Drive unit

Abstract

The objective of the invention is to provide a technique capable of achieving an appropriate turn-on speed. This driver device comprises: a gate-driving-circuit power source the output voltage of which can be changed; a power source that has a fixed voltage lower than the output voltage; a control unit that changes the output voltage of the gate-driving-circuit power source on the basis of information related to the load current of a semiconductor switching element; and a delay circuit that, when a gate driving signal is turned on, performs a control of suppling the fixed voltage to the gate of the semiconductor switching element for a predetermined time period and thereafter performs a control of suppling the output voltage to the gate.

Description

[Technical field]

[0001] The present disclosure relates to a drive device. [Background technology]

[0002] Various technologies have been proposed for driving devices that drive semiconductor switching elements such as voltage-controlled semiconductor switching elements. For example, Patent Documents 1 and 2 propose a technology that increases or decreases the voltage supplied to the gate of a voltage-controlled semiconductor switching element based on a load current in order to reduce steady-state loss in the voltage-controlled semiconductor switching element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4333802 [Patent Document 2] JP 2004-96830 A Summary of the Invention [Problem to be solved by the invention]

[0004] In general, when the load current of a semiconductor switching element is zero or low, the turn-on speed of the semiconductor switching element increases. Also, when the voltage applied to the gate of the semiconductor switching element increases sharply at the time of turning on the semiconductor switching element, the turn-on speed of the semiconductor switching element increases.

[0005] Despite these, the techniques of Patent Documents 1 and 2 simply increase the voltage applied to the gate, so that when the AC load current momentarily becomes zero or low, the voltage applied to the gate may be suddenly increased, causing a problem that the turn-on speed of the semiconductor switching element becomes excessive, resulting in large surge voltage and radiation noise.

[0006] Therefore, the present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide a technique capable of optimizing the turn-on speed. [Means for solving the problem]

[0007] The drive device according to the present disclosure is a drive device that drives a semiconductor switching element based on the on and off of a gate drive signal, and includes a gate drive circuit power supply that can change the output voltage, a power supply having a fixed voltage lower than the output voltage, a control unit that changes the output voltage of the gate drive circuit power supply based on relevant information related to the load current of the semiconductor switching element, and a delay circuit that, when the gate drive signal is turned on, controls the supply of the fixed voltage to the gate of the semiconductor switching element for a predetermined period of time, and then controls the supply of the output voltage to the gate. Effect of the Invention

[0008] According to the present disclosure, when the gate drive signal is turned on, a fixed voltage is supplied to the gate of the semiconductor switching element for a predetermined period, and then an output voltage is supplied to the gate. With this configuration, the turn-on speed can be optimized.

[0009] The objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0010] [Figure 1] 1 is a circuit diagram showing a configuration of a drive device according to a first embodiment. [Diagram 2] 1 is a circuit diagram showing a configuration of a drive device according to a first embodiment. [Diagram 3] 5 is a diagram showing a change pattern of a power supply output voltage according to the first embodiment. FIG. [Figure 4] 5 is a diagram illustrating the operation of the drive device according to the first embodiment. FIG. [Diagram 5]FIG. 13 is a circuit diagram showing a configuration of a drive device according to a modified example. [Figure 6] FIG. 11 is a circuit diagram showing a configuration of a drive device according to a second embodiment. [Figure 7] 10A to 10C are diagrams illustrating the operation of the drive device according to the second embodiment. [Figure 8] FIG. 11 is a circuit diagram showing a configuration of a drive device according to a third embodiment. [Figure 9] 13 is a diagram for explaining the operation of the drive device according to the third embodiment. FIG. [Figure 10] 13 is a diagram illustrating the operation of the drive device according to the third embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <Embodiment 1> Fig. 1 is a circuit diagram showing the configuration of a drive device according to embodiment 1. The drive device in Fig. 1 includes a gate drive circuit power supply E1, a PWM control section 1 which is a control section, a gate drive circuit 2, and a resistor RG.

[0012] The driving device in Fig. 1 is connected to the gate of a semiconductor switching element Q1, which is a voltage-controlled semiconductor switching element, and drives the semiconductor switching element Q1 based on the on and off of a gate driving signal.

