Semiconductor switching element drive circuit

Abstract

The purpose of the present invention is to provide a technique capable of changing a switching speed in accordance with temperature. A semiconductor switching element drive circuit includes an output voltage detection unit that generates a switching signal based on a temperature related to a semiconductor switching element and an output voltage of the semiconductor switching element. An output voltage for generating the switching signal by the output voltage detection section when the temperature is a first temperature is greater than an output voltage for generating the switching signal by the output voltage detection section when the temperature is a second temperature lower than the first temperature.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor switch element driving circuit. Background Art

[0002] It is known that semiconductor switching elements used in inverters and the like generate switching losses and surge voltages during turn-off. There is a trade-off between switching losses and surge voltages. If switching losses are reduced, surge voltages increase, and if surge voltages are reduced, switching losses increase.

[0003] As a technology for improving both switching loss and surge voltage during turn-off operation, a technology called active gate drive has been proposed (for example, Patent Document 1). In active gate drive, the switching speed is switched by switching the gate resistance value during turn-off operation of a semiconductor switch element. Prior art literature Patent Literature

[0004] Patent Document 1: Japanese Patent No. 4991446 Summary of the invention Technical problem to be solved by the invention

[0005] In the prior art, the timing of switching the switching speed in the turn-off action is fixed regardless of the temperature of the semiconductor switching element. However, there is a problem that even if the switching timing of the gate resistance value is appropriately adjusted when the junction temperature is at room temperature, the switching loss will still deteriorate when the junction temperature is high. In addition, when the junction temperature is low, the withstand voltage of the semiconductor element is generally reduced. Therefore, when the same driving conditions are used regardless of the junction temperature, there is a problem that the surge voltage may exceed the withstand voltage of the semiconductor element.

[0006] Therefore, the present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide a technology capable of changing a switching speed according to temperature. Technical means for solving technical problems

[0007] The semiconductor switching element driving circuit involved in the present disclosure is a semiconductor switching element driving circuit for driving the gate of a semiconductor switching element, including: a control unit, which switches the switching speed of the semiconductor switching element in a shutdown action based on a switching signal; and an output voltage detection unit, which generates the switching signal based on a temperature related to the semiconductor switching element and the output voltage of the semiconductor switching element, and the output voltage of the switching signal generated by the output voltage detection unit when the temperature is a first temperature is greater than the output voltage of the switching signal generated by the output voltage detection unit when the temperature is a second temperature lower than the first temperature.

[0008] The objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description and accompanying drawings. Effects of the Invention

[0009] According to the present disclosure, the output voltage detection unit generates a switching signal based on the temperature related to the semiconductor switching element and the output voltage of the semiconductor switching element, and the output voltage for generating the switching signal by the output voltage detection unit when the temperature is a first temperature is greater than the output voltage for generating the switching signal by the output voltage detection unit when the temperature is a second temperature lower than the first temperature. According to such a structure, the switching speed can be changed according to the temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a circuit diagram showing the configuration of a semiconductor switching element driving circuit according to the first embodiment. Figure 2 This is a diagram showing an example of a waveform during a turn-off operation of the semiconductor switch element according to the first embodiment. Figure 3 This is a circuit diagram showing the configuration of a semiconductor switching element driving circuit according to the second embodiment. Figure 4 This is a circuit diagram showing the configuration of a semiconductor switching element driving circuit according to a third embodiment. Figure 5 This is a circuit diagram showing the configuration of a semiconductor switching element driving circuit according to a fourth embodiment. DETAILED DESCRIPTION

[0011] The following describes the embodiments with reference to the accompanying drawings. The features described in the following embodiments are illustrative, and not all features are required. In addition, in the above description, the same or similar reference numerals are added to the same structural elements in multiple embodiments, and the different structural elements are mainly described.

