Short circuit detection circuit

Abstract

The short-circuit detection circuit includes: a capacitor element connected to a high potential side of a semiconductor switching element via a series connection of a diode and a resistance element; a short-circuit determination section that detects a terminal voltage of one terminal of the capacitor element, and determines that the semiconductor switching element is short-circuited when the terminal voltage is equal to or higher than a threshold voltage; and a voltage control section provided between the other terminal of the capacitor element and a low potential side of the semiconductor switching element, and performing switching of conduction and cutoff between the capacitor element and the semiconductor switching element, and applying a bias voltage between the capacitor element and the semiconductor switching element when the conduction is performed, and the short-circuit detection circuit can rapidly determine the short-circuit of the semiconductor switching element.

Description

TECHNICAL FIELD

[0001] The present application relates to, for example, a short-circuit detection circuit that detects a short circuit of a semiconductor switching element. BACKGROUND

[0002] In the past, as a function of detecting a short circuit of a semiconductor switching element, a method of detecting a voltage between terminals of the semiconductor switching element (DESAT method) is known. In a specific example of the "voltage between terminals" described here, if the semiconductor switching element is, for example, an insulated gate bipolar transistor (IGBT), the "voltage between terminals" is a voltage between a collector and an emitter, and if the semiconductor switching element is a MOSFET, the "voltage between terminals" is a voltage between a source and a drain. Generally, when the semiconductor switching element is in an on state, the voltage between the terminals of the semiconductor switching element decreases and stabilizes at a certain minimum voltage. On the other hand, when the semiconductor switching element becomes in a short-circuit state, the voltage between the terminals of the semiconductor switching element rises due to an overcurrent. By the rise of the voltage between the terminals, the voltage between the terminals becomes an abnormal voltage that is not generated in the on state. By detecting the abnormal voltage, it is possible to detect a short circuit of the semiconductor switching element (for example, refer to Patent Literature 1).

[0003] Here, in the method disclosed in Patent Literature 1, a high-voltage diode and a capacitor element are provided between a semiconductor device driving circuit and a semiconductor switching element, and the capacitor element is charged when the semiconductor switching element is in a short-circuit state, thereby detecting that the semiconductor switching element is in a short-circuit state. Specifically, in a case where the voltage of a terminal VDSH rises by charging the capacitor element by a constant current circuit and the voltage of the terminal VDSH becomes a constant value or more, it is determined that a short circuit has occurred in the semiconductor switching element.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: WO2014 / 115272 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, in the DESAT method in the semiconductor device of Patent Literature 1, the time until the determination that the semiconductor switching element is short-circuited is made is in a state where the short-circuit of the semiconductor switching element continues, and during this period, a failure can occur in the semiconductor switching element itself or in a mechanism upstream of the power conversion device that supplies power to the power conversion device due to heat generation at the time of short-circuit. Therefore, in the DESAT method, it is required to promptly perform processing from the occurrence of short-circuit until the determination is made. Therefore, a method of increasing the current that flows through the constant current circuit is generally known, but the increase in the consumption current of the circuit is not suitable for the power conversion device that is required to be power saving. On the other hand, although a method of increasing the speed of charging by reducing the capacitance of the capacitor element is known, since the terminal VDSH is easily affected by a variation in voltage due to external factors, there is a problem that a false determination of short-circuit can occur due to other influences such as noise.

[0009] The present application has been made to solve the above-described technical problem, and has an object to provide a short-circuit detection circuit capable of promptly performing determination of short-circuit of a semiconductor switching element without trying to achieve an increase in the charging current of a capacitor element and a reduction in the capacitance of the capacitor element.

[0010] Technical means for solving the technical problem

[0011] The short-circuit detection circuit disclosed in the present application is characterized by including: a capacitor element connected to a high potential side of a semiconductor switching element via a diode and a resistance element connected in series; a short-circuit determination section that detects a terminal voltage of one terminal of the capacitor element, and determines that the semiconductor switching element is short-circuited when the terminal voltage is equal to or higher than a threshold voltage; and a voltage control section provided between the other terminal of the capacitor element and a low potential side of the semiconductor switching element, and performing switching between conduction and cutoff between the capacitor element and the semiconductor switching element, and applying a bias voltage between the capacitor element and the semiconductor switching element when the conduction is performed.

