Semiconductor protection devices and power converters

Abstract

The present invention provides a semiconductor protection device comprising: a first determination unit (31) that outputs a first output signal when a gate voltage of a semiconductor switching element (1) exceeds a predetermined first threshold value; a second determination unit (32) that outputs a second output signal when the gate voltage exceeds a second threshold value greater than the first threshold value; and a third determination unit (33) that outputs a third output signal when a value based on a voltage of the semiconductor switching element or a value based on a current flowing through the semiconductor switching element during a period in which the semiconductor switching element is on exceeds a third threshold value. The semiconductor protection device is capable of high-speed short-circuit detection by using the first output signal to enable the determination operation by the third determination unit (33) and detecting that the semiconductor switching element (1) is in a short-circuit state on the basis of the logical product of the second output signal and the third output signal.

Description

Technical Field

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[0006]

[0001] The present disclosure relates to a semiconductor protection device and a power conversion device.

Background Art

[0002] Conventionally, in a power conversion device having a bridge circuit composed of semiconductor switching elements, when a short-circuit state occurs due to a failure or malfunction and an overcurrent flowing through the upper and lower arms is detected, there is a protection device that protects the power conversion device from large-scale destruction. Hereinafter, the overcurrent flowing through the upper and lower arms is referred to as a short-circuit current, and the detection of the short-circuit state is referred to as short-circuit detection.

[0003] Since the short-circuit current has a value larger than the current assumed during normal operation of the power conversion device, if protection is not performed early, the semiconductor switching element may be destroyed. Therefore, it is required to detect the short circuit at high speed and protect the semiconductor switching element from destruction.

[0004] As a technique related to the protection of a semiconductor switching element by short-circuit detection, a short-circuit detection technique using the potential of the high-potential terminal of a semiconductor switching element called non-saturated (Desat) detection is known (for example, see Patent Document 1). Desat detection is a technique for short-circuit detection by comparing the detected value of the potential of the high-potential terminal with a threshold value for the potential of the high-potential terminal.

[0005] In the technique disclosed in Patent Document 1, a circuit for detecting the potential of the high-potential terminal using a diode, a current source, and a capacitor connected to the high-potential terminal of the semiconductor switching element, and comparing the detected potential with a threshold value to perform short-circuit detection is provided. Until the voltage of the control terminal of the semiconductor switching element exceeds the threshold value, false detection of a short circuit can be prevented by setting the potential of the high-potential terminal to a low voltage.

[0006] Furthermore, by setting a high threshold for the potential of the high-potential terminal until the voltage of the control terminal of the semiconductor switching element exceeds the threshold, and then lowering the threshold after it exceeds the threshold, it is possible to detect a short circuit early if a short circuit occurs after the semiconductor switching element has been turned on. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 7183375 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in the technology disclosed in Patent Document 1, the threshold voltage for the control terminal of the semiconductor switching element is set to be higher than or equal to the Miller voltage. As a result, the Desat detection cannot be operated by the lock circuit for the time until the threshold voltage is exceeded, which delays short-circuit detection and poses a risk of damaging the semiconductor switching element.

[0009] This disclosure was made to solve the above-mentioned problems and aims to provide a semiconductor protection device capable of high-speed short-circuit detection. [Means for solving the problem]

[0010] The semiconductor protection device of this disclosure outputs a short-circuit detection signal to a gate drive circuit when it is determined that a semiconductor switching element is in a short-circuit state, and comprises: a first determination unit that outputs a first output signal when the gate voltage of the semiconductor switching element exceeds a predetermined first threshold; a second determination unit that outputs a second output signal when the gate voltage exceeds a second threshold greater than the first threshold; and a third determination unit that outputs a third output signal when a value based on the voltage of the semiconductor switching element or a value based on the current value flowing through the semiconductor switching element during the period when the semiconductor switching element is ON exceeds a third threshold, and the third determination unit is activated by lowering the third threshold with the first output signal, and the semiconductor switching element is detected to be in a short-circuit state based on the logical AND of the second output signal and the third output signal. [Effects of the Invention]

[0011] According to the semiconductor protection device of this disclosure, the determination operation of the output determination unit is activated when the gate voltage of the semiconductor switching element exceeds a first threshold, thereby enabling high-speed short-circuit detection. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram showing the basic configuration of the semiconductor protection device according to Embodiment 1. [Figure 2] This figure shows an example of the circuit of Embodiment 1 of the semiconductor protection device according to Embodiment 1. [Figure 3] This is a time chart for the normal operation of Example 1. [Figure 4] This is a time chart for operation under the condition of a short circuit in Example 1. [Figure 5] This figure shows an example of the circuit of Embodiment 2 of the semiconductor protection device according to Embodiment 1. [Figure 6] This figure shows an example of the circuit of Embodiment 3 of the semiconductor protection device according to Embodiment 1. [Figure 7] This figure shows an example of the circuit of Embodiment 4 of the semiconductor protection device according to Embodiment 1. [Figure 8] It is a diagram showing an example of a circuit of Example 5 of the semiconductor protection device according to Embodiment 1. [Figure 9] It is a time chart during normal driving of Example 5. [Figure 10] It is a time chart during driving under a short circuit occurrence in Example 5. [Figure 11] It is a diagram showing an example of a circuit of Example 6 of the semiconductor protection device according to Embodiment 1. [Figure 12] It is a time chart during normal driving of Example 6. [Figure 13] It is a time chart during driving under a short circuit occurrence in Example 6. [Figure 14] It is a diagram showing an example of a circuit of Example 7 of the semiconductor protection device according to Embodiment 1. [Figure 15] It is a diagram showing another example of a circuit of Example 7 of the semiconductor protection device according to Embodiment 1. [Figure 16] It is a time chart during normal driving of Example 7. [Figure 17] It is a time chart during driving under a short circuit occurrence in Example 7. [Figure 18] It is a block diagram showing a basic configuration of the semiconductor protection device according to Embodiment 2. [Figure 19] It is a block diagram showing a basic configuration of the semiconductor protection device according to Embodiment 3. [Figure 20] It is a schematic configuration diagram of a power conversion device provided with the semiconductor protection device according to Embodiment 4.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of the semiconductor protection device according to the present disclosure will be described with reference to the drawings. Note that the same reference numerals are assigned to the same contents and corresponding parts, and detailed descriptions thereof are omitted. Similarly, in the following embodiments, duplicate descriptions of the configurations with the same reference numerals are omitted.

[0014] Embodiment 1. <Basic configuration of semiconductor protection device according to Embodiment 1> Figure 1 is a block diagram showing the basic configuration of the semiconductor protection device according to Embodiment 1, and Figure 2 is a diagram showing an example of the circuit diagram of Example 1 of the semiconductor protection device according to Embodiment 1. The semiconductor protection device according to Embodiment 1 comprises a semiconductor switching element 1, a gate drive circuit 2 for driving the semiconductor switching element 1, a semiconductor protection device 3 that outputs a short-circuit detection signal Vsc to the gate drive circuit 2 when it is determined that the semiconductor switching element 1 is in a short-circuit state, and a gate resistor 4 connected between the control terminal, i.e., the gate terminal, of the semiconductor switching element 1 and the gate drive circuit 2.

