Control circuit for a semiconductor switching element

Abstract

One object is to provide a technique that enables a switching speed to be changed depending on a temperature. The drive circuit for a semiconductor switching element 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. The output voltage for generating the switching signal by the output voltage detection unit in a case where the temperature is a first temperature is greater than the output voltage for generating the switching signal by the output voltage detection unit in a case where the temperature is a second temperature lower than the first temperature.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a drive circuit for a semiconductor switching element. BACKGROUND TECHNOLOGY

[0002] It is known that in a semiconductor switching element used in an inverter or the like, switching loss and surge voltage are generated during a turn-off operation. There is a trade-off relationship between switching loss and surge voltage. As switching loss decreases, surge voltage increases, whereas switching loss increases as surge voltage decreases.

[0003] As a technique for improving both switching loss and surge voltage during the turn-off operation, a technique called active gate driving has been proposed (e.g., Patent Document 1). In active gate driving, a switching speed is switched by switching a gate resistance value during a turn-off operation of a semiconductor switching element. DOCUMENT ACCORDING TO THE PRIOR ART PATENT DOCUMENT

[0004] Patent Document 1: Japanese Patent No. 4991446 SUMMARY PROBLEM TO BE SOLVED BY THE INVENTION

[0005] In the conventional technology, a timing for switching the switching speed during the turn-off operation is determined regardless of a temperature of the semiconductor switching element. However, even if a switching timing of a gate resistance value is appropriately set in a case where a junction temperature is a normal temperature, there is a problem that the switching loss may deteriorate in a case where the junction temperature is high. Furthermore, in a case where the junction temperature is low, a withstand voltage of the semiconductor element gradually decreases. Therefore, in a case where driving conditions are the same regardless of the junction temperature, there is a problem that the surge voltage may exceed the withstand voltage of the semiconductor element.

[0006] The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a technique that enables a switching speed to be changed depending on temperature. MEANS TO SOLVE THE PROBLEM

[0007] A drive circuit for a semiconductor switching element according to the present disclosure is a drive circuit for a semiconductor switching element that drives a gate of a semiconductor switching element and includes a control unit that switches a switching speed during a 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 a temperature related to the semiconductor switching element and an output voltage of the semiconductor switching element, and the output voltage for generating the switching signal by the output voltage detection unit in a case where the temperature is a first temperature is larger than the output voltage for generating the switching signal by the output voltage detection unit in a case where the temperature is a second temperature lower than the first temperature.

[0008] Objects, features, aspects and advantages of the present disclosure will become more apparent 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 a temperature related to the semiconductor switching element and an output voltage of the semiconductor switching element, and the output voltage for generating the switching signal by the output voltage detection unit in a case where the temperature is a first temperature is greater than the output voltage for generating the switching signal by the output voltage detection unit in a case where the temperature is a second temperature lower than the first temperature. According to such a configuration, a switching speed can be changed depending on the temperature. BRIEF DESCRIPTION OF THE DRAWINGS [ Fig. 1] is a circuit diagram illustrating a configuration of a drive circuit for a semiconductor switching element according to a first embodiment. [ Fig. 2] is a diagram illustrating an example of a waveform during a turn-off operation of a semiconductor switching element according to the first embodiment. [ Fig. 3] is a circuit diagram illustrating a configuration of a drive circuit for a semiconductor switching element according to a second embodiment. [ Fig. 4] is a circuit diagram illustrating a configuration of a drive circuit for a semiconductor switching element according to a third embodiment. [ Fig. 5] is a circuit diagram illustrating a configuration of a drive circuit for a semiconductor switching element according to a fourth embodiment. DESCRIPTION OF THE EMBODIMENTS

[0010] Embodiments are described below with reference to the accompanying drawings. Features described in the following embodiments are examples, and not all features are essential. In the following description, similar component elements in a plurality of embodiments are assigned identical or similar reference numerals, and different component elements are primarily described. <Erste Ausführungsform>

[0011] Fig. 1 is a circuit diagram illustrating a configuration of a semiconductor switching element drive circuit (hereinafter sometimes abbreviated as "drive circuit") according to a first embodiment. The semiconductor switching element drive circuit drives a gate of a semiconductor switching element Q1. In the example of Fig. 1, the semiconductor switching element Q1 is an insulated-gate bipolar transistor (IGBT), but it may be a reverse-conducting IGBT (RC-IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). The semiconductor switching element Q1 may be made of ordinary silicon (Si) or a wide-band-gap semiconductor such as silicon carbide (SiC), gallium nitride (GaN), or diamond. When the semiconductor switching element Q1 is made of a wide-band-gap semiconductor, it is possible to achieve stable operation at high temperatures and high voltages and to increase the switching speed.

