JP2012016110A - Drive circuit of switching element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of difficulty in properly detecting the voltage of a gate in both situations: when a power switching element S#* is on-state and when it is off-state.SOLUTION: A gate and an emitter of a power switching element S#* is shorted with an off-holding switching element 40, with a gate voltage drop as a trigger. The off-holding switching element 40 is turned on by an integrated circuit (drive IC 20). Power sources 28 and 30 which apply a voltage to the gate of the power switching element S#* are different in terminal voltage from each other, and the rising of the gate voltage causes switching from the power source 30 whose terminal voltage is low to the power source 28 whose terminal voltage is high. The voltage of a terminal T1 is detected as a gate voltage when the power switching element S#* is in off state, and the voltage of a terminal T2 is detected as the gate voltage when the element is in on state.

Description

  The present invention includes an on-operation circuit for turning on a driving target switching element that is a voltage-controlled switching element, and an off-operation circuit for turning off the driving target switching element. The present invention relates to a driving circuit for a switching element that operates to turn on / off the driving target switching element.

  As this type of drive circuit, for example, as shown in Patent Document 1 below, a gate is formed using a dedicated switching element in order to keep the gate of an insulated gate bipolar transistor (IGBT) after the discharge process in an off state. Also proposed is a short circuit between the emitter and the emitter. Specifically, a part of the drive circuit is an integrated circuit, and the short circuit is performed by operating the dedicated switching element provided outside the integrated circuit based on the voltage of the input terminal.

  Further, as this type of drive circuit, for example, as seen in Patent Document 2 below, it is determined that the mirror period has ended based on the detection result of the gate voltage associated with the ON operation of the insulated gate bipolar transistor (IGBT). Thus, there has been proposed one that increases the gate application voltage.

JP 2010-750007 A Japanese Patent No. 4432215

  Incidentally, even in the drive circuit described in Patent Document 2, it is required to obtain the detection result of the gate applied voltage. However, the integrated circuit used for performing the short-circuiting process described in Patent Document 1 is required. The terminal voltage is inappropriate as a representation of the gate voltage.

  The present invention has been made in order to solve the above-described problems, and the object of the present invention is to control the voltage of the conduction control terminal both when the voltage-controlled switching element is in the on state and when it is in the off state. It is an object of the present invention to provide a driving circuit for a switching element that can be appropriately detected and used.

  Hereinafter, means for solving the above-described problems and the operation and effect thereof will be described.

  According to a first aspect of the present invention, there is provided an on operation circuit for turning on a drive target switching element that is a voltage control type switching element, and an off operation circuit for turning off the drive target switching element. A switching element drive circuit for turning on and off the drive target switching element by operating them, wherein the on operation circuit includes a charging path provided with a charging resistor, and is used for the off operation. The circuit includes a discharge path provided with a discharge resistor different from the charge resistor, and a conduction control terminal of the drive target switching element is a connection point between the charge resistor and the discharge resistor. Are connected to each of these via the drive target switching element during the ON operation period of the drive target switching element. On-operation change processing means for performing processing for changing the operation state of the on-operation circuit based on the detection result of the voltage at the control terminal, and the detection result of the voltage at the conduction control terminal during the off-operation period of the drive target switching element Off-operation change processing means for performing processing for changing the operation state of the off-operation circuit based on the on-operation change processing means, and the on-operation change processing means and the off-operation change processing means are integrated on a single chip. A detection result that is built in a circuit, both the charging resistor and the discharging resistor are externally attached to the integrated circuit, and is input to the on-operation change processing means; Each of the detection results input to the off operation change processing means includes a detection result of the voltage at the connection terminal of the discharging resistor and the integrated circuit, the charging resistor, and Characterized in that it comprises the allocation means allocates the detection result of the voltage of the connection terminal of the serial IC.

  In the ON operation period, the terminal voltage of the integrated circuit connected to the discharging resistor expresses the voltage of the conduction control terminal with higher accuracy than the terminal voltage of the integrated circuit connected to the charging resistor. . On the other hand, during the off-operation period, the terminal voltage of the integrated circuit connected to the charging resistor is more accurate than the voltage of the integrated circuit connected to the discharging resistor. Express. In the above invention, in view of this point, by providing the allocation means, the voltage of the voltage control type switching element is appropriately detected both when it is in the on state and when it is in the off state. Can be used.