[0012] Effects of the Invention

[0013] According to the short-circuit detection circuit disclosed in the present application, the following effects are obtained: in the case where the semiconductor switching element is short-circuited, by performing charging of the capacitor element only in a range higher than a set bias voltage, it is possible to promptly perform determination of detection of short-circuit of the semiconductor switching element without increasing the current that flows through the constant current circuit. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a circuit block diagram showing a system configuration including a semiconductor switching element to which the short-circuit detection circuit according to Embodiment 1 is connected.

[0015] Figure 2 is a timing chart for explaining an effect resulting from the operation of the short-circuit detection circuit according to Embodiment 1.

[0016] Figure 3 is a circuit block diagram showing a system structure including a semiconductor switching element to which the short-circuit detection circuit according to Embodiment 2 is connected.

[0017] Figure 4 is a circuit block diagram showing a system structure including a semiconductor switching element to which the short-circuit detection circuit according to Embodiment 3 is connected. DETAILED DESCRIPTION

[0018] Embodiment 1.

[0019] Figure 1 is a circuit block diagram showing a system structure including a semiconductor switching element to which the short-circuit detection circuit according to Embodiment 1 is connected. Figure 2 is a timing chart for explaining an effect resulting from the operation of the short-circuit detection circuit according to Embodiment 1. The present application is applied to a short-circuit detection circuit that detects a short-circuit of a semiconductor switching element of an inverter of a power conversion device for driving an electric motor of an automobile.

[0020] First, the configuration of the short-circuit detection circuit according to Embodiment 1 will be described. Figure 1 The configuration of the short-circuit detection circuit according to Embodiment 1 will be described. The short-circuit detection circuit 1 is configured by a constant current circuit 2, a short-circuit determination section 3 that determines a short-circuit of the semiconductor switching element 9 in accordance with a terminal voltage of a terminal 8 connected to the constant current circuit 2, a diode 4 whose cathode is connected to a terminal on the high potential side of the semiconductor switching element 9, a resistance element 5 and a capacitance element 6 connected between the diode 4 and the terminal 8, and a voltage control section 7 connected to the terminal 8, the capacitance element 6, and a terminal on the low potential side of the semiconductor switching element 9. Note that the difference from the general existing configuration is the presence or absence of the voltage control section 7, in which, in the existing configuration, the capacitance element 6 is directly connected to the low potential side of the semiconductor switching element 9. Figure 1

[0021] The short-circuit detection circuit 1 is configured by a constant current circuit 2, a short-circuit determination section 3 that determines a short-circuit of the semiconductor switching element 9 in accordance with a terminal voltage of a terminal 8 connected to the constant current circuit 2, a diode 4 whose cathode is connected to a terminal on the high potential side of the semiconductor switching element 9, a resistance element 5 and a capacitance element 6 connected between the diode 4 and the terminal 8, and a voltage control section 7 connected to the terminal 8, the capacitance element 6, and a terminal on the low potential side of the semiconductor switching element 9. Note that the difference from the general existing configuration is the presence or absence of the voltage control section 7, in which, in the existing configuration, the capacitance element 6 is directly connected to the low potential side of the semiconductor switching element 9.

[0022] The voltage control section 7 is configured by a voltage detection section 7a that performs comparison determination and amplification of the terminal voltage of the terminal 8, a switch 7b provided between the capacitance element 6 and the terminal on the low potential side of the semiconductor switching element 9 and serving as an active element that performs conduction and cutoff, and a bias voltage source 7c connected to the switch 7b. These configurations are the same as the circuit configuration of a so-called shunt regulator. Figure 1 ​The example shown illustrates the use of a comparator as the voltage detection unit 7a. Another example is the use of a bipolar transistor as a switch 7b, with its base terminal connected to the voltage detection unit 7a, its collector terminal connected to the capacitor element 6, and its emitter terminal connected to the bias voltage source 7c. The bias voltage source 7c is an example using a battery.

[0023] Next, regarding the relationship between the short-circuit detection action and the detection time of semiconductor switching elements, using... Figure 2 The timing diagram shown illustrates the differences between the structure of this embodiment 1 and the conventional structure.

[0024] First of all, Figure 2 In the conventional structure shown in (a), when the semiconductor switching element 9 is short-circuited, the terminal voltage Vd of terminal 8 rises at a constant slope (Id / Cd) based on the output current Id of the constant current circuit 2 and the capacitance Cd of the capacitor element 6. When the threshold voltage used to determine the short circuit of the semiconductor switching element 9 is set to Vth, the short-circuit determination unit 3 detects the detection time Td1, which is the time it takes for the terminal voltage Vd of terminal 8 to reach the threshold voltage Vth.