[0012] A diode D1 and an inductive load L1, connected in parallel, are connected between the semiconductor switching element Q1 and a power supply V1. The diode D1 conducts load current in a freewheeling manner when the semiconductor switching element Q1 is off. Power is supplied to the load L1 by the power supply V1.

[0013] The drive circuit for a semiconductor switching element according to the first embodiment includes a control unit 1, an output voltage detection unit D2, switches S1, S2 and S3 and gate resistors R1, R2 and R3.

[0014] The switch S1 and the gate resistor R1 are connected in series between a power supply V0 (for example, 15 V) and the gate of the semiconductor switching element Q1. The switch S2 and the gate resistor R2 are connected in series between a potential (for example, a ground potential) lower than the power supply V0 and the gate of the semiconductor switching element Q1. Similarly, the switch S3 and the gate resistor R3 are connected between a potential (ground potential in Fig. 1), which is lower than the power supply V0, and the gate of the semiconductor switching element Q1. Switches S1, S2, and S3 may be semiconductor switching elements, for example, or they may be other elements.

[0015] The control unit 1 controls the turning on and off of the switches S1, S2, and S3 based on a gate signal. When the control unit 1 turns on the switch S1 and turns off the switch S2, the gate of the semiconductor switching element Q1 is electrically connected to the power supply V0 and the gate resistor R1, and the semiconductor switching element Q1 is turned on. When the control unit 1 turns on the switch S2 or the switch S3 and turns off the switch S1, the gate of the semiconductor switching element Q1 is electrically connected to the ground potential and the gate resistor R2 or the gate resistor R3, and the semiconductor switching element Q1 is turned off.

[0016] In the above configuration, the resistance value of gate resistor R3 is larger than the resistance value of gate resistor R2. Accordingly, a switching speed during a turn-off operation in a case where semiconductor switching element Q1 is connected to gate resistor R3 is lower than a switching speed during a turn-off operation in a case where semiconductor switching element Q1 is connected to gate resistor R2. Note that a switching speed during a turn-off operation corresponds to a speed at which semiconductor switching element Q1 changes from an on-state to an off-state.

[0017] The control unit 1 switches a connection of the gate resistors R2 and R3 to the semiconductor switching element Q1 during a turn-off operation based on a switching signal from the output voltage detection unit 2, thereby switching the switching speed of the semiconductor switching element Q1 during the turn-off operation. The control unit 1 switches the switching speed from a high switching speed to a low switching speed by changing the gate resistance from the gate resistor R2 to the gate resistor R3 during the turn-off operation based on a switching signal (V high ) which is fed into an output detection from the output voltage detection unit 2, which will be described later.

[0018] Fig. Figure 2 is a diagram illustrating an example of a waveform during a turn-off operation of the semiconductor switching element Q1. t1 is a time at which the gate signal is turned off and a gate voltage (V GE ) begins to decrease. t2 is a time at which an output voltage (V CE ), which is a collector voltage, gradually begins to rise and the gate voltage (V GE ) stops decreasing and becomes a constant voltage (voltage of the Müller period). t3 is a time point at which the output voltage (V CE ) begins to rise rapidly. t4 is a time at which the output voltage (V CE ) a power supply voltage is reached and an output current (I C ) begins to decrease. t5 is a time at which the output current (I C ) becomes zero. t6 is a time at which the gate voltage (V GE ) becomes zero.

[0019] As in Fig. 2, during the turn-off process of the semiconductor switching element Q1, the output voltage (V CE ) during the period t3 to t4 to the power supply voltage and the output current (I C ) during the period t4 to t5. During the period t3 to t5 including these periods, a switching loss occurs, which is obtained by the output voltage × the output current. On the other hand, during the period t4 to t5 in which the output current decreases, a surge voltage caused by a parasitic inductance of an output current path such as the load L1 is added to the output voltage (V CE ) is generated.

