Semiconductor switching element drive circuit

Abstract

The purpose of the present invention is to provide a technology capable of changing a switching speed according to a temperature. This semiconductor switching element drive circuit comprises an output voltage detecting unit that generates a switch signal on the basis of a temperature pertaining to a semiconductor switching element and an output voltage of the semiconductor switching element. This semiconductor switching element drive circuit comprises an output voltage detecting unit that generates a switch signal on the basis of a temperature pertaining to a semiconductor switching element and an output voltage of the semiconductor switching element.

Description

Technical Field

[0001] The present disclosure relates to a driving circuit for a semiconductor switching element.

Background Art

[0002] In semiconductor switching elements used in inverters and the like, it is known that switching losses and surge voltages occur during the turn-off operation. There is a trade-off relationship between the switching loss and the surge voltage, such that when the switching loss is reduced, the surge voltage increases, and when the surge voltage is reduced, the switching loss increases.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the prior art, the timing for switching the switching speed during the turn-off operation is fixed regardless of the temperature of the semiconductor switching element. However, even if the switching timing of the gate resistance value is appropriately adjusted when the junction temperature is normal temperature, there is a problem that the switching loss may deteriorate when the junction temperature is high. Also, when the junction temperature is low, generally the breakdown voltage of the semiconductor element decreases, so there is a problem that the surge voltage may exceed the breakdown voltage of the semiconductor element when the driving conditions are the same regardless of the junction temperature.

[0006] Therefore, the present disclosure has been made in view of the above problems, and an object thereof is to provide a technique capable of changing the switching speed according to temperature.

Means for Solving the Problems

[0007] A semiconductor switching element drive circuit according to the present disclosure is a semiconductor switching element drive circuit that drives the gate of a semiconductor switching element, and includes a control unit that switches the switching speed during the turn-off operation of the semiconductor switching element based on a switching signal, and an output voltage detection unit that generates the switching signal based on the temperature of the semiconductor switching element and the output voltage of the semiconductor switching element. The output voltage for generating the switching signal by the output voltage detection unit when the temperature is a first temperature is larger 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.

[0008] The object, features, aspects, and advantages of the present disclosure will become clearer from the following detailed description and the 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 when the temperature is the first temperature, the output voltage for generating the switching signal by the output voltage detection unit is higher 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. With such a configuration, the switching speed can be changed according to the temperature.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described with reference to the accompanying drawings. The features described in the following embodiments are examples, and not all features are necessarily essential. Also, in the following description, the same or similar reference numerals are given to the same or similar components in a plurality of embodiments, and different components will be mainly described.

[0012] <Embodiment 1> FIG. 1 is a circuit diagram showing the configuration of a semiconductor switching element drive circuit (hereinafter sometimes abbreviated as "drive circuit") according to Embodiment 1. The semiconductor switching element drive circuit drives the gate of a semiconductor switching element Q1. In the example of FIG. 1, the semiconductor switching element Q1 is an IGBT (Insulated Gate Bipolar Transistor), but it may be an RC-IGBT (Reverse Conducting - IGBT) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Further, the material of the semiconductor switching element Q1 may be composed of ordinary silicon (Si), or may be composed of a wide bandgap semiconductor such as silicon carbide (SiC), gallium nitride (GaN), or diamond. When the semiconductor switching element Q1 is composed of a wide bandgap semiconductor, stable operation at high temperatures and high voltages, and an increase in switching speed are possible.

[0013] Between the semiconductor switching element Q1 and the power supply V1, a diode D1 and an inductive load L1 connected in parallel are connected. The diode D1 has a function of freewheeling the load current when the semiconductor switching element Q1 turns off. The load L1 is supplied with power by the power supply V1.

[0014] The semiconductor switching element drive circuit according to Embodiment 1 includes a control unit 1, an output voltage detection unit 2, switches S1, S2, S3, and gate resistors R1, R2, R3.

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

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

[0017] In the above configuration, the resistance value of gate resistor R3 is larger than the resistance value of gate resistor R2. Therefore, the switching speed during the turn-off operation when semiconductor switching element Q1 is connected to gate resistor R3 is lower than the switching speed during the turn-off operation when semiconductor switching element Q1 is connected to gate resistor R2. Note that the switching speed during the turn-off operation corresponds to the speed from when semiconductor switching element Q1 is in the on state to when it becomes in the off state.