[0012] <Implementation method 1> Figure 1 1 is a circuit diagram showing the structure of a semiconductor switch element drive circuit (hereinafter sometimes abbreviated as "drive circuit") according to Embodiment 1. The semiconductor switch element drive circuit drives the gate of the semiconductor switch element Q1. Figure 1In the example, the semiconductor switch element Q1 is an IGBT (Insulated Gate Bipolar Transistor), but it can also be an RC-IGBT (Reverse Conductive-IGBT) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). In addition, the material of the semiconductor switch element Q1 can be composed of ordinary silicon (Si), or can be composed of a wide bandgap semiconductor such as silicon carbide (SiC), gallium nitride (GaN) or diamond. When the semiconductor switch element Q1 is composed of a wide bandgap semiconductor, stable operation at high temperature and high voltage, and high switching speed can be achieved.

[0013] A diode D1 and an inductive load L1 connected in parallel are connected between the semiconductor switch element Q1 and the power supply V1. The diode D1 has a function of allowing the load current to flow when the semiconductor switch element Q1 is turned off. The load L1 is powered by the power supply V1.

[0014] The semiconductor switching element driving circuit of the first embodiment includes a control unit 1 , an output voltage detection unit 2 , switches S1 , S2 , and S3 , and gate resistors R1 , R2 , and R3 .

[0015] The switch S1 and the gate resistor R1 are connected in series between the power supply V0 (e.g., 15V) and the gate of the semiconductor switch element Q1. The switch S2 and the gate resistor R2 are connected in series between a potential lower than the power supply V0 (e.g., ground potential) and the gate of the semiconductor switch element Q1. Similarly, the switch S3 and the gate resistor R3 are connected in series between a potential lower than the power supply V0 (e.g., ground potential) and the gate of the semiconductor switch element Q1. Figure 1 The switches S1, S2, and S3 may be, for example, semiconductor switch elements, or other elements.

[0016] The control unit 1 controls the on and off of the switches S1, S2, and S3 based on the gate signal. When the switch S1 is turned on and the switch S2 is turned off by the control unit 1, the gate of the semiconductor switch element Q1 is electrically connected to the power supply V0 and the gate resistor R1, and the semiconductor switch element Q1 is turned on. When the switch S2 or the switch S3 is turned on and the switch S1 is turned off by the control unit 1, the gate of the semiconductor switch element Q1 is electrically connected to the ground potential and the gate resistor R2 or the gate resistor R3, and the semiconductor switch element Q1 is turned off.

[0017] In the above structure, the resistance value of the gate resistor R3 is greater than the resistance value of the gate resistor R2. Therefore, the switching speed in the turn-off operation when the semiconductor switch element Q1 is connected to the gate resistor R3 is lower than the switching speed in the turn-off operation when the semiconductor switch element Q1 is connected to the gate resistor R2. In addition, the switching speed in the turn-off operation corresponds to the speed at which the semiconductor switch element Q1 changes from the on state to the off state.

[0018] The control unit 1 switches the connection of the gate resistors R2 and R3 to the semiconductor switch element Q1 during the shutdown operation based on the switching signal from the output voltage detection unit 2, thereby switching the switching speed of the semiconductor switch element Q1 during the shutdown operation. The control unit 1 is based on the switching signal (V high ), in the turn-off action, the gate resistor R2 is switched to the gate resistor R3, thereby switching the larger switching speed to the smaller switching speed.

[0019] Figure 2 t1 is a diagram showing an example of waveforms when the semiconductor switch element Q1 is turned off. GE ) starts to decrease. t2 is the output voltage (V CE ) starts to increase slowly, and the gate voltage (V GE ) stops decreasing and becomes a constant voltage (Miller Period Voltage). t3 is the output voltage (V CE ) starts to increase sharply. t4 is the moment when the output voltage (V CE ) reaches the supply voltage and the output current (I C ) starts to decrease. t5 is the moment when the output current (I C ) becomes zero. t6 is the time when the gate voltage (V GE ) becomes zero.

[0020] like Figure 2 As shown, during the turn-off operation of the semiconductor switch element Q1, the output voltage (V CE ) increases to the power supply voltage during the period t3 to t4, and the output current (I C ) decreases during the period t4 to t5. In the period t3 to t5 including these periods, a switching loss of output voltage × output current occurs. On the other hand, during the period t4 to t5 when the output current decreases, the output voltage (V CE ) generates a surge voltage caused by the parasitic inductance of the output current path such as load L1.