[0015] <Outline description of the configuration of the semiconductor protection device in Example 1> As an example of a semiconductor protection device according to Embodiment 1 having the basic configuration shown in Figure 1, Example 1 is described in Figure 2. The semiconductor switching element 1 is described as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), but it is not limited to a MOSFET. For example, an IGBT (Insulated Gate Bipolar Transistor) may be used.

[0016] In Figure 2, the gate drive circuit 2 outputs a gate drive signal Vico for switching the semiconductor switching element 1 on and off. When the gate drive signal Vico becomes high voltage, a gate current flows through the gate resistor 4, increasing the control terminal voltage of the semiconductor switching element 1 (hereinafter referred to as the gate voltage Vgs), and the semiconductor switching element 1 turns on.

[0017] The semiconductor protection device 3 consists of a first determination unit 31, a second determination unit 32, an output determination unit 33, and a short-circuit detection unit 34. The first determination unit 31 sets a first threshold Vref1 for the gate voltage Vgs and compares the gate voltage Vgs with the first threshold Vref1. The first determination unit 31 outputs the first determination result Vout1 to the output determination unit 33 when the gate voltage Vgs becomes greater than (exceeds) the first threshold Vref1.

[0018] The second determination unit 32 sets a second threshold Vref2 for the gate voltage Vgs and compares the gate voltage Vgs with the second threshold Vref2. The second determination unit 32 outputs the second determination result Vout2 to the short-circuit detection unit 34 when the gate voltage Vgs exceeds the second threshold Vref2. Note that the first threshold Vref1 is set to a value lower than the second threshold Vref2.

[0019] The output determination unit 33 compares the detected value obtained by detecting the voltage at the high-potential terminal, low-potential terminal, or current flowing through the semiconductor switching element 1, or a calculated value based on the detected value, with the third threshold Vref3, and outputs the third determination result Vout3 to the short-circuit detection unit 34 if the third threshold Vref3 is exceeded and the first determination result Vout1 is input.

[0020] The short-circuit detection unit 34 determines that the semiconductor switching element 1 is in a short-circuit state when it receives the second determination result Vout2 and the third determination result Vout3, and outputs a short-circuit detection signal Vsc to the gate drive circuit 2.

[0021] The gate drive circuit 2 lowers the gate drive signal Vico to a low voltage when the short-circuit detection signal Vsc is input. When the gate drive signal Vico becomes low voltage, the gate voltage Vgs that was previously charged causes a gate current to flow through the gate resistor 4. This lowers the gate voltage Vgs, causing the semiconductor switching element 1 to turn off.

[0022] As described above, when the gate voltage Vgs rises when the semiconductor switching element 1 is turned on, the output determination unit 33 is activated when the gate voltage Vgs exceeds a first threshold Vref1 which is set to a value lower than the second threshold Vref2, thereby enabling early detection of a short circuit.

[0023] On the other hand, the short-circuit detection unit 34 does not detect a short circuit in the semiconductor switching element 1 until it receives the first determination result Vout1 output from the first determination unit 31. Therefore, even if the second determination unit 32 malfunctions due to noise or the like and outputs the second determination result Vout2, the third determination result Vout3 is not output. As a result, the semiconductor switching element 1 is not incorrectly determined to be in a short-circuit state, thus preventing the output of a short-circuit detection signal Vsc.

[0024] Furthermore, the short-circuit detection unit 34 does not determine if the semiconductor switching element 1 is short-circuited until the second determination result Vout2 output from the second determination unit 32 is input. Therefore, even if the output determination unit 33 malfunctions due to noise or the like and outputs a third determination result Vout3, the second determination result Vout2 has not been output, thus preventing a false determination that the semiconductor switching element 1 is short-circuited and preventing the output of a short-circuit detection signal Vsc.

[0025] <Detailed description of the configuration of the semiconductor protection device in Example 1> Figure 2 details the circuit configuration of the semiconductor protection device according to Example 1. In Figure 2, the first determination unit 31 includes a first comparator 311, which compares a first threshold Vref1 with the gate voltage Vgs. The first comparator 311 compares the first threshold Vref1 with the gate voltage Vgs and outputs the first judgment result Vout1 as a high voltage if the first threshold Vref1 is a larger value. The first comparator 311, in comparing the first threshold Vref1 with the gate voltage Vgs, outputs the first determination result Vout1 as a low voltage if the gate voltage Vgs is a larger value.

[0026] The second determination unit 32 includes a second comparator 321, which compares a second threshold Vref2 with the gate voltage Vgs. The second comparator 321 compares the second threshold Vref2 with the gate voltage Vgs, and if the second threshold Vref2 is larger, it outputs the second judgment result Vout2 as a low voltage. Conversely, if the gate voltage Vgs is a larger value, the second judgment result Vout2 is output as a high voltage.

[0027] The output determination unit 33 includes a diode 331, a current source 332, a desat capacitor 333, a detection lock unit 334, a third threshold changing unit 335, and a third comparator 336. The cathode of diode 331 is connected to the drain terminal of semiconductor switching element 1, which is the high-potential terminal of semiconductor switching element 1, and the anode of diode 331 is connected to the input terminal Co_in of third comparator 336. Although diode 331 is shown as a single component, it may be composed of multiple diodes, or other rectifier elements may be used.

[0028] The current source 332 is connected between the control power supply Vcc and the input terminal Co_in of the third comparator 336, and the Desat capacitor 333 is connected between the input terminal Co_in of the third comparator 336 and the source terminal of the semiconductor switching element 1, which is the reference potential.

[0029] The detection lock unit 334 is connected between the input terminal Co_in of the third comparator 336 and the first determination unit 31. The detection lock unit 334 holds the input terminal voltage Vcin of the third comparator 336 as a low voltage until the first determination result Vout1 output from the first determination unit 31 is input.

[0030] More specifically, the detection lock unit 334 consists of a diode and a logic inverter element. The anode of the diode in the detection lock unit 334 is connected to the input terminal Co_in of the third comparator 336, the cathode of the detection lock unit 334 is connected to the output side of the logic inverter element, and the input side of the logic inverter element is connected to the output side of the first determination unit 31.

[0031] If the first determination result Vout1 is a high voltage, the detection lock unit 334 uses a logic inversion element to set the cathode side of the diode to a low voltage, allowing current from the current source 332 to conduct, thereby maintaining the input terminal voltage Vcin of the third comparator 336 as a low voltage. On the other hand, if the first determination result Vout1 is a low voltage, the detection lock unit 334 uses a logic inversion element to raise the cathode side of the diode to a high voltage, thereby interrupting the current from the current source 332 and releasing the low voltage hold of the input terminal voltage Vcin of the third comparator 336.

[0032] Although the detection lock unit 334 is shown in Figure 2 as consisting of one diode and one logic inverter element, its configuration is not limited to this. For example, it may also be configured with a resistor connected to the diode and logic inverter element, or with multiple diodes and logic inverters connected to each other.