[0018] Based on the switching signal from the output voltage detection unit 2, the control unit 1 switches the connection of the gate resistors R2 and R3 to the semiconductor switching element Q1 during the turn-off operation, thereby switching the switching speed of the semiconductor switching element Q1 during the turn-off operation. The control unit 1 switches from a large switching speed to a small switching speed by switching from the gate resistor R2 to the gate resistor R3 during the turn-off operation based on the switching signal (V high ) input to the output sense from the output voltage detection unit 2 described later.

[0019] Figure 2 is a diagram showing an example of waveforms during the turn-off operation of the semiconductor switching element Q1. t 1 is the time point when the gate signal turns off and the gate voltage (V GE ) starts to decrease. t 2 is the time point when the output voltage (V CE ), which is the collector voltage, starts to increase gently and the gate voltage (V GE ) stops decreasing and becomes a constant voltage (Miller period voltage). t 3 is the time point when the output voltage (V CE ) starts to increase rapidly. t 4 is the time point when the output voltage (V CE ) reaches the power supply voltage and the output current (I C ) starts to decrease. t 5 is the time point when the output current (I C ) becomes zero. t 6 is the time point when the gate voltage (V GE ) becomes zero.

[0020] As shown in Figure 2, during the turn-off operation of the semiconductor switching element Q1, the output voltage (V 3 ~t 4 ) increases to the power supply voltage during the period t CE , and the output current (I 4 ~t 5 ) decreases during the period t C . Switching losses due to the output voltage × output current occur during the period t 3 ~t 5 including these periods. On the other hand, during the period when the output current decreases, t4 ~t 5 The surge voltage caused by the parasitic inductance of the output current path, such as the load L1, increases to the output voltage (V CE ) occurs.

[0021] The lower the switching loss, the more preferable it is because it causes heat generation in the semiconductor switching element Q1, etc. The lower the surge voltage, the more preferable it is because the sum of the surge voltage and the power supply voltage must be kept below the withstand voltage of the semiconductor switching element Q1, etc.

[0022] Here, if the resistance value of the gate resistor for turn-off is reduced, the switching speed during the turn-off operation of the semiconductor switching element Q1 increases, and the period t 3 ~t 5 However, the period t 4 ~t 5 The output current (I C ) change rate (ΔI C / Δt) becomes large, the surge voltage (=L×ΔI C / Δt) increases. Conversely, if the resistance value of the turn-off gate resistor is increased, the surge voltage decreases, but the switching loss increases. In this way, there is a trade-off between switching loss and surge voltage.

[0023] However, during the turn-off operation, t 4 If the control unit 1 reduces the gate resistance value to increase the switching speed, the period t 3 ~t 4 On the other hand, during the turn-off operation, the switching loss can be reduced. 4 Later, if the control unit 1 increases the gate resistance value to reduce the switching speed, the period t 4 ~t 5 Therefore, the time point at which the switching speed is reduced is t 4It is preferable that it becomes. Therefore, in the first embodiment, the switching speed is reduced as much as possible at the switching point shown in FIG. 2 at t 4 So that the output voltage detection unit 2 is configured to generate and output a switching signal (V high ) for switching the switching speed.

[0024] Next, the output voltage detection unit 2 will be described. As shown in FIG. 1, the output voltage detection unit 2 includes voltage dividing resistors R4, R5, a logic circuit U1, an operational amplifier U2, a comparator U3, and a changing unit 6. The changing unit 6 includes a resistor R6a and an N-type MOSFET 6b.

[0025] The voltage dividing resistors R4, R5 generate a voltage division (V CE ) of the output voltage (V sense ) of the semiconductor switching element Q1.

[0026] The logic circuit U1 is a circuit having a buffer function, and generates a switching signal based on the voltage division (V sense ) generated by the voltage dividing resistors R4, R5. In the first embodiment, when the voltage division (V sense ) is greater than a predetermined threshold value, the logic circuit U1 generates V high , which is a switching signal for reducing the switching speed, and when the voltage division (V sense ) is less than the threshold value, the logic circuit U1 generates V low . The threshold value used by the logic circuit U1 for the voltage division (V sense ) is set by the power supply voltage (V1) to the logic circuit U1. In the first embodiment, the power supply voltage of the logic circuit U1 is fixed at 5V, for example, and the threshold value used by the logic circuit U1 is fixed.

[0027] Note that when the delay time of the logic circuit U1 is smaller than the delay time of the analog comparator, the switching point for reducing the switching speed can be easily adjusted to t 4 in FIG. 2.