[0021] Since switching loss is a factor of heat generation of the semiconductor switch element Q1 etc., it is preferable that the switching loss is low. Since the sum of the surge voltage and the power supply voltage needs to be suppressed to below the withstand voltage of the semiconductor switch element Q1 etc., it is preferable that the surge voltage is low.

[0022] Here, when the resistance value of the gate resistor for turn-off is reduced, the switching speed of the semiconductor switch element Q1 in the turn-off operation becomes faster. Figure 2 The period t3 to t5 is shortened, and the switching loss is reduced. Figure 2 The output current (I C ) rate of change (ΔI C / Δt) becomes larger, so the surge voltage (=L×ΔI) generated by the parasitic inductance L in the output current path C / Δt) increases. Conversely, when the resistance value of the gate resistor for turn-off increases, the surge voltage decreases, but the switching loss increases. Thus, there is a trade-off relationship between switching loss and surge voltage.

[0023] However, if the control unit 1 increases the switching speed by reducing the gate resistance value before t4 in the shutdown operation, the switching loss during the period t3 to t4 can be reduced. On the other hand, if the control unit 1 increases the gate resistance value after t4 in the shutdown operation to reduce the switching speed, the surge voltage during the period t4 to t5 can be reduced. Therefore, the switching timing for reducing the switching speed is preferably Figure 2 Therefore, in the first embodiment, the output voltage detection unit 2 generates and outputs a switching signal (V high ), so that the switching time for reducing the switching speed is as short as possible Figure 2 t4 in. Next, the output voltage detection unit 2 will be described. Figure 1 As shown, the output voltage detection unit 2 includes voltage dividing resistors R4 and R5, a logic circuit U1, an operational amplifier U2, a comparator U3, and a change unit 6. The change unit 6 includes a resistor R6a and an N-type MOSFET 6b.

[0025] The voltage dividing resistors R4 and R5 generate the output voltage (V CE ) of the voltage divider (V sense ).

[0026] The logic circuit U1 is a circuit having a buffer function, and is based on the divided voltage (V sense ) generates a switching signal. In the first embodiment, when the voltage division (V sense) is greater than a predetermined threshold, the logic circuit U1 generates V as a switching signal to reduce the switching speed. high , when the voltage divider (V sense ) is less than the threshold, the logic circuit U1 generates V low About voltage division (V sense ) The threshold used in the logic circuit U1 is set according to the power supply voltage (V1) supplied to the logic circuit U1. In the first embodiment, the power supply voltage of the logic circuit U1 is fixed to 5V, for example, and the threshold used in the logic circuit U1 is fixed.

[0027] In addition, when the delay time of the logic circuit U1 is smaller than the delay time of the analog comparator, the switching time for reducing the switching speed can be easily adjusted to Figure 2 t4 in.

[0028] According to the above configuration, by appropriately setting the threshold used in the logic circuit U1 and appropriately setting the switching signal (V high ) timing, so that the switching time for reducing the switching speed can be set to Figure 2 Therefore, it is possible to achieve a reduction in switching loss and a reduction in surge voltage, which are in a trade-off relationship.

[0029] However, when the temperature associated with the semiconductor switch element Q1 (hereinafter sometimes abbreviated as "switching temperature") is at room temperature, even if the switching timing of the gate resistance value is appropriately adjusted, the switching loss sometimes deteriorates when the switching temperature is high. In addition, when the switching temperature is low, the withstand voltage of the semiconductor element is generally reduced, so when the same driving conditions are used regardless of the switching temperature, the surge voltage may exceed the withstand voltage of the semiconductor element. In addition, the switching temperature is, for example, the junction temperature, the temperature detected by the on-chip temperature sensing diode provided on the semiconductor switch element Q1, or the temperature detected by the thermistor on the insulating substrate of the semiconductor device including the semiconductor switch element Q1.

[0030] Therefore, in the turn-off operation of the semiconductor switch element Q1 , it is preferable to change the timing of switching the gate resistance value according to the switching temperature, that is, to reduce the switching speed.

