminal of the load LD through the second power supply terminal 12a. The second electric wire 10B is connected to the negative electrode of the power supply CS through the first power supply terminal 11b and to the second terminal of the load LD through the second power supply terminal 12b. The first electric wire 10A electrically connects the first power terminal 11a and the second power terminal 12a. The second electric wire 10B electrically connects the first power terminal 11b and the second power terminal 12b. In this embodiment, the second electric wire 10B is grounded. The power source CS may be a DC power source, a power generation device, or a power storage device. The load LD may be a DC load or an inverter circuit connected to the step-down DC-DC converter 10 . The power supply may be a step-up DC-DC converter or a bi-directional DC-DC converter. It may also be an isolated DC-DC converter (a forward type DC-DC converter, an active clamp forward converter, a full bridge converter, a flyback converter, a half bridge converter, etc.) having a transformer on the input side.

The first smoothing capacitor 13, the chopper circuit 14, and the second smoothing capacitor 15 are provided between the pair of first power terminals 11a, 11b and the pair of second power terminals 12a, 12b. The first smoothing capacitor 13 is provided on the first power terminal 11a side with respect to the chopper circuit 14 . A first terminal of the first smoothing capacitor 13 is connected to the first wire 10A, and a second terminal of the first smoothing capacitor 13 is connected to the second wire 10B. The second smoothing capacitor 15 is provided on the second power terminal 12b side with respect to the chopper circuit 14 . A first terminal of the second smoothing capacitor 15 is connected to the first wire 10A, and a second terminal of the second smoothing capacitor 15 is connected to the second wire 10B. In one example, the capacitance value of first smoothing capacitor 13 is smaller than the capacitance value of second smoothing capacitor 15 .

The chopper circuit 14 steps down the voltage of the pair of first power supply terminals 11a and 11b and outputs it as the voltage of the pair of second power supply terminals 12a and 12b. The chopper circuit 14 has a first transistor 14A, a second transistor 14B and a first inductor 14C. Normally-on transistors are used for the first transistor 14A and the second transistor 14B. Specifically, compound semiconductors are used as normally-on type transistors for the first transistor 14A and the second transistor 14B. Compound semiconductors are manufactured from gallium arsenide (GaAs), gallium nitride (GaN), and the like. In this embodiment, a HEMT (High Electron Mobility Transistor) is used as the compound semiconductor. A first terminal 14 x of the first inductor 14 C is connected to a first terminal of the second smoothing capacitor 15 . A first terminal 14x of the first inductor 14C is connected to the second power terminal 12a via the first wire 10A. A second terminal 14y of the first inductor 14C is connected to a first terminal (drain terminal) of the first transistor 14A and a second terminal (source terminal) of the second transistor 14B. A second terminal 14y of the first inductor 14C is connected to the first power terminal 11a via the first wire 10A.

The first transistor 14A is connected between the node between the first inductor 14C and the second terminal (source terminal) of the second transistor 14B and the second wire 10B connecting the first power terminal 11b and the second power terminal 12b. It is configured to be switchable between conduction and interruption. The second transistor 14B is configured to switch between conduction and interruption between the first inductor 14C and the first power supply terminal 11a.

A second terminal (source terminal) of the first transistor 14A is connected to the second wire 10B. A first terminal (drain terminal) of the first transistor 14A is connected to a second terminal (source terminal) of the second transistor 14B. A first terminal (drain terminal) of the second transistor 14B is connected to the first power supply terminal 11a.

The protection circuit 30 is a circuit that protects the first transistor 14A when a first current flows from the first terminal 14x of the first inductor 14C of the chopper circuit 14 toward the second terminal 14y. For example, when the power supply to the control unit 24 is stopped while the second smoothing capacitor 15 is charged, current flows from the second smoothing capacitor 15 to the first transistor 14A. In this case, the first current flowing from the first terminal 14x to the second terminal 14y of the first transistor 14A increases, and if the first current flows through the first transistor 14A, the first transistor 14A may fail. . The protection circuit 30 is a circuit for suppressing failure of the first transistor 14A by suppressing current flowing through the first transistor 14A. The protection circuit 30 has a second inductor 31 and a gate voltage generation circuit 32 .

The second inductor 31 is provided so as to be electrically insulated from the first inductor 14C and magnetically coupled to the first inductor 14C. The second inductor 31 is configured to have the same polarity as the first inductor 14C. Specifically, as shown in FIG. 2, the winding start position of the coil of the second inductor 31 is the same as the winding start position of the coil of the first inductor 14C. In this case, the value of inductance between the first inductor 14C and the second inductor 31 becomes a positive value. In this embodiment, the step-down DC-DC converter 10 has a transformer composed of the first inductor 14C, the second inductor 31, and an iron core. Thereby, the configuration in which the first inductor 14C and the second inductor 31 are magnetically coupled can be easily realized.

The gate voltage generation circuit 32 generates a negative voltage (gate voltage) based on the second current induced in the second inductor 31 by the first current of the first inductor 14C, and applies the negative voltage (gate voltage) to the first inductor 14C. This circuit outputs to the gate terminal of the transistor 14A. In this embodiment, the gate voltage generation circuit 32 generates a negative voltage (gate voltage) and outputs its negative voltage (gate voltage) to the gate terminal of the first transistor 14A. The gate voltage generation circuit 32 has a diode 33 , a capacitor 34 and a first switch element 35 .

A cathode of the diode 33 is connected to the second terminal 31 y of the second inductor 31 . The anode of diode 33 is connected to the first terminal of capacitor 34 . A first terminal 31x of the second inductor 31 and a second terminal of the capacitor 34 are each connected to the second wire 10B. Therefore, the diode 33 functions as a backflow prevention diode that prevents current from flowing from the second inductor 31 toward the capacitor 34 . The second terminal of the capacitor 34 connected to the second wire 10B constitutes a negative terminal, and the first terminal of the capacitor 34 constitutes a positive terminal.

A normally-on transistor, for example, is used for the first switch element 35 . In this embodiment, a MOSFET (metal-oxide-semiconductor field-effect transistor) is used for the first switch element 35 . A first terminal (drain terminal) of the first switch element 35 is connected to a gate terminal of the first transistor 14A. A second terminal (source terminal) of the first switch element 35 is connected to a node between the anode of the diode 33 and the first terminal of the capacitor 34 . As the first switch element 35, an IGBT (Insulated Gate Bipolar Transistor), another transistor such as a bipolar transistor, or another switch element such as a thyristor may be used. Alternatively, a normally-off transistor may be used as the first switch element 35 .

