Patent Publication Number: US-2023163758-A1

Title: Gate drive device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Patent Application No. PCT/JP2021/040385 filed on Nov. 2, 2021, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2020-197004 filed on Nov. 27, 2020. The entire disclosures of all of the above applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a gate drive device. 
     BACKGROUND 
     In the gate drive control of a gate-driven switching element, when the gate is driven with a predetermined drive performance, the following difficulties may arise due to variations in the gate capacitance of the switching element as a control target. 
     Since the switching elements have different gate capacities, when they are driven with the set drive performance, the gate voltages may be different from each other even if the gate charge Qg is the same, and this may cause variations in the ON or OFF gate drive time. 
     Therefore, in the switching element in the power system, since the surge voltages generated during switching also vary, it is necessary to determine the drive performance in view of the variation so that the surge voltage does not exceed the withstand voltage of the switching element. 
     Specifically, since there are variations in the characteristics of the switching elements, the drive performance is adjusted while observing the surge voltage in accordance with the minimum value of the standard corresponding to the gate capacitance or the gate capacitance. As a result, even if there are variations in the characteristics of the switching elements as the control target, the surge voltage can be suppressed from exceeding the withstand voltage. However, there may be a difficulty that the switching loss increases. 
     SUMMARY 
     According to an example, a gate drive device for driving a switching element may include: a gate drive circuit that drives a gate of the switching element based on a gate drive signal and a drive performance adjustment signal; a gate voltage detection circuit that outputs an on detection signal or an off detection signal when detecting that a gate voltage of the switching element reaches an on determination set value or an off determination set value; and a control circuit that outputs the drive performance adjustment signal to the gate drive circuit to match a gate drive time with a predetermined gate drive time set value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG.  1    is a diagram showing an electric configuration according to a first embodiment; 
         FIG.  2    is a flow diagram of a switching cycle according to the first embodiment; 
         FIG.  3    is a flow chart of an on drive time set process according to the first embodiment; 
         FIG.  4    is a timing chart according to the first embodiment; 
         FIG.  5    is a diagram showing an electric configuration according to a second embodiment; 
         FIG.  6    is a timing chart according to the second embodiment; 
         FIG.  7    is a diagram showing an electric configuration according to a third embodiment; 
         FIG.  8    is a timing chart according to the third embodiment; 
         FIG.  9    is a diagram showing an operation explanation according to the third embodiment; 
         FIG.  10    is a diagram showing an electric configuration according to a fourth embodiment; 
         FIG.  11    is a timing chart according to the fourth embodiment; 
         FIG.  12    is a diagram showing an operation explanation according to the fourth embodiment; 
         FIG.  13    is a diagram showing an electric configuration according to a fifth embodiment; 
         FIG.  14    is a diagram showing an electric configuration according to a sixth embodiment; 
         FIG.  15    is a diagram showing an electric configuration according to a seventh embodiment; 
         FIG.  16    is a diagram showing an electric configuration according to an eighth embodiment; 
         FIG.  17    is a diagram showing an electric configuration according to a ninth embodiment; 
         FIG.  18    is a diagram showing an electric configuration according to a tenth embodiment; 
         FIG.  19    is a timing chart of a first half according to the tenth embodiment; and 
         FIG.  20    is a timing chart of a second half according to the tenth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present embodiments provides a gate drive device for driving a plurality of switching elements within an on-drive time set in consideration of a reduction effect of a switching loss and with a surge voltage not exceeding a withstand voltage even if gate capacitances of the switching elements as a control target are different from each other due to a variation thereof. 
     The gate drive device according to the present embodiments that drives at least one gate-driven switching element, the gate drive device includes: at least one gate drive circuit that drives at least one gate of the at least one gate-driven switching element based on a gate drive signal and a drive performance adjustment signal for setting a gate drive performance; at least one gate voltage detection circuit that outputs an on detection signal or an off detection signal when detecting that a gate voltage of the at least one switching element reaches an on determination set value or an off determination set value; and at least one control circuit that outputs the drive performance adjustment signal to the at least one gate drive circuit to match a gate drive time, from when instructing an on drive or an off drive of the gate with the gate drive signal to when outputting a detection signal of the on drive or the off drive from the at least one gate voltage detection circuit, with a predetermined gate drive time set value. 
     By adopting the above configuration, the gate voltage of the switching element is detected by the gate voltage detection circuit with respect to the given gate drive time set value, so that the gate drive time of the on drive or the off drive is monitored. Further, the drive performance is adjusted and set by the control circuit, so that the current value of energizing the gate of the switching element with a constant current is controlled by the gate drive circuit, and the gate drive time is controlled to be the predetermined gate drive set value. 
     As a result, it is possible to appropriately set the drive performance so as to minimize variations in the gate drive time due to variations in the gate capacitance of the switching element with respect to the on drive time set value that is set preliminarily. Thus, it is possible to prevent the surge voltage from exceeding the withstand voltage, to maintain the gate voltage drive time appropriately and to prevent the switching loss from increasing. 
     First Embodiment 
     The description below explains a first embodiment of the present disclosure with reference to  FIGS.  1  through  4   . 
       FIG.  1    shows an electrical configuration, and a gate drive device  100  performs on/off drive control of, for example, an IGBT (Insulated Gate Bipolar Transistor)  1 , which is a gate-driven switching element as a control target. In this embodiment, the configuration provides performing an on-drive control. An off-drive circuit for performing an off-drive of the IGBT  1  is not shown in  FIG.  1   , but may be provided in the gate drive device  100  or may be provided separately. 
     The gate drive device  100  includes a control circuit  10 , a gate drive circuit  20  for performing the on-drive, and a gate voltage detection circuit  30 . The control circuit  10  receives an on-driving command signal Sonx from an external circuit for controlling on/off control of the IGBT  1  and is input an on-drive time set value Tons. The control circuit  10  outputs an on-drive signal Son to the on-drive circuit  20  in accordance with the supplied on-drive command signal Sonx, and outputs a drive performance voltage signal Sdx in accordance with the on-drive time set value Tons. The control circuit  10  also receives a gate detection signal Sg from the gate voltage detection circuit  30 . 
     The gate drive circuit  20  includes a P-channel MOS transistor  21  for gate drive, an error amplifier  22  and a constant current circuit  23 . The MOS transistor  21  has a source connected to the DC power supply Vcc for control through the resistor  2  and a drain connected to the gate of the IGBT  1 . A gate of the MOS transistor  21  is connected to an output terminal of the error amplifier  22 . 
