JP4556833B2 - Gate driver and motor driving device including the gate driver - Google Patents

Description

  The present invention relates to a gate driver suitable for driving a gate electrode of a power transistor such as a MOSFET or IGBT having a gate electrode with an oxide film insulated.

  The present invention also relates to information devices such as printers and copiers equipped with paper feed motors and scanner motors in the drive system, optical media devices and hard disk devices equipped with spindle motors and head actuators in the drive system, and air blowers. Home appliances such as air conditioners equipped with fan motors and compressor motors, refrigerators, air purifiers, water heaters equipped with combustion fan motors, washing machines equipped with washing tub drive motors, vacuum cleaners equipped with blower motors, or The present invention provides a motor driving apparatus suitable for driving induction motors, reluctance motors, stepping motors, etc., as well as brushless DC motors used in FA equipment such as component mounting machines, industrial robots, general-purpose inverters, and industrial equipment.

  In recent years, motors used in information devices such as printers, copiers, optical media devices, and hard disk devices have become more expensive than the motors mounted on them due to the speeding up, downsizing, and portability of devices. There is a strong desire for power saving while at the same time being small in output.

  Motors used in home appliances such as air conditioners, water heaters, refrigerators and washing machines are shifting from AC induction motors to brushless DC motors that are more efficient and can save power.

  In the field of industrial applications, a motor that has been a simple power source in the past is required to have a variable speed and high efficiency, and an inverter drive and a brushless motor are being promoted.

  In the FA field, servo motors are used for driving robots and mounting machines, and high-precision variable speed / positioning driving is performed.

  In general, a PWM (pulse width modulation) system is used to drive these motors with power saving or variable speed. The PWM method is a method for controlling the amount of power supplied to the drive winding by turning on or off the power transistor connected to the drive winding of the motor and changing the on / off ratio. This is a well-known driving method. This PWM method has been used for various motor drives used in home appliances, FA devices, and industrial devices for a long time. However, in recent years, the same method has been adopted for motor drives in information equipment due to the above-mentioned tendency. It has become to.

  As a power transistor used when the motor is driven by the PWM method, a MOSFET or IGBT suitable for an on / off operation is generally used. These power transistors are characterized in that the gate electrode is insulated by an oxide film.

  As a gate driver for driving the gate transistor to turn on / off, that is, to turn on or off such a power transistor having an oxide film insulated gate electrode, there is a conventional one described in Japanese Patent Laid-Open No. 4-230117. . This is provided with a pulse filter for the purpose of preventing malfunction of the gate driver due to the high switching speed (dV / dt is high) when the power transistor is turned on or off.

  FIG. 4 shows a configuration in which a power transistor is driven by this conventional gate driver.

  In FIG. 4, the power transistor 1 having a gate electrode insulated by an oxide film is a MOSFET, and the transistor 1 is configured such that the gate electrode is driven by a gate driver 70 to be turned on or off.

  The gate driver 70 includes a transistor 71 and a transistor 72. When the transistors 71 and 72 are alternately turned on and off, the gate electrode of the transistor 1 is set to a positive voltage or a zero voltage.

  That is, the transistor 71 is turned on, the transistor 72 is turned off, the gate electrode of the transistor 1 is set to a positive voltage, and this is made conductive. Also, the transistor 71 is turned off and the transistor 72 is turned on to set the gate electrode of the transistor 1 to zero voltage, which is cut off.

  However, the gate driver 70 with this configuration and operation steeply turns on or off the power transistor 1. This is because voltage application to the gate electrode of the transistor 1 is rapidly performed by turning the transistors 71 and 72 on and off.

  When the power transistor 1 is abruptly turned on or off, switching noise due to this increases, which may cause malfunction of peripheral devices and peripheral circuits. Or the transistor 1 itself may be destroyed. It also leads to a malfunction of the gate driver 70 itself.

  In addition, the publication describing the prior art only discloses an example of the technique for preventing the malfunction of the gate driver itself, and there is a fear of malfunction of peripheral devices and peripheral circuits due to the switching noise, A technique for solving the fear of destruction of the transistor 1 itself is not disclosed.

  In order to solve all of these, generally, as shown in FIG. 5, elements such as resistors 101 and 102, a diode 103, and a capacitor 107 are inserted between the gate driver 70 and the power transistor 1, The speed at which the power transistor 1 is turned on or off is adjusted.