[0028] According to the above configuration, the threshold value used by the logic circuit U1 is appropriately set, and the switching signal (Vhigh ) By appropriately setting the timing for generating and outputting, the switching time for reducing the switching speed can be set to t in FIG. 2 4 . Therefore, it is possible to realize the reduction of switching loss and the reduction of surge voltage, which are in a trade-off relationship.

[0029] However, when the temperature of the semiconductor switching 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 may deteriorate when the switching temperature is high. Also, when the switching temperature is low, generally the breakdown voltage of the semiconductor element decreases. Therefore, when the driving conditions are the same regardless of the switching temperature, the surge voltage may exceed the breakdown voltage of the semiconductor element. Note that the switching temperature is, for example, the junction temperature, the temperature detected by an on-chip temperature sense diode provided on the semiconductor switching element Q1, or the temperature detected by a thermistor on the insulating substrate of the semiconductor device including the semiconductor switching element Q1.

[0030] For the above reasons, during the turn-off operation of the semiconductor switching element Q1, it is desirable that the timing for switching the gate resistance value, that is, the timing for reducing the switching speed, be changed according to the switching temperature.

[0031] In consideration of the above, the output voltage detection unit 2 according to the first embodiment generates a switching signal (V CE ) based on the switching temperature and the output voltage (V high ) of the semiconductor switching element Q1. Thereby, the semiconductor switching element drive circuit according to the first embodiment can appropriately change the timing for reducing the switching speed based on the switching temperature. Hereinafter, the remaining components of the output voltage detection unit 2 capable of realizing this will be described.

[0032] The operational amplifier U2 receives a temperature sense voltage corresponding to the switch temperature and having a negative temperature characteristic, and a first reference voltage (V ref1 ). Since the temperature sense voltage has a negative temperature characteristic, it becomes smaller as the temperature increases. The operational amplifier U2 to which the resistors Ra and Rb are connected forms an inverting amplifier circuit, and the output (V var ) of the operational amplifier U2 is expressed by the following equation (1) using the first reference voltage (V ref1 ) and the temperature sense voltage (V s ). As the switch temperature increases, the temperature sense voltage (V s ) becomes smaller, so as can be seen from the following equation (1), the output (V var ) of the operational amplifier U2 that inverts the input increases.

[0033]

Equation

[0034] The comparator U3 receives the output (V var ) of the operational amplifier U2 and a second reference voltage (V ref2 ). The comparator U3 outputs V out based on the output (V var ) of the operational amplifier U2 and the second reference voltage (V ref2 ). When the output (V var ) of the operational amplifier U2 is greater than the threshold corresponding to the second reference voltage (V ref2 ), the output (V out ) of the comparator U3 is greater than the on-voltage of the MOSFET 6b. On the other hand, when the output (V var ) of the operational amplifier U2 is less than the threshold corresponding to the second reference voltage (V ref2 ), the output (V out ) of the comparator U3 is less than the on-voltage of the MOSFET 6b.

[0035] In the first embodiment, when the switch temperature is a relatively high first temperature, the output (V var ) of the operational amplifier U2 increases, and the output (V out) becomes larger than the on-voltage of MOSFET6b. On the other hand, when the switch temperature is a second temperature lower than the first temperature, the output (V var ) of the operational amplifier U2 becomes smaller, and the output (V out ) of the comparator U3 becomes smaller than the on-voltage of MOSFET6b.

[0036] The gate of MOSFET6b is connected to the output (V out ) of the comparator U3. The drain of MOSFET6b is connected to the connection point between the voltage dividing resistors R4 and R5 via the resistor R6a, and the source of MOSFET6b is connected to the ground potential. Note that the resistance value of MOSFET6b is smaller than that of the resistor R6a.

[0037] When the output (V out ) of the comparator U3, which is smaller than the on-voltage, is input to the gate of MOSFET6b, MOSFET6b turns off. Therefore, the voltage dividing resistor R4 is not substantially connected to the resistor R6a and is connected to the voltage dividing resistor R5. On the other hand, when the output (V out ) of the comparator U3, which is larger than the on-voltage, is input to the gate of MOSFET6b, MOSFET6b turns on. Therefore, the voltage dividing resistor R4 is connected to the combined resistor of the voltage dividing resistor R5 and the resistor R6a, which has a smaller resistance value than the voltage dividing resistor R5. Since the modification unit 6 includes the resistor R6a and MOSFET6b, based on the output (V out ) of the comparator U3, it is possible to change the resistance values of the voltage dividing resistors R4 and R5 and change the voltage division (V sense ).