     The error amplifier  22  has an inverting input terminal connected to the source of the MOS transistor  21  and a non-inverting input terminal connected to the DC power supply Vcc through the resistor  24  and to the constant current circuit  23 . The constant current circuit  23  is configured such that the constant current value is changed and set by the drive performance adjustment signal Sdx, and is configured to adjust the voltage applied to the non-inverting input terminal of the error amplifier  22  by flowing a constant current to the resistor  24 . 
     The error amplifier  22  outputs the voltage to the gate of the MOS transistor  21  to match the voltage, obtained by reducing the voltage generated in the resistor  24  with flowing the constant current of the constant current circuit  23  from the voltage of the DC power supply Vcc, with the voltage obtained by reducing the voltage generated with flowing the current in the resistor  2  from the voltage of the DC power supply Vcc. Thereby, the current flowing through the MOS transistor  21  is controlled to be a constant current. The constant current value that flows through the gate of the IGBT  1  by the MOS transistor  21  can be changed by adjusting the drive performance adjustment signal Sdx. 
     The gate voltage detection circuit  30  has a comparator  31  and a reference power supply  32 . The comparator  31  has a non-inverting input terminal connected to the gate of the IGBT  1  and an inverting input terminal connected to the reference power supply  32 . The reference power supply  32  is set to a voltage slightly lower than the gate voltage VG when the IGBT  1  is turned on as the reference voltage VrefU, and the comparator  31  outputs the gate detection signal Sg with the high level to the control circuit  10  when the gate voltage Vg of the IGBT  1  reaches the reference voltage VrefU. 
     Next, operation of the above-mentioned configuration will be described also with reference to  FIG.  2    to  FIG.  4   . In this embodiment, the gate drive device  10  controls the on-drive of the IGBT  1  so that the on-drive time Ton as the gate drive time approaches the on-driving time set value Tons. In this case, the gate capacitance of the IGBT  1  as the control target varies within the standard range. Therefore, when the gate is driven with a constant current, the gate voltage Vg varies even if the gate charge Qg is the same. Thus, the on-drive time Ton is controlled to approach the on-driving time set value Tons by adjusting and setting the constant current using the drive performance Sdx. 
       FIG.  2    shows the switching cycle flow of the on drive control operation of the IGBT  1  by the gate control device  100 . First, in step S 100 , when the on-drive command signal Sonx is given from the external circuit, the control circuit  10  inputs the signal Sonx, and then in step S 110 , if the drive performance adjustment signal Sdx has been updated, the control circuit  10  inputs the signal Sdx, and output to the gate drive circuit  20 . If the drive performance adjustment signal Sdx has not been updated, the previous value or the initial value is set. 
     Next, at step  120 , the control circuit  10  outputs the on drive signal Son with the high level “H” to the gate drive circuit  20  to flow the gate current through the IGBT  1 . Here, in the gate drive circuit  20 , when the on drive signal Son is given to the error amplifier  22 , the constant current set in the constant current circuit  23  flows from the DC power supply Vcc to the resistor  24 , and the voltage obtained by reducing the voltage between both ends of the resistor  24  from the power supply voltage Vcc is applied to the non-inverting input terminal of the error amplifier  22 . The error amplifier  22  applies a gate voltage to the MOS transistor  21  so that the voltage of the inverting input terminal approaches the same voltage as the voltage drop of the resistor  24  and causes a constant current to flow through the resistor  2 . 
     As a result, the gate of IGBT  1  is charged with a constant current, and in step S 130 , when the gate voltage Vg rises at a constant rate of voltage increase and reaches a predetermined gate voltage VG, the IGBT  1  is turned on. At this time, the gate voltage Vg of the IGBT  1  has been detected by the gate voltage detection circuit  30 , and the comparator  31  outputs to the control circuit  10  in step S 140  that it has reached the on state according to the gate detection signal Sg with the high level “H” when the gate voltage Vg has reached the reference voltage VrefU for detecting that the gate voltage Vg has almost reached the predetermined gate voltage VG. 
     After that, in step S 150 , when an on drive command signal is given from the external circuit, the control circuit  10  inputs the signal, and in step S 160 , outputs an off drive signal with a low level “L” to the gate drive circuit  20  to discharge the gate charge of the IGBT  1 . As a result, in step S 170 , the gate voltage Vg of the IGBT  1  decreases, and when it decreases below the threshold voltage, the IGBT  1  shifts to the off state. 
     Thereafter, by repeating the switching cycle in the same manner as described above, the gate control device  100  controls the on/off drive of the IGBT  1 . 
     Next, in the switching cycle, the flow of the setting process of the on drive time will be described with reference to  FIG.  3   . In this embodiment, in order to turn on the IGBT  1  with the given on-drive time set value Tons in the above-described switching cycle, the control circuit  10  adjusts the drive performance and sets the drive performance adjustment signal Sdx. 
     When the control circuit  10  starts the on/off drive control operation, first, in step S 200 , the timing of the on drive signal Son output in step S 120  and the detection timing of the gate detection signal Sg output in step S 140  described above are obtained. At S 210 , the time difference between these timings is calculated as the on drive time Ton. 
     After that, in step S 220 , the control circuit  10  determines whether or not the calculated value of the on-drive time Ton substantially matches the given on-drive time set value Tons. In this case, a slight range is set above and below the on-drive time set value Tons to provide a matching condition. Generally, they do not match at first, so the determination is “NO” and the process proceeds to the next step S 230 . 
     In step S 230 , the control circuit  10  determines whether or not the calculated value of the on-drive time Ton is greater than the given on-drive time set value Tons. In this case, when the on-drive time Ton is greater than the on-drive time set value Tons, the drive performance is small and the time until the turning on is long. Thus, the determination is made as “YES”, and the process proceeds to step S 240  to execute a process for increasing the drive performance. 
     Since the initial value of the drive performance is set to be small so that the surge voltage of the IGBT  1  does not exceed the withstand voltage, the drive performance is increased in a normal process. Here, in the next step S 250 , the control circuit  10  sets the drive performance adjustment signal Sdx corresponding to the increased drive performance. As a result, in the on-drive control of the switching cycle described above, the drive performance adjustment signal Sdx set in step S 110  is received as an updated value, and the constant current value of the constant current circuit  23  in the gate drive circuit  20  is increased. 
     By repeating the control as described above, the on-drive time Ton can be in a state in which the time Ton substantially matches the on-drive time set value Tons, and the control circuit  10  determines “YES” in step S 220  to maintain the drive performance, and terminates the process. As a result, even if the gate drive time Ton shifts due to variations in the gate capacitance of the IGBT  1 , it is possible to control that the gate drive time Ton matches the on drive time set value Tons by adjusting and setting the drive performance. 