  According to a second aspect of the present invention, in the first aspect of the invention, the on-operation change processing means turns on the drive target switching element via the charging path when the voltage of the conduction control terminal increases. It is characterized in that the charge rate of the electric charge is increased.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the off-operation circuit short-circuits the output terminal of the driving target switching element and the conduction control terminal separately from the discharge path. The switching element for off operation further turns on the switching element for short circuit based on detection of a decrease in the voltage of the conduction control terminal.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the off-operation change processing means detects the discharge based on a decrease in the voltage of the conduction control terminal. It is characterized in that the discharge rate of charges for turning on the drive target switching element via the path is increased.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein a connection point between the charging path and the discharging path and the conduction control terminal are connected by a common electrical path. The resistance value of the common electrical path is set to be smaller than both the resistance value of the charging resistor and the resistance value of the discharging resistor.

  The detection accuracy of the voltage of the conduction control terminal using the terminal voltage of the integrated circuit becomes higher as the voltage drop of the common electrical path is smaller. In the said invention, it was set as the said setting in view of this point.

1 is a system configuration diagram according to a first embodiment. FIG. The circuit diagram which shows the structure of the drive unit concerning the embodiment. The time chart which shows the aspect of the drive process of the switching element concerning the embodiment. The circuit diagram which shows the structure of the drive unit concerning 2nd Embodiment. The time chart which shows the aspect of the drive process of the switching element concerning the embodiment. The circuit diagram which shows the structure of the drive unit concerning 3rd Embodiment.

<First Embodiment>
Hereinafter, a first embodiment in which a drive circuit of a power conversion circuit according to the present invention is applied to a hybrid vehicle will be described with reference to the drawings.

  FIG. 1 shows the overall configuration of a motor generator control system according to this embodiment. Motor generator 10 is connected to high voltage battery 12 via inverter IV and boost converter CV. Here, boost converter CV connects capacitor 13, a pair of power switching elements Scp and Scn connected in parallel to capacitor 13, a connection point between the pair of power switching elements Scp and Scn, and the positive electrode of high voltage battery 12. And a reactor L. The voltage of the high voltage battery 12 (for example, “288V”) is boosted up to a predetermined voltage (for example, “666V”) by turning on / off the power switching elements Scp, Scn. On the other hand, the inverter IV includes a series connection body of power switching elements Sup and Sun, a series connection body of power switching elements Svp and Svn, and a series connection body of power switching elements Swp and Swn. Body connection points are connected to the U, V, and W phases of motor generator 10, respectively. In the present embodiment, an insulated gate bipolar transistor (IGBT) is used as these power switching elements Sup, Sun, Svp, Svn, Swp, Swn, Scp, Scn. In addition, diodes Dup, Dun, Dvp, Dvn, Dwp, Dwn, Dup, and Dun are connected in antiparallel to these.

  The control device 16 is a control device that uses the low-voltage battery 14 as a power source. The controller 16 controls the motor generator 10 and operates the inverter IV and the converter CV to control the control amount as desired. Specifically, operation signals gcp and gcn are output to drive unit DU to operate power switching elements Scp and Scn of converter CV. Further, in order to operate the power switching elements Sup, Sun, Svp, Svn, Swp, Swn of the inverter IV, the operation signals gup, gun, gvp, gvn, gwp, gwn are output to the drive unit DU. Here, the high-potential side operation signals gcp, gup, gvp, gwp and the corresponding low-potential side operation signals gcn, gun, gvn, gwn are complementary signals. In other words, the power switching elements Scp, Sup, Svp, Swp on the high potential side and the corresponding power switching elements Scn, Sun, Svn, Swn on the low potential side are alternately turned on.

  FIG. 2 shows the configuration of the drive unit DU.

  As shown in the figure, the drive unit DU includes a drive IC 20 that is a one-chip semiconductor integrated circuit. The terminal T1 of the drive IC 20 is connected to the gate of the power switching element S ** (# = u, v, w, c; * = n, p) via a charging resistor 32 for adjusting the charging speed of the gate. It is connected to the. On the other hand, the drive IC 20 includes power supplies 28 and 30 that supply charges for charging the conduction control terminal (gate) so as to turn on the power switching element S **. The power supplies 28 and 30 are short-circuited to the terminal T1 through the selector 26 and the input terminal and output terminal of the charging switching element 24.