Note that by inserting elements such as the resistors 101 and 102 and the diode 103 in this way, the gate electrode of the transistor 1 is operated by the action of these inserted elements and an input capacitance (not shown) of the gate electrode of the transistor 1. It is well known that the voltage application speed to the capacitor becomes slow, and the conduction or interruption speed can be adjusted.
JP-A-4-230117

  However, in the gate driver according to the above-described prior art, as described above, the switching speed is reduced by adjusting the speed at which the power transistor is turned on or off, and optimization is performed to protect the power transistor from destruction. In addition, many elements such as resistors and diodes need to be inserted between the gate driver and the power transistor.

When a motor driving device is configured using such a gate driver, a plurality of power transistors 1, 2, 3 are used to drive the motor driving windings 100, 200, 300 as shown in FIG. 4, 5, and 6 are required, and the above-described insertion elements such as resistors and diodes are required in proportion to the number of power transistors. Specifically, resistors 111, 112, 114, 115, 131, 132, 134, 135, 151, 152, 154, 155, diodes 113, 116, 133, 136, 153, 156, capacitors 117, 118, 137, 138 157, 158, etc. are required.

  As described above, the gate driver according to the prior art and the motor driving device using the gate driver require a large number of insertion elements for optimizing the conduction or cutoff speed of the power transistor, and the cost of these insertion elements and the increase in the assembly process, There are problems such as a complicated layout design of the printed circuit board and an increase in the board area.

  In other words, this also contributes to hindering price reduction and downsizing of the motor drive device and the equipment on which the motor drive device is mounted.

  In order to improve this, it is conceivable to simply replace the transistors 71 and 72 constituting the gate driver 70 in FIG. 4 with a constant current source.

  By replacing it with a constant current source, the voltage application speed to the gate electrode of the transistor is moderated without the insertion element such as the above-described resistor or diode due to the action of the constant current value and the input capacitance of the power transistor gate electrode. Become. As a result, the power transistor is gradually turned on or off.

  Incidentally, the constant current source is generally composed of a current mirror circuit as shown in FIG.

  In FIG. 7, when the power transistor 1 is switched from the cut-off state to the conductive state, the output current I202 of the current mirror circuit by the transistors 201 and 202 becomes the gate current to the power transistor 1, and the gate voltage of the power transistor 1 is increased. This is made conductive.

  In order to generate the current I202, it is needless to say that the current source 200 is required for the current mirror circuit, but the output current I200 flows even after the power transistor 1 is turned on, and this is the gate driver. Circuit loss.

  Similarly, when the power transistor 1 is switched from the conductive state to the cut-off state, a loss is caused by the current source that is the source of the current mirror circuit in the current source 12.

  Therefore, simply replacing the current source causes a problem relating to the power loss of the gate driver.

In order to solve the above problems, a gate driver of the present invention is a gate driver that controls a first power transistor and a second power transistor having a gate electrode insulated in series between power supply terminals, The gate driver causes a current to flow into the gate electrode when the first power transistor is turned on, and raises the gate potential from the gate electrode when shutting off the first power transistor. A second current source that draws current and lowers the gate potential; a third current source that raises the gate potential by flowing current into the gate electrode when the second power transistor is turned on; and the second power transistor When shutting off, the current is drawn from the gate electrode and the gate potential is lowered. The first current source outputs a first current value when the first power transistor is switched from the cut-off state to the conductive state, and after the switch to the conductive state, the first power source is in that state The second current source outputs a third current value when switching the first power transistor from the conductive state to the cutoff state, and switches to the cutoff state. After that, a fourth current value for maintaining the state is output, and the second and fourth current values are smaller than the first and third current values, and the second When the power transistor is switched from the cut-off state to the conductive state by the third current source, the second current source outputs the third current value so as to prevent the potential increase of the gate electrode of the first power transistor. Also configured to It is.

  According to the gate driver of the present invention, the first and second power transistors connected in series between the power supply terminals are connected to the constant current source by using the gate driver for controlling conduction / cutoff of the first and second power transistors. The current source is configured to output an appropriate current value (first current value or third current value) to the gate electrode when the power transistor is turned on / off.

  Thus, if the current value to be output to the current source is appropriately set, the switching speed of the power transistor can be adjusted to turn on or off, and the time for the power transistor to change from conduction to cutoff, or from cutoff to conduction Therefore, the gate driver can be reduced in size and cost.

  In addition, after the power transistor is switched to the conductive or cut-off state, only the minimum necessary current (second current value or fourth current value) for maintaining the state is output from the current source to the gate electrode. Thus, power consumption of the gate driver can be suppressed.

