Protection device

Abstract

To provide a protection device capable of quickly protecting a synchronous rectification step-down chopper circuit.SOLUTION: A protection device 1 for protecting a synchronous rectification step-down chopper circuit 2 includes: a switch 10 that is provided between the step-down chopper circuit 2 and a power supply device 3 that supplies power to the step-down chopper circuit 2 and is closed when supplying power; an input current detection part 12 that detects a current value of an input current of the step-down chopper circuit 2; and a control part 16 for opening the switch 10 in the closed state when the current value detected by the input current detection part 12 exceeds a setting upper limit value at the time of a short-circuit failure of a switching element 21 of the step-down chopper circuit 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a protection device for protecting a synchronous rectification type step-down chopper circuit and a load. [Background technology]

[0002] Conventionally, power supply devices have been used to convert the voltage value of a DC voltage output from a DC power supply. An example of such a power supply device is described in Patent Document 1, the source of which is shown below.

[0003] Patent Document 1 describes a power supply device. This power supply device includes a diode rectification type step-down chopper circuit that steps down a DC voltage from a diode bridge, and an isolated DC / DC converter that is provided in series with the step-down chopper circuit at a downstream stage. When a switching element in the step-down chopper circuit short-circuits and the output voltage of the step-down chopper circuit becomes higher than a predetermined value, the power supply device opens the switching element in the DC / DC converter to stop operation of the DC / DC converter, preventing overvoltage from being applied to electronic components in the DC / DC converter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-178342 Summary of the Invention [Problem to be solved by the invention]

[0005] A step-down chopper circuit includes a coil and a capacitor. Therefore, when a switching element of the step-down chopper circuit is short-circuited, the time from when the step-down chopper circuit is started until the output voltage exceeds a predetermined value is determined by the time constants of the coil and the capacitor. Therefore, the protection configuration described in Patent Document 1 cannot quickly protect the step-down chopper circuit depending on the time constants of the coil and the capacitor.

[0006] Furthermore, from the viewpoint of achieving high efficiency, a synchronous rectification type step-down chopper circuit is sometimes used as the step-down chopper circuit. When a configuration for monitoring and protecting the output voltage as described in Patent Document 1 is applied to such a synchronous rectification type step-down chopper circuit, if the low-side switching element is closed in the event of a short-circuit fault in the high-side switching element, the output voltage of the step-down chopper circuit cannot increase, and current flows to the low-side switching element via the high-side switching element, making it impossible to protect the step-down chopper circuit.

[0007] Therefore, there is a need for a protection device that can quickly protect a synchronous rectification type step-down chopper circuit. [Means for solving the problem]

[0008] A characteristic configuration of the protection device according to the present invention is that it is a protection device for protecting a synchronous rectification type step-down chopper circuit, and includes: a switch that is provided between the step-down chopper circuit and a power supply device that supplies power to the step-down chopper circuit and is closed when the power is supplied; an input current detection unit that detects a current value of an input current to the step-down chopper circuit; and a control unit that changes the switch from the closed state to an open state when the current value detected by the input current detection unit exceeds a set upper limit value in the event of a short-circuit failure of a switching element on a high side of the step-down chopper circuit.

[0009] As described above, in a synchronous rectification step-down chopper circuit, when a short-circuit fault occurs in the high-side switching element, if the low-side switching element is closed, current flows to the low-side switching element via the high-side switching element, increasing the input current of the synchronous rectification step-down chopper circuit. According to the above characteristic configuration, when this input current exceeds a set upper limit, the control unit opens the switch, thereby stopping the power supply to the synchronous rectification step-down chopper circuit. This makes it possible to quickly protect the synchronous rectification step-down chopper circuit. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a protection device applied to a step-down chopper circuit. [Figure 2] FIG. 10 is a timing chart of the protection device and the step-down chopper circuit. [Figure 3] FIG. 1 is a diagram showing a protection device applied to two step-down chopper circuits. [Figure 4] FIG. 1 is a diagram showing a protection device applied to two step-down chopper circuits. DETAILED DESCRIPTION OF THE INVENTION

[0011] The protection device according to the present invention is configured to have a function of protecting a synchronous rectification type step-down chopper circuit. However, the protection device is not limited to the following embodiment, and various modifications are possible within the scope of the gist thereof.