  Further, the terminal T2 of the drive IC 20 is connected to the gate of the power switching element S ## via a discharge resistor 34 for adjusting the discharge rate of the gate. On the other hand, the drive IC 20 includes a discharge switching element 36 that opens and closes between the terminal T4 connected to the emitter of the power switching element S ** and the terminal T2, thereby short-circuiting the terminal T2 and the terminal T4. Connected.

  Specifically, the terminal T1 is connected to the gate via the dedicated charging path Lc and the common path La, and the terminal T2 is connected to the gate via the discharging dedicated path Ld and the common path La. . Here, the dedicated charging path Lc and the dedicated discharging path Ld are connected at the connection point N1, and the connecting point N1 and the gate are short-circuited by the common path La. Further, each of the charging dedicated path Lc and the discharging dedicated path Ld is provided with a charging resistor 32 and a discharging resistor 34, respectively, and thereby the resistance values of the charging dedicated path Lc and the discharging dedicated path Ld. Is sufficiently larger than the resistance value of the common path La.

  The drive IC 20 includes a drive circuit 22 that drives the power switching element S ##. In the drive circuit 22, the charging switching element 24 and the discharging switching element 36 are complementarily turned on / off based on the operation signal g ** input to the drive unit DU via an insulating means such as a photocoupler (not shown). As a result, the power switching element S ## is driven. That is, when the operation signal g ** becomes logic “H” to instruct to turn on the power switching element S **, the charging switching element 24 is turned on and the discharging switching element 36 is turned on. Is turned off to charge the gate of the power switching element S ## with positive charge. Further, when the operation signal g ** becomes logic “L” to instruct the power switching element S ** to be turned off, the charging switching element 24 is turned off and the discharging switching element 36 is turned off. By turning on, positive charge is discharged from the gate of the power switching element S ##.

  The drive unit DU performs a process of increasing the gate applied voltage and increasing the gate charging speed during the process of charging the gate to switch the power switching element S ** to the ON state. That is, the terminal voltage VH of the power supply 28 is set higher than the terminal voltage VL of the power supply 30, and the voltage between the output terminal and the conduction control terminal of the power switching element S ** (gate-emitter voltage: gate voltage Vge) is the mirror period. The gate applied voltage is increased from the terminal voltage VL to the terminal voltage VH. Thus, after the surge is suppressed by limiting the speed at which the current flowing through the power switching element S ** is switched to the ON state, the loss is reduced by promptly increasing the applied voltage.

  The drive unit DU further includes an N-channel MOS field effect transistor (off-holding switching element 40) for short-circuiting between the gate and emitter of the power switching element S ##. The off-holding switching element 40 is provided as close as possible to the power switching element S ## so as to connect the gate and the emitter of the power switching element S ** with a low resistance. Of the paths connecting the gate and the emitter of the power switching element S **, the impedance of the path including the off-holding switching element 40 is set to be lower than the impedance of the path including the discharge resistor 34. Has been. This is because between the input terminal (collector) and output terminal (emitter) of the power switching element S ** and the gate when the power switching element S ** is turned off in response to the operation signal g **. This is to prevent the power switching element S ## from being erroneously turned on by superimposing high-frequency noise on the gate through the parasitic capacitance of the power switching element S **.

  That is, when a current flows from the gate of the power switching element S ## to the discharging resistor 34 due to high-frequency noise, the voltage of the gate increases due to the voltage drop of the discharging resistor 34, so that the power switching element S ** may be turned on. On the other hand, when the off-holding switching element 40 is provided, current flows from the gate of the power switching element S ## to the off-holding switching element 40 due to high frequency noise. Since the impedance of this path is very small, the amount of increase in the gate voltage can be ignored, and the power switching element S ** can be held in the off state.

  The gate of the off holding switching element 40 is connected to the off holding circuit 42 in the drive IC 20 via the terminal T3. The off-holding circuit 42 performs a process of turning on the off-holding switching element 40 when the gate voltage of the power switching element S ## becomes a predetermined voltage. The off hold circuit 42 monitors a signal output from the drive circuit 22 to the gate of the discharge switching element 36 and turns off the off hold switching element 40 in synchronization with the discharge switching element 36 being turned off. It also performs processing to operate.