[0033] The third threshold changing unit 335 is connected between the threshold input terminal Co_th of the third comparator 336 and the first determination unit 31. If the first determination result Vout1 output from the first determination unit 31 is a high voltage, the third comparator 336 maintains the threshold input terminal voltage Vco_th at a high voltage. If the first determination result Vout1 output from the first determination unit 31 is a low voltage, the third threshold value Vref3 is output to the threshold input terminal Co_th of the third comparator 336.

[0034] More specifically, the third threshold changing unit 335 has two resistors, each connected in series. One end of the series-connected resistors is connected to the control power supply Vcc, and the other end is connected to the first determination unit 31. The connection point of the series-connected resistors is connected to the threshold input terminal Co_th of the third comparator 336. Furthermore, the third threshold changing unit 335 maintains the threshold input terminal voltage Vco_th of the third comparator 336 at a high voltage when the first judgment result Vout1 is a high voltage, and outputs a third threshold Vref3 based on the voltage division ratio of the two resistors and the voltage value of the control power supply Vcc when the first judgment result Vout1 is a low voltage, which is a value lower than the high voltage.

[0035] Although the third threshold changing unit 335 is described as having a configuration of two resistors, it is not limited to this configuration. For example, two or more resistors may be used, or a diode may be added to the resistor connected to the first determination unit 31.

[0036] The third comparator 336 compares the input terminal voltage Vcin with the threshold input terminal voltage Vco_th. If the threshold input terminal voltage Vco_th is greater, the third judgment result Vout3 is output as a low voltage. Conversely, if the input terminal voltage Vcin of the third comparator 336 is greater, the third judgment result Vout3 is output as a high voltage.

[0037] The short-circuit detection unit 34 outputs a short-circuit detection signal Vsc to the gate drive circuit 2 when the logical AND of the second determination result Vout2 output from the second determination unit 32 and the third determination result Vout3 output from the output determination unit 33 is 1.

[0038] <Operation of the semiconductor protection device in Example 1 during normal operation> Next, the operation of the semiconductor protection device according to Example 1 will be described with reference to Figures 3 and 4. Figure 3 is a time chart to explain the operation of the semiconductor switching element 1 during normal operation.

[0039] In Figure 3, when the gate drive signal Vico becomes high voltage at time t11 (Figure 3a), the gate voltage Vgs begins to rise (Figure 3d). At time t12, the gate voltage Vgs exceeds the first threshold Vref1 (Figure 3d), and the first determination unit 31 outputs the first determination result Vout1 as a low voltage (Figure 3f).

[0040] At time t12, when the detection lock unit 334 receives the first determination result Vout1, it releases the hold of the low voltage at the input terminal Co_in of the third comparator 336 (Figure 3e). Furthermore, at time t12, when the first determination result Vout1 is input to the third threshold changing unit 335, it releases the high voltage hold and outputs the third threshold Vref3 to the threshold input terminal Co_th of the third comparator 336 (Figure 3e). Furthermore, at time t12, the high voltage hold of the detection lock unit 334 is released, so current from the current source 332 flows into the Desat capacitor 333, and the input terminal voltage Vcin of the third comparator 336 begins to rise in a degree of change corresponding to the amount of current that flows in and the capacitance of the Desat capacitor 333 (Figure 3e).

[0041] At time t13, when the gate voltage Vgs exceeds the on-voltage threshold of the semiconductor switching element 1, the semiconductor switching element 1 turns on, the drain current Id, which is the main current of the semiconductor switching element 1, begins to conduct (Figure 3b), and the drain voltage Vds, which is the high-potential terminal voltage of the semiconductor switching element 1, begins to decrease (Figure 3c). Although the gate voltage Vgs is set to output a low voltage of the first determination result Vout1 before it exceeds the first threshold Vref1 (Figures 3d and 3f), the first threshold Vref1 may be set to output a low voltage of the first determination result Vout1 after it exceeds the first threshold Vref1. The first threshold Vref1 may be set to the on-voltage threshold of the semiconductor switching element 1, but is not necessarily limited to this.

[0042] At time t14, the rate at which the gate voltage Vgs rises decreases as the Miller capacitance of the semiconductor switching element 1 begins to charge (Figure 3d). The period from time t14 to time t15 is the charging period of the Miller capacitance of semiconductor switching element 1, and this period is sometimes called the Miller period. During the Miller period, the drain voltage Vds also decreases (Figure 3c), and the rate of change from time t14 to time t15 is larger than the rate of change from time t13 to time t14.

[0043] At time t15, as the drain voltage Vds decreases, the current from the current source 332 begins to flow into the semiconductor switching element 1 via the diode 331, so the voltage at the input terminal of the third comparator 336, Vcin, stops rising (Figure 3e). Furthermore, as the drain voltage Vds decreases further, the charge stored in the Desat capacitor 333 is discharged to the semiconductor switching element 1 via the diode 331, causing the voltage at the input terminal of the third comparator 336, Vcin, to decrease (Figure 3e).

[0044] At time t16, the gate voltage Vgs exceeds the second threshold Vref2 (Figure 3d), and the second determination unit 32 outputs the second determination result Vout2 as a high voltage (Figure 3g). Furthermore, from time t16 onward, the input terminal voltage Vcin of the third comparator 336 converges to the sum of the drain voltage Vds and the ON voltage of the diode 331 (Figure 3e). Since the on-voltage of diode 331 can be obtained by design, the output determination unit 33 can detect the value of the drain voltage Vds.

[0045] Between time t11 and time t16, and after time t16, the input terminal voltage Vcin of the third comparator 336 does not exceed the threshold input terminal voltage Vco_th of the third comparator 336 (Figure 3e), so the third judgment result Vout3 maintains a low voltage and does not output a high voltage (Figure 3h).

[0046] In Figure 3, the third judgment result Vout3 maintains a low voltage from time t11 to t16 and after time t16. However, the third threshold Vref3 may be set so that the input terminal voltage Vcin of the third comparator 336 falls below the threshold input terminal voltage Vco_th of the third comparator 336 before time t16, when the second judgment result Vout2 is output.

[0047] In this way, the third threshold Vref3 is set so that the third determination result Vout3 becomes a low voltage by at least time t16. Since the short-circuit detection unit 34 does not get 1 in the logical AND of the second determination result Vout2 and the third determination result Vout3, the short-circuit detection signal Vsc is held at a low voltage (Figure 3i). In this way, since the short-circuit detection signal Vsc is not input to the gate drive circuit 2, the semiconductor switching element 1 is not turned off.

[0048] <Operation of the semiconductor protection device in Example 1 under the condition of a short circuit> Figure 4 is a time chart illustrating the operation of the semiconductor switching element 1 according to Embodiment 1 during operation under the condition of a short circuit.

[0049] In Figure 4, at time t21, the gate drive circuit 2 outputs the gate drive signal Vico as a high voltage (Figure 4a), and the gate voltage Vgs begins to rise (Figure 4m).