The control circuit 20 has drive circuits 21 to 23 and a control section 24 that controls the drive circuits 21 to 23 .
The drive circuit 21 is electrically connected to the gate terminal of the first transistor 14A. The drive circuit 21 outputs to the gate terminal of the first transistor 14A a gate voltage for controlling switching between the conductive state (ON state) and cutoff state (OFF state) of the first transistor 14A. The drive circuit 22 is electrically connected to the gate terminal of the second transistor 14B. The drive circuit 22 outputs to the gate terminal of the second transistor 14B a gate voltage for controlling switching between the conductive state and the cutoff state of the second transistor 14B. The drive circuit 23 is electrically connected to the gate terminal of the first switch element 35 . The drive circuit 23 outputs to the gate terminal of the first switch element 35 a gate voltage for controlling switching between the conductive state and the cut-off state of the first switch element 35 . Here, the conductive state of the first transistor 14A is a state in which the drain terminal and the source terminal of the first transistor 14A are conductive. The cutoff state of the first transistor 14A is a state in which the drain terminal and the source terminal of the first transistor 14A are electrically insulated. The conductive state and cutoff state of the second transistor 14B and the conductive state and cutoff state of the first switch element 35 are the same as the conductive state and cutoff state of the first transistor 14A. Since the first transistor 14A, the second transistor 14B, and the first switch element 35 are normally-on type transistors, they are cut off when a gate voltage is applied, and when no gate voltage is applied, It becomes conductive.

The control circuit 20 may have a drive circuit common to the first transistor 14A, the second transistor 14B, and the first switch element 35 instead of the drive circuits 21-23. Further, the control circuit 20 may have a drive circuit common to the first transistor 14A and the second transistor 14B instead of the drive circuits 21 and 22. FIG. In this case, the first transistor 14A and the second transistor 14B operate complementarily, and the drive circuit has a NOT circuit. Therefore, when the drive circuit outputs the gate voltage to the gate terminal of the first transistor 14A, it does not output the gate voltage to the gate terminal of the second transistor 14B. Further, when the drive circuit outputs the gate voltage to the gate terminal of the second transistor 14B, the drive circuit does not output the gate voltage to the gate terminal of the first transistor 14A.

The second switch element 25 in the protection circuit 30 is provided between the first output terminal 21a of the drive circuit 21 and the gate terminal of the first transistor 14A. A normally-off transistor, for example, is used for the second switch element 25 . In this embodiment, a MOSFET is used for the second switch element 25 . A first terminal (drain terminal) of the second switch element 25 is connected to the first output terminal 21 a of the drive circuit 21 . A second terminal (source terminal) of the second switch element 25 is connected to the gate terminal of the first transistor 14A. A first terminal (drain terminal) of the first switch element 35 is connected to a second terminal (source terminal) of the second switch element 25 . A gate terminal of the second switch element 25 is connected to the second output terminal 21 b of the drive circuit 21 . Therefore, the drive circuit 21 outputs to the gate terminal of the second switch element 25 a gate voltage for controlling switching between the conductive state and the cut-off state of the second switch element 25 . As the second switch element 25, an IGBT (Insulated Gate Bipolar Transistor), another transistor such as a bipolar transistor, or another switch element such as a thyristor may be used. Since the second switch element 25 is a normally-off transistor, when a gate voltage is applied to the gate terminal of the second switch element 25, it becomes conductive, and the gate voltage is applied to the gate terminal of the second switch element 25. If not, it will be blocked.

The control unit 24 is electrically connected to the drive circuits 21-23. The control unit 24 has an arithmetic processing unit that executes a predetermined control program. The arithmetic processing unit has, for example, a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The control unit 24 may have one or more microcomputers. The control unit 24 may have a plurality of arithmetic processing units arranged separately at a plurality of locations. Control unit 24 further has a storage unit. The storage unit stores various control programs and information used for various control processes. The storage unit has, for example, nonvolatile memory and volatile memory.

The control unit 24 executes the voltage step-down process according to the control program. Specifically, the control unit 24 controls the first transistor 14A and the second transistor 14B so that the voltage of the pair of first power supply terminals 11a and 11b is stepped down and output from the pair of second power supply terminals 12a and 12b. do.

More specifically, based on the voltage across the terminals of the first smoothing capacitor 13 and the voltage across the terminals of the second smoothing capacitor 15, the control unit 24 reduces the voltage of the pair of first power supply terminals 11a and 11b. At the same time, control signals for adjusting the duty ratios for turning on and off the first transistor 14A and the second transistor 14B are output to the drive circuits 21 and 22 . The control unit 24 also outputs a control signal to turn off the first switch element 35 and a control signal to turn off the second switch element 25 to the drive circuits 21 and 23 .

Next, the operation of the protection circuit 30 will be described together with its effects.
When the power supply to the control unit 24 is stopped, the gate voltage is not applied to the gate terminals of the first transistor 14A, the second transistor 14B, the first switch element 35, and the second switch element 25. FIG. Since the first transistor 14A, the second transistor 14B, and the first switch element 35 are normally-on transistors, they are in a conducting state. On the other hand, since the second switch element 25 is a normally-off transistor, it is in a cut-off state. Therefore, the gate terminal of the first transistor 14A is disconnected from the drive circuit 21 and connected to the protection circuit 30. FIG.

When the power supply to the control unit 24 is stopped while the second smoothing capacitor 15 is fully charged, current flows from the second smoothing capacitor 15 to the chopper circuit 14 . In other words, the first current flows from the first terminal 14x of the first inductor 14C to the second terminal 14y via the second power supply terminal 12a. At this time, a second current induced by the first current of the first inductor 14C flows through the second inductor 31 magnetically coupled to the first inductor 14C. A second current of the second inductor 31 flows through the second wire 10B and charges the capacitor 34 . Therefore, the potential of the second terminal (negative terminal) of the capacitor 34 becomes higher than the potential of the first terminal (positive terminal), and the voltage across the terminals of the capacitor 34 becomes a negative voltage. Since the first switch element 35 is in a conductive state, the voltage across the terminals of the capacitor 34 is applied to the gate terminal of the first transistor 14A as a voltage lower than the threshold voltage of the first transistor 14A. In other words, a gate voltage for turning off the first transistor 14A is applied to the gate terminal of the first transistor 14A. As a result, the first transistor 14A is turned off, so that the current flowing from the first terminal 14x to the second terminal 14y of the first inductor 14C is suppressed from flowing through the first transistor 14A.