[0020] The switching loss is preferably low because the switching loss causes heat generation of the semiconductor switching element Q1 and the like. The surge voltage is preferably low because the sum of the surge voltage and the power supply voltage must be suppressed to be equal to or less than the withstand voltage of the semiconductor switching element Q1 and the like.

[0021] When a resistance value of a gate resistor is reduced for turning off, the switching speed during the turning off operation of the semiconductor switching element Q1 increases and the period t3 to t5 becomes Fig. 2 shortens and the switching loss decreases. However, since a rate of change (ΔI C / Δt) of the output current (I C ) of the semiconductor switching element Q1 in the period t4 to t5 in Fig. 2 increases, the surge voltage generated by the parasitic inductance L of the output current path (= L × ΔI C / Δt). Conversely, if the gate resistance is increased for turn-off, the surge voltage decreases but the switching loss increases. As described above, switching loss and surge voltage are in a trade-off relationship.

[0022] However, if the control unit 1 decreases the gate resistance value to increase the switching speed before t4 during the turn-off operation, the switching loss in the period t3 to t4 can be reduced. On the other hand, if the control unit 1 increases the gate resistance value to decrease the switching speed after t4 during the turn-off operation, the surge voltage in the period t4 to t5 can be reduced. Therefore, a switching time at which the switching speed is reduced is preferably t4 in Fig. 2. In the first embodiment, therefore, the output voltage detection unit 2 is configured to detect the switching signal (V high) for switching the switching speed, so that the switching time at which the switching speed is reduced is as close as possible to t4 in Fig. 2 becomes.

[0023] Next, the output voltage detection unit 2 is described. As shown in Fig. 1, 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 changing unit 6. The changing unit 6 includes a resistor R6a and an N-type MOSFET 6b.

[0024] The voltage dividing resistors R4 and R5 generate a divided voltage (V sense ) of the output voltage (V CE ) of the semiconductor switching element Q1.

[0025] The logic circuit U1 is a circuit with a buffer function and generates a switching signal based on the divided voltage (V sense ). In the first embodiment, the logic circuit U1 generates V high , which is a switching signal to reduce the switching speed when the divided voltage (V sense ) is greater than a predetermined threshold, and generates V low , if the divided voltage (V sense ) is smaller than the threshold value. The threshold value used in the logic circuit U1 with respect to the divided voltage (V sense ) is set by 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 set to, for example, 5 V, and the threshold value used in the logic circuit U1 is fixed.

[0026] Note that in a case where a delay time of the logic circuit U1 is shorter than a delay time of an analog comparator, the switching time at which the switching speed is reduced is simply set to t4 of Fig. 2 can be set.

[0027] According to the above configuration, by appropriately setting the threshold value used in the logic circuit U1 and the timing at which the switching signal (V high ) is generated and output by the output voltage detection unit 2, is suitably adjusted, the switching time for reducing the switching speed to t4 in Fig. 2. Therefore, it is possible to achieve a reduction in switching loss and a reduction in surge voltage, which are in a conflicting relationship.

[0028] However, even if the switching timing of the gate resistance value is appropriately adjusted, when a temperature related to the semiconductor switching element Q1 (hereinafter also abbreviated as "switch temperature") is a normal temperature, switching loss may deteriorate if the switch temperature is high. Furthermore, in a case where the switch temperature is low, a withstand voltage of the semiconductor element generally decreases. Therefore, in a case where driving conditions are the same regardless of the switch temperature, the surge voltage may undesirably exceed the withstand voltage of the semiconductor element.Note that the switch temperature is, for example, a junction temperature, a temperature detected by an on-chip temperature measuring diode arranged on the semiconductor switching element Q1, or a temperature detected by a thermistor arranged in an insulating substrate of a semiconductor device including the semiconductor switching element Q1.

[0029] For the above reason, it is desirable that the timing for switching the gate resistance value, that is, the timing for reducing the switching speed during the turn-off operation of the semiconductor switching element Q1, be changed depending on the switch temperature.