[0025] Here, as Figure 2 As shown in (a), the detection time Td1 for the short circuit determination unit 3 to determine that a short circuit has occurred is Td1 = Cd × Vth / Id. Therefore, when the terminal voltage Vd of terminal 8 is detected to reach the threshold voltage Vth, the short circuit determination unit 3 determines that the semiconductor switching element 9 is short-circuited and outputs the output voltage Vout to notify the external device (not shown) of the detection time Td1 (the case where the output voltage rises is shown here).

[0026] In contrast, Figure 2 (b) In the structure of Embodiment 1 shown, the switch 7b is in the open state as the initial state of the voltage control unit 7. In this state, the low potential side of the capacitor element 6 is not electrically fixed, and its function as a capacitor is not utilized. Therefore, the capacitor element 6 with capacitance Cd is not charged, and the terminal voltage Vd of the terminal 8 rises with a steep slope. Specifically, since charging is performed only through the tiny parasitic capacitance component generated in the wiring of the terminal 8, when the parasitic capacitance of the wiring is Ck, the slope of the voltage rise is (Id / Ck). Although it also depends on the circuit structure, the parasitic capacitance component is generally very small relative to the capacitor element 6 (Cd >> Ck).

[0027] In the case where the semiconductor switching element 9 is short-circuited, after the terminal voltage Vd of the terminal 8 reaches the bias voltage Voff set in advance by the bias voltage source 7c, the switch 7b is turned on by the output voltage Va of the voltage detection section 7a, and the low potential side of the capacitor element 6 is fixed at the bias voltage Voff. That is, when the terminal voltage Vd and the bias voltage Voff become the same potential, the conduction between the capacitor element 6 and the semiconductor switching element 9 is made. Thereby, the charging of the capacitor element 6 to the capacitor Cd is started, and the slope of the voltage rise changes to (Id / Cd). When the threshold voltage for determining the short-circuit of the semiconductor switching element 9 is set to Vth, the short-circuit determination section 3 detects the detection time Td2 which is the time when the terminal voltage Vd of the terminal 8 reaches the threshold voltage Vth.

[0028] Here, as shown in Figure 2 (b), the detection time Td2 determined as short-circuited by the short-circuit determination section 3 is Td2=Ck x Voff / Id+Cd x (Vth-Voff) / Id. Thereby, when the terminal voltage Vd of the terminal 8 reaches the threshold voltage Vth is detected, the short-circuit determination section 3 determines that the semiconductor switching element 9 is short-circuited, and outputs the output voltage Vout to notify the detection time Td2 to the external device (not shown) (here, the case where the output voltage rises is shown).

[0029] Therefore, in the case where the semiconductor switching element 9 is short-circuited, in Figure 2 (b), the terminal voltage Vd of the terminal 8 sharply increases to the bias voltage Voff, and then rises with the slope (Id / Cd). On the other hand, in Figure 2 (a) which does not have the voltage control section, the terminal voltage Vd of the terminal 8 slowly rises with the slope (Id / Cd). The time until the threshold voltage Vth of Figure 2 (b) is reached (the detection time Td2) is shorter than the time until the threshold voltage Vth of Figure 3 (a) is reached (the detection time Td1). Thereby, the short-circuit of the semiconductor switching element 9 can be detected in a shorter time.

[0030] As an example, in the case where the parasitic capacitance Ck is sufficiently small so as to have no effectiveness with respect to the capacitance Cd of the capacitor element 6, and the bias voltage Voff is set to half of the threshold voltage Vth, the detection time Td2 (=Cd x (0.5 x Vth) / Id=1 / 2 x Td1) of the short-circuit of the semiconductor switching element 9 can achieve the detection of the short-circuit in half the time of the detection time Td1 of the short-circuit of the semiconductor switching element 9 in the conventional structure which does not have the voltage control section.

[0031] Further, the bias voltage Voff must be set to be smaller than the threshold voltage Vth. The reason for this is that, in order not to erroneously detect a short circuit due to a transient factor caused by external disturbance noise, in the voltage range around the threshold voltage Vth, the filtering effect of the capacitive element 6 needs to be exerted.