[0013] The semiconductor switching element Q1 according to the first embodiment is used in an inverter circuit as shown in Fig. 2, and constitutes the inverter circuit. In the inverter circuit of Fig. 2, flywheel diodes D1 to D6 are connected in parallel to the semiconductor switching elements Q1 to Q6, respectively. The semiconductor switching elements Q2, Q4, and Q6, which are the upper arms, and the semiconductor switching elements Q1, Q3, and Q5, which are the lower arms, are connected in series, respectively, and the three sets of upper and lower arms are connected in parallel to a power source E2. For convenience, Fig. 2 is omitted in Fig. 1, and the semiconductor switching element Q1 is connected to the power source E2 via a load unit 9.

[0014] In the following description, the semiconductor switching element Q1 will be described as being a metal oxide semiconductor field effect transistor (MOSFET), but as will be described later, the semiconductor switching element Q1 is not limited to a MOSFET.

[0015] Next, the components of the drive device according to the first embodiment will be described in detail.

[0016] The gate drive circuit power supply E1 is configured to be able to change the output voltage, which is the voltage that the gate drive circuit power supply E1 outputs. Hereinafter, the output voltage of the gate drive circuit power supply E1 may also be referred to as the power supply output voltage.

[0017] The PWM control unit 1 outputs a gate drive signal having a rectangular waveform to the gate drive circuit 2. The PWM control unit 1 varies the duty ratio, which is the ratio between the on time and the off time of the gate drive signal, to control the output of the gate drive circuit 2, thereby controlling the load current of the semiconductor switching element Q1. The load current of the semiconductor switching element Q1 is, for example, a current flowing between the source and drain of the semiconductor switching element Q1 connected to a load unit 9 or the like.

[0018] Furthermore, the PWM control unit 1 outputs a voltage control signal to the gate drive circuit power supply E1. The PWM control unit 1 performs control to change the power supply output voltage of the gate drive circuit power supply E1 by changing the voltage control signal based on related information related to the load current of the semiconductor switching element Q1. In the present embodiment 1, the related information related to the load current is a change pattern of the power supply output voltage that is predetermined for the effective value of the load current, and this change pattern is stored in advance in the PWM control unit 1.

[0019] Fig. 3 is a diagram showing an example of a change pattern of the power supply output voltage. The thin solid line indicates the instantaneous value of the load current, the thin dotted line indicates the effective value of the load current, and the thick solid line indicates the change pattern of the power supply output voltage. The instantaneous value of the load current corresponds to the waveform of the gate drive signal, and changes depending on whether the gate drive signal is on or off. An AC current indicated by the instantaneous value of the load current flows through the load connected to the outputs (U, V, W) in Fig. 2.

[0020] The PWM control unit 1 controls the power supply output voltage of the gate drive circuit power supply E1 so as to increase the power supply output voltage of the gate drive circuit power supply E1 when the effective value of the load current is large, and to decrease the power supply output voltage of the gate drive circuit power supply E1 when the effective value of the load current is small. The PWM control unit 1 may increase or decrease the power supply output voltage of the gate drive circuit power supply E1 in stages as shown in Fig. 3, or may make it proportional to the effective value of the load current. For example, the PWM control unit 1 may change the power supply output voltage of the gate drive circuit power supply E1 based on the number of times the gate drive signal is turned on and off and a predetermined change pattern.

[0021] The resistor RG in FIG. 1 is connected between the gate of the semiconductor switching element Q1 and the gate drive circuit 2.

[0022] The gate drive circuit 2 in FIG. 1 includes a power supply E3, a first switch S1, a second switch S2, a third switch S3, an inverter circuit INV which is a NOT circuit, and a delay circuit DLC.

[0023] The power supply E3 has a fixed voltage lower than the power supply output voltage of the gate drive circuit power supply E1.

[0024] One end of the first switch S1 is connected to a power source E3, and the other end of the first switch S1 is connected to a resistor RG. The on and off of the first switch S1 is controlled by a delay circuit DLC.

[0025] One end of the second switch S2 is connected to the gate drive circuit power supply E1, and the other end of the second switch S2 is connected to a resistor RG. The on and off of the second switch S2 is controlled by a delay circuit DLC.

[0026] One end of the third switch S3 is connected to the reference voltage GND, and the other end of the third switch S3 is connected to the resistor RG. The on and off of the third switch S3 is controlled by a gate drive signal inverted by the inverter circuit INV.