     When the on-drive time Ton becomes equal to or less than the on-drive time set value Tons while repeating the control in this manner, the control circuit  10  determines “NO” in step S 230 , and proceeds to step S 260 . In this case, the control circuit  10  controls to decrease the drive performance. As a result, when the process proceeds to step S 250 , the control circuit  10  newly sets the updated drive performance adjustment signal Sdx, thereby controlling the on drive time Ton to match the on drive time set value Tons again. 
     Next, the above control operation will be described with reference to the timing chart of  FIG.  4   . 
     When the on-drive signal Son with the high level is output at time t 0 , and then, the on-drive time set value Tons elapses at time t 1 , and the gate voltage Vg reaches the reference voltage VrefU at time t 2 . Thus, the detection signal Vg changes to a high level. After that, when the gate voltage Vg reaches VG, the IGBT  1  is turned on. 
     The control circuit  10  calculates a period from time t 0  to t 2  as an on drive time Tona (here, a indicates the first time, hereinafter b, c, and so on) according to the on drive time Ton. Since this on-drive time Tona is longer than the on-drive time set value Tons, in order to shorten it, the control circuit  10  changes the drive performance adjustment signal Sdx adjusted to increase the drive performance from the initial value Sdx 0  to Sdxa. 
     At this time, the amount of increase in the drive performance adjustment signal Sdx may be varied within a predetermined range, or may be set according to the difference between the on drive time Ton and the on drive time set value Tons. 
     As a result, in the next on state, when the on drive signal Son with the high level is output at time t 4 , and then, the on drive time set value Tons elapses at time t 5 , and the gate voltage Vg reaches the reference voltage VrefU, so that the gate detection signal Vg changes to the high level, and after that, when the gate voltage Vg reaches VG, the IGBT  1  is turned on. 
     The control circuit  10  calculates the period from time t 4  to t 5  as the on-drive time Ton as the on-drive time Tonb (at the second time). This on-drive time Tonb is substantially the same as the on-drive time set value Tons. In this state, the control circuit  10  maintains the drive performance. 
     In this embodiment, the gate voltage is detected by the gate voltage detection circuit  30  to monitor the on-drive time Ton with respect to the given on-drive time set value Tons, and the control circuit  10  sets and adjusts the drive performance so that the current value of the constant current supply to the gate of the IGBT  1  is controlled by the gate drive circuit  20 . 
     As a result, it is possible to appropriately set the drive performance so as to minimize variations in the on drive time Ton due to variations in the gate capacitance of the IGBT  1  as the control target with respect to the on drive time set value Tons that is set preliminarily. Thus, it is possible to prevent the surge voltage from exceeding the withstand voltage, to maintain the gate voltage drive time appropriately and to prevent the switching loss from increasing. 
     In the above-described embodiment, the gate drive circuit  20  is configured to charge the gate of the IGBT  1  by supplying a constant current based on the drive performance. Thus, the configuration for setting and changing the increasing speed of the gate voltage Vg of the IGBT  1  is simple, and it is possible to provide a simple configuration for adjusting the on drive time. 
     In the above-described embodiment, the comparator  31  is provided as the gate voltage detection circuit  30 . Alternatively, the present embodiment may not be limited to this feature, and may be provided as an A/D converter that converts the gate voltage Vg of the IGBT  1  into digital data. In this case, the same control can be performed by executing the process for obtaining the gate detection signal in the control circuit  10  using the gate detection signal as the digital data based on the gate voltage. 
     Second Embodiment 
       FIGS.  5  to  6    show a device according to a second embodiment, and portions different from the first embodiment will be described below. In this embodiment, the gate drive device  110  is configured to drive two IGBTs  1   a  and  1   b . Here, two IGBTs  1   a  and  1   b  are connected in parallel. 
       FIG.  5    shows an electrical configuration, and the gate drive device  110  includes two sets of the control circuit  10 , the gate drive circuit  20 , and the gate voltage detection circuit  30  in the gate drive device  100  shown in the first embodiment in respective IGBTs  1   a  and  1   b . The configuration of each set is indicated by adding a suffix “a” to the configuration of the IGBT  1   a  and adding a suffix “b” to the configuration of the IGBT  1   b.    
     The control circuits  10   a  and  10   b  are provided with the same on-drive signal Sonx and on-drive time set value Tons. The control circuit  10   a  provides the gate drive circuit  20   a  with the on drive signal Son 1  and the drive performance adjustment signal Sdx 1 . The control circuit  10   a  also receives a gate detection signal Sg 1  from the gate voltage detection circuit  30   a . In addition, the control circuit  10   b  provides the gate drive circuit  20   b  with the on drive signal Son 2  and the drive performance adjustment signal Sdx 2 . The control circuit  10   b  also receives a gate detection signal Sg 2  from the gate voltage detection circuit  30   b.    
     As a result, as shown in  FIG.  6   , the control circuits  10   a  and  10   b  perform the same control as in the first embodiment in accordance with the common on-drive time set value Tons, thereby adjusting the drive performance of the gate drive circuits  20   a ,  20   b  to an optimum state, so that it is possible to drive to match both the on-drive time Ton 1  of the IGBT  1   a  and the on-drive time Ton 2  of the IGBT  1   b  with the on-drive time set value Tons. 
     According to the second embodiment, it is possible to appropriately set the drive performance so as to minimize variations in the on drive time Ton 1 , Ton 2  due to variations in the gate capacitance of the IGBTs  1   a  and  1   b  as the control target with respect to the on drive time set value Tons that is set preliminarily. Thus, it is possible to prevent the surge voltage from exceeding the withstand voltage, to maintain the gate voltage drive time appropriately and to prevent the switching loss from increasing. 
     Third Embodiment 
       FIG.  7    to  FIG.  9    show a third embodiment, and different portions from the first embodiment will be described below. In this embodiment, the gate drive device  120  is configured to have a sense current detection circuit  40  instead of the gate voltage detection circuit  30 . Also, the IGBT  1  has a sense emitter terminal capable of detecting a sense current. A sense emitter terminal of the IGBT  1  is connected to the ground via a resistor  3  for current detection. 
     The sense current detection circuit  40  has operational amplifiers  41  and  42  and a capacitor  43 . The sense current detection circuit  40  retrieves a terminal voltage Vsen generated across the resistor  3  by a sense current Isen flowing from the sense emitter terminal of the IGBT  1  to the resistor  3 , and outputs an output through two operational amplifiers  41  and  42  as a buffer to the control circuit  11  as a sense current detection signal Ssen. 