Effects of the present embodiment will be described.
(1-1) The protection circuit 30 generates a negative voltage based on the second current induced in the second inductor 31 by the first current flowing from the first terminal 14x to the second terminal 14y of the first inductor 14C. is configured to The normally-on first transistor 14A is cut off by a negative voltage applied to its gate terminal. Therefore, even if the power supply to the control unit 24 is stopped while the second smoothing capacitor 15 is fully charged, it is possible to prevent current from flowing from the second smoothing capacitor 15 to the first transistor 14A. can be suppressed, and the failure of the first transistor 14A can be suppressed.

(1-2) The gate voltage generation circuit 32 includes a diode 33 whose cathode is connected to the first terminal 31x of the second inductor 31, a capacitor 34 connected to the anode of the diode 33, and a gate terminal of the first transistor 14A. and a first switch element 35 provided between the capacitor 34 and the capacitor 34 . According to this configuration, the voltage across the terminals of the capacitor 34 becomes a negative voltage due to the second current induced in the second inductor 31 by the first current of the first inductor 14C. When the first switch element 35 is turned on, the voltage across the terminals of the capacitor 34 is applied to the gate terminal of the first transistor 14A via the first switch element 35. FIG. The normally-on first transistor 14A is cut off by a negative voltage applied to its gate terminal. In this way, when the current flows from the first terminal 14x to the second terminal 14y of the first inductor 14C, the first transistor 14A is cut off. flow is suppressed. As a result, failure of the first transistor 14A can be suppressed.

(1-3) Since the first switch element 35 is a normally-on transistor, when power supply to the control unit 24 is stopped, no gate voltage is applied to the gate terminal of the first switch element 35. , the first switch element 35 becomes conductive. Therefore, when the power supply to the control unit 24 is stopped, the voltage across the terminals of the capacitor 34 can be reliably applied to the gate terminal of the first transistor 14A.

(1-4) Since the second switch element 25 is a normally-off transistor, when the power supply to the control unit 24 is stopped, no gate voltage is applied to the gate terminal of the second switch element 25. , the second switch element 25 is turned off. Therefore, when the power supply to the control unit 24 is stopped, the gate terminal of the first transistor 14A can be disconnected from the drive circuit 21 . Therefore, since only the voltage across the terminals of the capacitor 34 is applied to the gate terminal of the first transistor 14A, a negative voltage can be reliably applied to the gate terminal of the first transistor 14A. Therefore, it is possible to accurately switch the first transistor 14A from the cut-off state to the conductive state.

(Second embodiment)
The protection circuit of the power supply device of the second embodiment will be described with reference to FIG. This embodiment differs from the first embodiment in the configuration of the protection circuit. In the following description, the same reference numerals are given to the same components as in the first embodiment, and the description thereof may be omitted.

The protection circuit 70 of this embodiment is a circuit that protects the first transistor 14A when a first current flows from the first terminal 14x to the second terminal 14y of the first inductor 14C of the chopper circuit 14 . The protection circuit 70 has a second switch element 25 , a second inductor 71 , a first switch element 72 , a first generation circuit 80 and a second generation circuit 90 . The second inductor 71 has the same configuration as the second inductor 31 of the first embodiment. The first switch element 72 has the same configuration as the first switch element 35 of the first embodiment. In this embodiment, the step-down DC-DC converter 10 has a transformer composed of the first inductor 14C, the second inductor 71, and an iron core. The first generation circuit 80 and the second generation circuit 90 generate a gate voltage for turning off the first transistor 14A based on the second current induced in the second inductor 71 by the first current of the first inductor 14C. It constitutes a voltage generation circuit. The first generator circuit 80 is electrically connected to the second inductor 71 and the second generator circuit 90 . The second generation circuit 90 is electrically connected to the gate terminal of the first transistor 14A through the first switch element 72. As shown in FIG. The first generation circuit 80 is configured to generate a positive voltage based on the second current induced in the second inductor 71 by the first current of the first inductor 14C, and output the positive voltage to the second generation circuit 90. . The second generating circuit 90 is an inverting amplifier circuit that inverts a positive voltage into a negative voltage and outputs it to the gate terminal of the first transistor 14A.

The first generator circuit 80 has a diode 81 and a capacitor 82 . The anode of diode 81 is connected to second terminal 71 y of second inductor 71 . The cathode of diode 81 is connected to the first terminal of capacitor 82 . A second terminal of capacitor 82 is grounded. A second terminal of the grounded capacitor 82 constitutes a negative terminal, and a first terminal of the capacitor 82 constitutes a positive terminal. A first terminal 71x of the second inductor 71 is grounded.

The second generation circuit 90 has an operational amplifier 91 , a first resistor 92 , a second resistor 93 , a third resistor 94 and a capacitor 95 .
An inverting input terminal of the operational amplifier 91 is connected via a first resistor 92 to a node between the cathode of the diode 81 and the first terminal of the capacitor 82 in the first generating circuit 80 . Also, the inverting input terminal of the operational amplifier 91 is connected to the output terminal of the operational amplifier 91 via the second resistor 93 . The amplification factor (gain) of the operational amplifier 91 is set according to the resistance value of the first resistor 92 and the resistance value of the second resistor 93 . A capacitor 95 is connected in parallel with the second resistor 93 between the inverting input terminal and the output terminal of the operational amplifier 91 . As a result, the capacitor 95 reduces high frequency noise in the input signal input to the operational amplifier 91 . A non-inverting input terminal of the operational amplifier 91 is connected to the second wire 10B via a third resistor 94 serving as a bias compensation resistor.

As shown in FIG. 2, a negative voltage is supplied to the negative power supply terminal of the operational amplifier 91 and a positive voltage is supplied to the positive power supply terminal of the operational amplifier 91 .
A first terminal (drain terminal) of the first switch element 72 is connected to a node between the gate terminal of the first transistor 14A and the second terminal (source terminal) of the second switch element 25 . A first terminal (drain terminal) of the first switch element 72 is connected to a second terminal (source terminal) of the second switch element 25 . A second terminal (source terminal) of the first switch element 72 is connected to the output terminal of the second generation circuit 90 . Specifically, the second terminal (source terminal) of the first switch element 72 is connected to the output terminal of the operational amplifier 91 . A gate terminal of the first switch element 72 is connected to the drive circuit 23 . Therefore, the drive circuit 23 outputs to the gate terminal of the first switch element 72 a gate voltage for controlling switching between the conductive state and the cut-off state of the first switch element 72 .