[0050] At time t22, the gate voltage Vgs becomes the first threshold Vref1 (Figure 4m), and the first determination unit 31 outputs the first determination result Vout1 as a low voltage (Figure 4o). Furthermore, at time t22, when the detection lock unit 334 receives the first determination result Vout1, it releases the low voltage hold of the input terminal voltage Vcin of the third comparator 336 (Figure 4n). Furthermore, at time t22, when the first determination result Vout1 is input to the third threshold changing unit 335, it releases the high voltage hold and outputs the third threshold Vref3 to the threshold input terminal Co_th of the third comparator 336 (Figure 4n). Furthermore, at time t22, the low voltage hold of the detection lock unit 334 is released, so current from the current source 332 flows into the Desat capacitor 333, and the input terminal voltage Vcin of the third comparator 336 begins to rise in accordance with the amount of current that flows in and the capacitance of the Desat capacitor 333 (Figure 4n).

[0051] At time t23, when the gate voltage Vgs exceeds the on-voltage threshold of the semiconductor switching element 1, the semiconductor switching element 1 turns on, and the drain current Id begins to conduct (Figure 4k). When the drain current Id begins to conduct, the drain voltage Vds begins to decrease (Figure 4l). However, unlike Figure 3, Figure 4 shows the semiconductor switching element 1 being driven under short-circuit conditions, so the rate of change in the drain voltage Vds is smaller compared to normal operation, and a high voltage is maintained.

[0052] Since the drain voltage Vds does not decrease, the current from the current source 332 does not flow into the semiconductor switching element 1 through the diode 331, and the voltage at the input terminal of the third comparator 336, Vcin, continues to rise. Furthermore, since the semiconductor switching element 1 is driven under a short circuit, the gate voltage Vgs does not experience a Miller period, and therefore the rate of increase of the gate voltage Vgs does not decrease.

[0053] At time t24, the gate voltage Vgs exceeds the second threshold Vref2 (Figure 4m), so the second determination unit 32 outputs the second determination result Vout2 as a high voltage (Figure 4p).

[0054] At time t25, the input terminal voltage Vcin of the third comparator 336 exceeds the threshold input terminal voltage Vco_th of the third comparator 336 (Figure 4n), so the output determination unit 33 outputs the third determination result Vout3 as a high voltage (Figure 4q). Furthermore, at time t25, the logical AND of the second judgment result Vout2 and the third judgment result Vout3 is 1, so the short-circuit detection unit 34 outputs the short-circuit detection signal Vsc as a high voltage (Figure 4r). Furthermore, at time t25, the gate drive circuit 2 receives the short-circuit detection signal Vsc, so it outputs the gate drive signal Vico as a low voltage (Figure 4j), and the gate voltage Vgs begins to decrease (Figure 4m). At time t26, the drain current Id is completely cut off (Figure 4k).

[0055] In this way, Embodiment 1 of the semiconductor protection device according to Embodiment 1 can prevent misjudgment of a short-circuit state during normal operation of the semiconductor switching element 1 and protect the semiconductor switching element 1 from damage during operation in a short-circuit state by the following actions. (1) When the gate voltage Vgs of the semiconductor switching element exceeds the first threshold Vref1, the third threshold Vref3 is lowered and the determination operation of the output determination unit 33 is activated, thereby enabling high-speed short-circuit detection. (2) Furthermore, by setting the threshold for the potential of the high-potential terminal to a high voltage until the gate voltage Vgs of the control terminal of the semiconductor switching element exceeds the first threshold Vref1, and then lowering the third threshold Vref3 after the threshold is exceeded, a short circuit can be detected early if a short circuit occurs after the semiconductor switching element has been turned on. (3) Furthermore, until the voltage of the control terminal of the semiconductor switching element exceeds the first threshold Vref1, false detection of a short circuit can be prevented by setting the input terminal voltage Vcin of the high-potential terminal to a low potential.

[0056] <Semiconductor protection device of Example 2> As an example of a semiconductor protection device according to Embodiment 1 having the basic configuration of Figure 1, Embodiment 2 will be described in Figure 5. Components similar to those in Figure 2 are denoted by the same reference numerals, and their descriptions are omitted. Figure 5 differs from Embodiment 1 in that the first determination unit 31 includes a transistor element 312. Although the transistor element 312 is described as a bipolar transistor, it is not limited to bipolar transistors. For example, a MOSFET may be used.

[0057] In Figure 5, the base terminal of the transistor element 312 is connected to the gate terminal of the semiconductor switching element 1 via a resistor, and the emitter terminal of the transistor element 312 is connected to a reference potential. Furthermore, the collector terminal of the transistor element 312 corresponds to the first determination result Vout1 output from the first determination unit 31, and the first determination result Vout1 is output to the output determination unit 33.

[0058] The first threshold Vref1 set in the first determination unit 31 corresponds to the on-voltage threshold of the transistor element 312. When the gate voltage Vgs becomes greater than the on-voltage threshold of transistor element 312, transistor element 312 turns on and outputs a low voltage from its collector terminal. Thus, even when a transistor element 312 is used in the first determination unit 31, the same effects as in Example 1 are achieved, while also reducing the number of circuit elements.

[0059] <Semiconductor protection device of Example 3> As an example of a semiconductor protection device according to Embodiment 1 having the basic configuration shown in Figure 1, Embodiment 3 is described in Figure 6. Components similar to those in Figure 2 are denoted by the same reference numerals, and their descriptions are omitted. Figure 6 differs from Embodiment 1 in that the output determination unit 33 includes a current detector 337.

[0060] In Figure 6, the output determination unit 33 includes a third threshold changing unit 335, a third comparator 336, and a current detector 337. The current detector 337 detects the drain current Id of the semiconductor switching element 1 and outputs the detected result to the input terminal Co_in of the third comparator 336. The third threshold Vref3 is set so that when the first determination result Vout1 becomes a high voltage, it becomes a value greater than or equal to the drain current Id that is expected during the normal operation of the semiconductor switching element 1. The third comparator 336 compares the detected drain current Id output from the current detector 337 with the third threshold Vref3. If the detected drain current Id is a larger value, the third judgment result Vout3 is output as a high voltage.

[0061] Even when the current detector 337 is used in the output determination unit 33 in this way, the same effects as in Embodiment 1 of the semiconductor protection device according to Embodiment 1 are achieved, and since the Desat capacitor 333, current source 332, etc. are not required, the number of circuit elements can be reduced.

[0062] <Semiconductor protection device of Example 4> As an example of a semiconductor protection device according to Embodiment 1 having the basic configuration shown in Figure 1, Embodiment 4 is described in Figure 7. Components similar to those in Figure 6 are denoted by the same reference numerals, and their descriptions are omitted. In Figure 7, the output determination unit 33 differs from Embodiment 3 in that it includes an inductor 338 and an integrating circuit 339.

[0063] In Figure 7, the output determination unit 33 includes a third threshold changing unit 335, a third comparator 336, an inductor 338, and an integrating circuit 339. Inductor 338 is connected in series with semiconductor switching element 1 as shown in Figure 7, and is configured so that a drain current Id flows through it. The inductor 338 may be constructed, for example, using the parasitic inductance component of the winding or wiring.

[0064] The integrating circuit 339 detects the voltage generated between the inductor 338 and the reference potential of the source terminal of the semiconductor switching element 1. It calculates the drain current Id from the integrated value of the detected voltage and the inductance value of the inductor 338, and outputs it to the input terminal Co_in of the third comparator 336.