[0012] [First embodiment] The protection device 1 of this embodiment will be described below. Fig. 1 is a diagram schematically illustrating the configuration of the protection device 1 applied to a synchronous rectification type step-down chopper circuit 2. As shown in Fig. 1, the protection device 1 is configured with a switch 10, an input current detection unit 12, an output current detection unit 14, and a control unit 16, and each functional unit is constructed using hardware or software, or both, with a CPU as a core component, in order to perform processing related to the protection of the synchronous rectification type step-down chopper circuit 2.

[0013] 1, the step-down chopper circuit 2 includes a high-side switching element 21, a low-side switching element 22, a coil 23, and a capacitor 24. The step-down chopper circuit 2 is configured to receive power supply from the power supply device 3 across a first power supply line 91 and a second power supply line 92, and to output DC power across a third power supply line 93 and a fourth power supply line 94. In this embodiment, the fourth power supply line 94 is connected to the second power supply line 92. Here, "connected" means that the power supplies are electrically connected in a state where they have the same potential, and this also applies to the following description.

[0014] 1, the switching element 21 and the switching element 22 are configured using n-channel MOS-FETs (metal-oxide-semiconductor field-effect transistors). The drain terminal of the switching element 21 is connected to a first power supply line 91, and the source terminal of the switching element 22 is connected to a second power supply line 92. The source terminal of the switching element 21 is connected to the drain terminal of the switching element 22. The gate terminals of the switching element 21 and the switching element 22 are each connected to the control unit 16.

[0015] The switching element 21 and the switching element 22 are each provided with a diode 21D, 22D across the source terminal and the drain terminal, the cathode terminal of which is connected to the drain terminal and the anode terminal of which is connected to the source terminal.

[0016] One terminal of the coil 23 is connected to the source terminal of the switching element 21. The other terminal of the coil 23 is connected to a third power supply line 93. A capacitor 24 is provided between the other terminal of the coil 23 and a fourth power supply line 94.

[0017] The switching element 21 and the switching element 22 are each driven by the control unit 16, but are driven complementarily so that they are not in the closed state at the same time. Specifically, when the switching element 21 is in the closed state, the switching element 22 is driven to the open state, and when the switching element 22 is in the closed state, the switching element 21 is driven to the open state. Of course, a dead time during which both the switching element 21 and the switching element 22 are in the open state may be provided between the timing when the switching element 21 is changed from the closed state to the open state and the timing when the switching element 22 is changed from the open state to the closed state, and between the timing when the switching element 22 is changed from the closed state to the open state and the timing when the switching element 21 is changed from the open state to the closed state.

[0018] In this embodiment, the closed state means the on state, i.e., the state in which the gate voltage is equal to or greater than the threshold voltage of the MOS-FET and the drain current flows, and the open state means the off state, i.e., the state in which the gate voltage is less than the threshold voltage of the MOS-FET and the drain current does not flow.

[0019] The step-down chopper circuit 2 converts the voltage value of the DC power supplied from the power supply device 3 into DC power composed of a voltage having a lower voltage value than the voltage value of the DC power supplied from the power supply device 3. A detection result corresponding to the potential difference between the third power supply line 93 and the fourth power supply line 94 is transmitted to the control unit 16 from a voltage detection unit (not shown) provided across the third power supply line 93 and the fourth power supply line 94. The control unit 16 drives the switching elements 21 and 22 by feedback control based on the detection result.

[0020] In this embodiment, the switch 10 is provided between the step-down chopper circuit 2 and the power supply device 3 that supplies power to the step-down chopper circuit 2. In the example of FIG. 1 , the switch 10 is provided across the positive terminal of the power supply device 3 and the first power supply line 91. In this embodiment, an n-channel MOS-FET is used for the switch 10. The drain terminal of the switch 10 is connected to the positive terminal of the power supply device 3 via a fifth power supply line 95, and the source terminal of the switch 10 is connected to the first power supply line 91. Therefore, the switch 10 is provided as a load switch. The gate terminal of the switch 10 is connected to the control unit 16.

[0021] A diode 10D is provided across the source and drain terminals of the switch 10. The cathode terminal is connected to the drain terminal and the anode terminal is connected to the source terminal. The switch 10 is closed by the control unit 16 when power is supplied to the step-down chopper circuit 2.

[0022] The input current detection unit 12 detects the current value of the input current to the step-down chopper circuit 2. The input current to the step-down chopper circuit 2 is a current input from the power supply device 3 to the step-down chopper circuit 2, and in this embodiment corresponds to the current flowing through a fifth power supply line 95 that connects the positive terminal of the power supply device 3 and the drain terminal of the switch 10.