Next, the operation of the protection circuit 70 will be described.
When the power supply to the control unit 24 is stopped, no gate voltage is applied to the gate terminals of the first transistor 14A, the second transistor 14B, the first switch element 72, and the second switch element 25. FIG. Therefore, the normally-on type first transistor 14A, the second transistor 14B, and the first switch element 72 are in a conductive state, and the normally-off type second switch element 25 is in a cut-off state. The capacitor 82 stores a positive voltage proportional to the difference (Vin-Vout) between the output voltage of the power supply CS and the voltage (output voltage) between the pair of second power supply terminals 12a and 12b during normal operation. A negative bias lower than the threshold voltage of the first transistor 14A is generated from the second generating circuit 90 by electric charges accumulated in the capacitor 82 as the second switch element 25 is turned off and the first switch element 72 is turned on, and the first transistor 14A is turned on. A negative bias will be applied between the gate and source.

The operational amplifier 91 of the second generation circuit 90 inverts the positive voltage of the first generation circuit 80 (the voltage across the terminals of the capacitor 82) into a negative voltage, amplifies it with a predetermined gain, and outputs it. Since the normally-on first switch element 72 is in a conductive state, the negative voltage output from the operational amplifier 91 is applied to the gate terminal of the first transistor 14A. As a result, the first transistor 14A is turned off. Thus, according to this embodiment, the same effects as (1-1), (1-3), and (1-4) of the first embodiment can be obtained.

(Third Embodiment)
The protection circuit of the power supply device of the third embodiment will be described with reference to FIG. This embodiment differs from the first embodiment in the configuration of the protection circuit. In the following description, the same reference numerals are given to the same components as in the first embodiment, and the description thereof may be omitted.

The protection circuit 100 of the present embodiment is designed for a case where a current flows from the first terminal 14x of the first inductor 14C to the second terminal 14y and a case where a current flows from the second terminal 14y of the first inductor 14C to the first terminal 14x. Both are circuits that protect the first transistor 14A. The protection circuit 100 has a second switch element 25 , a second inductor 101 , a first switch element 102 , a first generation circuit 110 and a second generation circuit 120 . The second inductor 101 has the same configuration as the second inductor 31 of the first embodiment. The first switch element 102 has the same configuration as the first switch element 35 of the first embodiment. In this embodiment, the step-down DC-DC converter 10 has a transformer composed of a first inductor 14C, a second inductor 101, and an iron core. The first generation circuit 110 and the second generation circuit 120 generate a gate voltage for turning off the first transistor 14A based on the second current induced in the second inductor 101 by the first current of the first inductor 14C. It constitutes a voltage generation circuit. The first generator circuit 110 is electrically connected to the second inductor 101 and the second generator circuit 120 . The second generation circuit 120 is electrically connected to the gate terminal of the first transistor 14A through the first switch element 102. As shown in FIG. The first generation circuit 110 is configured to generate a negative voltage based on the second current induced in the second inductor 101 by the first current of the first inductor 14C, and output the negative voltage to the second generation circuit 120. . The second generating circuit 120 is an inverting amplifier circuit that inverts the positive voltage applied to the second generating circuit 120 into a negative voltage and outputs the negative voltage to the gate terminal of the first transistor 14A.

The first generation circuit 110 has a first diode 111 , a first anti-backflow diode 112 , a first capacitor 113 , a second diode 114 , a second anti-backflow diode 115 , a second capacitor 116 and a third diode 117 .

A second terminal 101 y of the second inductor 101 is connected to the anode of the first diode 111 . A cathode of the first diode 111 is grounded. The anode of the second diode 114 is connected to the first terminal 101x of the second inductor 101 . The cathode of the second diode 114 is grounded.

The first backflow prevention diode 112 and the first capacitor 113 are connected in series. A cathode of the first backflow prevention diode 112 is connected to the second terminal 101 y of the second inductor 101 . The anode of the first backflow prevention diode 112 is connected to the first terminal of the first capacitor 113 . A second terminal of the first capacitor 113 is grounded. Thus, the first backflow prevention diode 112 and the first capacitor 113 are connected in parallel with the first diode 111 . The second terminal of the grounded first capacitor 113 constitutes a negative terminal, and the first terminal of the first capacitor 113 constitutes a positive terminal.

The second backflow prevention diode 115 and the second capacitor 116 are connected in series. A cathode of the second backflow prevention diode 115 is connected to the first terminal 101x of the second inductor 101 . The anode of the second backflow prevention diode 115 is connected to the first terminal of the second capacitor 116 . A second terminal of the second capacitor 116 is grounded. Thus, the second backflow prevention diode 115 and the second capacitor 116 are connected in parallel with the second diode 114 . The second terminal of the grounded second capacitor 116 constitutes a negative terminal, and the first terminal of the second capacitor 116 constitutes a positive terminal. Also, the second backflow prevention diode 115 and the second capacitor 116 are provided in parallel with the first backflow prevention diode 112 and the first capacitor 113 with the second inductor 101 interposed therebetween.

A third diode 117 is provided in parallel with the second inductor 101 . The cathode of the third diode 117 is connected to the node between the anode of the first backflow prevention diode 112 and the first terminal of the first capacitor 113 . The anode of the third diode 117 is connected to the node between the anode of the second anti-backflow diode 115 and the first terminal of the second capacitor 116 .

The second generation circuit 120 has an operational amplifier 121 , a first resistor 122 , a second resistor 123 , a third resistor 124 , a first capacitor 125 , a second capacitor 126 and a third capacitor 127 .

A positive power supply terminal of the operational amplifier 121 is connected to the second wire 10B via the second capacitor 126 . A first terminal of the second capacitor 126 is connected to the second wire 10B, and a second terminal of the second capacitor 126 is connected to the positive power terminal of the operational amplifier 121 . A negative power supply terminal of the operational amplifier 121 is connected to the cathode of the third diode 117 . A negative power supply terminal of the operational amplifier 121 is connected to the second wire 10B via the third capacitor 127 . The second capacitor 126 and the third capacitor 127 serve as bypass capacitors that remove noise inside the operational amplifier 121 .

The inverting input terminal of the operational amplifier 121 is connected via the first resistor 122 to the node between the first terminal 14x of the first inductor 14C and the first terminal of the second smoothing capacitor 15 . Also, the inverting input terminal of the operational amplifier 121 is connected to the output terminal of the operational amplifier 121 via the second resistor 123 . The amplification factor (gain) of the operational amplifier 121 is set according to the resistance value of the first resistor 122 and the resistance value of the second resistor 123 . A first capacitor 125 is connected in parallel with a second resistor 123 between the inverting input terminal and the output terminal of the operational amplifier 121 . Thereby, the first capacitor 125 reduces high frequency noise in the input signal input to the operational amplifier 121 . A non-inverting input terminal of the operational amplifier 121 is connected to the second wire 10B via a third resistor 124 serving as a bias compensation resistor. A first terminal of the third resistor 124 is connected to the second wire 10B, and a second terminal of the third resistor 124 is connected to the non-inverting input terminal of the operational amplifier 121 . A node between the second terminal of the third resistor 124 and the non-inverting input terminal of the operational amplifier 121 is connected to a node between the second terminal of the second capacitor 126 and the positive power supply terminal of the operational amplifier 121 .