     The control circuit  11  retrieves the sense voltage Vsen input from the sense current detection circuit  40  and the preset on-drive command signal Sonx, and outputs an on-drive signal Son based on the on-drive command signal Sonx to the gate drive circuit  20 . In addition, the control circuit  11  outputs the drive performance during the on drive to the constant current circuit  23  of the gate drive circuit  20  as the drive performance adjustment signal Sdx. 
     In this embodiment, the control circuit  11  adjusts the drive performance of the IGBT  1  during the on-drive to be an appropriate level according to the sense current detection signal Ssen, and outputs the signal Ssen as the drive performance adjustment signal Sdx to the gate drive circuit  20  for setting and updating. 
     In this case, the control circuit  11  updates and sets the gate driving circuit  20  so as to reduce the drive performance when it is determined based on the sense current detection signal Ssen from the sense current detection circuit  40  that the sense current Isen of the IGBT  1  has increased, and when it is determined that the current of the IGBT  1  has decreased, the control circuit  11  updates and sets the gate driving circuit  20  so as to increase the drive performance. 
     As a result, when the sense current detection signal Ssen of the IGBT  1  is small, the current flowing through the IGBT  1  is small and the surge voltage is also small, so that the drive performance can be increased compared to the previous switching operation. Also, when the sense current detection signal Ssen of the IGBT  1  is large, the current flowing through the IGBT  1  is large and the surge voltage is large. Thus, the drive performance is reduced compared to the previous switching operation to restrict the surge voltage. 
     The contents of the above control will be described with reference to the timing chart of  FIG.  8   . In the drawing, it is assumed that the sample hold timing of the sense current detection signal Ssen is set after the gate voltage reaches a predetermined level and in a state where the IGBT  1  is sufficiently turned on. For this reason, although not shown in  FIG.  7   , the timing may be set by detecting the gate voltage of the IGBT  1 , or the timing may be set after a certain period of time has passed since the high-level on drive signal Son was output. 
     When the on-drive command signal Sonx is input, the control circuit  11  sets the drive performance determined at the time of the previous switching operation as the drive performance adjustment signal Sdx 0  in “state 1”, and sets the on-drive timing as a high level on drive signal Son at time t 0  to input it to the gate drive circuit  20 . As a result, the gate drive circuit  20  charges the gate of the IGBT  1  by supplying a constant current to the gate of the IGBT  1  based on the input drive performance adjustment signal Sdx 0 . The gate voltage Vg of the IGBT  1  rises, and at time t 1 , the IGBT  1  transitions to the on state indicated by “state 1” in the drawing. 
     When the current flows while the IGBT  1  is in the on state, a sense current Isen proportional to this current flows from the sense emitter terminal through the resistor  3 . As a result, a sense voltage Vsen corresponding to the product of the resistance value of the resistor  3  and the sense current Isen is generated at the terminal of the resistor  3 . This sense voltage Vsen is detected by the sense current detection circuit  40  at time t 2 , and a sense current detection signal Ssen 0  is transmitted to the control circuit  11 . 
     After that, when the current of the IGBT  1  decreases and the sense current signal decreases from Ssen 0  to Ssena in the switching cycle “at the time of state transition”, the control circuit  11  determines the drive performance according to the decreased sense current signal Ssena. In this case, since the sense current signal Ssena is decreased, in the next switching cycle from time t 4  to t 8 , which is “at the time of state transition”, the drive performance is transmitted as the drive performance adjustment signal which is increased from Sdx 0  to Sdxa to the gate drive circuit  20  at time t 7  when the turning-off start time. The relationship between the level of the sense current signal Ssen and the drive performance Sdx at this time is as shown in  FIG.  9   . 
     For example, when the sense current Isena is small, the current of the IGBT  1  is small and the surge voltage is small. Thus, the drive performance of the previous switching operation is increased from Sdxa to Sdxb. Conversely, when the sense current Isenb is large, the current of the IGBT  1  is large and the surge voltage is large. Thus, the drive performance of the previous switching operation is decreased from Sdxb to Sdxa. 
     In this embodiment, the control circuit  11  increases the drive performance adjustment signal to be output to the gate drive circuit  20  at time t 7  to Sdxa, which is substantially equivalent to setting the on drive time set value Ton short, so that the on-drive time Ton is also adjusted to a short time. 
     According to the third embodiment as described above, the sense current detection circuit  40  is provided, and the drive performance is adjusted according to the level of the sense current detection signal Ssen by the control circuit  11  according to the relationship shown in  FIG.  9   . Thus, the switching loss can be reduced while controlling the surge voltage of the IGBT  1 . 
     In the above embodiment, the sense current detection circuit  40  is configured by a combination of operational amplifiers, alternatively, the A/D converter may convert the sense voltage Vsen into a sense current detection signal Ssen of digital data and output it to the control circuit  11 . Thus, the level may be determined in the control circuit  11 . 
     Fourth Embodiment 
       FIG.  10    to  FIG.  12    show a fourth embodiment, and different portions from the first embodiment will be described below. In this embodiment, the gate drive device  130  has a configuration in which the sense current detection circuit  40  of the third embodiment is added to the configuration of the gate drive device  100  of the first embodiment. 
     In this configuration, the control circuit  12  instead of the control circuit  10  includes input signals of a preset on-drive command signal Sonx, an on-drive time set value Tons, a gate detection signal Sg from the gate voltage detection circuit  30 , and the sense current detection signal Ssen from the sense current detection circuit  40 . 
     The control circuit  12  sets the on-drive timing from the on-drive command signal Sonx, outputs the on-drive signal Son to the gate drive circuit  20 , and outputs the drive performance at the time of on-drive as the drive performance adjustment signal Sdx. 
     Further, the control circuit  12  outputs the drive performance during on-drive as the drive performance adjustment signal Sdx according to the comparison result and the sense current detection signal Ssen by comparing the on drive time Ton from the output timing of the high-level on-drive signal Son to the input of the gate detection signal Sg with the preset on-drive time set value Tons. 
     As a result, the control circuit  12  changes and sets the drive performance while detecting the change in the current of the IGBT  1  based on the change in the level of the sense current detection signal Ssen, and further, sets and change the drive performance so that the on drive time Ton reaches the set on drive set value Tons. As a result, the IGBT  1  can be turned on with the optimum on-drive time Tons while protecting against the surge voltage. 
     A specific control operation will be described with reference to  FIG.  11   . 