[0023] The input current detection unit 12 may be of a type that is directly connected to the fifth power supply line 95 and detects a current value, such as a moving coil ammeter or a moving iron ammeter. Alternatively, the input current detection unit 12 may be of a type that is clamped to the fifth power supply line 95 and detects the magnetic flux density of the magnetic flux generated around the fifth power supply line 95 in accordance with the current flowing through the fifth power supply line 95, and detects the current value in accordance with the detection result of this magnetic flux density. The detection result of the input current detection unit 12 is transmitted to the control unit 16.

[0024] The output current detection unit 14 detects the current value of the output current of the step-down chopper circuit 2. The output current of the step-down chopper circuit 2 is a current flowing from the step-down chopper circuit 2 to a load (not shown), and corresponds to the current flowing through the third power supply line 93 in this embodiment.

[0025] Like the input current detection unit 12, the output current detection unit 14 may be of a type that is directly connected to the third power supply line 93 and detects a current value, or may be of a type that is clamped to the third power supply line 93 and detects the magnetic flux density of the magnetic flux generated around the fifth power supply line 95 in accordance with the current flowing through the fifth power supply line 95, and detects the current value in accordance with the detection result of this magnetic flux density. The detection result of the output current detection unit 14 is transmitted to the control unit 16.

[0026] As described above, the switching element 21 and the switching element 22 are complementarily driven by the control unit 16. That is, the control unit 16 drives the switching elements 21 and 22 to alternate between a first state in which the switching element 21 is in a closed state and the switching element 22 is in an open state, and a second state in which the switching element 21 is in an open state and the switching element 22 is in a closed state. In the first state, the step-down chopper circuit 2 allows a current to flow through the switching element 21 and the coil 23, and in the second state, a current to flow through the switching element 22 and the coil 23.

[0027] When considering a MOS-FET failure, it generally occurs in a short circuit mode where the source terminal and the drain terminal are shorted (short circuit failure). If the step-down chopper circuit 2 is not provided with the protection device 1, for example, if the switching element 21 fails in a short circuit mode, the potential of the third power supply line 93 becomes higher than the desired value, and the control unit 16 drives the switching element 21 to open. Then, because the control unit 16 does not know that the switching element 21 has failed in the short circuit mode, it drives the switching element 22 to close. As a result, current continues to flow from the power supply device 3 to the switching element 22 via the switching element 21, leading to failure of the switching element 22 as well.

[0028] On the other hand, in a case where the protection device 1 is provided in the step-down chopper circuit 2 as in this embodiment, if the switching element 21 fails in the short mode and the control unit 16 drives the switching element 21 to the open state and the switching element 22 to the closed state, a current flows from the power supply device 3 to the switching element 22 via the switching element 21. However, before the switching element 22 fails, the input current detection unit 12 detects a current value that is greater than the expected current value of the input current, and the control unit 16 changes the switch 10 from the closed state to the open state. That is, when the switching element 21 on the high side of the step-down chopper circuit 2 fails in the short mode (short-circuit failure), the control unit 16 changes the closed state of the switch 10 to the open state when the current value detected by the input current detection unit 12 exceeds a set upper limit. This prevents a continuous current from flowing from the power supply device 3 to the switching element 22 via the switching element 21, thereby preventing a failure of the switching element 22. The set upper limit value should be set to a value that is greater than the current value (effective value) of the input current in a steady state and smaller than the current value of the input current when both switching element 21 and switching element 22 are in a closed state.

[0029] Furthermore, the protection device 1 can cut off the overcurrent to the step-down chopper circuit 2 and protect the step-down chopper circuit 2 not only in a short mode in which the source terminal and drain terminal of the switching element 21 are short-circuited, but also when the source terminal and drain terminal of the switching element 22 are short-circuited.

[0030] Furthermore, if any abnormality occurs on the load side of the step-down chopper circuit 2, the current value of the output current of the step-down chopper circuit 2 increases. In this case, the detection result of the output current detection unit 14 increases above the current value in the steady state. Therefore, when the current value detected by the output current detection unit 14 exceeds a set upper limit, the control unit 16 switches the switch 10 from the closed state to the open state. This prevents current from flowing from the power supply device 3 to the load side via the step-down chopper circuit 2, thereby preventing overcurrent on the load side. Note that this set upper limit is different from the set upper limit used when switching the switch 10 from the closed state to the open state in response to the detection result of the input current detection unit 12. It is preferable that this set upper limit is set to a value greater than the current value (effective value) of the output current in the steady state and smaller than the current value of the output current when a pair of input terminals of the load are short-circuited.