[0032] Specifically, in the normal driving state of the usual semiconductor switching element 9, the sum of the voltage generated at the terminal on the high potential side due to the current flowing between the on-resistance of the semiconductor switching element 9 and the terminal, the on-voltage of the diode 4, and the voltage generated at the resistive element 5 by the output current Id of the constant current circuit 2 is generated at the terminal 8 as a stable voltage component, and thus it is desirable to set the bias voltage Voff to be equal to or smaller than the stable voltage so that the filtering effect can be exerted in a range higher than the stable voltage. That is, the bias voltage Voff is set to be equal to or smaller than the terminal voltage Vd generated at the input of the short circuit determination section 3 when the semiconductor switching element 9 is normally driven, and the capacitive element 6 and the semiconductor switching element 9 are made to be able to be turned on when the semiconductor switching element 9 is normally driven.

[0033] Thus, in the short circuit detection circuit according to Embodiment 1, by providing the voltage detection section that performs comparison determination and amplification of the terminal voltage, and the voltage control section composed of the switching element and the bias voltage source provided between the capacitive element and the low potential side terminal of the semiconductor switching element, the capacitive element is charged only in a range higher than the bias voltage, and thus it has the effect of being able to quickly detect and determine a short circuit of the semiconductor switching element without increasing the energizing current of the constant current circuit.

[0034] Embodiment 2.

[0035] Figure 3 is a circuit block diagram showing the system structure including the semiconductor switching element to which the short circuit detection circuit according to Embodiment 2 is connected. The difference from Embodiment 1 is that the voltage control section 7 of the short circuit detection circuit 1 according to Embodiment 2 is composed of a second resistive element 7d connected in parallel to the capacitive element 6, and a Zener diode 7e connected in series to the capacitive element 6. In the Zener diode 7e, the anode is connected to the low potential side of the semiconductor switching element 9, and the cathode is connected to the capacitive element. The Zener diode 7e corresponds to the entirety of the voltage detection section 7a, the switch 7b, and the bias voltage source 7c of Embodiment 1. As to the other structures, since they are the same as in Embodiment 1, the description is omitted. The feature of this embodiment is that it is generally a small and inexpensive component, the number of components is small, and the component itself does not need power to operate, and thus it is extremely practical.

[0036] Next, the operation of the short circuit detection circuit according to this Embodiment 2 is explained in detail based on Figure 3 the difference from Embodiment 1. InFigure 4 The semiconductor switching element 9, which is the object of the short-circuit determination, is illustrated in the middle.

[0037] The specific operation is described. In the initial state, the Zener diode 7e is in the off state, and the voltage Vd of the terminal 8 rises at a steep slope, as in Embodiment 1. Since the terminal voltage Vd is input to the cathode of the Zener diode 7e via the second resistance element 7d, in the case where the on voltage (turn-on voltage) of the Zener diode 7e is Vz, the Zener diode 7e becomes in the on state at the time when Vd = Vz is reached. That is, Voff = Vz in Embodiment 1, and the on state of the Zener diode 7e corresponds to the on state of the switch 7b in Embodiment 1.

[0038] Therefore, in the range where Vd > Vz, the capacitor element 6 is charged as in the case of Embodiment 1, but in the on state of the Zener diode 7e, since the on current flowing into the Zener diode 7e via the second resistance element 7d is generated, when this on current is set to Iz, the rising slope of the terminal voltage Vd of the terminal 8 is (Id - Iz) / Cd. As a result, the detection time Td2 of the short circuit is Td2 = Ck x Voff / (Id - Iz) + Cd x (Vth - Voff) / (Id - Iz).

[0039] Thus, when the terminal voltage Vd of the terminal 8 is detected to reach the threshold voltage Vth, the short-circuit determination section 3 determines that the semiconductor switching element 9 is short-circuited, and outputs the output voltage Vout to notify the external device (not illustrated) of the detection time Td2 (here, the case where the output voltage rises is shown).

[0040] Since the purpose of the present application is to accelerate the charging of the capacitor element 6 to rapidly detect the short circuit of the semiconductor switching element 9, it is desirable to set the current Iz flowing through the Zener diode 7e as small as possible in the range where the Zener diode 7e can stably maintain the on state, and the second resistance element 7d is provided in order to adjust the current Iz.

[0041] Since the Zener diode 7e used in the present embodiment generally requires a current of several μA to several tens of μA to stably maintain the on state, when, for example, the output current Id of the constant current circuit 2 is a current of about 1 mA, it is necessary to adjust the constant of the second resistance element 7d so that the current Iz flowing through the Zener diode 7e is about one-tenth or less of the output current Id of the constant current circuit 2. The bias voltage can be adjusted by using Zener diodes having different on voltages (breakdown voltages).