[0038] In the first embodiment, when the switch temperature is a relatively high first temperature, the output (V out ) of the comparator U3 becomes larger than the on-voltage of MOSFET6b, and the voltage dividing resistor R4 is connected to the combined resistor having a relatively small resistance value. On the other hand, when the switch temperature is a second temperature lower than the first temperature, the output (V out ) of the comparator U3 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] As a result, when the divided voltage (V sense ) becomes equal to the threshold value of the logic circuit U1, regarding the output voltage (V CE ) of the semiconductor switching element Q1, the output voltage (V CE ) when the switch temperature is the first temperature is larger than the output voltage (V CE ) when the switch temperature is the second temperature. That is, the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 when the switch temperature is the first temperature is larger than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 when the switch temperature is the second temperature.

[0040] <Summary of Embodiment 1> According to the semiconductor switching element drive circuit according to the first embodiment as described above, the output voltage detection unit 2 generates a switching signal based on the switch temperature and the output voltage (V CE ) of the semiconductor switching element Q1. And the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 when the switch temperature is the first temperature is larger than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 when the switch temperature is the second temperature. Here, as shown in FIG. 2, during the turn-off operation of the semiconductor switching element Q1, the output voltage (V CE ) of the semiconductor switching element Q1 increases with time, and although not shown, the tendency is substantially the same regardless of the temperature. For this reason, the timing for reducing the switching speed when the switch temperature is the relatively high first temperature can be made later than the timing for reducing the switching speed when the switch temperature is the relatively low second temperature. That is, the switching speed can be changed according to the switch temperature.

[0041] Therefore, while appropriately adjusting the switching timing of the gate resistance value when the temperature related to the semiconductor switching element Q1 is normal temperature, the timing can be appropriately adjusted when the temperature is high. Further, while reducing the switching loss when the temperature related to the semiconductor switching element Q1 is normal temperature, the surge voltage when the temperature is low can be reduced.

[0042] <Embodiment 2> FIG. 3 is a circuit diagram showing the configuration of a semiconductor switching element drive circuit according to the second embodiment. The semiconductor switching element drive circuit according to the second embodiment and the semiconductor switching element drive circuit according to the first embodiment differ in the configuration of the output voltage detection unit 2.

[0043] The output voltage detection unit 2 according to the second embodiment includes voltage dividing resistors R4 and R5 that generate a divided voltage (V CE ) of the output voltage (V sense ) of the semiconductor switching element Q1, and a logic circuit U1 that generates a switching signal (V sense ) based on the divided voltage (V high ).

[0044] In the second embodiment, the voltage dividing resistors R4 and R5 include one or more thermistors provided in the vicinity of the semiconductor switching element Q1, and the one or more thermistors change the divided voltage (V sense ) based on the switch temperature.

[0045] Note that at least one of the voltage dividing resistors R4 and R5 may be a thermistor. For example, a PTC thermistor having a positive temperature characteristic is used for the voltage dividing resistor R4, and an NTC thermistor having a negative temperature characteristic is used for the voltage dividing resistor R5. Since the divided voltage (V sense ) is expressed as V CE ×R5 / (R4 + R5), when these thermistors are used when the output voltage (V CE ) is the same, as the switch temperature increases, the divided voltage (V sense) becomes smaller. As a result, when the switch temperature is the first temperature, the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 is larger than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 when the switch temperature is the second temperature.

[0046] <Summary of Embodiment 2> According to the semiconductor switching element drive circuit according to Embodiment 2 as described above, the output voltage detection unit 2 generates a switching signal based on the switch temperature and the output voltage (V CE ) of the semiconductor switching element Q1. And when the switch temperature is the first temperature, the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 is larger than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 when the switch temperature is the second temperature. Therefore, the timing for reducing the switching speed when the switch temperature is the relatively high first temperature can be made later than the timing for reducing the switching speed when the switch temperature is the relatively low second temperature. As a result, the same effect as in Embodiment 1 can be obtained.

[0047] Note that the resistance value of the PTC thermistor is almost constant at about room temperature, but rises rapidly when it exceeds a certain temperature. On the other hand, the resistance value of the NTC thermistor rises gently as the temperature rises. Therefore, when an NTC thermistor is used for the voltage dividing resistor R5, it becomes easy to control the timing for reducing the switching speed.

[0048] <Embodiment 3> FIG. 4 is a circuit diagram showing the configuration of the semiconductor switching element drive circuit according to Embodiment 3. The semiconductor switching element drive circuit according to Embodiment 3 and the semiconductor switching element drive circuit according to Embodiment 1 differ in the configuration of the output voltage detection unit 2.