[0027] When the gate drive signal is turned on, the delay circuit DLC controls to turn on the first switch S1 and turn off the second switch S2 so that the fixed voltage of the power supply E3 is supplied to the gate of the semiconductor switching element Q1 for a predetermined period. After the fixed voltage of the power supply E3 is supplied to the gate for a predetermined period, the delay circuit DLC controls to turn off the first switch S1 and turn on the second switch S2 so that the power supply output voltage of the gate drive circuit power supply E1 is supplied to the gate of the semiconductor switching element Q1.

[0028] When the gate drive signal is turned off, the delay circuit DLC controls to turn off the first switch S1 and the second switch S2. In this case, the third switch S3 is turned on by the gate drive signal inverted by the inverter circuit INV, and the reference voltage GND is supplied to the gate of the semiconductor switching element Q1. That is, in the first embodiment, the first switch S1, the second switch S2, and the third switch S3 are turned on exclusively.

[0029] <Operation> Fig. 4 is a diagram showing the operation of the drive device according to the first embodiment. Hereinafter, the output voltage of the gate drive circuit 2 may be referred to as a circuit output voltage to distinguish it from the power supply output voltage of the gate drive circuit power supply E1. Fig. 4 shows the gate drive signal, the on and off of the first switch S1, the on and off of the second switch S2, the circuit output voltage, and the gate voltage of the semiconductor switching element Q1.

[0030] At time T0, when the gate drive signal changes from off to on, the first switch S1 is turned on. As a result, the circuit output voltage becomes the voltage of the power supply E3, and the gate voltage rises. The period from time T1 to time T2 is the mirror period, during which the gate voltage is constant at a voltage lower than the voltage of the power supply E3. When the mirror period ends at time T2, the gate voltage rises to approach the fixed voltage of the power supply E3.

[0031] At time T3, the gate voltage becomes approximately the fixed voltage of the power supply E3. In the example of Fig. 4, at that timing, the first switch S1 is turned off and the second switch S2 is turned on under the control of the delay circuit DLC. As a result, the circuit output voltage becomes the power supply output voltage of the gate drive circuit power supply E1, and the gate voltage continues to rise even after time T3.

[0032] 4, the timing at which the first switches S1 and S2 are switched is the same as the timing at which the gate voltage becomes approximately the fixed voltage of the power supply E3, but this is not limited to this. For example, the timing at which the first switches S1 and S2 are switched may be before or after the timing at which the gate voltage becomes approximately the fixed voltage of the power supply E3, or may be during the mirror period.

[0033] After time T3 in FIG. 4, as described above, when the load current is low, the power supply output voltage is low, and when the load current is high, the power supply output voltage is high, which is reflected in the circuit output voltage and the gate voltage.

[0034] Although not shown, when the gate drive signal changes from on to off, the first switch S1 and the second switch S2 are turned off and the third switch S3 is turned on, causing the circuit output voltage to become the reference voltage GND, the gate voltage to drop, and the semiconductor switching element Q1 to turn off.

[0035] <Summary of the first embodiment> According to the driving device of the first embodiment, the PWM control unit 1 changes the power supply output voltage of the gate drive circuit power supply E1 based on the related information related to the load current of the semiconductor switching element Q1. As a result, as shown in Figs. 3 and 4, the gate voltage applied to the semiconductor switching element Q1 increases when the load current increases, so that the voltage when the semiconductor switching element Q1 is on can be reduced and the steady-state loss of the semiconductor switching element Q1 can be reduced. In addition, the ratio of the time during which the device operates under the maximum load current condition to the total operating time is reduced, and the average voltage applied to the gate of the semiconductor switching element Q1 and the gate drive circuit 2 becomes lower than the maximum voltage of the power supply output voltage of the gate drive circuit power supply E1. This is expected to reduce the failure of the gate of the semiconductor switching element Q1 and the gate drive circuit 2.

[0036] Generally, when the load current of the semiconductor switching element is zero or low, the turn-on speed of the semiconductor switching element increases. Also, when the voltage applied to the gate of the semiconductor switching element increases abruptly when the element is turned on, the turn-on speed of the semiconductor switching element increases. Therefore, if the gate voltage is increased in a straight line in response to an increase in the effective value of the load current in order to reduce the steady-state loss of the semiconductor switching element Q1, the voltage applied to the gate may increase abruptly when the instantaneous value of the AC load current is zero or low. In this case, the turn-on speed of the semiconductor switching element Q1 becomes excessive, resulting in problems such as increased surge voltage and increased radiation noise.