[0031] In consideration of the above, the output voltage detection unit 2 of the first embodiment is configured to detect the output voltage of the semiconductor switch element Q1 based on the switching temperature and the output voltage (V CE ) to generate the switching signal (V high ). Thus, the semiconductor switch element drive circuit of the first embodiment can appropriately change the timing of reducing the switching speed based on the switching temperature. The remaining components of the output voltage detection unit 2 that can achieve this will be described below.

[0032] The temperature sensing voltage corresponding to the switch temperature and having a negative temperature characteristic and the first reference voltage (V ref1 ) is input to the operational amplifier U2. The temperature sensing voltage has a negative temperature characteristic, so the higher the temperature, the smaller the temperature sensing voltage. The operational amplifier U2 connected with resistors Ra and Rb forms an inverting amplifier circuit. The output (V var ) uses the first reference voltage (V ref1 ) and the temperature sensing voltage (V S ) is expressed by the following equation (1). Since the temperature sensing voltage (V s ) decreases as the switch temperature increases. Therefore, from the following formula (1), it can be seen that the output (V var ) becomes larger.

[0033] [Mathematical formula 1] The output of operational amplifier U2 (V var ) and the second reference voltage (V ref2 ) is input to the comparator U3. The comparator U3 is based on the output (V var ) and the second reference voltage (V ref2 ) Output V out When the output of operational amplifier U2 (V var ) is greater than the second reference voltage (V ref2 ) threshold, the output of comparator U3 (V out ) is greater than the on-state voltage of MOSFET6b. On the other hand, when the output of operational amplifier U2 (V var ) is less than the second reference voltage (V ref2 ) threshold, the output of comparator U3 (V out ) is less than the on-state voltage of MOSFET6b.

[0035] In the first embodiment, when the switch temperature is a relatively high first temperature, the output (V var ) becomes larger, the output of comparator U3 (V out ) becomes larger than the on-state voltage of MOSFET6b. On the other hand, when the switch temperature is a second temperature lower than the first temperature, the output (V var ) becomes smaller, the output of comparator U3 (V out ) becomes smaller than the on-voltage of MOSFET6b.

[0036] The gate of MOSFET6b is connected to the output (V out), the drain of MOSFET6b is connected to the connection point between the voltage-dividing resistor R4 and the voltage-dividing resistor R5 via the resistor R6a, and the source of MOSFET6b is connected to the ground potential. In addition, the resistance value of MOSFET6b is smaller than that of the resistor R6a.

[0037] When the output of comparator U3 is less than the on-state voltage (V out ) is input to the gate of MOSFET6b, MOSFET6b is turned off, so the voltage-dividing resistor R4 is not actually connected to the resistor R6a, but is connected to the voltage-dividing resistor R5. On the other hand, when the output of the comparator U3 (V out ) is input to the gate of MOSFET6b, MOSFET6b is turned on, so the voltage-dividing resistor R4 is connected to the synthetic resistor composed of the voltage-dividing resistor R5 and the resistor R6a, which has a smaller resistance value than the voltage-dividing resistor R5. Since the changing unit 6 includes the resistor R6a and the MOSFET6b, it can be based on the output (V out ) Change the resistance value of the voltage divider resistors R4 and R5 to change the voltage divider (V sense ).

[0038] In the first embodiment, when the switch temperature is the relatively high first temperature, the output (V out ) becomes greater than the on-voltage of MOSFET6b, and the voltage dividing resistor R4 is connected to the synthetic resistor having a relatively small resistance value. On the other hand, when the switching temperature is a second temperature lower than the first temperature, the output (V out ) becomes smaller than the on-voltage of MOSFET6b, and the voltage-dividing resistor R4 is connected to the voltage-dividing resistor R5 having a relatively large resistance value.

[0039] Therefore, when the voltage divider (V sense ) is equal to the threshold of the logic circuit U1, the output voltage (V CE ), when the switch temperature is the first temperature, the output voltage (V CE ) is greater than the output voltage (V CE That is, when the switching temperature is the first temperature, the output voltage (V CE ) becomes greater than the output voltage (V CE ) is larger.