     When the on-drive command signal Sonx is input, the control circuit  12  sets the drive performance determined at the time of the previous switching operation as the drive performance adjustment signal Sdx, and sets the on-drive timing as a high level on drive signal Son at time t 0  to input it to the gate drive circuit  20 . 
     The gate drive circuit  20  charges the gate of the IGBT  1  with a constant current based on the input drive performance, thereby increasing the gate voltage Vg and turning on the IGBT  1 . At this time, when the gate voltage Vg of the IGBT  1  exceeds the reference voltage VrefU for detecting the on state, the gate voltage detection circuit  30  detects it and outputs a high-level gate detection signal Sg to the control circuit  12 . 
     Also, while the IGBT  1  is in an on state, a current flows through the IGBT  1 , and a mirror current flows from the sense emitter terminal to the resistor  3  to generate a sense voltage Vsen which is the product of these currents. A sense current detection circuit  40  detects the sense voltage Vsen and outputs a sense current detection signal Ssen to the control circuit  12 . 
     The control circuit  12  sets the drive performance by comparing the on-drive time Ton from the on-drive timing to the detection of the gate voltage with a preset on-drive time set value Tons. In this case, when the on-drive time Ton is longer than the on-drive time set value Tons, the drive performance adjustment signal Sdx is set so as to increase the drive performance over the previous switching operation. When the on-drive time Ton is shorter than the on-drive time set value Tons, the drive performance is lowered from the previous switching operation. 
     Further, the control circuit  12  determines the drive performance according to the sense current detection signal Ssen, and transmits the drive performance to the gate drive circuit  20  as the drive power adjustment signal Sdx. In this case, changing and setting the drive performance is substantially equivalent to changing and setting the on drive time set value Tons. 
     For example, when the sense current Isena is small, the current of the IGBT  1  is small and the surge voltage is small. Thus, the drive performance of the previous switching operation is increased from Sdxa to Sdxb. As shown in  FIG.  12   , this means that the on-drive time set value Tons is changed and set from Tons 1  to a longer on-drive time set value Tons 2 . 
     Conversely, when the sense current Isenb is large, the current of the IGBT  1  is large and the surge voltage is large. Thus, the drive performance of the previous switching operation is decreased from Sdxb to Sdxa. As shown in  FIG.  12   , this means that the on-drive time set value Tons is changed and set from Tons 2  to a shorter on-drive time set value Tons 1 . 
     According to the fourth embodiment, the drive performance is determined by the control circuit  12  based on the on drive time Ton and the sense current detection signal Son obtained by mirroring the current of the IGBT  1 . Therefore, the on drive time Ton is set to the predetermined on drive time set value Tons and the drive performance can be changed according to the current of the IGBT  1 , so that the switching loss can be reduced while controlling the surge voltage of the IGBT  1 . 
     Fifth Embodiment 
       FIG.  13    shows a fifth embodiment. Differences from the first embodiment will be described below. In this embodiment, the gate drive device  140  is configured to include the control circuit  13 , the gate drive circuit  50  for off-drive, and the gate voltage detection circuit  30   a.    
     The control circuit  13  receives an off-driving command signal Soffx from an external circuit for controlling on/off control of the IGBT  1  and is input an off-drive time set value Toffs. The control circuit  13  outputs an off-drive signal Soff to the gate drive circuit  50  in accordance with the supplied off-drive command signal Soffx, and outputs a drive performance voltage signal Sdy in accordance with the off-drive time set value Toffs. Further, the control circuit  13  receives the gate detection signal Sg that has been switched to the off state, from the gate voltage detection circuit  30   a.    
     The gate drive circuit  50  includes a N-channel MOS transistor  51  for gate drive, an error amplifier  52  and a constant current circuit  53 . The MOS transistor  51  has a source connected to the ground via the resistor  2  and a drain connected to the gate of the IGBT  1 . A gate of the MOS transistor  51  is connected to an output terminal of the error amplifier  52 . 
     The error amplifier  52  has an inverting input terminal connected to the source of the MOS transistor  51  and a non-inverting input terminal connected to the ground via the resistor  54  and connected to the DC power supply Vcc through the constant current circuit  53 . The constant current circuit  53  is configured such that the constant current value is changed and set by the drive performance voltage signal Sdy, and is configured to adjust the voltage applied to the non-inverting input terminal of the error amplifier  52  by flowing a constant current to the resistor  54 . 
     The error amplifier  52  outputs the voltage to the gate of the MOS transistor  51  to match the voltage generated in the resistor  54  with flowing the constant current of the constant current circuit  53  according to the voltage of the DC power supply Vcc, with the voltage generated with flowing the current in the resistor  2  according to the voltage of the DC power supply Vcc. Thereby, the current flowing through the MOS transistor  51  is controlled to be a constant current. The constant current value that flows from the gate of the IGBT  1  to the ground by the MOS transistor  51  can be changed by adjusting the drive performance voltage signal Sdy. 
     The gate voltage detection circuit  30   a  has a comparator  31  and a reference power supply  33 . The comparator  31  has a non-inverting input terminal connected to the gate of the IGBT  1  and an inverting input terminal connected to the reference power supply  32 . The reference voltage VrefD of the reference power supply  33  is set to a voltage slightly higher than the gate voltage when the IGBT  1  is turned off, and the comparator  31  outputs the gate detection signal Sg with the high level to the control circuit  13  showing that it is switched to the off state when the gate voltage Vg of the IGBT  1  drops to the reference voltage VrefD. 
     By adopting the above configuration, although there is a difference in the on/off operations, by performing the off drive control of the IGBT  1  in substantially the same manner as in the first embodiment, the off drive time Toff is set to match the off drive time set value Toffs. 
     In this embodiment, the gate voltage vg is detected by the gate voltage detection circuit  30   a  to monitor the off drive time Ton with respect to the given off drive time set value Toffs, and the control circuit  13  sets and adjusts the drive performance so that the current value of the constant current supply to the gate of the IGBT  1  is controlled by the gate drive circuit  50 . 
     As a result, it is possible to appropriately set the drive performance so as to minimize variations in the off drive time Toff due to variations in the gate capacitance of the IGBT  1  as the control target with respect to the off drive time set value Toffs that is set preliminarily. Thus, it is possible to prevent the surge voltage from exceeding the withstand voltage, to maintain the gate voltage drive time appropriately and to prevent the switching loss from increasing. 
     In the above-described embodiment, the gate drive circuit  50  is configured to discharge the gate of the IGBT  1  by flowing a constant current based on the drive performance. Thus, the configuration for setting and changing the decreasing speed of the gate voltage Vg of the IGBT  1  is simple, and it is possible to provide a simple configuration for adjusting the off drive time. 