[0042] Thus, in the short-circuit detection circuit according to Embodiment 2, by providing the voltage control section composed of the resistance element connected in parallel with the capacitor element and the Zener diode connected in series with the capacitor element, as in Embodiment 1, the capacitor element is charged only in a range higher than the set bias voltage, and thus, it is possible to rapidly detect and determine the short circuit of the semiconductor switching element without increasing the energizing current of the constant current circuit. In addition, the voltage control section of Embodiment 2 has a small number of components, and it is possible to expect the excellent effect of reliably performing the detection determination of the short circuit with a simple structure.

[0043] Embodiment 3

[0044] ​ is a circuit block diagram showing the system structure including the semiconductor switching element to which the short-circuit detection circuit according to Embodiment 3 is connected. The difference from Embodiment 2 is that a third resistance element 7f is further provided in parallel with the Zener diode 7e with respect to the structure of the voltage control section 7 of the short-circuit detection circuit 1 of Embodiment 2. As to the other structures, since they are the same as those of Embodiment 2, the description thereof is omitted. Embodiment 3 aims at suppressing the influence due to the individual difference of the on-voltage of the Zener diode 7e, that is, the variation of the detection time Td2 of the short circuit of the semiconductor switching element 9.

[0045] Embodiment 3 will be described focusing on the effect due to the third resistance element 7f. In general, the on-voltage Vz of the Zener diode has a positive characteristic with respect to the variation of the on-current Iz. Thus, for example, in the case where the on-voltage Vz is low due to the individual difference, it is expected that the on-voltage Vz is increased by increasing the on-current Iz to eliminate the influence due to the individual difference.

[0046] In the case of the structure of Embodiment 2, when the resistance value of the second resistance element 7d is Rd, the relationship between the on-voltage Vz of the Zener diode 7e and the on-current Iz can be expressed as

[0047] Iz = (Vd - Vz) / Rd (1)

[0048] By further transforming Equation (1), it can be expressed as

[0049] Iz + Vz / Rd = Vd / Rd (2).

[0050] The above equation showing the correlation between the on-voltage Vz of the Zener diode 7e and the on-current Iz means that, when the on-voltage Vz is changed due to the individual difference, the on-current Iz is changed in the opposite direction on the circuit structure in order to satisfy the equation, to eliminate the influence due to the individual difference of the Zener diode 7e.

[0051] On the other hand, in the case of the structure of Embodiment 3, when the resistance value of the third resistance element 7f is Rf, the correlation between the on voltage Vz and the on current Iz of the Zener diode 7e can be expressed as

[0052] Iz= (Vd - Vz) / Rd - Vz / Rf (3)

[0053] Further transforming equation (3), it can be expressed as

[0054] Iz+ Vz (1 / Rd + 1 / Rf) = Vd / Rd (4).

[0055] Equation (4) is also the same as equation (2) of Embodiment 2, the change of the on current Iz with respect to the on voltage Vz changes in the opposite direction to eliminate the influence of the individual difference of the Zener diode 7e, but since the coefficient of the second term on the left side of equation (4) adds the component of 1 / Rf, it means that the change of the on current Iz with respect to the on voltage Vz changes more greatly.

[0056] Therefore, in the case of using a Zener diode with a large individual difference in on voltage, or in the case of needing to suppress the deviation of the detection time Td2 to design with high accuracy, the present embodiment becomes an effective means.

[0057] Thus, in the short-circuit detection circuit according to Embodiment 3, as the voltage control section, two resistance elements connected in series are connected in parallel with the capacitance element, and a Zener diode connected in series with the capacitance element is provided, so that, as in Embodiments 1 and 2, the capacitance element is charged only in a range higher than the bias voltage, whereby it has the effect that the short circuit of the semiconductor switching element can be rapidly detected and determined without increasing the current of the constant current circuit, and in the case of using a Zener diode in the voltage control section as in Embodiment 2, even if there is an individual difference in the on voltage characteristics of the Zener diode, it is possible to expect the excellent effect of suppressing the deviation of the detection time of the short circuit.

[0058] The above describes embodiments that rapidly detect the short circuit of the semiconductor switching element without increasing the current loss of the short-circuit detection circuit and without reducing the filtering effect of noise. In order to achieve the above-mentioned object, any one of these embodiments can be adopted, and in addition, the functions can be omitted or each embodiment can be used in combination as needed.

[0059] Although the present application has been described with respect to a structure applied to a short-circuit detection circuit that detects a short-circuit of a semiconductor switching element of an inverter of a power conversion device used for driving a motor of an automobile, it is of course also effective even in the case of detecting a short-circuit of a semiconductor switching element used for other circuit devices using a semiconductor switching element. In addition, although an example in which a transistor is used as a switch used in a voltage control section has been described, other active elements represented by an FET can also be used.