A first terminal (drain terminal) of the first switch element 102 is connected to a node between the gate terminal of the first transistor 14A and the second terminal (source terminal) of the second switch element 25 . A first terminal (drain terminal) of the first switch element 102 is connected to a second terminal (source terminal) of the second switch element 25 . A second terminal (source terminal) of the first switch element 102 is connected to the output terminal of the second generation circuit 120 . Specifically, the second terminal (source terminal) of the first switch element 102 is connected to the output terminal of the operational amplifier 121 . A gate terminal of the first switch element 102 is connected to the drive circuit 23 . Therefore, the drive circuit 23 outputs to the gate terminal of the first switch element 102 a gate voltage for controlling switching between the conductive state and the cut-off state of the first switch element 102 .

Next, operation of the protection circuit 100 will be described. The protection circuit 100 protects the first current from the first terminal 14x of the first inductor 14C to the second terminal 14y and the first current from the second terminal 14y of the first inductor 14C to the first terminal 14x. Negative voltages appearing on both result in a circuit that protects the first transistor 14A.

When the power supply to the control unit 24 is stopped, no gate voltage is applied to the gate terminals of the first transistor 14A, the second transistor 14B, the first switch element 102, and the second switch element 25. FIG. Therefore, the normally-on type first transistor 14A, the second transistor 14B, and the first switch element 102 are in a conductive state, and the normally-off type second switch element 25 is in a cut-off state. Each of the first capacitor 113 and the second capacitor 116 has a negative voltage proportional to the output voltage (Vout) during steady operation, and a voltage (output voltage) between the output voltage of the power supply CS and the pair of second power supply terminals 12a and 12b. A negative voltage proportional to the difference (Vin-Vout) between and is generated. The smaller of the negative voltages generated in the first capacitor 113 and the second capacitor 116 is applied to the negative power supply terminal of the operational amplifier 121 . A negative bias is applied between the gate and source of the first transistor 14A from the second generation circuit 120 through the first switch element 102 by the voltage applied to the negative side power supply and the voltage remaining in the second smoothing capacitor 15. It will be. As a result, when the load current due to the load LD is small, the charge remains in the second smoothing capacitor 15, and the voltage remains between the pair of second power supply terminals 12a and 12b (output terminal). 14A is cut off to prevent current from flowing from the first terminal 14x of the first inductor 14C to the second terminal 14y, thereby preventing current from flowing from the second smoothing capacitor 15 to the first transistor 14A. Suppressed. On the other hand, in the unlikely event that a current is generated from the second smoothing capacitor 15 from the first terminal 14x of the first inductor 14C to the second terminal 14y, the first capacitor 113 is connected to the first backflow prevention diode 112 and the second inductor 101. A current flows from the second terminal 101y to the first terminal 101x and the second diode 114, and a corresponding negative voltage is generated across the first capacitor 113. FIG. As a result, a negative bias can be generated between the gate and source of the first transistor 14A in the same manner as described above.

The operational amplifier 121 performs the inversion based on the difference between the first potential (the potential of the first wire 10A) applied to the inverting input terminal and the second potential (the potential of the second wire 10B) applied to the non-inverting input terminal. is amplified to a predetermined gain and output as a negative voltage. Since the normally-on first switch element 102 is in a conductive state, the negative voltage output from the operational amplifier 121 is applied to the gate terminal of the first transistor 14A. By applying a gate voltage lower than the threshold voltage of the first transistor 14A, the first transistor 14A is turned off.

Effects of the present embodiment will be described. This embodiment can obtain the same effect as (1-4) of the first embodiment.
(3-1) When the first current flows from the first terminal 14x of the first inductor 14C to the second terminal 14y, and when the first current flows from the second terminal 14y of the first inductor 14C to the first terminal 14x, the protection circuit 100 A circuit that protects the first transistor 14A from negative voltages that occur both when the first current flows toward the first transistor 14A. Therefore, voltage is applied to the negative power supply terminal of the operational amplifier 121 regardless of the direction of the first current flowing through the first inductor 14C. A gate voltage can be generated for application to the gate terminal of the first transistor 14A. Therefore, when the stopped power supply to the control unit 24 is restarted, the gate voltage can be quickly applied from the operational amplifier 121 to the gate terminal of the first transistor 14A.

(3-2) The first generating circuit 110 supplies the first capacitor 113 and the second capacitor 116 with a negative voltage proportional to the output voltage (Vout) during steady-state operation, the output voltage of the power source CS, and a pair of second capacitors 113 and 116, respectively. It generates a negative voltage proportional to the difference (Vin-Vout) from the voltage (output voltage) between the power supply terminals 12a and 12b. This negative voltage drives the operational amplifier 121 to generate a gate voltage to be applied to the gate terminal of the first transistor 14A.

(3-3) Since the first switch element 102 is a normally-on transistor, when the power supply to the control unit 24 is stopped, the gate voltage is not applied to the gate terminal of the first switch element 102. , the first switch element 102 becomes conductive. Therefore, when the power supply to the control unit 24 is stopped, the voltage across the terminals of the first capacitor 113 can be reliably applied to the gate terminal of the first transistor 14A.

(Fourth embodiment)
The protection circuit of the power supply device of the fourth embodiment will be described with reference to FIG. This embodiment differs from the fourth embodiment in the configuration of the first generation circuit in the protection circuit. In the following description, the same reference numerals may be given to the same components as in the fourth embodiment, and the description thereof may be omitted.