     In the above-described embodiment, the comparator  31  is provided as the gate voltage detection circuit  30   a . Alternatively, the present embodiment may not be limited to this feature, and may be provided as an A/D converter that converts the gate voltage Vg of the IGBT  1  into digital data. In this case, the same control can be performed by executing the process for obtaining the gate detection signal in the control circuit  13  using the gate detection signal as the digital data based on the gate voltage. 
     Further, in the above-described embodiment, the configuration for performing the off-drive control has been shown, alternatively, this configuration can also be applied as a configuration in which this configuration is combined with each of the first to fourth embodiments. This allows both on and off drive control to be implemented. 
     Sixth Embodiment 
       FIG.  14    shows a sixth embodiment. Differences from the first embodiment will be described below. In this embodiment, the gate drive device  150  is configured to include the control circuit  14 , the gate drive circuit  50  for off-drive, and the sense current detection circuit  40 . Also, the IGBT  1  has a sense emitter terminal capable of detecting a sense current. A sense emitter terminal of the IGBT  1  is connected to the ground via a resistor  3  for current detection. 
     The control circuit  14  retrieves the sense voltage Vsen input from the sense current detection circuit  40  and the preset off-drive command signal Soffx, and outputs an off-drive signal Soff based on the off-drive command signal Soffx to the gate drive circuit  50 . In addition, the control circuit  14  outputs the drive performance during the off drive to the constant current circuit  53  of the gate drive circuit  50  as the drive performance adjustment signal Sdy. 
     In this embodiment, the control circuit  14  adjusts the drive performance of the IGBT  1  during the off-drive to be an appropriate level according to the sense current detection signal Ssen, and outputs the signal Ssen as the drive performance adjustment signal Sdy to the gate drive circuit  50  for setting and updating. 
     In this case, the control circuit  14  updates and sets the gate driving circuit  50  so as to reduce the drive performance when it is determined based on the sense current detection signal Ssen from the sense current detection circuit  40  that the sense current Isen of the IGBT  1  has increased, and when it is determined that the current of the IGBT  1  has decreased, the control circuit  11  updates and sets the gate driving circuit  20  so as to increase the drive performance. 
     As a result, when the sense current detection signal Ssen of the IGBT  1  is small, the current flowing through the IGBT  1  is small and the surge voltage is also small, so that the drive performance can be increased compared to the previous switching operation. Also, when the sense current detection signal Ssen of the IGBT  1  is large, the current flowing through the IGBT  1  is large and the surge voltage is large. Thus, the drive performance is reduced compared to the previous switching operation to restrict the surge voltage. 
     According to the sixth embodiment as described above, the sense current detection circuit  40  is provided, and the drive performance is adjusted according to the level of the sense current detection signal Ssen by the control circuit  14 . Thus, the switching loss can be reduced while controlling the surge voltage of the IGBT  1 . 
     In the above embodiment, the sense current detection circuit  40  is configured by a combination of operational amplifiers, alternatively, the A/D converter may convert the sense voltage Vsen into a sense current detection signal Ssen of digital data and output it to the control circuit  14 . Thus, the level may be determined in the control circuit  14 . 
     Further, in the above-described embodiment, the configuration for performing the off-drive control has been shown, alternatively, this configuration can also be applied as a configuration in which this configuration is combined with each of the first to fourth embodiments. This allows both on and off drive control to be implemented. 
     Seventh Embodiment 
       FIG.  15    shows a seventh embodiment. Differences from the first embodiment will be described below. In this embodiment, the gate drive device  160  has a configuration in which the sense current detection circuit  40  of the sixth embodiment is added to the configuration of the gate drive device  140  of the fifth embodiment. 
     In this configuration, the control circuit  15  instead of the control circuit  13  includes input signals of a preset off-drive command signal Soffx, an off-drive time set value Toffs, a gate detection signal Sg from the gate voltage detection circuit  30   a , and the sense current detection signal Ssen from the sense current detection circuit  40 . 
     The control circuit  15  sets the off-drive timing from the off-drive command signal Soffx, outputs the off-drive signal Soff to the gate drive circuit  50 , and outputs the drive performance at the time of off-drive according to the drive performance adjustment signal Sdy. 
     Further, the control circuit  15  outputs the drive performance during off-drive as the drive performance adjustment signal Sdy according to the comparison result and the sense current detection signal Ssen by comparing the off drive time Toff from the output timing of the high-level off-drive signal Soff to the input of the gate detection signal Sg with the preset off-drive time set value Toffs. 
     As a result, the control circuit  15  changes and sets the drive performance while detecting the change in the current of the IGBT  1  based on the change in the level of the sense current detection signal Ssen, and further, sets and change the drive performance so that the off drive time Toff reaches the set off drive set value Toffs. As a result, the IGBT  1  can be off-driven at the optimum off-drive time set value Toffs while protecting against the surge voltage. 
     According to the seventh embodiment, the drive performance is determined by the control circuit  15  based on the off drive time Toff and the sense current detection signal Ssen obtained by mirroring the current of the IGBT  1 . Therefore, the off drive time Toff is set to the predetermined off drive time set value Toffs and the drive performance can be changed according to the current of the IGBT  1 , so that the switching loss can be reduced while controlling the surge voltage of the IGBT  1 . 
     Further, in the above-described embodiment, the configuration for performing the off-drive control has been shown, alternatively, this configuration can also be applied as a configuration in which this configuration is combined with each of the first to fourth embodiments. This allows both on and off drive control to be implemented. 
     Eighth Embodiment 
       FIG.  16    shows an eighth embodiment. Differences from the first embodiment will be described below. In this embodiment, the gate drive device  170  is configured to have a temperature detection circuit  60  instead of the gate voltage detection circuit  30 . Also, the IGBT  1  is provided with a diode  4  in the vicinity thereof for detecting the temperature by means of the forward voltage Vf. 
     The temperature detection circuit  60  has a constant current circuit  61  and an A/D converter  62 . The temperature detection circuit  60  causes a constant current circuit  61  to pass a predetermined current through the diode  4  arranged near the IGBT  1 , retrieves the forward voltage Vf at this time into the A/D converter  62 , and converts it into a digital signal as a temperature detection signal St to output the signal St to the control circuit  16 . 
     The control circuit  16  receives a preset on-drive command signal Sonx and a temperature detection signal St input from the temperature detection circuit  60 , and outputs an on-drive signal Son according to the on-drive command signal Sonx to the gate drive circuit  20 . In addition, the control circuit  16  outputs the drive performance of the IGBT  1  during the on drive to the constant current circuit  23  of the gate drive circuit  20  as the drive performance adjustment signal Sdx. 