[0060] Although various exemplary embodiments and examples have been described in the present application, the various features, modes and functions described in one or more embodiments are not limited to the application of the specific embodiments, and can be applied to the embodiments individually or in various combinations.

[0061] Therefore, it can be considered that an infinite number of modifications not exemplified are also included in the technical scope disclosed in the present application. For example, cases in which at least one constituent element is modified, added or omitted, and cases in which at least one constituent element is extracted and combined with constituent elements of other embodiments are included.

[0062] In addition, in the drawings, the same reference numerals denote the same or corresponding parts.

[0063] Explanation of Reference Numerals

[0064] 1 Short-circuit detection circuit

[0065] 2 Constant current circuit

[0066] 3 Short-circuit determination section

[0067] 4 Diode

[0068] 5 Resistor element

[0069] 6 Capacitor element

[0070] 7 Voltage control section

[0071] 7a Voltage detection section

[0072] 7b Switch

[0073] 7c Bias voltage source

[0074] 7d Second resistor element

[0075] 7e Zener diode

[0076] 7f Third resistor element

[0077] 8 Terminal

[0078] 9 Semiconductor switching element

Claims

1. A short-circuit detection circuit, characterized in that, include: A capacitor element is connected to the high-potential side of a semiconductor switching element via a diode and a resistor element connected in series; A short-circuit determination unit detects the terminal voltage of one terminal of the capacitor element and determines that the semiconductor switching element is short-circuited when the terminal voltage is above a threshold voltage. as well as A voltage control unit is provided between another terminal of the capacitor element and the low-potential side of the semiconductor switching element, and switches the capacitor element and the semiconductor switching element on and off, and applies a bias voltage between the capacitor element and the semiconductor switching element when the capacitor element is on.

2. The short-circuit detection circuit as described in claim 1, characterized in that, When the terminal voltage and the bias voltage are at the same potential, the capacitor element and the semiconductor switching element are turned on.

3. The short-circuit detection circuit as described in claim 2, characterized in that, The voltage control unit comprises a voltage detection unit, a bias voltage source, and a transistor. The voltage detection unit compares and determines the terminal voltage and amplifies the terminal voltage. The bias voltage source applies the bias voltage. The base terminal of the transistor is connected to the voltage detection unit, the collector terminal is connected to the capacitor element, and the emitter terminal is connected to the bias voltage source. When the terminal voltage and the bias voltage are at the same potential, the voltage control unit uses the output voltage from the voltage detection unit to turn on the transistor.

4. The short-circuit detection circuit as described in claim 2, characterized in that, The voltage control unit consists of a Zener diode and a second resistor. The anode of the Zener diode is connected to the low-potential side of the semiconductor switching element, and the cathode is connected to the capacitor element. The second resistor element is connected to the cathode of the Zener diode and is connected in parallel with the capacitor element. When the terminal voltage and the Zener diode's forward voltage, which is equivalent to the bias voltage, are at the same potential, the voltage control unit turns on the Zener diode.

5. The short-circuit detection circuit as described in any one of claims 1 to 4, characterized in that, The bias voltage is set to be less than the threshold voltage, and the capacitor element is made to conduct between the semiconductor switching element until the semiconductor switching element is determined to be short-circuited.

6. The short-circuit detection circuit as described in any one of claims 1 to 4, characterized in that, The bias voltage is set below the terminal voltage generated at the input of the short-circuit determination unit when the semiconductor switching element is normally driven, so that the capacitor element and the semiconductor switching element can conduct when the semiconductor switching element is normally driven.

7. The short-circuit detection circuit as described in claim 5, characterized in that, The bias voltage is set below the terminal voltage generated at the input of the short-circuit determination unit when the semiconductor switching element is normally driven, so that the capacitor element and the semiconductor switching element can conduct when the semiconductor switching element is normally driven.

8. The short-circuit detection circuit as described in claim 4, characterized in that, The resistance value of the second resistor element is adjusted so that the current flowing through the second resistor element is less than one-tenth of the output current of the constant current circuit, and the constant current circuit charges the capacitor element.

9. The short-circuit detection circuit as described in claim 4 or 8, characterized in that, The circuit includes a third resistor element connected in parallel with the Zener diode. The short-circuit detection circuit uses the current flowing through the third resistor element and the current flowing through the Zener diode to eliminate individual differences in the Zener diode's forward voltage.

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