[0040] <Summary of Implementation 1> According to the semiconductor switch element drive circuit of the first embodiment as described above, the output voltage detection unit 2 detects the output voltage (V CE ) generates a switching signal. Furthermore, when the switch temperature is the first temperature, the output voltage (V CE ) becomes greater than the output voltage (V CE ) is larger. Here, Figure 2 As shown, during the turn-off operation of the semiconductor switch element Q1, the output voltage (V CE ) increases with time, and although not shown, the trend is basically the same regardless of the temperature. Therefore, the timing of reducing the switching speed when the switching temperature is a relatively high first temperature can be made later than the timing of reducing the switching speed when the switching temperature is a relatively low second temperature. That is, the switching speed can be changed according to the switching temperature.

[0041] Therefore, the switching timing of the gate resistance value can be appropriately adjusted when the temperature associated with the semiconductor switch element Q1 is at room temperature, and the timing can be appropriately adjusted when the temperature is high. In addition, the switching loss can be reduced when the temperature associated with the semiconductor switch element Q1 is at room temperature, and the surge voltage can be reduced when the temperature is low.

[0042] <Implementation method 2> Figure 3 : is a circuit diagram showing the configuration of a semiconductor switching element drive circuit according to Embodiment 2. The semiconductor switching element drive circuit according to Embodiment 2 is different from the semiconductor switching element drive circuit according to Embodiment 1 in the configuration of an output voltage detection unit 2 .

[0043] The output voltage detection unit 2 of the second embodiment includes voltage-dividing resistors R4 and R5 for generating an output voltage (V CE ) of the voltage divider (V sense ); and a logic circuit U1 for determining the voltage based on the voltage divider (V sense ) generates a switching signal (V high ).

[0044] In the second embodiment, the voltage-dividing resistors R4 and R5 include one or more thermistors provided near the semiconductor switch element Q1, and the one or more thermistors change the voltage division (V sense ).

[0045] In addition, at least one of the voltage divider resistors R4 and R5 may be a thermistor. For example, a PTC thermistor with a positive temperature characteristic is used for the voltage divider resistor R4, and an NTC thermistor with a negative temperature characteristic is used for the voltage divider resistor R5. sense ) is represented by V CE ×R5 / (R4+R5), so if the output voltage (V CE ) are the same, the voltage divider (V sense ) becomes smaller. Thus, when the switch temperature is the first temperature, the output voltage (V CE ) becomes greater than the output voltage (V CE ) is larger. <Summary of Implementation 2> According to the semiconductor switch element drive circuit of the second embodiment as described above, the output voltage detection unit 2 detects the output voltage (V CE ) generates a switching signal. Furthermore, when the switch temperature is the first temperature, the output voltage (V CE ) becomes greater than the output voltage (V CE ) is greater. Therefore, the timing of reducing the switching speed when the switching temperature is a relatively high first temperature can be made later than the timing of reducing the switching speed when the switching temperature is a relatively low second temperature. As a result, the same effect as that of embodiment 1 can be obtained.

[0047] In addition, the resistance value of the PTC thermistor is basically constant at room temperature, but when a certain temperature is exceeded, the resistance value of the PTC thermistor rises sharply. On the other hand, the resistance value of the NTC thermistor rises slowly as the temperature rises. Therefore, when the NTC thermistor is used as the voltage divider resistor R5, the timing of reducing the switching speed can be easily controlled.

[0048] <Implementation method 3> Figure 4 : is a circuit diagram showing the configuration of a semiconductor switching element drive circuit according to Embodiment 3. The semiconductor switching element drive circuit according to Embodiment 3 is different from the semiconductor switching element drive circuit according to Embodiment 1 in the configuration of an output voltage detection unit 2 .

[0049] The output voltage detection unit 2 of the third embodiment includes voltage-dividing resistors R4 and R5 for generating an output voltage (VCE ) of the voltage divider (V sense ); logic circuit U1, which is used based on the voltage division (V sense ) generates a switching signal (V high ); and operational amplifier U2.