[0030] In view of the above, the output voltage detection unit 2 of the first embodiment is configured to detect the switching signal (V high ) based on the switch temperature and the output voltage (V CE) of the semiconductor switching element Q1. Thus, the semiconductor switching element driving circuit according to the first embodiment can appropriately change the timing for reducing the switching speed based on the switch temperature. The remaining constituent elements of the output voltage detection unit 2 that can realize this are described below.

[0031] A temperature detection voltage corresponding to the switch temperature and having negative temperature characteristics, and a first reference voltage (V ref1 ) are fed into the operational amplifier U2. Since the temperature detection voltage has negative temperature characteristics, the temperature detection voltage decreases with increasing temperature. The operational amplifier U2, to which the resistors Ra and Rb are connected, forms an inverting amplifier circuit, and an output (V var) of the operational amplifier U2 is calculated using the first reference voltage (V ref1 ) and the temperature detection voltage (V s ) is expressed by the following formula (1). As the switch temperature increases, the temperature detection voltage (V s ) and therefore the output (V var ) of the operational amplifier U2, which inverts the input, as can be seen from the following formula (1). [Mathematical Formula 1] Vvar=(1+RbRa)Vref−RbRaVs

[0032] The edition (V var ) of the operational amplifier U2 and a second reference voltage (V ref2 ) are fed into the comparator U3. The comparator U3 outputs the voltage (V var ) of the operational amplifier U2 and the second reference voltage (V ref2 ) V out In a case where the output (V var ) of the operational amplifier U2 is greater than one of the second reference voltage (Vref2 ) corresponding threshold, the output (V out ) of the comparator U3 is greater than an on-voltage of the MOSFET 6b. On the other hand, in a case where the output (V var ) of the operational amplifier U2 is smaller than that of the second reference voltage (V ref2 ) corresponding threshold, the output (V out ) of the comparator U3 is smaller than the on-voltage of the MOSFET 6b.

[0033] In the first embodiment, in a case where the switch temperature is a relatively high first temperature, the output (V var ) of the operational amplifier U2 becomes large and the output (V out ) of the comparator U3 is smaller than the on-voltage of the MOSFET 6b. On the other hand, in a case where the switch temperature is a second temperature which is lower than the first temperature, the output (V var ) of the operational amplifier U2 is small and the output (V out) of the comparator U3 is smaller than the on-voltage of the MOSFET 6b.

[0034] A gate of the MOSFET 6b is connected to the output (V out ) of comparator U3, a drain of MOSFET 6b is connected to a junction point between voltage-dividing resistor R4 and voltage-dividing resistor R5, with resistor R6a interposed therebetween, and a source of MOSFET 6b is connected to ground potential. A resistance value of MOSFET 6b is smaller than resistor R6a.

[0035] If the output (V out ) of the comparator U3, which is smaller than the on-voltage, is fed into the gate of the MOSFET 6b, the MOSFET 6b is turned off, and therefore the voltage-dividing resistor R4 is essentially not 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 greater than the on-voltage, is fed into the gate of the MOSFET 6b, the MOSFET 6b is turned on, and therefore the voltage-dividing resistor R4 is connected to a combined resistor of the voltage-dividing resistor R5 and the resistor R6a, which has a smaller resistance than the voltage-dividing resistor R5. Since the changing unit 6 includes the resistor R6a and the MOSFET 6b, it is possible to divide the voltage (V sense ) by changing the resistance values of the voltage dividing resistors R4 and R5 based on the output (V out ) of the comparator U3.

[0036] In the first embodiment, in a case where the switch temperature is the relatively high first temperature, the output (V out) of the comparator U3 is greater than the on-voltage of the MOSFET 6b, and the voltage-dividing resistor R4 is connected to the combined resistor, which has a relatively small resistance value. On the other hand, in a case where the switch temperature is a second temperature lower than the first temperature, the output (V out ) of the comparator U3 is smaller than the on-voltage of the MOSFET 6b and the voltage dividing resistor R4 is connected to the voltage dividing resistor R5, which has a relatively large resistance value.