  Further, when the second power transistor is switched from the cut-off state to the conductive state, the first power transistor is pulled out from the gate electrode of the first power transistor at a third current value by the second current source, so that the first power transistor can have a feedback capacitance. Due to the influence of the above, it is possible to prevent the potential of the gate electrode from being raised and conducting, and conducting simultaneously with the second power transistor and short-circuiting between the power terminals.

The gate driver of the present invention is a gate driver that controls a first power transistor and a second power transistor having gate electrodes insulated in series and connected between power supply terminals. When a power transistor is turned on, a current is supplied to the gate electrode to raise the gate potential, and when the first power transistor is turned off, a current is drawn from the gate electrode to obtain a gate potential. When the second current source to be lowered and the second power transistor are brought into conduction, a current is supplied to the gate electrode, and the third current source to raise the gate potential and the second power transistor are shut off. At least a fourth current source that draws current from the gate electrode and lowers the gate potential; The first current source outputs a first current value when switching the first power transistor from the cut-off state to the conductive state, and maintains the state after switching to the conductive state. The second current source outputs a third current value when the second power source switches the first power transistor from the conductive state to the cut- off state, and changes the state after switching to the cut-off state. A fourth current value to be held, wherein the second and fourth current values are smaller than the first and third current values, and the second power transistor is connected to the second power transistor. When switching from the cut-off state to the conductive state by the three current sources, the second current source is configured to output the third current value, thereby preventing the potential increase of the gate electrode of the first power transistor. is there.

Thus, if the current value (first current value or third current value) output to the current source is appropriately set, the switching speed of the power transistor can be adjusted, and the power transistor can be cut off from the conduction. The time for changing to the state or the time for changing from the interruption to the conduction state can be adjusted by a few elements, and the gate driver can be reduced in size and cost.

  In addition, after the power transistor is switched to the conductive or cut-off state, only the minimum necessary current (second current value or fourth current value) for maintaining the state is output from the current source to the gate electrode. Thus, power consumption of the gate driver can be suppressed.

  Further, when the second power transistor is switched from the cut-off state to the conductive state by the third current source, the first power transistor is extracted from the gate electrode of the first power transistor at a third current value by the second current source, thereby It is possible to prevent the power transistor from conducting by raising the potential of its gate electrode due to the influence of the feedback capacitance, and conducting at the same time as the second power transistor, thereby causing a short circuit between the power supply terminals.

  The motor drive device of the present invention is connected in series between the gate driver, a single-phase or multiple-phase motor drive winding, and a power supply terminal, and one end of the drive winding is connected to the series connection point. A first power transistor and a second power transistor, wherein the first and second power transistors are provided in accordance with the number of phases of the drive winding, and all have a gate electrode that is insulated with an oxide film, A plurality of gate drivers are provided corresponding to each of the plurality of first and second power transistors.

  As a result, noise reduction associated with switching of the power transistor during PWM driving can be realized with a few elements, and the motor driving device can be reduced in size and cost.

  In addition, after the power transistor during PWM driving is switched to the conductive or cut-off state, the power consumption of the motor drive device is suppressed by outputting only the minimum current necessary to maintain the state. Can do.

  Further, while switching the second power transistor during the PWM drive from the cut-off state to the conductive state, by drawing current from the gate electrode of the first power transistor, the second power transistor is turned on simultaneously with the second power transistor and is connected between the power supply terminals. Can be prevented from being short-circuited.

  FIG. 1 is a schematic view of a gate driver of the present invention.

  In FIG. 1, power transistors 1 and 2 are transistors having gate electrodes insulated with oxide films. MOSFETs and IGBTs are well known as this type of transistor, but in this embodiment, MOSFETs are described as specific examples.

  Power transistors 1 and 2 are connected in series between power supply terminals, and each gate electrode is connected to a gate driver 7.

  The gate driver 7 includes current sources 11, 12 and 21, 22, a gate switching controller 8, and a gate current controller 9.

  Current sources 11 and 12 are connected in series, and the connection point is connected to the gate electrode of power transistor 1.

  Similarly, current sources 21 and 22 are also connected in series, and the connection point is connected to the gate electrode of power transistor 2.

  The gate switching controller 8 outputs signals G1 and G2 for turning on and off the power transistors 1 and 2 to the gate current controller 9.