The protection circuit 130 of this embodiment is a circuit that protects the first transistor 14A when a first current flows from the first terminal 14x to the second terminal 14y of the first inductor 14C of the chopper circuit 14 . The protection circuit 130 has a second switch element 25 , a second inductor 131 , a first switch element 132 , a first generation circuit 140 and a second generation circuit 150 . The second inductor 131 has the same configuration as the second inductor 31 of the first embodiment. The first switch element 132 has the same configuration as the first switch element 35 of the first embodiment. In this embodiment, the step-down DC-DC converter 10 has a transformer composed of a first inductor 14C, a second inductor 131, and an iron core. The first generation circuit 140 and the second generation circuit 150 generate a gate voltage for turning off the first transistor 14A based on the second current induced in the second inductor 131 by the first current of the first inductor 14C. It constitutes a voltage generation circuit. The first generator circuit 140 is electrically connected to the second inductor 131 and the second generator circuit 150 . The second generation circuit 150 is electrically connected to the gate terminal of the first transistor 14A through the first switch element 132. As shown in FIG. The first generation circuit 140 is configured to generate a positive voltage based on the second current induced in the second inductor 131 by the first current of the first inductor 14C, and output the positive voltage to the second generation circuit 150. . The second generating circuit 150 is an inverting amplifier circuit that inverts a positive voltage into a negative voltage and outputs it to the gate terminal of the first transistor 14A. The second generation circuit 150 has the same circuit configuration as the second generation circuit 120 of the fourth embodiment. Therefore, each component of the second generation circuit 150 is given the same reference numeral as each component of the second generation circuit 120 .

The first generation circuit 140 has a diode 141 and a capacitor 142 . A cathode of the diode 141 is connected to the first terminal 131x of the second inductor 131 . The anode of diode 141 is connected to the first terminal of capacitor 142 . A second terminal of capacitor 142 is grounded. Therefore, the second terminal of the capacitor 142, which is grounded, constitutes a negative terminal, and the first terminal constitutes a positive terminal. A second terminal 131y of the second inductor 131 is grounded.

A negative power supply terminal of the operational amplifier 121 of the second generation circuit 150 is connected to a node between the anode of the diode 141 and the first terminal (positive terminal) of the capacitor 142 .
A first terminal (drain terminal) of the first switch element 132 is connected to a node between the gate terminal of the first transistor 14A and the second terminal (source terminal) of the second switch element 25 . A first terminal (drain terminal) of the first switch element 132 is connected to a second terminal (source terminal) of the second switch element 25 . A second terminal (source terminal) of the first switch element 132 is connected to the output terminal of the second generation circuit 150 . Specifically, the second terminal (source terminal) of the first switch element 132 is connected to the output terminal of the operational amplifier 121 . A gate terminal of the first switch element 132 is connected to the drive circuit 23 . Therefore, the drive circuit 23 outputs to the gate terminal of the first switch element 132 a gate voltage for controlling switching between the conductive state and the cut-off state of the first switch element 132 .

Next, the operation of the protection circuit 130 will be described.
When the power supply to the control unit 24 is stopped, no gate voltage is applied to the gate terminals of the first transistor 14A, the second transistor 14B, the first switch element 132, and the second switch element 25. FIG. Therefore, the normally-on type first transistor 14A, the second transistor 14B, and the first switch element 132 are in a conductive state, and the normally-off type second switch element 25 is in a cut-off state. A negative voltage proportional to the difference (Vin-Vout) between the output voltage of the power supply CS and the voltage (output voltage) between the pair of second power supply terminals 12a and 12b is generated in the capacitor 142 during normal operation. A negative voltage generated in the capacitor 142 is applied to the negative power supply terminal of the operational amplifier 121 . Due to the voltage applied to the negative power supply terminal and the voltage remaining in the second smoothing capacitor 15, a negative bias is applied between the gate and source of the first transistor 14A from the second generation circuit 120 via the first switch element 132. will be applied. As a result, when the load current due to the load LD is small, the charge remains in the second smoothing capacitor 15, and the voltage remains between the pair of second power supply terminals 12a and 12b (output terminal). 14A is cut off, the phenomenon of current flowing from the first terminal 14x of the first inductor 14C to the second terminal 14y is prevented, and the current can flow from the second smoothing capacitor 15 to the first transistor 14A. Suppressed.

The operational amplifier 121 performs the inversion based on the difference between the first potential (the potential of the first wire 10A) applied to the inverting input terminal and the second potential (the potential of the second wire 10B) applied to the non-inverting input terminal. is amplified to a predetermined gain and output as a negative voltage. Since the normally-on first switch element 132 is in a conductive state, the negative voltage output from the operational amplifier 121 is applied to the gate terminal of the first transistor 14A. By applying a gate voltage lower than the threshold voltage of the first transistor 14A, the first transistor 14A is turned off. Thus, according to this embodiment, the same effects as (1-1), (1-3), and (1-4) of the first embodiment can be obtained.

(Change example)
Each of the above-described embodiments is an example of a form that the protection circuit of the power supply device and the power supply device according to the present disclosure can take, and is not intended to limit the form. The protection circuit of the power supply device and the power supply device related to the present disclosure may take forms different from those illustrated in the above embodiments. One example is a form in which a part of the configuration of each of the above embodiments is replaced, changed, or omitted, or a form in which a new configuration is added to each of the above embodiments. In the following modified examples, the same reference numerals as in the above embodiments are given to the parts that are common to the above embodiments, and the description thereof will be omitted.

- In the first embodiment, the configuration of the gate voltage generation circuit 32 that generates a negative voltage based on the power generated by the second inductor 31 and outputs the negative voltage to the gate terminal of the first transistor 14A can be arbitrarily changed. is. In the first example, the gate voltage generation circuit 160 as shown in FIG. 5 may be used. The gate voltage generating circuit 160 has a first diode 161 , a first anti-backflow diode 162 , a first capacitor 163 , a second diode 164 , a second anti-backflow diode 165 , a second capacitor 166 and a third diode 167 .

The anode of the first diode 161 is connected to the second terminal 31y of the second inductor 31 . A cathode of the first diode 161 is grounded. The anode of the second diode 164 is connected to the first terminal 31x of the second inductor 31 . The cathode of the second diode 164 is grounded.

The first backflow prevention diode 162 and the first capacitor 163 are connected in series. A cathode of the first backflow prevention diode 162 is connected to the second terminal 31 y of the second inductor 31 . The anode of the first backflow prevention diode 162 is connected to the first terminal of the first capacitor 163 . A second terminal of the first capacitor 163 is grounded. Thus, the first backflow prevention diode 162 and the first capacitor 163 are connected in parallel with the first diode 161 . The second terminal of the first capacitor 163, which is grounded, constitutes a negative terminal, and the first terminal constitutes a positive terminal.