[0065] Even when using an inductor 338 and an integrating circuit 339 in the output determination unit 33 in this way, the same effects as in Example 3 are achieved, and since a Desat capacitor 333, a current source 332, etc. are not required, the number of circuit elements can be reduced.

[0066] <Semiconductor protection device of Example 5> As an example of a semiconductor protection device according to Embodiment 1 having the basic configuration shown in Figure 1, Embodiment 5 is described in Figure 8. Components similar to those in Figure 2 are denoted by the same reference numerals, and their descriptions are omitted. In Figure 8, Embodiment 5 differs from Embodiment 1 in that the output determination unit 33 includes a third threshold filter 3301.

[0067] For example, in Example 1, the input terminal voltage Vcin of the third comparator 336 increases in a manner corresponding to the amount of current flowing from the current source 332 to the Desat capacitor 333 and the capacitance of the Desat capacitor 333. Therefore, if there is variation in the amount of current output from the current source 332, or if the capacitance of the Desat capacitor 333 deteriorates, the increase in the input terminal voltage Vcin of the third comparator 336 may increase significantly. In this case, during normal operation of the semiconductor switching element 1, the input terminal voltage Vcin of the third comparator 336 may exceed the threshold input terminal voltage Vco_th of the third comparator 336, causing the third judgment result Vout3 to be output as a high voltage and potentially leading to an incorrect output of the short-circuit detection signal Vsc. In view of this problem, Example 5 is configured to reduce the rate of change from the high voltage of the threshold input terminal voltage Vco_th of the third comparator 336 to the third threshold Vref3.

[0068] In Figure 8, the output determination unit 33 includes a diode 331, a current source 332, a desat capacitor 333, a detection lock unit 334, a third threshold changing unit 335, a third comparator 336, and a third threshold filter 3301.

[0069] The third threshold filter 3301 is a filter that reduces the rate at which the threshold input terminal voltage Vco_th of the third comparator 336 changes from a high voltage to the third threshold Vref3 when the first determination result Vout1 output from the first determination unit 31 becomes a low voltage and the third threshold changing unit 335 outputs the third threshold Vref3.

[0070] <Operation of the semiconductor protection device in Example 5 during normal operation> Next, the operation of the semiconductor protection device according to Example 5 will be described with reference to Figures 9 and 10. Figure 9 is a time chart to explain the operation of the semiconductor switching element 1 during normal operation. Note that the same reference numerals are used for operations similar to those described in Figure 3 in Example 1, and their explanations are omitted.

[0071] Figure 9 differs from Figure 3 in that the voltage of the input terminal voltage Vcin of the third comparator 336 rises rapidly (see Figure 9e). As mentioned above, this indicates a case where the rate of increase of the voltage of the input terminal voltage Vcin of the third comparator 336 is large.

[0072] Referring to Figure 9, the input terminal voltage Vcin of the third comparator 336 is greater than the value of the third threshold Vref3 at time t33 at time t33 between t31 and t32 (Vcin in Figure 9e). In this case, with the configuration of Example 1, the third judgment result Vout3 becomes high voltage during the period from time t31 to t32. Therefore, if the second judgment result Vout2 is set to become high voltage during the period from time t31 to t32, the short-circuit detection signal Vsc will become high voltage, resulting in a false detection of a short circuit.

[0073] In contrast, in the configuration of Example 5, the threshold input terminal voltage Vco_th of the third comparator 336 in Figure 9 differs from that in Figure 3 in that the rate of change to the third threshold Vref3 when the first judgment result Vout1 becomes a low voltage is slower (Vco_th in Figure 9e). This is because the rate of change of the third threshold Vref3 is reduced by the third threshold filter 3301. Therefore, the rate of change of the threshold input terminal voltage Vco_th of the third comparator 336 is slow, and the input terminal voltage Vcin of the third comparator 336 does not exceed the third threshold Vref3, so the third judgment result Vout3 is low voltage even during the period from time t31 to t32.

[0074] In Figure 9, the third judgment result Vout3 maintains a low voltage from time t11 to t15. However, the third threshold Vref3 and the third threshold filter 3301 may be set before time t15 so that the input terminal voltage Vcin of the third comparator 336 falls below the threshold input terminal voltage Vco_th of the third comparator 336.

[0075] <Operation of the semiconductor protection device in Example 5 when a short circuit occurs> Figure 10 is a time chart illustrating the operation of the semiconductor switching element 1 according to Embodiment 5 during operation under short-circuit conditions. The same reference numerals are used for operations similar to those in Figure 4, and their explanations are omitted.

[0076] In Figure 10, as in Figure 9, the voltage rise rate of the input terminal voltage Vcin of the third comparator 336 is faster than in Figure 3. In Figure 10, as in Figure 4, the short-circuit detection signal Vsc becomes high voltage, the drain current Id is interrupted, and the semiconductor switching element 1 is protected from damage due to a short circuit.

[0077] Thus, Example 5 achieves the effects of Example 1, and also prevents the semiconductor switching element 1 from being mistakenly identified as being in a short-circuit state and outputting a short-circuit detection signal Vsc during normal operation of the semiconductor switching element 1, even when the degree of increase of the input terminal voltage Vcin of the third comparator 336 varies in the increasing direction.

[0078] <Semiconductor protection device of Example 6> As an example of a semiconductor protection device according to Embodiment 1 having the basic configuration shown in Figure 1, Embodiment 6 is described in Figure 11. Components similar to those in Figure 8 are denoted by the same reference numerals, and their descriptions are omitted. Embodiment 6 differs from Embodiment 5 in that the output determination unit 33 includes a Vcin initial value setting unit 3302.

[0079] To reduce the losses of semiconductor switching elements 1, there are semiconductor switching elements that can switch on and off at a higher speed than conventional elements. For example, in semiconductor switching elements capable of high-speed switching, such as SiC-MOSFETs (Silicon Carbide Metal Oxide Semiconductor Field Effect Transistors) or GaN-HEMTs (Gallium Nitride High Electron Mobility Transistors), in the configuration of Embodiment 1 shown in Figure 2, during turn-on switching, the voltage of the Desat capacitor 333 is discharged through the parasitic capacitance component of the diode 331 connected to the high-potential terminal of the semiconductor switching element 1. This delays short-circuit detection and may cause the semiconductor switching element 1 to be destroyed.

[0080] In view of these problems, the semiconductor protection device according to Example 6 is configured to pre-charge the input terminal voltage Vcin of the third comparator 336. In other words, in Figure 11, the output determination unit 33 includes a diode 331, a Desat capacitor 333, a third threshold changing unit 335, a third comparator 336, a third threshold filter 3301, and a Vcin initial value setting unit 3302.

[0081] The Vcin initial value setting unit 3302 pre-charges the input terminal voltage Vcin of the third comparator 336 to the Vcin initial value Vcin_i. The initial value of Vcin, Vcin_i, is set to be lower than the high voltage of the threshold input terminal voltage Vco_th of the third comparator 336, and higher than the third threshold Vref3.

[0082] More specifically, in Figure 11, the Vcin initial value setting unit 3302 has two resistors, each connected in series. One end of the series-connected resistors is connected to the control power supply Vcc, and the other end is connected to the reference potential. The connection point between the series-connected resistors is connected to the input terminal Co_in of the third comparator 336. Note that although the Vcin initial value setting unit 3302 in Figure 11 is composed of two resistors, it is not limited to this configuration, and multiple resistors may be used.