[0037] As a result, with respect to the output voltage (V CE ) of the semiconductor switching element Q1 in a case where the divided voltage (V sense ) is equal to the threshold value of the logic circuit U1, the output voltage (V CE ) in a case where the switch temperature is the first temperature, greater than the output voltage (V CE) in a case where 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 in a case where the switch temperature is the first temperature is greater than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the second temperature. <Zusammenfassung der ersten Ausführungsform>

[0038] According to the drive circuit for a semiconductor switching element of the first embodiment as described above, the output voltage detection unit 2 generates the switching signal based on the switch temperature and the output voltage (V CE ) of the semiconductor switching element Q1. The output voltage (V CE) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the first temperature is greater than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the second temperature. As in Fig. 2, during the turn-off process of the semiconductor switching element Q1, the output voltage (V CE) of the semiconductor switching element Q1 increases with time, and the tendency is substantially the same regardless of the temperature (not illustrated). Therefore, the timing for reducing the switching speed in a case where the switch temperature is the relatively high first temperature can be set later than the timing for reducing the switching speed in a case where the switch temperature is the relatively low second temperature. That is, the switching speed can be changed depending on the switch temperature.

[0039] Therefore, it is possible to properly adjust the switching timing of the gate resistance value when the temperature of the semiconductor switching element Q1 is normal, and to properly adjust the timing when the temperature is high. Furthermore, it is possible to reduce switching loss when the temperature of the semiconductor switching element Q1 is normal and reduce surge voltage when the temperature is low. <Zweite Ausführungsform>

[0040] Fig. 3 is a circuit diagram illustrating a configuration of a semiconductor switching element drive circuit according to a 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 from each other in the configuration of the output voltage detection unit 2.

[0041] An output voltage detection unit 2 according to the second embodiment includes voltage dividing resistors R4 and R5 which generate a divided voltage (V sense ) an output voltage (V CE ) of the semiconductor switching element Q1, and a logic circuit U1 which generates a voltage (V sense ) a switching signal (V high ) is generated.

[0042] In the second embodiment, the voltage dividing resistors R4 and R5 include one or more thermistors arranged near the semiconductor switching element Q1, and the one or more thermistors change the divided voltage (V sense ).

[0043] Note that it is only necessary that at least one of the voltage-dividing resistors R4 and R5 is a thermistor. For example, a PTC thermistor with a positive temperature specification is used as the voltage-dividing resistor R4, and an NTC thermistor with a negative temperature specification is used as the voltage-dividing resistor R5. Since the divided voltage (V sense ) as V CE × R5 / (R4 + R5), the divided voltage (V sense) as the switch temperature increases when these thermistors are used in a case where the output voltage (V CE ) is equal to. Accordingly, the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the first temperature greater than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the second temperature. <Zusammenfassung der zweiten Ausführungsform>

[0044] According to the drive circuit for a semiconductor switching element of the second embodiment as described above, the output voltage detection unit 2 generates the switching signal based on the switch temperature and the output voltage (V CE ) of the semiconductor switching element Q1. The output voltage (V CE) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the first temperature is greater than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the second temperature. Therefore, the timing for reducing the switching speed in a case where the switch temperature is the relatively high first temperature can be set later than the timing for reducing the switching speed in a case where the switch temperature is the relatively low second temperature. As a result, effects similar to those of the first embodiment can be obtained.

[0045] Note that the resistance value of a PTC thermistor is essentially constant at approximately normal temperature, but increases rapidly above a certain temperature. On the other hand, the resistance value of an NTC thermistor gradually increases with increasing temperature. Therefore, by using an NTC thermistor as the voltage-dividing resistor R5, it is easy to control the timing for reducing the switching speed. <Dritte Ausführungsform>

[0046] Fig. 4 is a circuit diagram illustrating a configuration of a semiconductor switching element drive circuit according to a third embodiment. The semiconductor switching element drive circuit according to the third embodiment and the semiconductor switching element drive circuit according to the first embodiment differ from each other in the configuration of the output voltage detection unit 2.

[0047] An output voltage detection unit 2 according to the third embodiment includes voltage dividing resistors R4 and R5 which generate a divided voltage (V sense ) an output voltage (V CE ) of the semiconductor switching element Q1, a logic circuit U1 which, based on the divided voltage (V sense ) a switching signal (V high ) and an operational amplifier U2.