[0050] The temperature sensing voltage corresponding to the switch temperature and having a negative temperature characteristic and the first reference voltage (V ref1 ) is input to the operational amplifier U2. The operational amplifier U2 connected with resistors Ra and Rb forms an inverting amplifier circuit. The output (V var ) uses the first reference voltage (V ref1 ) and the temperature sensing voltage (V S ) is expressed by the above formula (1). Since the temperature sensing voltage (V s ) decreases as the switch temperature increases. Therefore, from the above formula (1), it can be seen that the output (V var ) becomes larger.

[0051] In the third embodiment, the output (V var ) is input to the logic circuit U1 instead of the power supply voltage. Therefore, based on the output of the operational amplifier U2 (V var ) to control the logic circuit U1 and the voltage divider (V sense That is, the operational amplifier U2 controls the threshold of the logic circuit U1 based on the temperature sensing voltage.

[0052] According to the above configuration, when the switch temperature is a relatively high first temperature, the threshold of the logic circuit U1 becomes large, and when the switch temperature is a second temperature lower than the first temperature, the threshold of the logic circuit U1 decreases. Thus, when the switch temperature is the first temperature, the output voltage (V CE ) becomes greater than the output voltage (V CE ) is larger.

[0053] <Summary of Implementation 3> According to the semiconductor switch element drive circuit of the third embodiment as described above, the output voltage detection unit 2 detects the output voltage (V CE ) generates a switching signal. Furthermore, when the switch temperature is the first temperature, the output voltage (V CE ) becomes greater than the output voltage (V CE) is greater. Therefore, the timing of reducing the switching speed when the switching temperature is a relatively high first temperature can be made later than the timing of reducing the switching speed when the switching temperature is a relatively low second temperature. As a result, the same effect as that of embodiment 1 can be obtained.

[0054] <Implementation method 4> Figure 5 : is a circuit diagram showing the configuration of a semiconductor switching element drive circuit according to the fourth embodiment. The semiconductor switching element drive circuit according to the fourth embodiment is different from the semiconductor switching element drive circuit according to the first embodiment in the configuration of an output voltage detection unit 2 .

[0055] The output voltage detection unit 2 of the fourth embodiment includes voltage-dividing resistors R4 and R5 for generating an output voltage (V CE ) of the voltage divider (V sense ); logic circuit U1, which is used based on the voltage division (V sense ) generates a switching signal (V high ); and operational amplifier U4.

[0056] connected to the resistors Ra and Rb and electrically connected to the first reference voltage (V ref1 ) constitutes a non-inverting amplifier circuit. The temperature sensing voltage corresponding to the switch temperature and having a negative temperature characteristic is input to the + input terminal of the operational amplifier U4. Therefore, the temperature sensing voltage (V s ) decreases as the switch temperature increases, so the output of the non-inverting operational amplifier U4 (V out ) is reduced. The output terminal of the operational amplifier U4 is connected to the other end of the voltage-dividing resistor R5 which is different from the end connected to the voltage-dividing resistor R4. CE ) and the output of operational amplifier U4 (V out ) is expressed by the following formula (2): sense The second term on the right side of the following equation (2) is used to make the partial pressure (V sense ) offset voltage, which is offset by the output of operational amplifier U4 (V out ) is represented. Therefore, the operational amplifier U4 of the fourth embodiment generates a voltage divided by the temperature sensing voltage (V sense ) offset voltage.

[0058] [Mathematical formula 2] The output of operational amplifier U4 (V out) decreases as the switch temperature increases, so the voltage divider (V sense ) is reduced. Thus, when the switching temperature is the first temperature, the output voltage (V CE ) becomes greater than the output voltage (V CE ) is larger.

[0060] <Summary of Implementation Method 4> According to the semiconductor switch element drive circuit of the fourth embodiment as described above, the output voltage detection unit 2 detects the output voltage (V CE ) generates a switching signal. Furthermore, when the switch temperature is the first temperature, the output voltage (V CE ) becomes greater than the output voltage (V CE ) is greater. Therefore, the timing of reducing the switching speed when the switching temperature is a relatively high first temperature can be made later than the timing of reducing the switching speed when the switching temperature is a relatively low second temperature. As a result, the same effect as that of embodiment 1 can be obtained.