  Here, in the present embodiment, the gate application voltage of the drive IC 20 is used as the application voltage of the drive IC 20 by using the gate application voltage used in the above-described gate charge rate increase process and the off-holding switching element 40 operation process. Reduce the number of terminals. However, in this case, a common terminal cannot be used for these two processes. That is, because the terminal T1 and the power supplies 28 and 30 are short-circuited, the voltage at the terminal T1 becomes the voltage of the power supplies 28 and 30 when the power switching element S ## is turned on. During processing, the voltage at the terminal T1 is not an accurate representation of the gate voltage Vge. On the other hand, due to the short circuit between the terminal T2 and the terminal T4, the voltage at the terminal T2 becomes the voltage at the terminal T4 during the OFF operation process, so that the voltage at the terminal T2 accurately matches the gate voltage Vge. It cannot be expressed in Incidentally, the reason why the charging resistor 32 and the discharging resistor 34 are externally attached to the drive IC 20 is that they serve as adjusting elements for adjusting the charging rate and discharging rate of the gate.

  In the present embodiment, in view of the above situation, the voltage at the terminal T2 is detected as the gate voltage Vge during the ON operation process, and the voltage at the terminal T1 is detected as the gate voltage Vge during the OFF operation process. Hereinafter, a process for increasing the gate charging speed and an operation process for the off-holding switching element 40, which are performed by using the detection method of the gate voltage Vge, will be described.

  FIG. 3 shows the above two processes according to the present embodiment. Specifically, FIG. 3A shows the transition of the state of the charging switching element 24, FIG. 3B shows the transition of the state of the discharging switching element 36, and FIG. 3C shows the gate voltage. 3 (d) shows the transition of the voltage state at the terminal T2, FIG. 3 (e) shows the transition of the voltage state at the terminal T1, and FIG. 3 (f) FIG. 3G shows the transition of the operating state of the off-holding switching element 40. FIG.

  As shown in the figure, during the period when the charging switching element 24 is in the ON state, the voltage at the terminal T2 accurately represents the gate voltage Vge. For this reason, when this voltage exceeds the threshold voltage VthH, it is possible to detect the end of the mirror period with high accuracy, and based on this, the process of increasing the gate applied voltage from the terminal voltage VL to the terminal voltage VH is performed. Can do. On the other hand, during the period in which the discharge switching element 36 is in the on state, the voltage at the terminal T1 accurately represents the gate voltage Vge. For this reason, when this voltage falls below the threshold voltage VthL (<VthH), the end of the mirror period can be detected with high accuracy, and the on-hold switching element 40 can be turned on based on this. .

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) The gate voltage Vge during the ON operation process is detected as the voltage at the terminal T2, and the gate voltage Vge during the OFF operation process is detected as the voltage at the terminal T1. Thus, the ON operation process and the OFF operation process can be performed while detecting the gate voltage Vge with high accuracy both during the ON operation process and during the OFF operation process.

(2) The connection point N1 between the dedicated charging path Lc and the dedicated discharging path Ld and the gate of the power switching element S ** are short-circuited by the common path La. Thereby, the gate voltage Vge based on the voltages of the terminals T1 and T2 can be performed with higher accuracy.
<Second Embodiment>
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 4 shows a circuit configuration of the drive unit DU according to the present embodiment. In FIG. 4, members corresponding to those shown in FIG. 2 are given the same reference numerals for convenience.

  In the present embodiment, as a process for increasing the gate charging speed, a process for reducing the resistance value of the dedicated charging path Lc is performed. This can be achieved by short-circuiting the power supply 28 to the terminals T1a and T1b via the charging switching elements 24a and 24b, respectively, and connecting the charging resistors 32a and 32b to the terminals T1a and T1b, respectively. . As a result, the dedicated charging path Lc becomes a path including the charging resistor 32a and a path including the charging resistor 32b.

  In addition, the present embodiment also has a function of performing processing for increasing the gate discharge rate. This is to reduce the tail current as much as possible in view of the fact that the tail current flows through the power switching element S ## even after the mirror period has elapsed due to the off operation process. In the present embodiment, such a process is realized by a process of reducing the resistance value of the dedicated discharge path Ld. This can be achieved by short-circuiting the terminal T4 to the terminals T2a and T2b via the discharge switching elements 36a and 36b, respectively, and connecting the discharge resistors 34a and 34b to the terminals T2a and T2b, respectively. . Thereby, the discharge exclusive path Ld becomes a path including the discharge resistor 34a and a path including the discharge resistor 34b.