     In this embodiment, the control circuit  16  adjusts the drive performance of the IGBT  1  during the on-drive to be an appropriate level according to the temperature detection signal St, and outputs the signal Ssen as the drive performance adjustment signal Sdx to the gate drive circuit  20  for setting and updating. 
     In this case, the control circuit  16  updates and sets the gate drive circuit  20  so as to reduce the drive performance when it is determined that the temperature of the IGBT  1  has decreased based on the temperature detection signal St from the temperature detection circuit  60 , and to increase the drive performance when it is determined that the temperature of the IGBT  1  has increased. 
     As a result, when the temperature of the IGBT  1  is low, the surge voltage of the IGBT  1  increases, and can be suppressed by lowering the drive performance compared to the previous switching operation. In addition, when the temperature of the IGBT  1  is high, the surge voltage of the IGBT  1  becomes small, so that the drive performance can be increased compared to the previous switching operation. 
     According to the eighth embodiment, the temperature detection circuit  60  for detecting the temperature of the IGBT  1  from the forward voltage Vf of the diode  4  is provided, and the control circuit  16  adjusts the drive performance according to the detected temperature of the IGBT  1 . Therefore, it is possible to reduce the switching loss while controlling the surge voltage of the IGBT  1 . 
     Ninth Embodiment 
       FIG.  17    shows a ninth embodiment. Differences from the first embodiment will be described below. In this embodiment, the gate drive device  180  is configured to have a power supply voltage detection circuit  70  instead of the gate voltage detection circuit  30 . Also, a voltage dividing circuit  5  for detecting the DC voltage VH of the high voltage power supply connected to the IGBT  1  is arranged. The voltage dividing circuit  5  includes a series circuit of resistors  5   a  and  5   b  that divides the DC voltage VH of the high voltage power supply. 
     The power supply voltage detection circuit  70  has an input circuit  71  and an A/D converter  72 . The input circuit  71  retrieves the terminal voltage Vh of the resistor  5   b  obtained by dividing the DC voltage VH of the high-voltage power supply by the voltage dividing circuit  5 , and inputs it to the A/D converter  72  as an analog voltage signal. The A/D converter  72  converts the voltage signal output from the input circuit  71  into a digital signal corresponding to the voltage of the high-voltage power supply, and inputs it to the control circuit  17  as the power supply voltage detection signal SV. 
     The control circuit  17  receives a preset on-drive command signal Sonx and a power supply voltage detection signal SV input from the power supply voltage detection circuit  70 , and outputs an on-drive signal Son according to the on-drive command signal Sonx to the gate drive circuit  20 . In addition, the control circuit  17  outputs the drive performance during the on drive to the constant current circuit  23  of the gate drive circuit  20  as the drive performance adjustment signal Sdx. 
     In this embodiment, the control circuit  17  adjusts the drive performance of the IGBT  1  during the on-drive to be an appropriate level according to the power supply voltage detection signal SV, and outputs the signal Ssen as the drive performance adjustment signal Sdx to the gate drive circuit  20  for setting and updating. 
     In this case, the control circuit  17  updates and sets the gate drive circuit  20  so as to reduce the drive performance when it determines that the power supply voltage HV applied to the IGBT  1  has increased based on the power supply voltage detection signal SV from the power supply voltage detection circuit  70 . When it is determined that the power supply voltage HV has decreased, the setting is updated so as to increase the drive performance. 
     As a result, when the DC voltage VH of the high-voltage power supply applied to the IGBT  1  is high, the surge voltage of the IGBT  1  increases, and can be suppressed by lowering the drive performance compared to the previous switching operation. Also, when the DC voltage VH is low, the surge voltage of the IGBT  1  is small, so that the drive performance can be increased compared to the previous switching operation. 
     According to the ninth embodiment as described above, the DC voltage VH applied to the IGBT  1  is divided by the voltage dividing circuit  5 , and the power supply voltage detection circuit  70  is arranged to detect the divided voltage Vh corresponding to the power supply voltage as the power supply voltage signal SV of the digital signal. Further, the control circuit  17  is provided to adjust the drive performance according to the magnitude of the DC voltage VH. Thus, the switching loss can be reduced while controlling the surge voltage of the IGBT  1 . 
     Tenth Embodiment 
       FIG.  18    to  FIG.  20    show a tenth embodiment, and different portions from the first embodiment will be described below. In this embodiment, the gate drive device  190  has a configuration in which another gate voltage detection circuit  80  is added in addition to the gate voltage detection circuit  30  in the configuration of the gate drive device  100  of the first embodiment. 
     The gate voltage detection circuit  80  has a comparator  81  and a reference power supply  82 . The comparator  81  has a non-inverting input terminal connected to the gate of the IGBT  1  and an inverting input terminal connected to the reference power supply  82 . The reference power supply  82  is set to a voltage slightly lower than the mirror voltage Vm as the reference voltage VrefM in order to detect the timing when the gate voltage Vg of the IGBT  1  shifts to the mirror period. 
     The comparator  81  outputs a high level gate detection signal SgM to the control circuit  10  when the gate voltage Vg of the IGBT  1  reaches the reference voltage VrefM. Further, it is assumed that the gate detection signal Sg detected by the gate voltage detection circuit  30  corresponding to the gate detection signal SgM of the gate voltage detection circuit  80  is output as the gate detection signal SgU. 
     The level of the gate voltage Vg detected by the gate voltage detection circuit  80  may not be limited to a value for detecting the mirror voltage Vm, alternatively, may be a value for setting the reference voltage VrefM in order to detect the voltage with the middle level at which the gate voltage Vg is shifted to the on state. 
     In this configuration, the control circuit  18  instead of the control circuit  10  receives the preset on-drive command signal Sonx, the on-drive time set value Tons 1 , the on-drive time set value Tons 2 , the gate detection signal SgM, and the gate detection signal SgU. Further, the control circuit  18  sets the on-drive timing from the on-drive command signal Sonx, outputs the on-drive signal Son to the gate drive circuit  20 , and outputs the drive performance at the time of on-drive as the drive performance adjustment signal Sdx to the gate drive circuit  20 . 
     The control circuit  18  outputs the drive performance during the on drive as the drive performance adjustment signal Sdx according to the comparison result by comparing the first on-drive time Ton 1 , from the output timing of the high-level on-drive signal Son until the gate voltage Vg reaches the reference voltage VrefM and the gate detection signal SdM is input, with a preset first on-drive time set value Tons 1 . 