[0037] In contrast, in the first embodiment, the gate voltage applied initially when the semiconductor switching element Q1 is turned on is fixed to the fixed voltage of the power supply E3. Therefore, the increase in the gate voltage of the semiconductor switching element becomes gentle. This makes it possible to suppress an increase in the turn-on speed caused by an increase in the power supply output voltage of the gate drive circuit power supply E1, and therefore to suppress an increase in the surge voltage and radiation noise.

[0038] In the first embodiment, the PWM control unit 1 changes the power supply output voltage of the gate drive circuit power supply E1 based on a predetermined change pattern. Therefore, even if the load current waveform is a sine wave or the like, the power supply output voltage of the gate drive circuit power supply E1 can be appropriately changed. Note that even if the load current waveform is a sine wave or the like, there may be cases where the need to appropriately change the power supply output voltage of the gate drive circuit power supply E1 is low and the effective value of the load current of the semiconductor switching element Q1 is detected. In such cases, the PWM control unit 1 may measure the effective value of the load current of the semiconductor switching element Q1 and change the power supply output voltage of the gate drive circuit power supply E1 based on the effective value, rather than based on a predetermined change pattern.

[0039] <Modification> The semiconductor switching element Q1 may be, for example, an IGBT (Insulated Gate Bipolar Transistor) or an RC-IGBT (Reverse Conducting - IGBT). The material of the semiconductor switching element Q1 may be ordinary silicon (Si), or may be a wide band gap semiconductor such as silicon carbide (SiC), gallium nitride (GaN), or diamond. When the material of the semiconductor switching element Q1 is a wide band gap semiconductor, stable operation under high temperature and high voltage and high switching speed are possible.

[0040] Although the gate drive circuit 2 in Fig. 1 includes an inverter circuit INV, the gate drive circuit 2 does not have to include the inverter circuit INV. For example, when the first switch S1, the second switch S2, and the third switch S3 are composed of an NPN transistor, an NPN transistor, and a PNPN transistor, respectively, as in the complementary transistors in Fig. 5, the inverter circuit INV is not necessary. Also, as long as the circuit output voltage as in Fig. 4 can be obtained, the configuration of the gate drive circuit 2 is not limited to the configuration in Fig. 1.

[0041] This modified example may also be applied as appropriate to the following second and subsequent embodiments.

[0042] <Embodiment 2> 6 is a circuit diagram showing the configuration of a drive device according to the present embodiment 2. In the following, among the components according to the present embodiment 2, components that are the same as or similar to the components described above are given the same or similar reference symbols, and different components will be mainly described.

[0043] The configuration of the drive device in Fig. 6 is the same as that of the drive device in Fig. 1, except that the PWM control unit 1 is replaced with a control unit 3 and the load unit 9 is replaced with an inductive load L1 and a flywheel diode D1. The drain of the semiconductor switching element Q1 is connected to a power source E2 via the inductive load L1 and the flywheel diode D1 connected in parallel.

[0044] A gate drive signal used as an S / H (sampling and holding) instruction and a load current detection signal indicating the load current of the sampled semiconductor switching element Q1 are input to the control unit 3 in Fig. 6. The control unit 3 changes the power supply output voltage of the gate drive circuit power supply E1 based on the load current of the semiconductor switching element Q1 sampled when the gate drive signal is turned off.

[0045] In other words, the control unit 3 performs control to change the power supply output voltage of the gate drive circuit power supply E1 by changing the voltage control signal based on relevant information related to the load current of the semiconductor switching element Q1. The relevant information here is the load current sampled when the gate drive signal is turned off.

[0046] Other configurations of the embodiment 2 are similar to those of the embodiment 1. For example, when the gate drive signal is turned on, the delay circuit DLC performs control to supply a fixed voltage of the power supply E3 to the gate of the semiconductor switching element Q1 for a predetermined period, and then performs control to supply the power supply output voltage of the gate drive circuit power supply E1 to the gate.