[0031] In the example of FIG. 1, the output current detection unit 14 is provided on the load side of one terminal of the capacitor 24. However, by providing the output current detection unit 14 on the coil 23 side of one terminal of the capacitor 24, it is possible to configure the switch 10 to be in an open state to stop the flow of current to the step-down chopper circuit 2 when, for example, both ends of the capacitor 24 are short-circuited (when the output of the step-down chopper circuit 2 is short-circuited).

[0032] In the example of FIG. 1, the fuse 80 is provided in the subsequent stage of the output current detection unit 14, but the fuse 80 does not necessarily have to be provided.

[0033] FIG. 2 shows an example of a timing chart of the protection device 1 and the step-down chopper circuit 2. (1) in FIG. 2 is the voltage waveform at point A in FIG. 1 (the voltage waveform at the gate terminal of the switch 10). (2) in FIG. 2 is the voltage waveform at point B in FIG. 1 (the voltage waveform at the gate terminal of the switching element 21). (3) in FIG. 2 is the voltage waveform at point C as viewed from point D in FIG. 1 (the potential difference between the drain terminal and the source terminal of the switching element 21). (4) in FIG. 2 is the voltage waveform at point E in FIG. 1 (the voltage waveform at the gate terminal of the switching element 22). (5) in FIG. 2 is the current waveform at point F in FIG. 1 (the current waveform of the input current). (6) in FIG. 2 is the current waveform at point G in FIG. 1 (the current waveform of the output current). For ease of understanding, it is assumed in FIG. 2 that the step-down chopper circuit 2 is in a steady state at time t0.

[0034] Between t0 and t1, the switch 10 is closed (#1), and DC power is supplied from the power supply device 3 to the step-down chopper circuit 2. Furthermore, the switching elements 21 and 22 are driven complementarily to each other (#2, #3), and an output current of a desired current value is output from the step-down chopper circuit 2 (#4).

[0035] At t1, even though switching element 21 is in the open state, the potential difference between the drain terminal and source terminal of switching element 21 is zero (#5). In other words, switching element 21 is in the short mode failure state at t1. When switching element 22 is closed in this state (#6), the input current increases (#7). When the input current exceeds the set upper limit, switch 10 is opened (#8). This cuts off the current to step-down chopper circuit 2 (#9), and operation of step-down chopper circuit 2 stops.

[0036] As described above, the protection device 1 of this embodiment cuts off the power supplied to the step-down chopper circuit 2 depending on the magnitude of the input current (magnitude of the current value) of the step-down chopper circuit 2, thereby preventing an overcurrent from flowing to the step-down chopper circuit 2 and the load side of the step-down chopper circuit 2, and thereby protecting the step-down chopper circuit 2 and the load side of the step-down chopper circuit 2 by preventing an overcurrent from flowing or an overvoltage from being applied. Furthermore, the protection device 1 is configured without including any components that increase the time constant, such as a capacitor or a coil, between the input current detection unit 12 and the switching elements 21, 22, so that there is no delay (lengthening) in the time from when a fault occurs in short mode until the fault is detected, and the step-down chopper circuit 2 can be quickly protected.

[0037] Here, in FIG. 1, an example has been described in which the protection device 1 is applied to a single step-down chopper circuit 2, but as shown in FIG. 3, it is also possible to apply the protection device 1 to multiple (two in the example of FIG. 3) step-down chopper circuits 2 arranged in parallel with each other.

[0038] 3, one of the two step-down chopper circuits 2, step-down chopper circuit 2A, is configured to include a high-side switching element 21A, a low-side switching element 22A, a coil 23A, and a capacitor 24, and the other of the two step-down chopper circuits 2, step-down chopper circuit 2B, is configured to include a high-side switching element 21B, a low-side switching element 22B, a coil 23B, and a capacitor 24. In other words, capacitor 24 is shared by step-down chopper circuit 2A and step-down chopper circuit 2B.

[0039] In addition, each of switching element 21A and switching element 22A is provided with a diode 21DA, 22DA across its source terminal and drain terminal, with the cathode terminal connected to the drain terminal and the anode terminal connected to the source terminal, and each of switching element 21B and switching element 22B is provided with a diode 21DB, 22DB across its source terminal and drain terminal, with the cathode terminal connected to the drain terminal and the anode terminal connected to the source terminal.