[0049] The output voltage detection unit 2 according to the third embodiment generates a divided voltage (V CE ) of the output voltage (V sense ) of the semiconductor switching element Q1 by voltage dividing resistors R4 and R5, and includes a logic circuit U1 that generates a switching signal (V sense ) based on the divided voltage (V high ), and an operational amplifier U2.

[0050] A temperature sense voltage corresponding to the switch temperature and having a negative temperature characteristic and a first reference voltage (V ref1 ) are input to the operational amplifier U2. The operational amplifier U2 with resistors Ra and Rb connected constitutes an inverting amplifier circuit, and the output (V var ) of the operational amplifier U2 is represented by the above formula (1) using the first reference voltage (V ref1 ) and the temperature sense voltage (V s ). As the switch temperature increases, the temperature sense voltage (V s ) decreases. Therefore, as can be seen from the above formula (1), the output (V var ) of the operational amplifier U2 that inverts the input increases.

[0051] In the third embodiment, the output (V var ) of the operational amplifier U2 is input to the logic circuit U1 instead of the power supply voltage. For this reason, the threshold value compared with the divided voltage (V sense ) in the logic circuit U1 is controlled based on the output (V var ) of the operational amplifier U2. That is, the operational amplifier U2 controls the threshold value of the logic circuit U1 based on the temperature sense voltage.

[0052] With the above configuration, when the switch temperature is a relatively high first temperature, the threshold value of the logic circuit U1 increases, and when the switch temperature is a second temperature lower than the first temperature, the threshold value of the logic circuit U1 decreases. As a result, the output voltage (V CE ) for generating a switching signal by the output voltage detection unit 2 when the switch temperature is the first temperature is larger than the output voltage (V CE ) for generating a switching signal by the output voltage detection unit 2 when the switch temperature is the second temperature.

[0053] <Summary of Embodiment 3> According to the semiconductor switching element drive circuit according to Embodiment 3 as described above, the output voltage detection unit 2 generates a switching signal based on the switch temperature and the output voltage (V CE ) of the semiconductor switching element Q1. When the switch temperature is the first temperature, the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 is higher than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 when the switch temperature is the second temperature. Therefore, the timing for reducing the switching speed when the switch temperature is the relatively high first temperature can be made later than the timing for reducing the switching speed when the switch temperature is the relatively low second temperature. As a result, the same effect as in Embodiment 1 can be obtained.

[0054] <Embodiment 4> FIG. 5 is a circuit diagram showing the configuration of the semiconductor switching element drive circuit according to Embodiment 4. The semiconductor switching element drive circuit according to Embodiment 4 and the semiconductor switching element drive circuit according to Embodiment 1 differ in the configuration of the output voltage detection unit 2.

[0055] The output voltage detection unit 2 according to Embodiment 4 includes voltage dividing resistors R4 and R5 that generate a voltage division (V CE ) of the output voltage (V sense ) of the semiconductor switching element Q1, a logic circuit U1 that generates a switching signal (V sense ) based on the voltage division (V high ), and an operational amplifier U4.

[0056] The operational amplifier U4 to which resistors Ra and Rb are connected and which is electrically connected to the first reference voltage (V ref1 ) via the resistor Ra constitutes a non-inverting amplifier circuit. A temperature sense 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 higher the switch temperature, the higher the temperature sense voltage (V s) becomes smaller, so the output (V of the operational amplifier U4 that does not invert the input out ) becomes smaller.

[0057] The output terminal of the operational amplifier U4 is connected to the other end of the voltage dividing resistor R5 that is different from the one end connected to the voltage dividing resistor R4. As a result, the voltage division (V sense ) is represented by the following equation (2) using the output voltage (V CE ) of the semiconductor switching element Q1 and the output (V out ) of the operational amplifier U4. The second term on the right side of equation (2) represents an offset voltage for offsetting the voltage division (V sense ), and is represented by the output (V out ) of the operational amplifier U4. Therefore, the operational amplifier U4 according to Embodiment 4 generates an offset voltage for offsetting the voltage division (V sense ) based on the temperature sense voltage.

[0058]

Equation

[0059] As the switch temperature increases, the output (V out ) of the operational amplifier U4 becomes smaller, so the voltage division (V sense ) in equation (2) becomes smaller. As a result, the output voltage (V CE ) for generating the switching signal in the output voltage detection unit 2 when the switch temperature is the first temperature is larger than the output voltage (V CE ) for generating the switching signal in the output voltage detection unit 2 when the switch temperature is the second temperature.