[0048] A temperature detection voltage corresponding to the switch temperature and having negative temperature characteristics, and a first reference voltage (V ref1 ) are fed into the operational amplifier U2. The operational amplifier U2, to which resistors Ra and Rb are connected, forms an inverting amplifier circuit, and an output (V var ) of the operational amplifier U2 is determined by the above formula (1) using the first reference voltage (V ref1 ) and the temperature detection voltage (V s ). As the switch temperature increases, the temperature detection voltage (V s ) decreases, and therefore the output (V var ) of the operational amplifier U2, which inverts the input, as can be seen from the formula (1) above.

[0049] In the third embodiment, the output (V var) of the operational amplifier U2 is fed into the logic circuit U1 instead of the power supply voltage. Therefore, a threshold value corresponding to the divided voltage (V sense ) in the logic circuit U1 is to be compared based on the output (V var ) of the operational amplifier U2. That is, the operational amplifier U2 controls the threshold of the logic circuit U1 based on the temperature detection voltage.

[0050] With the above configuration, the threshold value of the logic circuit U1 is large in a case where the switch temperature is a relatively high first temperature, and the threshold value of the logic circuit U1 is small in a case where the switch temperature is a second temperature lower than the first temperature. Accordingly, the output voltage (V CE) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the first temperature greater than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the second temperature. <Zusammenfassung der dritten Ausführungsform>

[0051] According to the drive circuit for a semiconductor switching element of the third embodiment as described above, the output voltage detection unit 2 generates the switching signal based on the switch temperature and the output voltage (V CE ) of the semiconductor switching element Q1. The output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the first temperature is greater than the output voltage (V CE) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the second temperature. Therefore, the timing for reducing the switching speed in a case where the switch temperature is the relatively high first temperature can be set later than the timing for reducing the switching speed in a case where the switch temperature is the relatively low second temperature. As a result, effects similar to those of the first embodiment can be obtained. <Vierte Ausführungsform>

[0052] Fig.5 is a circuit diagram illustrating a configuration of a semiconductor switching element drive circuit according to a fourth embodiment. The semiconductor switching element drive circuit according to the fourth embodiment and the semiconductor switching element drive circuit according to the first embodiment differ from each other in the configuration of the output voltage detection unit 2.

[0053] An output voltage detection unit 2 according to the fourth embodiment includes voltage dividing resistors R4 and R5 which generate a divided voltage (V sense ) an output voltage (V CE ) of the semiconductor switching element Q1, a logic circuit U1 which, based on the divided voltage (V sense ) a switching signal (V high ) and an operational amplifier U4.

[0054] The operational amplifier U4, to which resistors Ra and Rb are connected and which is connected to a first reference voltage (V ref1 ) with the resistor Ra arranged therebetween, forms a non-inverting amplifier circuit. A temperature detection voltage corresponding to a switch temperature and having negative temperature characteristics is fed to a (+) input terminal of the operational amplifier U4. Accordingly, as the switch temperature increases, the temperature detection voltage (V s ) and takes the output (V out ) of the operational amplifier U4, which does not invert the input.

[0055] An output terminal of the operational amplifier U4 is connected to the other end of the voltage dividing resistor R5, which is different from an end connected to the voltage dividing resistor R4. Thus, the divided voltage (V sense) using an output voltage (V CE ) of the semiconductor switching element Q1 and the output (V out ) of the operational amplifier U4 is expressed by the following formula (2). The second term on the right side of the following formula (2) represents an offset voltage to compensate for the divided voltage (V sense ) and is determined by the output (V out ) of the operational amplifier U4. Therefore, according to the fourth embodiment, the operational amplifier U4 generates the offset voltage for offsetting the divided voltage (V sense ) based on the temperature detection voltage. [Mathematical Formula 2] Vsense=R5R4+R5VCE+R5R4+R5Vout

[0056] As the switch temperature increases, the output (V out ) of the operational amplifier U4 decreases, and therefore the divided voltage (V sense ) of formula (2). Accordingly, the output voltage (V CE) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the first temperature greater than the output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the second temperature. <Zusammenfassung der vierten Ausführungsform>

[0057] According to the drive circuit for a semiconductor switching element of the fourth embodiment as described above, the output voltage detection unit 2 generates the switching signal based on the switch temperature and the output voltage (V CE ) of the semiconductor switching element Q1. The output voltage (V CE ) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the first temperature is greater than the output voltage (V CE) for generating the switching signal by the output voltage detection unit 2 in a case where the switch temperature is the second temperature. Therefore, the timing for reducing the switching speed in a case where the switch temperature is the relatively high first temperature can be set later than the timing for reducing the switching speed in a case where the switch temperature is the relatively low second temperature. As a result, effects similar to those of the first embodiment can be obtained.