     In addition, the control circuit  18  outputs the drive performance from the time when the gate voltage Vg reaches the reference voltage VrefM as the drive performance adjustment signal Sdx according to the comparison result by comparing the second on drive time Ton 2 , from the timing when the gate detection signal SgM is input until the gate detection signal SgU is input, with a preset second on-drive time set value Tons 2 . 
     That is, the drive performance set by the control circuit  18  is configured to be set by adjusting each of the first on drive time Ton 1  and the second on drive time Ton 2 . As a result, the IGBT  1  can be turned on with the optimum on-drive time Tons while protecting against the surge voltage. 
     Next, a specific control operation will be described with reference to  FIGS.  19  and  20   . 
     When the on-drive command signal Sonx is input, the control circuit  18  sets the drive performance determined at the time of the previous switching operation as the drive performance adjustment signal Sdx, and sets the on-drive timing as a high level on drive signal Son at time t 0  to input it to the gate drive circuit  20 . As a result, the gate drive circuit  20  supplies a constant current to the gate of the IGBT  1  based on the input drive performance adjustment signal Sdx to charge the gate, thereby increasing the gate voltage Vg of the IGBT  1 . 
     When the gate voltage Vg of the IGBT  1  rises and exceeds the reference voltage VrefM of the gate voltage detection circuit  80 , it is detected by the gate voltage detection circuit  80  and the gate detection result is transmitted to the control circuit  18  as a high level gate detection signal SgM. 
     The control circuit  18  sets the drive performance during the on drive by comparing the on-drive time Ton 1  from the on-drive timing to the detection of the reference voltage VrefM according to the gate voltage Vg with a preset on-drive time set value Tons 1 . In this case, when the on-drive time Ton 1  is longer than the on-drive time set value Tons 1 , the drive performance adjustment signal Sdx is set so as to increase the drive performance over the previous switching operation. When the on-drive time Ton 1  is shorter than the on-drive time set value Tons 1 , the drive performance is lowered from the previous switching operation. 
     Further, when the gate voltage Vg exceeds the reference voltage VrefM, the control circuit  18  inputs the drive performance determined by the previous switching operation to the gate drive circuit  20  as the drive performance adjustment signal Sdx. 
     Since the gate drive circuit  20  charges the gate of the IGBT  1  based on the input drive performance, the gate voltage Vg further increases. When the gate voltage Vg exceeds the reference voltage VrefU, gate detection is performed by the gate voltage detection circuit  30 , and the gate detection result is transmitted to the control circuit  18  as a high-level gate detection signal SgU. 
     Regarding the drive performance when the reference voltage VrefM for gate detection is exceeded, the control circuit  18  increases the drive performance when the reference voltage VrefM for gate detection is exceeded, from the previous switching operation when the on drive time Ton 2  is larger than the second on drive time set value Tons 2  by comparing the on drive time Ton 2  from the time when the gate detection signal SgM is input until the reference voltage VrefU for gate detection is detected, with the pre-set second on-drive time set value Tons 2 . When the on-drive time Ton 2  is shorter than the second on-drive time set value Tons 2 , the drive performance when the reference voltage VrefM is exceeded is reduced compared to the time of the previous switching operation. 
     Thus, by setting the on-drive time Ton 1  and the on-drive time Ton 2 , respectively, the switching loss and the surge voltage can be optimally set. 
       FIG.  20    shows how the gate voltage Vg changes from time t 6  to t 8  shown in  FIG.  19   . In the drawing, the on-drive time Ton 1  after the gate voltage Vg is turned on at time t 0  until it reaches the reference voltage VrefM. 
     is compared with the first on-driving time set value Tons 1 , so that it functions as the region Z 1  for mainly determining the surge voltage of the IGBT  1 . Also, the on drive time Ton 2  from time t 1  until the gate voltage Vg reaches the reference voltage VrefU is compared with the second on drive time set value Tons 2 , so that it functions as a region Z 2  that mainly determines the switching loss. 
     According to this embodiment, the gate voltage detection circuit  30  that detects the gate voltage Vg with the reference voltage VrefU at the on drive level and the gate voltage detection circuit  80  that detects the gate voltage Vg with the reference voltage VrefM at the middle level are provided. The control circuit  18  compares using the first on-drive time set value Tons 1  and the second on-drive time set value Tons 2 , thereby setting the drive performance of the gate drive circuit  20  in two stages. Thus, each of the surge voltage and the switching loss can be individually controlled. 
     In the above-described embodiment, an example of the configuration in which the gate voltage detection circuit  80  is added to the configuration of the first embodiment is shown, alternatively, the configuration may not be limited to this feature, and may be combined with the configuration of other embodiments. 
     Other Embodiments 
     The present disclosure should not be limited to the embodiments described above. Various embodiments may further be implemented without departing from the scope of the present disclosure, and may be modified or expanded as described below. 
     In the above embodiments, the first embodiment shows one IGBT driven, and the second embodiment shows two IGBTs driven, alternatively, three or more IGBTs may be driven. It can also be configured to drive two or more IGBTs in other embodiments. 
     Further, in each of the above-described embodiments, the case of applying to the IGBT as a gate-driven switching element has been shown, alternatively, the present embodiments may not be limited to these features, and may be applied to MOS transistors, MOS transistors using SiG, other gate-driven switching elements or the like. 
     In the above-described embodiments, the first to fourth embodiments show the embodiments of the configuration in which the IGBT  1  is controlled to on-drive, and the fifth to the seventh embodiments show the embodiments of the configuration in which the IGBT  1  is controlled to off-drive. By combining these, it is also possible to have a configuration that includes both the configuration for on-drive control and the configuration for off-drive control. 
     Further, in each of the above-described embodiments, the gate drive circuit configured to drive the gate of the IGBT  1  with a constant current is shown as the gate drive circuit. Alternatively, it may not be limited to this feature. It may be configured to drive the gate in other methods. 
     Further, in the above-described fourth embodiment, an example of a configuration in which the configuration of the third embodiment is combined with the configuration of the first embodiment has been described. A configuration obtained by combining the configuration of the first embodiment or other embodiments with the configurations of the temperature detection circuit in the eighth embodiment and the power supply voltage detection circuit of the ninth embodiment can also be used. 
     It is noted that a flowchart or the processing of the flowchart in the present application includes sections (also referred to as steps), each of which is represented, for instance, as S 100 . Further, each section can be divided into several sub-sections while several sections can be combined into a single section. Furthermore, each of thus configured sections can be also referred to as a device, module, or means. 
     While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.