[0060] <Summary of Embodiment 4> According to the semiconductor switching element drive circuit according to Embodiment 4 as described above, the output voltage detection unit 2 generates a switching signal based on the switch temperature and the output voltage (V CE ) of the semiconductor switching element Q1. And when the switch temperature is the first temperature, the output voltage (V CE) is for generating a switching signal by the output voltage detection unit 2 when the switch temperature is the second temperature, and the output voltage (V CE ) is larger. Therefore, the timing for reducing the switching speed when the switch temperature is the relatively high first temperature can be made later than the timing for reducing the switching speed when the switch temperature is the relatively low second temperature. As a result, the same effects as those in the first embodiment can be obtained.

[0061] A capacitor may be provided between the voltage dividing resistor R5 and the ground potential on the side of the operational amplifier U4. According to such a configuration, the resistance to external noise can be enhanced.

[0062] <Modification Example> The first reference voltage (V ref1 ) in the first, third, and fourth embodiments may be the voltage of a variable power supply. When configured in this way, the deviation of voltage division caused by manufacturing variations, the deviation of the threshold value of the logic circuit U1, and the deviation of the temperature sense voltage can be corrected. Also, when the first reference voltage (V ref1 ) is fixed, even if the threshold value of the logic circuit U1 deviates, by using variable resistors or the like for the voltage dividing resistors R4 and R5, the deviation of voltage division and the like can be adjusted by the ratio of the resistance values of the voltage dividing resistors R4 and R5. Note that the trigger voltage (V CE ), which is the voltage division of the output voltage (V trigger ) for the logic circuit U1 to generate a switching signal, is represented by the following formula (3) using the threshold value (U1 th ) of the logic circuit U1.

[0063]

Equation

[0064] 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 increases by x times, since R4 >> R5, the resistance value of the voltage dividing resistor R4 may be made x times smaller. Note that the voltage dividing resistors R4 and R5 may include one or more variable resistors so that such adjustment can be made.

[0065] Note that it is possible to freely combine each embodiment and each modification example, or to appropriately modify or omit each embodiment and each modification example.

Description of Reference Numerals

[0066] 1 Control unit, 2 Output voltage detection unit, 6 Change unit, R4, R5 Voltage dividing resistors, Q1 Semiconductor switching element, U1 Logic circuit, U2, U4 Operational amplifiers, U3 Comparator.

Claims

1. A semiconductor switching element drive circuit for driving a gate of a semiconductor switching element, a control unit that switches a switching speed during a turn-off operation of the semiconductor switching element based on a switching signal; an output voltage detection unit that generates the switching signal based on a temperature of the semiconductor switching element and an output voltage of the semiconductor switching element, comprising: wherein an output voltage for generating the switching signal by the output voltage detection unit when the temperature is a first temperature is higher than an 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. A semiconductor switching element drive circuit.

2. The semiconductor switching element drive circuit according to claim 1, wherein the output voltage detection unit a voltage dividing resistor that generates a voltage division of the output voltage; a logic circuit that generates the switching signal based on the voltage division; an operational amplifier to which a temperature sense voltage corresponding to the temperature and having a negative temperature characteristic and a first reference voltage are input; a comparator to which an output of the operational amplifier and a second reference voltage are input; a changing unit that changes a resistance value of the voltage dividing resistor based on an output of the comparator to change the voltage division, comprising a semiconductor switching element drive circuit.

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

4. The semiconductor switching element drive circuit according to claim 1, wherein the output voltage detection unit a voltage dividing resistor that generates a voltage division of the output voltage; a logic circuit that generates the switching signal based on the voltage division and a threshold value; an operational amplifier that controls the threshold value of the logic circuit based on a temperature sense voltage corresponding to the temperature and having a negative temperature characteristic, and to which a first reference voltage is input, comprising a semiconductor switching element drive circuit.

5. The semiconductor switching element drive circuit according to claim 1, wherein the output voltage detection unit a voltage dividing resistor that generates a voltage division of the output voltage; a logic circuit that generates the switching signal based on the voltage division, Based on the temperature sense voltage having a negative temperature characteristic corresponding to the temperature, an offset voltage for offsetting the voltage division is generated, and an operational amplifier electrically connected to a first reference voltage and A semiconductor switching element drive circuit including.

6. The semiconductor switching element drive circuit according to claim 2, 4, or 5, wherein The semiconductor switching element drive circuit, wherein the first reference voltage is the voltage of a variable power supply.

Images