[0047] <Operation> Fig. 7 is a diagram showing the operation of the control unit 3 that changes the power supply output voltage of the gate drive circuit power supply E1, among the operations of the drive device according to embodiment 2. Note that, among the operations of the drive device according to embodiment 2, the operation related to the circuit output voltage of the gate drive circuit 2 is similar to the operation related to the circuit output voltage explained in embodiment 1 using Fig. 4. The following mainly explains the operation of the control unit 3 that changes the power supply output voltage of the gate drive circuit power supply E1.

[0048] When the semiconductor switching element Q1 is turned off, the load current flows back to the flywheel diode D1 as shown by the dashed line in FIG. 7 due to the inductive load L1 in FIG.

[0049] The control unit 3 samples the load current of the semiconductor switching element Q1 at timings t1, t3, t5, ... when the semiconductor switching element Q1 is turned off. Then, the control unit 3 changes the power supply output voltage of the gate drive circuit power supply E1 based on the sampled load current during the off periods t1 to t2, t3 to t4, ... of the semiconductor switching element Q1, and then maintains the power supply output voltage until the next timings t3, t5, .... For example, the control unit 3 increases the power supply output voltage if the sampled load current is larger than that of the previous sampling, and decreases the power supply output voltage if the sampled load current is smaller than that of the previous sampling. The control unit 3 may increase or decrease the power supply output voltage of the gate drive circuit power supply E1 in a stepwise manner, or may make it proportional to the effective value of the load current.

[0050] <Summary of the second embodiment> According to the drive device of the second embodiment, the control unit 3 changes the power supply output voltage of the gate drive circuit power supply E1 based on related information related to the load current of the semiconductor switching element Q1. This makes it possible to reduce steady-state loss in the semiconductor switching element Q1, as in the first embodiment, and to reduce failures in the gate of the semiconductor switching element Q1 and the gate drive circuit 2. Also, in the second embodiment, as in the first embodiment, the gate voltage that is initially applied when the semiconductor switching element Q1 is turned on is fixed to a fixed voltage of the power supply E3, as in the first embodiment, so that increases in surge voltage and radiation noise can be suppressed, as in the first embodiment.

[0051] For example, in the conventional technology such as Patent Document 2, the power supply output voltage of the gate drive circuit power supply E1 is changed during the period when the semiconductor switching element Q1 is on, so that the change must be short so as not to affect the semiconductor switching element Q1 during the change.

[0052] In contrast, in the second embodiment, the control unit 3 changes the power supply output voltage of the gate drive circuit power supply E1 based on the load current of the semiconductor switching element Q1 sampled when the gate drive signal is turned off. With this configuration, the power supply output voltage of the gate drive circuit power supply E1 can be changed while the semiconductor switching element Q1 is off, so that the influence of the change in the power supply output voltage on the semiconductor switching element Q1 can be suppressed. Also, the change in the instantaneous value of the load current can be reflected to some extent in the change in the power supply output voltage of the gate drive circuit power supply E1.

[0053] <Embodiment 3> 8 is a circuit diagram showing the configuration of a drive device according to the present embodiment 3. In the following, among the components according to the present embodiment 3, components that are the same as or similar to the components described above are given the same or similar reference symbols, and different components will be mainly described.

[0054] The drive device of FIG. 8 includes a gate drive circuit power supply E1, a control unit 4, a gate drive circuit 5, a first resistor RG1, and a second resistor RG2.

[0055] 8 is connected to the gate of a semiconductor switching element Q1 and drives the semiconductor switching element Q1 based on the on and off of a gate drive signal. The drain of the semiconductor switching element Q1 is connected to a power source E2 via an inductive load L1 and a flywheel diode D1 connected in parallel.

[0056] Next, the components of the drive device according to the third embodiment will be described in detail.

[0057] The gate drive circuit power supply E1 is configured so that the power supply output voltage, which is the voltage output by the gate drive circuit power supply E1, is variable.

[0058] Similar to the control unit 3 according to the second embodiment, the control unit 4 changes the power supply output voltage of the gate drive circuit power supply E1 based on the load current of the semiconductor switching element Q1 sampled when the gate drive signal is turned off. The control unit 4 in Fig. 8 is capable of outputting an on-resistance switching signal to an AND circuit U1 of the gate drive circuit 5, which will be described later.

[0059] The first resistor RG1 and the second resistor RG2 are connected between the gate of the semiconductor switching element Q1 and the gate drive circuit 5.