[0083] <Operation of the semiconductor protection device in Example 6 during normal operation> Next, the operation of the semiconductor protection device according to Example 6 will be described with reference to Figures 12 and 13. Figure 12 is a time chart to explain the operation of the semiconductor switching element 1 during normal operation. In Figure 12, there is a difference from Figure 9 in that the rate of increase of the drain current Id and the rate of change of the gate voltage Vgs are rapid, but the turn-on operation of the semiconductor switching element 1 is the same as in Figure 9, so the explanation will be omitted.

[0084] Figure 12e differs from Figure 9 in that the input terminal voltage Vcin of the third comparator 336 is pre-charged to the initial value Vcin_i.

[0085] When the gate voltage Vgs exceeds the on-voltage threshold of the semiconductor switching element 1, the semiconductor switching element 1 turns on, the drain current Id begins to conduct (Figure 12a), and the drain voltage Vds begins to decrease (Figure 12c).

[0086] At time t13, the drain voltage Vds changes significantly due to the characteristics of the semiconductor switching element 1. At this time t13, the voltage across the Desat capacitor 333 is discharged through the parasitic capacitance component of the diode 331 connected to the high-potential terminal of the semiconductor switching element 1, causing the input terminal voltage Vcin of the third comparator 336 to drop significantly (Figure 12e).

[0087] By exceeding the Miller period at time t14, the rate of change of the drain voltage Vds decreases after time t14, and the voltage of the Desat capacitor 333 stops discharging through the parasitic capacitance component of diode 331. As a result, the input terminal voltage Vcin of the third comparator 336 begins to rise to its initial value Vcin_i (Figure 12e).

[0088] Subsequently, as the drain voltage Vds decreases, the charge stored in the Desat capacitor 333 is discharged to the semiconductor switching element 1 via the diode 331, causing the voltage at the input terminal of the third comparator 336, Vcin, to decrease (Figure 12e).

[0089] As the voltage of the input terminal voltage Vcin of the third comparator 336 decreases, it does not exceed the threshold input terminal voltage Vco_th of the third comparator 336 (Figure 12e), so the third judgment result Vout3 maintains a low voltage and does not output a high voltage (Figure 12h).

[0090] At times t11 to t15, the third judgment result Vout3 maintains a low voltage (Figure 12h). However, before time t15, the third threshold Vref3 and the third threshold filter 3301 may be set so that the input terminal voltage Vcin of the third comparator 336 falls below the threshold input terminal voltage Vco_th of the third comparator 336.

[0091] Furthermore, although the third judgment result Vout3 maintains a low voltage from time t11 to t15, the initial value Vcin_i may be set before time t15 so that the input terminal voltage Vcin of the third comparator 336 falls below the threshold input terminal voltage Vco_th of the third comparator 336. In this way, the third determination result Vout3 is set to be a low voltage at least until time t15.

[0092] <Operation of the semiconductor protection device in Example 6 when a short circuit occurs> Figure 13 is a time chart illustrating the operation of the semiconductor switching element 1 according to Embodiment 6 during operation under the condition of a short circuit. Figure 13 differs from Figure 10 in that the rate of increase in drain current Id or the rate of change of gate voltage Vgs is rapid, but the turn-on and turn-off operations of semiconductor switching element 1 are the same as in Figure 10, so the explanation is omitted. Furthermore, it differs from Figure 10 in that the input terminal voltage Vcin of the third comparator 336 is pre-charged to the initial value Vcin_i.

[0093] When the gate voltage Vgs exceeds the on-voltage threshold of the semiconductor switching element 1, the semiconductor switching element 1 turns on and the drain current Id begins to conduct (Figure 13k). As the drain current Id begins to conduct, the drain voltage Vds begins to decrease (Figure 13l), and the voltage across the Desat capacitor 333 is discharged through the parasitic capacitance component of the diode 331 connected to the high-potential terminal of the semiconductor switching element, causing the input terminal voltage Vcin of the third comparator 336 to drop significantly (Figure 13n).

[0094] Similar to Figure 10, since the semiconductor switching element 1 is driven under a short circuit, a high voltage is applied to the semiconductor switching element 1, and the input terminal voltage Vcin of the third comparator 336 begins to rise to the initial value Vcin_i (Figure 13n).

[0095] At time t24, the input terminal voltage Vcin of the third comparator 336 exceeds the threshold input terminal voltage Vco_th of the third comparator 336 (Figure 13n), so the output determination unit 33 outputs the third determination result Vout3 as a high voltage (Figure 13q). Furthermore, at time t24, the short-circuit detection unit 34 outputs a short-circuit detection signal Vsc as a high voltage because the logical AND of the second judgment result Vout2 and the third judgment result Vout3 is 1 (Figure 13r).

[0096] In this way, Embodiment 6 outputs a short-circuit detection signal Vsc early, even when the voltage of the Desat capacitor 333 is discharged through the parasitic capacitance component of the diode 331, thereby protecting the semiconductor switching element 1 from damage.

[0097] <Semiconductor protection device of Example 7> As an example of a semiconductor protection device according to Embodiment 1 having the basic configuration shown in Figure 1, Embodiment 7 will be described in Figure 14. In Figure 14, the output determination unit 33 differs from that in Figure 2 of Embodiment 1 in that it includes a time change detection circuit 3303 and a logic circuit 3304. Components similar to those in Figure 2 are denoted by the same reference numerals and their descriptions are omitted.

[0098] As shown in Figures 3 and 4, the rate of change of the drain voltage Vds differs between normal operation and operation under short-circuit conditions, with the degree of change in the drain voltage Vds under short-circuit conditions being smaller compared to normal operation. Example 7 is carried out in consideration of this condition, and a short circuit in the semiconductor switching element 1 is detected by utilizing the fact that the rate of change of the drain voltage Vds is different.

[0099] In Figure 14, the output determination unit 33 in Embodiment 7 consists of a third threshold changing unit 335, a third comparator 336, a time change detection circuit 3303, and a logic circuit 3304. In Figure 14, when comparing the input terminal voltage Vcin of the third comparator 336 with the threshold input terminal voltage Vco_th of the third comparator 336, if the threshold input terminal voltage Vco_th is a larger value, the fourth judgment result Vout4 is output as a low voltage. Conversely, if the input terminal voltage Vcin is a larger value, the fourth judgment result Vout4 is output as a high voltage.

[0100] The time change detection circuit 3303 detects the time change in the high-potential terminal voltage of the semiconductor switching element 1 and outputs that time change to the input terminal Co_in of the third comparator 336. In Figure 14, the time-change detection circuit 3303 is composed of a capacitor with one end connected to the drain terminal of the semiconductor switching element 1, a resistor connected between the other end of the capacitor and a reference potential, and an inverting amplifier that inverts the sign of the detected potential Vdet at the connection point of the capacitor and resistor and outputs it to the third comparator 336. However, the circuit is not limited to this configuration.