  The operation of the charging switching elements 24 a and 24 b and the operation of the discharging switching elements 36 a and 36 b are performed by the drive circuit 22 based on the output of the comparator 60. That is, the voltage of the power source 28 is divided by the resistors 50, 52, and 54 to generate the threshold voltages VthH and VthL, and the voltage at the terminal T1a is compared with the voltage at the terminal T2a and the threshold voltage VthH. And means (comparator 60) for comparing the magnitude of the threshold voltage VthL. Specifically, in order to switch a pair of input voltages of the comparator 60, a selector 58 that switches the voltages of the terminals T1a and T2a and a selector 56 that switches the threshold voltages VthH and VthL are provided.

  FIG. 5 shows the above two processes according to the present embodiment. Specifically, FIG. 5 (a1) shows the transition of the state of the charging switching element 24a, FIG. 5 (a2) shows the transition of the state of the charging switching element 24b, and FIG. 5 (b1) shows the state for discharging. The transition of the state of the switching element 36a is shown, and FIG. 5B2 shows the transition of the state of the switching element 36b for discharge. 5C shows the transition of the state of the gate voltage, FIG. 5D shows the transition of the voltage state of the terminal T2a, and FIG. 5E shows the state of the voltage of the terminal T1a. FIG. 5 (f) shows the transition of the selection state of the selector 58, and FIG. 5 (g) shows the transition of the selection state of the selector 56.

  As shown in the figure, during the charging operation process (period in which the charging switching element 24 a is turned on), the terminal B is selected by the selector 58 and the terminal C is selected by the selector 56. Then, when the voltage at the terminal T2a exceeds the threshold voltage VthH, the charging switching element 24b is switched on, the resistance value of the dedicated charging path Lc is reduced, and the charging speed is increased.

On the other hand, during the off operation process (a period in which the charging switching element 24 a is turned off), the terminal A is selected by the selector 58 and the terminal D is selected by the selector 56. Then, when the voltage at the terminal T1a falls below the threshold voltage VthL, the discharge switching element 36b is switched on, the resistance value of the dedicated discharge path Ld is reduced, and the discharge speed is increased.
<Third Embodiment>
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the second embodiment.

  FIG. 6 shows a circuit configuration of the drive unit DU according to the present embodiment. In FIG. 6, members corresponding to those shown in FIG. 4 are given the same reference numerals for convenience.

In the present embodiment, a means (comparator 62) that compares the voltage of the terminal T2a and the threshold voltage VthH, a means (comparator 64) that compares the voltage of the terminal T1a and the threshold voltage VthL, and outputs thereof Switching means (selector 66). Thereby, the drive circuit 22 can perform the same processing as in the second embodiment based on the output of the selector 66.
<Other embodiments>
Each of the above embodiments may be modified as follows.
“On-operation circuit”
The circuit for increasing the charging rate of the gate is not limited to those exemplified in the above embodiments. For example, the charging switching element may be constituted by a bipolar transistor and the base current may be manipulated.
“Off-operation circuit”
The circuit for increasing the gate discharge rate is not limited to that exemplified in the second and third embodiments. For example, you may comprise with the means to reduce the electric potential of the output terminal of the switching element 36 for discharge. Further, for example, the discharge switching element may be constituted by a bipolar transistor and its base current may be manipulated.
"On-operation change processing means"
The detection method of the end of the mirror period is not limited to detecting that the gate voltage exceeds the threshold voltage VthH. For example, it may be one that detects the rising speed of the gate voltage (detects the rising speed after the rising speed of the gate voltage is reduced).
"Change processing means for off operation"
The method for detecting the end of the mirror period is not limited to detecting that the gate voltage is lower than the threshold voltage VthL. For example, it may be one that detects a decrease rate of the gate voltage (detects an increase after the decrease rate of the gate voltage decreases).

Both the off operation process of the off-holding switching element 40 and the process of operating the discharge switching elements 36a and 36b may be performed based on the gate voltage.
"About allocation means"
In the second and third embodiments, the voltage at the terminal T2b may be used in the ON operation period. In the second and third embodiments, the voltage at the terminal T1b may be used in the off operation period.