[0040] In this case, power can be supplied to the load from two step-down chopper circuits 2A, 2B, thereby increasing the supply capacity compared to when a single step-down chopper circuit 2 is used. Therefore, when a short-circuit fault occurs in the high-side switching element 21, the set upper limit value, which is the threshold for switching the switch 10 from the closed state to the open state, can be set according to the increased power supply. In this case, if either one of the two high-side switching elements 21A, 21B fails in the short-circuit mode, the protection device 1 can provide protection.

[0041] Second Embodiment Next, a second embodiment of the protection device 1 will be described. Fig. 4 is a diagram illustrating the protection device 1 of the second embodiment. In the example of Fig. 4, similar to the step-down chopper circuit 2 shown in Fig. 3, the protection device 1 is applied to two step-down chopper circuits 2A and 2B that are provided in parallel with each other.

[0042] The example in Fig. 4 is similar to the example in Fig. 3 in that a switch 10 is provided between the power supply device 3 and the step-down chopper circuits 2A, 2B, but differs from the example in Fig. 3 in that a plurality of (two in the example in Fig. 4) input current detection units 12 are provided in each of the step-down chopper circuits 2A, 2B. The following describes the protection device 1 of this embodiment, focusing mainly on the differences from the example in Fig. 3.

[0043] The step-down chopper circuit 2A is provided with an input current detection unit 12A, and the step-down chopper circuit 2B is provided with an input current detection unit 12B. As shown in FIG. 4, the first power supply line 91 branches at a node n. The input current detection unit 12A is provided between the node n and the switching element 21A, and the input current detection unit 12B is provided between the node n and the switching element 21B. The input current detection unit 12A detects the current value of the input current to the step-down chopper circuit 2A, and the input current detection unit 12B detects the current value of the input current to the step-down chopper circuit 2B. Therefore, it is preferable that the input current detection unit 12A and the input current detection unit 12B set upper limit values ​​for the step-down chopper circuit 2A and the step-down chopper circuit 2B, respectively.

[0044] As a result, when the switching element 21A of the step-down chopper circuit 2A fails in the short mode and the current value detected by the input current detection unit 12A exceeds the set upper limit value, the control unit 16 can change the switch 10 from the closed state to the open state, and when the switching element 21B of the step-down chopper circuit 2B fails in the short mode and the current value detected by the input current detection unit 12B exceeds the set upper limit value, the control unit 16 can change the switch 10 from the closed state to the open state.

[0045] Other Embodiments

[0046] Next, other embodiments of the protection device 1 will be described.

[0047] In the above embodiment, the switch 10 is configured using an n-channel MOS-FET, but the switch 10 may be configured using a p-channel MOS-FET. Alternatively, the switch 10 may be configured using an IGBT (Insulated Gate Bipolar Transistor) or a bipolar transistor.

[0048] In the above embodiment, the control unit 16 has been described as controlling the driving of the step-down chopper circuit 2 and the driving of the switch 10, but the control unit that drives the step-down chopper circuit 2 and the control unit that drives the switch 10 may be different control units.

[0049] In the above embodiment, in FIGS. 3 and 4, an example has been described in which the capacitor 24 is shared when configuring a plurality of step-down chopper circuits 2, but the capacitor 24 may be provided for each of the plurality of step-down chopper circuits 2.

[0050] In the above embodiment, an example was given in which a plurality of step-down chopper circuits 2 are configured and a coil 23 is provided for each step-down chopper circuit 2, but a single coil 23 may be shared by a plurality of step-down chopper circuits 2.

[0051] In the above embodiment, the protection device 1 is described as including the output current detection unit 14, but the protection device 1 does not necessarily have to include the output current detection unit 14.

[0052] In the above embodiment, an example has been described in which a single switch 10 is provided when multiple step-down chopper circuits 2 are provided as shown in Fig. 4, but a configuration including multiple switches 10 is also possible. Specifically, in Fig. 4, instead of providing a switch 10 on the first power supply line 91, a switch 10 may be provided between node n and switching element 21A, and a switch 10 may be provided between node n and switching element 21B. In this case, it becomes possible to stop driving the step-down chopper circuit 2 of the two step-down chopper circuits 2A, 2B whose input current value exceeds the set upper limit, and continue driving the step-down chopper circuit 2 whose input current value is less than the set upper limit.

[0053] In the above embodiment, an example was described in which the switch 10 is provided between the positive terminal of the power supply device 3 and the step-down chopper circuit 2, but the switch 10 may also be provided between the negative terminal of the power supply device 3 and the step-down chopper circuit 2.