[0060] The gate drive circuit 5 in FIG. 8 includes a first switch S1, a second switch S2, a third switch S3, an inverter circuit INV which is a NOT circuit, and an AND circuit U1.

[0061] One end of the first switch S1 is connected to the gate drive circuit power supply E1, and the other end of the first switch S1 is connected to the first resistor RG1, and the on and off of the first switch S1 is controlled by a gate drive signal, so that the first resistor RG1 can be connected between the gate drive circuit power supply E1 and the gate of the semiconductor switching element Q1.

[0062] One end of the second switch S2 is connected to the gate drive circuit power supply E1, and the other end of the second switch S2 is connected to the second resistor RG2, and the second switch S2 is turned on and off by an output signal of the AND circuit U1. This allows the second resistor RG2 to be connected in parallel with the first resistor RG1 between the gate drive circuit power supply E1 and the gate of the semiconductor switching element Q1.

[0063] One end of the third switch S3 is connected to the reference voltage GND, and the other end of the third switch S3 is connected to the resistor RG. The on and off of the third switch S3 is controlled by a gate drive signal inverted by the inverter circuit INV.

[0064] The AND circuit U1 performs an AND operation based on the on-resistance switching signal from the control unit 4 and the gate drive signal, and outputs the result as the output signal of the AND circuit U1. In other words, the AND circuit U1 outputs on only when the on-resistance switching signal is on and the gate drive signal is on.

[0065] Hereinafter, the resistance connected to the gate of the semiconductor switching element Q1 when it is turned on is referred to as the turn-on gate resistance. The control unit 4 according to the third embodiment selectively performs high resistance control in which the turn-on gate resistance is high and low resistance control in which the turn-on gate resistance is low, based on the load current. This operation of the control unit 4 will be described in detail later.

[0066] <Operation> Of the operations of the drive device according to the third embodiment, the operation of changing the power supply output voltage of the gate drive circuit power supply E1 is similar to the operation described in the second embodiment with reference to FIG.

[0067] In the third embodiment, when the load current of the semiconductor switching element Q1 sampled when the gate drive signal is on is equal to or less than the threshold value TH1 in FIG. 9, the control unit 4 outputs an on-resistance switching signal indicating off. When the on-resistance switching signal indicating off is output and the gate drive signal is on, the first switch S1 turns on and the second switch S2 and the third switch S3 turn off. Therefore, the power supply output voltage of the gate drive circuit power supply E1 is supplied to the gate of the semiconductor switching element Q1 via the first resistor RG1. Therefore, as shown in FIG. 9, the turn-on gate resistance when the load current is equal to or less than the threshold value TH1 is the first resistor RG1.

[0068] On the other hand, when the load current of the semiconductor switching element Q1 sampled when the gate drive signal is on exceeds the threshold value TH1 in FIG. 9, the control unit 4 outputs an on-resistance switching signal indicating on. When the on-resistance switching signal indicating on is output and the gate drive signal is on, the first switch S1 and the second switch S2 are turned on and the third switch S3 is turned off. Therefore, the power supply output voltage of the gate drive circuit power supply E1 is supplied to the gate of the semiconductor switching element Q1 via the first resistor RG1 and the second resistor RG2. Therefore, as shown in FIG. 9, when the load current exceeds the threshold value TH1, the turn-on gate resistance is the parallel combined resistance (RG1×RG2 / (RG1+RG2)) of the first resistor RG1 and the second resistor RG2.

[0069] As described above, when the load current of the semiconductor switching element Q1 sampled when the gate drive signal is on is equal to or less than the threshold TH1, high resistance control is performed in which the turn-on gate resistance becomes the first resistor RG1. On the other hand, when the load current of the semiconductor switching element Q1 sampled when the gate drive signal is on exceeds the threshold TH1, low resistance control is performed in which the turn-on gate resistance becomes the parallel combined resistance of the first resistor RG1 and the second resistor RG2.

[0070] Furthermore, if the load current of the semiconductor switching element Q1 sampled when the gate drive signal is on is equal to or less than a threshold TH2 that is larger than the threshold TH1 in Fig. 9, the control unit 4 maintains the power supply output voltage of the gate drive circuit power supply E1 constant. On the other hand, if the load current of the semiconductor switching element Q1 sampled when the gate drive signal is on exceeds the threshold TH2 in Fig. 9, the control unit 4 increases the power supply output voltage of the gate drive circuit power supply E1 as the load current increases.