[0058] Note that a capacitor can be placed between the voltage-dividing resistor R5 and a ground potential on the operational amplifier U4 side. With such a configuration, the resistance to external noise can be increased or improved. <modifikation>

[0059] At the first reference voltage (V ref1 ) in the first, third, and fourth embodiments may be a voltage of a variable power supply. According to such a configuration, it is possible to correct a deviation of the divided voltage, a deviation of the threshold value of the logic circuit U1, and a deviation of the temperature detection voltage that occur due to manufacturing variations. Furthermore, in a case where the first reference voltage (V ref1 ), even if the threshold value of the logic circuit U1 is allowed to deviate, the deviation of the divided voltage or the like can be adjusted by a ratio of resistance values of the voltage dividing resistors R4 and R5 by using variable resistors or the like as the voltage dividing resistors R4 and R5. Note that a trigger voltage (V trigger ), which is a divided voltage of the output voltage (V CE ) for generating the switching signal by the logic circuit U1, using a threshold value (U1 th ) of the logic circuit U1 is expressed by the following formula (3). [Mathematical Formula 3] Vtrigger=R4+R5R5U1th

[0060] For example, in a case where 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, it is only necessary to decrease the resistance value of the voltage dividing resistor R4 by an x ratio in a case where the threshold value (U1 th ) increases by an x-ratio, since R4 >> R5. Note that the voltage-dividing resistors R4 and R5 may comprise one or more variable resistors, allowing for such an adjustment.

[0061] The embodiments and modifications may be freely combined and changed or omitted as appropriate. EXPLANATION OF REFERENCE SYMBOLS 1 control unit 2 Output voltage detection unit 6 Change unit R4, R5 voltage dividing resistor Q1 semiconductor switching element U1 logic circuit U2, U4 operational amplifiers U3 Comparator< / modifikation>

Claims

[1] A semiconductor switching element driving circuit that drives a gate of a semiconductor switching element, the semiconductor switching element driving circuit comprising: a control unit that switches a switching speed during a 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 a temperature with respect to the semiconductor switching element and an output voltage of the semiconductor switching element, wherein the output voltage for generating the switching signal by the output voltage detection unit in a case where the temperature is a first temperature is greater than the output voltage for generating the switching signal by the output voltage detection unit in a case where the temperature is a second temperature which is lower than the first temperature. [2] A drive circuit for a semiconductor switching element according to claim 1, wherein the output voltage detection unit comprises a voltage dividing resistor that generates a divided voltage of the output voltage, a logic circuit that generates the switching signal based on the divided voltage, an operational amplifier into which a temperature detection voltage corresponding to the temperature and having negative temperature characteristics and a first reference voltage are fed, a comparator into which an output of the operational amplifier and a second reference voltage are fed, and a changing unit that changes the divided voltage by changing a resistance value of the voltage dividing resistor based on an output of the comparator. [3] A drive circuit for a semiconductor switching element 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, and the voltage dividing resistor contains one or more thermistors that change the divided voltage based on temperature. [4] A drive circuit for a semiconductor switching element according to claim 1, wherein the output voltage detection unit comprises a voltage dividing resistor that 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 that controls the threshold value of the logic circuit based on a temperature detection voltage corresponding to the temperature and having negative temperature characteristics, and to which a first reference voltage is input. [5] A drive circuit for a semiconductor switching element according to claim 1, wherein the output voltage detection unit comprises a voltage dividing resistor that 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 that generates an offset voltage for offsetting the divided voltage based on a temperature detection voltage that corresponds to the temperature and has negative temperature characteristics, and that is electrically connected to a first reference voltage. [6] A drive circuit for a semiconductor switching element according to claim 2, 4 or 5, wherein the first reference voltage is a voltage of a variable power supply.

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