[0054] In the above embodiment, an example was described in which the number of the step-down chopper circuits 2 was two, but the number of the step-down chopper circuits 2 may be three or more.

[0055] In the above embodiment, an example has been described in which the protection device 1 protects a synchronous rectification type step-down chopper circuit 2. The protection device 1 can be used to protect a switching element or coil constituting a diode rectification type step-up chopper circuit from a short-circuit fault, or can be used to protect a switching element or coil constituting a diode rectification type step-down chopper circuit from a short-circuit fault. Furthermore, the protection device 1 can be used to protect a switching element or coil constituting a diode rectification type inverting chopper circuit from a short-circuit fault.

[0056] [Summary of the above embodiment] The protection device 1 described above will now be outlined.

[0057] (1) The protection device 1 protects a synchronous rectification type step-down chopper circuit 2, and is provided between the step-down chopper circuit 2 and a power supply device 3 that supplies power to the step-down chopper circuit 2. The protection device 1 includes: a switch 10 that is closed when power is supplied; an input current detection unit 12 that detects the current value of the input current to the step-down chopper circuit 2; and a control unit 16 that changes the closed state of the switch 10 to an open state when the current value detected by the input current detection unit 12 exceeds a set upper limit value in the event of a short-circuit fault in the high-side switching element 21 of the step-down chopper circuit 2.

[0058] In the synchronous rectification step-down chopper circuit 2, when the high-side switching element 21 experiences a short-circuit fault and the low-side switching element 22 is closed, a current flows to the low-side switching element 22 via the high-side switching element 21, increasing the input current of the synchronous rectification step-down chopper circuit 2. According to this configuration, when this input current exceeds a set upper limit, the control unit 16 opens the switch 10, thereby stopping the power supply to the synchronous rectification step-down chopper circuit 2. This makes it possible to quickly protect the synchronous rectification step-down chopper circuit 2.

[0059] (2) In the protection device 1 described in (1), the step-down chopper circuit 2 can also be applied to a case where a plurality of step-down chopper circuits 2 are provided in parallel with each other.

[0060] According to this configuration, even if a plurality of step-down chopper circuits 2 are provided to increase the current capacity, the protection device 1 can provide protection.

[0061] (3) In the protection device 1 described in (1), it is preferable that the plurality of input current detection units 12 are provided for the plurality of step-down chopper circuits 2, respectively.

[0062] According to this configuration, it is possible to easily identify which of the multiple step-down chopper circuits 2 has a switching element 21 in a short-circuited state.

[0063] (4) The protection device 1 described in (1) or (2) preferably further comprises an output current detection unit 14 that detects the current value of the output current of the step-down chopper circuit 2, and the control unit 16 changes the switch 10 from a closed state to an open state when the current value detected by the output current detection unit 14 exceeds a set upper limit value.

[0064] According to this configuration, the switch 10 is opened when an abnormality occurs on the load side of the step-down chopper circuit 2, thereby protecting the step-down chopper circuit 2. [Industrial Applicability]

[0065] The technology according to the present disclosure can be used in a protection device that protects a synchronous rectification type step-down chopper circuit. [Explanation of symbols]

[0066] 1: protection device, 2: step-down chopper circuit, 2A: step-down chopper circuit, 2B: step-down chopper circuit, 10: switch, 12: input current detection unit, 12A: input current detection unit, 12B: input current detection unit, 14: output current detection unit, 16: control unit

Claims

1. A protection device for protecting a synchronous rectification type step-down chopper circuit, a switch provided between the step-down chopper circuit and a power supply device that supplies power to the step-down chopper circuit, the switch being closed when power is supplied; an input current detection unit that detects a current value of an input current of the step-down chopper circuit; a control unit that changes the switch from the closed state to an open state when the current value detected by the input current detection unit exceeds a set upper limit value in the event of a short-circuit fault in a switching element on a high side of the step-down chopper circuit; A protective device comprising:

2. 2. The protection device according to claim 1, wherein a plurality of the step-down chopper circuits are provided in parallel with each other.

3. 3. The protection device according to claim 2, wherein a plurality of the input current detection units are provided for a plurality of the step-down chopper circuits, respectively.

4. further comprising an output current detection unit that detects a current value of the output current of the step-down chopper circuit, The protection device according to claim 1 or 2, wherein the control unit changes the switch from the closed state to the open state when the current value detected by the output current detection unit exceeds a set upper limit value.

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