The second backflow prevention diode 165 and the second capacitor 166 are connected in series. A cathode of the second backflow prevention diode 165 is connected to the first terminal 31x of the second inductor 31 . The anode of the second backflow prevention diode 165 is connected to the first terminal of the second capacitor 166 . A second terminal of the second capacitor 166 is grounded. Thus, the second backflow prevention diode 165 and the second capacitor 166 are connected in parallel with the second diode 164 . The second terminal of the second capacitor 166, which is grounded, constitutes a negative terminal, and the first terminal constitutes a positive terminal. The second backflow prevention diode 165 and the second capacitor 166 are provided in parallel with the first backflow prevention diode 162 and the first capacitor 163 with the second inductor 31 interposed therebetween.

The third diode 167 is provided in parallel with the second inductor 31 . The cathode of the third diode 167 is connected to the node between the anode of the first backflow prevention diode 162 and the first terminal of the first capacitor 163 . The anode of the third diode 167 is connected to the node between the anode of the second anti-backflow diode 165 and the first terminal of the second capacitor 166 .

A first terminal (drain terminal) of the first switch element 35 is connected to a gate terminal of the first transistor 14A. A second terminal (source terminal) of the first switch element 35 is connected to the anode of the third diode 167 . A second terminal (source terminal) of the first switch element 35 is connected to a first terminal of the second capacitor 166 .

The protection circuit 30A having such a gate voltage generation circuit 160 operates when the first current flows from the first terminal 14x of the first inductor 14C to the second terminal 14y and when the first current flows from the second terminal 14y of the first inductor 14C to the first terminal 14y. The circuit protects the first transistor 14A both when the first current flows through the terminal 14x. The first capacitor 163 and the second capacitor 166 each have a negative voltage proportional to the output voltage (Vout) which is the voltage between the pair of second power supply terminals 12a and 12b during steady operation, the output voltage of the power supply CS and the pair of second capacitors 163 and 166, respectively. A negative voltage proportional to the difference (Vin-Vout) from the voltage (output voltage) between the two power supply terminals 12a and 12b is generated. The smaller of the negative voltages generated in the first capacitor 163 and the second capacitor 166 is applied between the gate and source of the first transistor 14A along with the conduction of the first switch element 35 and the interruption of the second switch element 25. be. By setting the voltage to the gate voltage below the threshold voltage of the first transistor 14A, the cut-off state of the first transistor 14A is maintained. As a result, when the load current due to the load LD is small, the charge remains in the second smoothing capacitor 15, and the voltage remains between the pair of second power supply terminals 12a and 12b (output terminal). 14A is cut off, the phenomenon of current flowing from the first terminal 14x of the first inductor 14C to the second terminal 14y is prevented, and the current can flow from the second smoothing capacitor 15 to the first transistor 14A. Suppressed. On the other hand, in the unlikely event that a current is generated from the second smoothing capacitor 15 from the first terminal 14x of the first inductor 14C toward the second terminal 14y, the first capacitor 163, the first backflow prevention diode 162, the second inductor A current flows from the second terminal 31 y of the capacitor 31 to the first terminal 31 x and the second diode 164 , and a corresponding negative voltage is generated across the first capacitor 163 . As a result, it has the function of generating a negative bias between the gate and source of the first transistor 14A, as described above.

In the second example, the gate voltage generation circuit 170 as shown in FIG. 6 may be used. The gate voltage generation circuit 170 has a diode 171 and a capacitor 172 . The gate voltage generation circuit 170 has a configuration in which the diode 33 and the capacitor 34 of the gate voltage generation circuit 32 of the first embodiment are connected to the first terminal 31x of the second inductor 31 . Specifically, the cathode of the diode 171 of the gate voltage generation circuit 170 is connected to the first terminal 31x of the second inductor 31 . The anode of diode 171 is connected to the first terminal of capacitor 172 . A second terminal of capacitor 172 is grounded. Therefore, the second terminal of the capacitor 172, which is grounded, constitutes a negative terminal, and the first terminal constitutes a positive terminal. A second terminal 31y of the second inductor 31 is grounded.

A first terminal (drain terminal) of the first switch element 35 is connected to a gate terminal of the first transistor 14A. A second terminal (source terminal) of the first switch element 35 is connected to a node between the anode of the diode 171 and the first terminal of the capacitor 172 .

The protection circuit 30B having such a gate voltage generation circuit 170 serves as a circuit that protects the first transistor 14A. A negative voltage proportional to the difference (Vin-Vout) between the output voltage of the power supply CS and the voltage (output voltage) between the second power supply terminals 12a and 12b is generated in the capacitor 172 during normal operation. The negative voltage generated in the capacitor 172 is applied between the gate and source of the first transistor 14A as the first switch element 35 is turned on and the second switch element 25 is turned off. By making the voltage lower than the threshold voltage of the first transistor 14A, the blocking state of the first transistor 14A is maintained. As a result, when the load current due to the load LD is small, the charge remains in the second smoothing capacitor 15, and the voltage remains between the pair of second power supply terminals 12a and 12b (output terminal). 14A is cut off, the phenomenon of current flowing from the first terminal 14x of the first inductor 14C to the second terminal 14y is prevented, and the current can flow from the second smoothing capacitor 15 to the first transistor 14A. Suppressed.

- In the third embodiment, a generation circuit that generates a voltage to be input to the inverting input terminal of the operational amplifier 121 of the second generation circuit 120 may be added. In one example, the protection circuit 100A further includes a third generation circuit 190, as shown in FIG. The first generation circuit 110, the second generation circuit 120, and the third generation circuit 190 turn off the first transistor 14A based on the third current induced in the third inductor 191 by the first current of the first inductor 14C. It constitutes a gate voltage generation circuit that generates a gate voltage for The third generation circuit 190 is a closed circuit in which a third inductor 191, a diode 192, and a capacitor 193 are connected in series. More specifically, the second terminal 191 y of the third inductor 191 is connected to the anode of the diode 192 . The cathode of diode 192 is connected to the first terminal of capacitor 193 . A second terminal of the capacitor 193 is connected to a first terminal 191 x of the third inductor 191 . The third inductor 191 is provided so as to be electrically insulated from the first inductor 14C and magnetically coupled to the first inductor 14C. The third inductor 191 is configured to have the same polarity as the first inductor 14C. Specifically, as shown in FIG. 7, the winding start position of the coil of the third inductor 191 is the same as the winding start position of the coil of the first inductor 14C. In this case, the value of inductance between the first inductor 14C and the third inductor 191 becomes a positive value.