[0061] In addition, a capacitor may be provided between the voltage dividing resistor R5 and the ground potential on the operational amplifier U4 side. According to such a structure, the resistance to external noise can be improved.

[0062] <Modification> The first reference voltage (V ref1 ) can be a voltage of a variable power supply. In such a configuration, voltage division deviation caused by manufacturing deviation, threshold deviation of the logic circuit U1, and temperature sensing voltage deviation can be corrected. ref1 ) is fixed, even if the threshold of the logic circuit U1 varies, the voltage-dividing deviation can be adjusted by using a variable resistor or the like as the voltage-dividing resistors R4 and R5, thereby using the resistance ratio of the voltage-dividing resistors R4 and R5. In addition, as the output voltage (V CE ) of the divided trigger voltage (V trigger ) uses the threshold value of logic circuit U1 (U1 th ) is represented by the following formula (3).

[0063] [Mathematical formula 3] For example, when the resistance value of the voltage-dividing resistor R4 is 100 kΩ and the resistance value of the voltage-dividing resistor R5 is 1 kΩ, when the threshold value U1 th When the voltage is increased by x times, since R4>>R5, the resistance value of the voltage-dividing resistor R4 can be reduced to one-x. In addition, the voltage-dividing resistors R4 and R5 can include more than one variable resistor to enable such adjustment.

[0065] In addition, the embodiments and the modifications can be freely combined, and the embodiments and the modifications can be appropriately modified or omitted. Description of symbols 1 control unit, 2 output voltage detection unit, 6 change unit, R4, R5 voltage dividing resistors, Q1 semiconductor switch element, U1 logic circuit, U2, U4 operational amplifiers, U3 comparator.

Claims

1. A semiconductor switch element driving circuit for driving a gate of a semiconductor switch element, characterized in that: include: a control unit configured to switch a switching speed of the semiconductor switch element in a turn-off operation based on a switching signal; as well as an output voltage detection unit that generates the switching signal based on a temperature associated with the semiconductor switch element and an output voltage of the semiconductor switch element, The output voltage for generating the switching signal by the output voltage detection section when the temperature is a first temperature is greater than the output voltage for generating the switching signal by the output voltage detection section when the temperature is a second temperature lower than the first temperature.

2. The semiconductor switch element driving circuit according to claim 1, wherein: The output voltage detection unit comprises: A voltage-dividing resistor, which generates a divided voltage of the output voltage; a logic circuit, the logic circuit generating the switching signal based on the divided voltage; an operational amplifier to which a temperature sensing voltage corresponding to the temperature and having a negative temperature characteristic and a first reference voltage are input; a comparator to which the output of the operational amplifier and a second reference voltage are input; and A changing unit changes the divided voltage by changing the resistance value of the voltage-dividing resistor based on the output of the comparator.

3. The semiconductor switch element driving circuit according to claim 1, wherein: The output voltage detection unit comprises: A voltage-dividing resistor that generates a divided voltage of the output voltage; and a logic circuit that generates the switching signal based on the divided voltage, The voltage-dividing resistor includes one or more thermistors that change the divided voltage based on the temperature.

4. The semiconductor switch element driving circuit according to claim 1, wherein: The output voltage detection unit comprises: A voltage-dividing resistor, which generates a divided voltage of the output voltage; a logic circuit that generates the switching signal based on the divided voltage and a threshold value; and An operational amplifier controls the threshold of the logic circuit based on a temperature sensing voltage corresponding to the temperature and having a negative temperature characteristic, and is input with a first reference voltage.

5. The semiconductor switch element driving circuit according to claim 1, wherein: The output voltage detection unit comprises: A voltage-dividing resistor, which generates a divided voltage of the output voltage; a logic circuit that generates the switching signal based on the divided voltage; and An operational amplifier generates an offset voltage for offsetting the divided voltage based on a temperature sensing voltage corresponding to the temperature and having a negative temperature characteristic, and is electrically connected to a first reference voltage.

6. The semiconductor switch element driving circuit according to any one of claims 2, 4 and 5, characterized in that: The first reference voltage is a voltage of a variable power supply.

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