[0101] For example, since the detected potential Vdet at the connection point of the capacitor and resistor takes a negative voltage value lower than the reference potential when the semiconductor switching element 1 is driven, as shown in Figure 15, the third threshold Vref3 output from the third threshold changing unit 335 may be set to a negative value without performing a sign inversion of the detected potential Vdet at the connection point of the capacitor and resistor, and the comparison in the third comparator 336 may be performed using a negative voltage value.

[0102] In Figure 15, the third threshold changing unit 335 includes two resistors that divide the control negative power supply Vee, which has a negative voltage value, and an inverting amplifier that inverts the sign of the first judgment result Vout1. Until the first judgment result Vout1 is input, the threshold input terminal voltage Vco_th of the third comparator 336 is set to be less than or equal to the voltage value of the control negative power supply Vee. When the first judgment result Vout1 is input, a third threshold Vref3 based on the voltage division ratio of the control negative power supply Vee and the two resistors is output to the threshold input terminal Co_th of the third comparator 336.

[0103] The third comparator 336 compares the input terminal voltage Vcin with the threshold input terminal voltage Vco_th of the third comparator 336. If the threshold input terminal voltage Vco_th of the third comparator 336 is smaller, the fourth judgment result Vout4 is output as a low voltage. If the input terminal voltage Vcin is smaller, the fourth judgment result Vout4 is output as a high voltage.

[0104] The third threshold changing unit 335 consists of two resistors that divide the control negative power supply Vee, which has a negative voltage value, and an inverting amplifier that inverts the sign of the first determination result Vout1, but this configuration is not limited to this configuration.

[0105] In Figure 14, the logic circuit 3304 is composed of an RS flip-flop circuit, and if the first judgment result Vout1 is a high voltage, and subsequently if the first judgment result Vout1 is a low voltage and the fourth judgment result Vout4 is a low voltage, the third judgment result Vout3 is output as a high voltage. Furthermore, the logic circuit 3304 outputs the third decision result Vout3 as a low voltage when the first decision result Vout1 is a low voltage and the fourth decision result Vout4 is also a low voltage, and continues to output the third decision result Vout3 as a low voltage until the first decision result Vout1 becomes a high voltage. Note that while logic circuit 3304 is composed of RS flip-flop circuits, it is not limited to this.

[0106] <Operation of the semiconductor protection device in Example 7 during normal operation> Next, the operation of the semiconductor protection device according to Example 7 will be described with reference to Figures 16 and 17. Figure 16 is a time chart to explain the operation of the semiconductor switching element 1 during normal operation. Note that the same reference numerals are used for operations similar to those in Figure 3, and their explanations are omitted.

[0107] In Figure 16, at time t12, the first threshold Vref1 is exceeded (Figure 16d), resulting in the first judgment result Vout1 becoming a low voltage (Figure 16f) and the third judgment result Vout3 becoming a high voltage (Figure 16h).

[0108] At time t13, a drain current Id begins to conduct through the semiconductor switching element 1 (Figure 16b), and as the drain voltage Vds changes, the input terminal voltage Vcin of the third comparator 336 rises. However, because the change in drain voltage Vds is not large, it does not exceed the third threshold Vref3.

[0109] At time t14, the rate of change of the drain voltage Vds increases, causing the input terminal voltage Vcin of the third comparator 336 to rise significantly. At time t51, it exceeds the third threshold Vref3 (Figure 16e), resulting in the fourth judgment result Vout4 becoming a high voltage (Figure 16i). Furthermore, at time t51, the fourth judgment result Vout4 is at a high voltage and the first judgment result Vout1 is at a low voltage (Figure 16f), so the third judgment result Vout3 is at a low voltage (Figure 16h).

[0110] At time t16, the second judgment result Vout2 is a high voltage (Figure 16g), but the third judgment result Vout3 is a low voltage (Figure 16h), so a short circuit in semiconductor switching element 1 is not misidentified.

[0111] <Operation of the semiconductor protection device in Example 7 when a short circuit occurs> Figure 17 is a time chart illustrating the operation of the semiconductor switching element 1 according to Embodiment 7 during operation under short-circuit conditions. Note that the same reference numerals are used for operations similar to those in Figure 4, and their explanations are omitted.

[0112] At time t22, the first threshold Vref1 is exceeded, resulting in the first judgment result Vout1 becoming a low voltage and the third judgment result Vout3 becoming a high voltage.

[0113] At time t23, drain current Id begins to conduct through semiconductor switching element 1 (Figure 17l), and as the drain voltage Vds changes (Figure 17m), the input terminal voltage Vcin of the third comparator 336 rises (Figure 17o). However, because the change in drain voltage Vds is not large (Figure 17m), it does not exceed the third threshold Vref3 (Figure 17o).

[0114] By time t24, the input terminal voltage Vcin of the third comparator 336 does not exceed the third threshold Vref3 (Figure 17o). Therefore, at time t24, the second judgment result Vout2 becomes a high voltage (Figure 17q), and both the second judgment result Vout2 and the third judgment result Vout3 become high voltages. As a result, the short-circuit detection unit 34 outputs a short-circuit detection signal Vsc as a high voltage (Figure 17t).

[0115] In this way, Embodiment 7 of the semiconductor protection device according to Embodiment 1 outputs a short-circuit detection signal Vsc early, even when detecting a short circuit based on a change in drain voltage, thereby protecting the semiconductor switching element 1 from damage.

[0116] Embodiment 2. <Basic configuration of semiconductor protection device according to Embodiment 2> Figure 18 is a block diagram showing the basic configuration of a semiconductor protection device according to Embodiment 2. The semiconductor protection device according to Embodiment 2 differs from Embodiment 1 in that it includes a gate resistor 5 for soft turn-off, and when a short circuit is detected, the gate of the semiconductor switching element 1 is turned off by the gate resistor 5 for soft turn-off. Components similar to those in Figure 1 are denoted by the same reference numerals and their descriptions are omitted.

[0117] When a short-circuit current is conducted through the semiconductor switching element 1, the short-circuit detection is performed, and when the short-circuit current is interrupted, there is a risk that the semiconductor switching element 1 may be destroyed by the overvoltage generated in the drain voltage Vds. In view of this problem, a soft turn-off gate resistor 5 is provided, and when a short-circuit is detected, the semiconductor switching element 1 is turned off by the soft turn-off gate resistor 5.

[0118] The gate resistor 5 for soft turn-off is connected between the gate drive circuit 2A and the control terminal of the semiconductor switching element 1, and has a larger resistance value than the gate resistor 4. Having a larger resistance value than the gate resistor 4 makes it possible to make the drain current of the semiconductor switching element 1 during turn-off more gradual than during normal operation.

[0119] Thus, the semiconductor protection device according to Embodiment 2 can prevent overvoltage damage to the semiconductor switching element 1 when a short circuit is detected and the semiconductor switching element 1 is turned off.

[0120] Embodiment 3. <Basic configuration of semiconductor protection device according to Embodiment 3> Figure 19 is a block diagram showing the basic configuration of a semiconductor protection device according to Embodiment 3. The semiconductor protection device according to Embodiment 3 differs from Embodiment 1 in that it includes a fourth determination unit 31A, and outputs the gate drive signal Vico output from the gate drive circuit 2 to the fourth determination unit 31A, and the fourth determination unit 31A outputs a first determination result Vout1 based on the gate drive signal Vico, which differs from Embodiment 1. Components similar to those in Figure 1 are denoted by the same reference numerals and their descriptions are omitted.