A positive voltage is generated across the capacitor 193 in proportion to the difference (Vin-Vout) between the output voltage of the power supply CS and the voltage (output voltage) between the second power supply terminals 12a and 12b during normal operation. By applying this voltage to the negative power supply terminal of the operational amplifier 121 , a negative voltage is generated from the second generation circuit 120 . This voltage is applied between the gate and source of the first transistor 14A as the second switch element 25 is cut off and the first switch element 132 is turned on. The operational amplifier 121 inverts the positive voltage and outputs a negative voltage to the first switch element 102 . When the power supply to the control unit 24 stops, the normally-on first switch element 102 becomes conductive, so the negative voltage output from the operational amplifier 121 is applied to the gate terminal of the first transistor 14A. By setting the voltage to the gate voltage below the threshold voltage of the first transistor 14A, the cut-off state of the first transistor 14A is maintained. When electric charge remains in the second smoothing capacitor 15, reverse current flow to the first transistor 14A can be suppressed.

- In the fourth embodiment, a generation circuit that generates a voltage to be input to the inverting input terminal of the operational amplifier 121 of the second generation circuit 150 may be added. In one example, as shown in FIG. 8, the protection circuit 130A has the same circuit as the third generation circuit 190 (see FIG. 7) of the modification of the fourth embodiment. In this case, the first generator circuit 140, the second generator circuit 150, and the third generator circuit 190 generate the first transistor current based on the third current induced in the third inductor 191 by the first current of the first inductor 14C. A gate voltage generating circuit is configured to generate a gate voltage for turning off 14A.

- In each of the above embodiments and modifications, the second transistor 14B may be a normally-off transistor.
- In each of the above-described embodiments and modifications, a drive circuit that generates a gate voltage for controlling switching between the conductive state and the cut-off state of the second switch element 25 may be provided separately from the drive circuit 21 . In this case, the drive circuit 21 is configured so as to apply a gate voltage to the gate terminal of the first transistor 14A and not apply a gate voltage to the gate terminal of the second switch element 25 .

The protection circuit 30 or the like in each of the above embodiments and modifications may be a circuit that protects the second transistor 14B instead of or in addition to the protection of the first transistor 14A.

- In each of the above-described embodiments and modifications, the control circuit 20 may be provided separately from the power supply device (step-down DC-DC converter 10). That is, the control circuit 20 does not have to be included in the components of the power supply.

10 Step-down DC-DC converter (power supply device)
11a, 11b -- a pair of first power supply terminals 12a, 12b -- a pair of second power supply terminals 14A -- a first transistor 14C -- a first inductor 14x -- a first terminal 14y -- a second terminal 21 -- a drive circuit 21a -- a first output terminal (output terminal)
25 Second switch elements 30, 30A, 30B, 70, 100, 100A, 130, 130A Protection circuits 31, 71, 101, 131 Second inductors 31x, 71x, 101x, 131x First terminals 31y, 71y, 101y, 131y... second terminals 32, 160, 170... gate voltage generation circuits 33, 81, 141, 171... diodes 34, 82, 142, 172... capacitors 35, 72, 102, 132... first switch elements 80, 110 , 140... First generation circuits 111, 161... First diodes 113, 163... First capacitors 112, 162... First backflow prevention diodes 114, 164... Second diodes 116, 166... Second capacitors 115, 165... 2 backflow prevention diodes 117, 167... third diodes 90, 120, 150... second generating circuit

Claims (11)

A protection circuit for protecting the transistor in a power supply device having a normally-on transistor and a first inductor connected to the transistor,
a second inductor electrically insulated from the first inductor and magnetically coupled with the first inductor;
a gate voltage generation circuit for generating a gate voltage for turning off the transistor based on a second current induced in the second inductor by a first current of the first inductor;
a power supply protection circuit. In the gate voltage generation circuit, when the first current flows from the first terminal to the second terminal of the first inductor, the current is induced in the second inductor and flows from the first terminal to the second terminal of the second inductor. 2. The protection circuit of a power supply device according to claim 1, wherein said gate voltage is generated based on said second current. The gate voltage generation circuit is
a diode whose cathode is connected to the first terminal of the second inductor;
a capacitor connected to the anode of the diode;
a first switch element having a first terminal connected to the gate terminal of the transistor and having a second terminal connected between the anode of the diode and the capacitor;
The protection circuit of the power supply device according to claim 2, comprising: The gate voltage generation circuit is
a diode having an anode connected to the second terminal of the second inductor;
a capacitor connected to the cathode of the diode and the first terminal of the second inductor;
an inverting amplifier circuit that converts the positive voltage of the capacitor into a negative voltage and outputs the voltage to the gate terminal of the transistor;
a first switch element having a first terminal connected to the gate terminal of the transistor and having a second terminal connected to the output terminal of the inverting amplifier circuit;
The protection circuit of the power supply device according to claim 2, comprising: 5. The power supply device protection circuit according to claim 3, wherein the first switch element is a normally-on transistor. The gate voltage generation circuit is configured to control the voltage when the first current flows from the first terminal to the second terminal of the first inductor and when the first current flows from the second terminal to the first terminal of the first inductor. 2. The power supply protection circuit of claim 1, wherein both are configured to generate the gate voltage based on the second current flowing through the second inductor. The gate voltage generation circuit is
a first diode having an anode connected to the second terminal of the second inductor;
a first capacitor having a first terminal connected to the cathode of the first diode;
a first backflow prevention diode having an anode connected to the second terminal of the first capacitor and a cathode connected to the second terminal of the second inductor;
a second diode having an anode connected to the first terminal of the second inductor;
a second capacitor having a first terminal connected to the cathode of the second diode;
a second anti-backflow diode having an anode connected to the second terminal of the second capacitor and a cathode connected to the first terminal of the second inductor;
a third diode having a cathode connected to the first terminal of the first capacitor and an anode connected to the first terminal of the second capacitor;
a second generation circuit connected to the first generation circuit for inverting the positive voltage of the first generation circuit to a negative voltage and outputting the negative voltage to the gate terminal of the transistor;
a first switch element having a first terminal connected to the gate terminal of the transistor and having a second terminal connected to the output terminal of the second generation circuit;
The protection circuit of the power supply device according to claim 6, comprising: The power supply device protection circuit according to claim 7, wherein the first switch element is a normally-on transistor. The power supply device further includes a drive circuit electrically connected to the gate terminal of the transistor and applying a gate voltage to the gate terminal of the transistor,
The protection circuit according to any one of claims 1 to 8, further comprising a second switch element having a first terminal connected to the output terminal of the drive circuit and a second terminal connected to the gate terminal of the transistor. Protection circuit for power supply as described. The power supply device protection circuit according to claim 9, wherein the second switch element is a normally-off transistor. A power supply device comprising the protection circuit according to any one of claims 1 to 10.

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