The first embodiment also includes comparison means for comparing the magnitude of the threshold voltage VthH and the voltage at the terminal T2, and comparison means for comparing the magnitude of the threshold voltage VthL and the voltage at the terminal T1. The comparison means may be the same hardware to change the input signal, or another hardware may be provided to select the output signal. In this case, a process (drive circuit 22) to which the output of the comparison means is input may perform a process for operating the off-holding switching element 40 and a process for increasing the charging speed.
"About gate resistance"
A resistor may be provided in the common path La. However, even in this case, it is desirable to make both the resistance value of the charging resistor 32 and the resistance value of the discharging resistor 34 smaller. At this time, the detection accuracy of the gate voltage can be increased as the resistance value of the common path La is made smaller than both of the resistance values.

  A resistor may be provided between the output terminal of the discharge switching element 36 and the output terminal of the switching element S ##. Even in this case, when the discharge resistor 34 is externally attached to the drive I20, the voltage at the terminal T1 is used to increase the detection accuracy of the gate voltage during the off operation period. Is desirable.

A resistor may be provided between the input terminal of the charging switching element 24 and the charge supply source for turning on the switching element S **. Even in this case, when the charging resistor 32 is externally attached to the drive IC 20, the voltage at the terminal T2 is used to increase the detection accuracy of the gate voltage during the ON operation period. Is desirable.
"others"
-As a power converter circuit comprised by a drive object switching element, it is not restricted to the inverter IV and converter CV connected between a vehicle-mounted rotary machine and a battery. For example, a DCDC converter that steps down the voltage of the high-voltage battery in order to supply the power of the in-vehicle high-voltage battery to the low-voltage battery may be used.

  The driving target switching element is not limited to the IGBT but may be, for example, a MOS field effect transistor.

  DESCRIPTION OF SYMBOLS 20 ... Drive IC, 36 ... Discharge switching element, 34 ... Discharge resistor, 40 ... Off-holding switching element (one embodiment of short-circuiting switching element), 42 ... Off-holding circuit, S ## ... Power switching element , IV... Inverter (one embodiment of power conversion circuit), CV... Converter (one embodiment of power conversion circuit).

Claims (5)

An on-operation circuit for turning on the drive target switching element, which is a voltage-controlled switching element, and an off-operation circuit for turning off the drive target switching element, and by operating these In the drive circuit of the switching element for turning on / off the driving target switching element,
The on-operation circuit includes a charging path provided with a charging resistor,
The off operation circuit includes a discharge path provided with a discharging resistor different from the charging resistor,
The conduction control terminal of the driving target switching element is connected to each of these via a connection point of the charging resistor and the discharging resistor,
On-operation change processing means for performing processing to change the operation state of the on-operation circuit based on the detection result of the voltage of the conduction control terminal of the drive target switching element during the on-operation period of the drive target switching element;
An off operation change processing means for performing a process of changing the operation state of the off operation circuit based on the detection result of the voltage of the conduction control terminal in the off operation period of the drive target switching element;
The on-operation change processing means and the off-operation change processing means are built in a one-chip integrated circuit,
Both the charging resistor and the discharging resistor are externally attached to the integrated circuit,
A detection result input to the on-operation change processing means and a detection result input to the off-operation change processing means include a detection result of a voltage at the connection terminal of the discharging resistor and the integrated circuit, respectively. A switching element drive circuit comprising: allocation means for allocating the charging resistor and a detection result of a voltage at a connection terminal of the integrated circuit.   The on-operation change processing means increases a charge rate of charge for turning on the driving switching element via the charging path by increasing a voltage of the conduction control terminal. The drive circuit of the switching element according to claim 1. The off-operation circuit further includes a short-circuit switching element that short-circuits the output terminal of the drive target switching element and the conduction control terminal separately from the discharge path,
3. The switching element drive circuit according to claim 1, wherein the off-operation change processing means turns on the short-circuit switching element based on detection of a decrease in voltage of the conduction control terminal. .   The off-operation change processing means increases a discharge rate of electric charges for turning on the drive target switching element via the discharge path based on detection of a decrease in the voltage of the conduction control terminal. The drive circuit for a switching element according to claim 1, wherein: The connection point between the charging path and the discharging path and the conduction control terminal are connected by a common electrical path,
The resistance value of the common electric path is set to be smaller than both of the resistance value of the charging resistor and the resistance value of the discharging resistor. The drive circuit of the switching element of any one of Claims 1.

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