[0071] 10 is a diagram showing the operation of the drive device according to the third embodiment, specifically, a diagram showing the transition of the gate voltage of the semiconductor switching element Q1 due to the operation of the drive device. The dotted line shows the circuit output voltage of the gate drive circuit 2 during high resistance control in which the turn-on gate resistance is high, and the solid line shows the circuit output voltage of the gate drive circuit 2 during low resistance control in which the turn-on gate resistance is low. When the load current of the semiconductor switching element Q1 is small, high resistance control is performed, the increase in the gate voltage of the semiconductor switching element becomes gradual, and the switching speed becomes slow. On the other hand, when the load current of the semiconductor switching element Q1 is large, low resistance control is performed, and the switching speed becomes high.

[0072] <Summary of the Third Embodiment> According to the drive device of the third embodiment, the control unit 4 changes the power supply output voltage of the gate drive circuit power supply E1 based on the load current of the semiconductor switching element Q1 sampled when the gate drive signal is turned off. This makes it possible to reduce steady-state loss of the semiconductor switching element Q1 and to reduce failures of the gate of the semiconductor switching element Q1 and the gate drive circuit 2, similar to the first and second embodiments.

[0073] As in the second embodiment, the power supply output voltage of the gate drive circuit power supply E1 is changed while the semiconductor switching element Q1 is off, so that it is possible to prevent the influence of the change in the power supply output voltage on the semiconductor switching element Q1. Also, the change in the instantaneous value of the load current can be reflected to some extent in the change in the power supply output voltage of the gate drive circuit power supply E1.

[0074] In the third embodiment, when the load current of the semiconductor switching element Q1 is equal to or less than the threshold TH1, the turn-on gate resistance is high. This reduces the switching speed at turn-on, making it possible to suppress surge voltage and radiation noise. On the other hand, when the load current of the semiconductor switching element Q1 exceeds the threshold TH1, the turn-on gate resistance is low. This increases the switching speed at turn-on, making it possible to reduce switching loss during the turn-on period.

[0075] If it is desired to reduce the turn-on speed when the load current increases, an inverted signal of the on-resistance switching signal may be used instead of the on-resistance switching signal. In this case, the turn-on gate resistance increases, so that the turn-on speed can be reduced.

[0076] It should be noted that the embodiments and modifications may be freely combined, and the embodiments and modifications may be modified or omitted as appropriate.

[0077] The above description is illustrative in all respects and is not restrictive. It is understood that countless variations not illustrated can be envisioned. [Explanation of symbols]

[0078] 1 PWM control section, 3, 4 control section, DLC delay circuit, E1 gate drive circuit power supply, E3 power supply, Q1 semiconductor switching element, RG1 first resistor, RG2 second resistor.

Claims

1. A drive device that drives a semiconductor switching element based on on and off of a gate drive signal, a gate drive circuit power supply capable of changing an output voltage; a power supply having a fixed voltage lower than the output voltage; A control unit that changes the output voltage of the gate drive circuit power supply based on relevant information related to a load current of the semiconductor switching element; a delay circuit that performs control to supply the fixed voltage to the gate of the semiconductor switching element for a predetermined period when the gate drive signal is turned on, and then performs control to supply the output voltage to the gate; A drive device comprising:

2. 2. The drive device according to claim 1, A drive device, wherein the related information is a change pattern of the output voltage that is predetermined with respect to an effective value of the load current.

3. 2. The drive device according to claim 1, The relevant information is the load current sampled when the gate drive signal is turned off.

4. A drive device that drives a semiconductor switching element based on on and off of a gate drive signal, a gate drive circuit power supply capable of changing an output voltage; a control unit that changes the output voltage of the gate drive circuit power supply based on a load current of the semiconductor switching element sampled when the gate drive signal is turned off; a first resistor connectable between the gate drive circuit power supply and the gate of the semiconductor switching element; a second resistor that can be connected in parallel with the first resistor between the gate drive circuit power supply and the gate of the semiconductor switching element; Equipped with The control unit includes: a drive device that selectively controls, based on the load current, to supply the output voltage of the gate drive circuit power supply to the gate via the first resistor, and controls to supply the output voltage of the gate drive circuit power supply to the gate via the first resistor and the second resistor.

Images