[0121] In the semiconductor protection device described in Embodiment 1, variations in gate capacitance between terminals of the semiconductor switching element cause a delay in the output of the first determination result Vout1 output from the first determination unit 31, which can delay short-circuit detection and potentially damage the semiconductor switching element 1.

[0122] In light of these challenges, the fourth determination unit 31A sets a fourth threshold Vref4 and compares the gate drive signal Vico output from the gate drive circuit 2 with the fourth threshold Vref4 to output a first determination result Vout1. The fourth determination unit 31A outputs the first determination result Vout1 to the output determination unit 33 when the gate drive signal Vico exceeds the fourth threshold Vref4.

[0123] Thus, the semiconductor protection device according to Embodiment 3 can suppress the effects of variations in gate capacitance between terminals of the semiconductor switching element 1 by outputting a first determination result Vout1 based on a fourth threshold Vref4.

[0124] Embodiment 4. Figure 20 is a schematic diagram of a power converter equipped with a semiconductor protection device according to Embodiment 4. The power converter according to Embodiment 4 consists of a plurality of semiconductor switching elements 1, a semiconductor drive device 6, a high-voltage power supply 7, and a motor 8.

[0125] In Figure 20, the power conversion device according to this embodiment 4 is configured as a bridge circuit using six semiconductor switching elements 1 and supplies power from a high-voltage power supply 7 to a motor 8, and the semiconductor switching elements 1 are driven by a semiconductor drive device 6. The semiconductor drive device 6 includes a gate drive circuit 2, a semiconductor protection device 3, and a gate resistor 4. The semiconductor drive device 6 may also include a gate resistor 5 for soft turn-off. The semiconductor protection device 3 included in the semiconductor drive device 6 may be any of the semiconductor protection devices 3 described in Embodiments 1 to 3.

[0126] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable to the embodiments individually or in various combinations. Accordingly, countless variations not illustrated are conceivable within the scope of the art disclosed in this specification. These include, for example, modifying, adding or omitting at least one component, or even extracting at least one component and combining it with components of other embodiments. [Explanation of Symbols]

[0127] 1: Semiconductor switching element, 2, 2A: Gate drive circuit, 3: Semiconductor protection device, 4: Gate resistor, 5: Gate resistor for soft turn-off, 6: Semiconductor drive device, 7: High voltage power supply, 8: Motor, 31: First determination unit, 31A: Fourth determination unit, 32: Second determination unit, 33: Output determination unit, 34: Short circuit detection unit, 311: First comparator, 321: Second comparator, 331: Diode, 332: Current source, 333: Desat capacitor, 334: Detection lock unit, 335: Third threshold change unit, 336: Third comparator, 312: Transistor element, 337: Current detector, 338: Inductor, 339: Integrating circuit, 3301: Third threshold filter, 3302: Vcin initial value setting unit.

Claims

1. A semiconductor protection device that outputs a short-circuit detection signal to a gate drive circuit when it is determined that a semiconductor switching element is in a short-circuit state, A first determination unit that outputs a first output signal when the gate voltage of the semiconductor switching element exceeds a predetermined first threshold, A second determination unit outputs a second output signal when the gate voltage exceeds a second threshold greater than the first threshold. A third determination unit outputs a third output signal when a value based on the voltage of the semiconductor switching element or a value based on the current flowing through the semiconductor switching element exceeds a third threshold value during the period when the semiconductor switching element is turned on. Equipped with, A semiconductor protection device that activates the third determination unit by lowering the third threshold with the first output signal, and detects that the semiconductor switching element is in a short-circuit state based on the logical AND of the second output signal and the third output signal.

2. A semiconductor protection device that outputs a short-circuit detection signal to a gate drive circuit when it is determined that a semiconductor switching element is in a short-circuit state, A first determination unit that outputs a first output signal when the gate drive signal of the semiconductor switching element exceeds a predetermined first threshold, A second determination unit outputs a second output signal when the gate voltage of the semiconductor switching element exceeds a second threshold. A third determination unit outputs a third output signal when a value based on the voltage of the semiconductor switching element or a value based on the current flowing through the semiconductor switching element exceeds a third threshold value during the period when the semiconductor switching element is turned on. Equipped with, A semiconductor protection device that activates the determination operation of the third determination unit by lowering the third threshold with the first output signal, and detects that the semiconductor switching element is in a short-circuit state based on the logical AND of the second output signal and the third output signal.

3. The semiconductor protection device according to claim 1 or 2, wherein the third determination unit is a comparison circuit that compares the third threshold value with a value based on the voltage of the semiconductor switching element or a value based on the current flowing through the semiconductor switching element, and the third threshold value is held at a high voltage before the first output signal is output.

4. The semiconductor protection device according to claim 3, characterized in that, after the first output signal is output to the third determination unit, the rate of decrease from the high voltage is set according to a value based on the voltage of the semiconductor switching element or a value based on the current flowing through the semiconductor switching element.

5. The semiconductor protection device according to claim 1 or 2, characterized in that the first threshold voltage is the on-voltage of a transistor element.

6. The semiconductor protection device according to claim 1 or 2, characterized in that when the third determination unit compares the third threshold value with a value based on the voltage of the semiconductor switching element, one input is connected to the high-potential terminal of the semiconductor switching element via a Desat capacitor and a current source.

7. The semiconductor protection device according to claim 1 or 2, characterized in that when the third determination unit compares the third threshold value with a value based on the current flowing through the semiconductor switching element, one input is connected to a current detector located at the high-potential terminal of the semiconductor switching element.

8. The semiconductor protection device according to claim 1 or 2, characterized in that when the third determination unit compares the third threshold value with a value based on the current flowing through the semiconductor switching element, one input is connected via an integrating circuit to an inductor located at the low potential terminal of the semiconductor switching element.

9. A semiconductor protection device that outputs a short-circuit detection signal to a gate drive circuit when it is determined that a semiconductor switching element is in a short-circuit state, A first determination unit that outputs a first output signal when the gate voltage of the semiconductor switching element exceeds a predetermined first threshold, A second determination unit outputs a second output signal when the gate voltage exceeds a second threshold greater than the first threshold. A third determination unit is provided, wherein the first input is connected to a circuit whose voltage changes from a high voltage to a third threshold voltage in accordance with the first output signal, the second input is connected to the high potential terminal of the semiconductor switching element via a Desat capacitor, the second input is set to a voltage higher than the third threshold voltage, and the third determination unit outputs a third output signal when the value of the first input becomes the value of the second input. Equipped with, A semiconductor protection device that activates the determination operation of the third determination unit by lowering the third threshold with the first output signal, and detects that the semiconductor switching element is in a short-circuit state based on the logical AND of the second output signal and the third output signal.

10. A power conversion device that drives a semiconductor switching element and performs power conversion using a semiconductor drive device equipped with a semiconductor protection device according to any one of claims 1, 2, and 9.

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