  The gate current controller 9 outputs a signal C11 to the current source 11, similarly outputs a signal C12 to the current source 12, outputs a signal C21 to the current source 21, and outputs a signal C22 to the current source 22. Output. The output currents of the current sources 11, 12, 21, and 22 are determined based on the signals C11, C12, C21, and C22, and the power transistors 1 and 2 are controlled.

  Here, 11 is a first current source, 12 is a second current source, 21 is a third current source, and 22 is a fourth current source.

  A method for controlling the gate driver 7 will be specifically described.

For example, when the power transistor 1 is switched from the cut-off state to the conductive state, the gate switching controller 8 changes the signal G1 from the “L” level to the “H” level as shown in FIG. As a result, the gate current controller 9 outputs a signal C11 to the first current source 11. As a result, the first current source 11 outputs the first current value I11a, flows current into the gate electrode of the power transistor 1, raises the potential of the gate electrode, and makes the power transistor 1 conductive. (Period of symbol (A) in FIG. 2)
After the power transistor 1 is switched to the conductive state, the signal C11 is controlled so that the first current source 11 becomes the minimum second current value I11b necessary for the power transistor 1 to maintain the conductive state. This is to suppress the power loss of the first current source 11. (Period of symbol (B) in FIG. 2)
Next, when the power transistor 1 is switched from the conductive state to the cut-off state, the gate switching controller 8 changes the signal G1 from the “H” level to the “L” level. As a result, the gate current controller 9 outputs the signal C12 to the second current source 12. As a result, the second current source 12 outputs a third current value I12a, draws a current from the gate electrode of the power transistor 1, and lowers the potential of the gate electrode to shut off the power transistor 1. (Period of symbol (C) in FIG. 2)
After the power transistor 1 is switched to the cut-off state, the signal C12 is controlled so that the second current source 12 has a minimum fourth current value I12b necessary for holding the cut-off state of the power transistor 1. This is to suppress the power loss of the second current source 12. (Period of symbol (D) in FIG. 2)
On the other hand, when switching the power transistor 2 from the cutoff state to the conductive state, the gate switching controller 8 changes the signal G2 from the 'L' level to the 'H' level. As a result, the gate current controller 9 outputs the signal C21 to the third current source 21. As a result, the third current source 21 outputs a current value I21a, flows a current into the gate electrode of the power transistor 2, raises the potential of the gate electrode, and makes the power transistor 2 conductive. (Period of symbol (E) in FIG. 2)
After the power transistor 2 is switched to the conductive state, the signal C21 is controlled so that the third current source 21 has a minimum current value I21b necessary for the power transistor 2 to maintain the conductive state. This is to suppress the power loss of the third current source 21. (Period of symbol (F) in FIG. 2)
Next, when the power transistor 2 is switched from the conductive state to the cut-off state, the gate switching controller 8 changes the signal G2 from the “H” level to the “L” level. As a result, the gate current controller 9 outputs the signal C22 to the fourth current source 22. As a result, the fourth current source 22 outputs a current value I22a, draws a current from the gate electrode of the power transistor 2, and lowers the potential of the gate electrode to shut off the power transistor 2. (Period of symbol (G) in FIG. 2)
After the power transistor 2 is switched to the cut-off state, the signal C22 is controlled so that the fourth current source 22 has a minimum current value I22b necessary for maintaining the cut-off state of the power transistor 2. This is to suppress the power loss of the fourth current source 22. (Period of symbol (H) in FIG. 2)
Here, when the power transistor 2 is switched from the cut-off state to the conductive state (period (E) in FIG. 2), the power transistor 1 is also turned on and the power supply terminals are short-circuited, and a solution to this problem. explain about.

  Before the power transistor 2 is switched to the conductive state, a current of the motor winding flows through a parasitic diode (also referred to as a body diode) existing between the source and drain of the power transistor 1, and the potential of the source electrode is close to the power supply potential. Suppose that it is in a high potential state. By switching the power transistor 2 from this state to the conductive state, the potential of the source electrode of the power transistor 1 changes to a low potential close to the ground potential. At the same time, the potential of the gate electrode of the power transistor 1 also changes from a high potential to a low potential as the potential of the source electrode changes. However, at this time, the potential of the gate electrode rises with respect to the potential of the source electrode due to the influence of the feedback capacitance existing between the gate and the drain of the power transistor 1, the power transistor 1 is also conducted, and the power supply terminals are short-circuited. There is a problem of end.

  In order to solve this problem, when the power transistor 2 is switched from the cut-off state to the conductive state, current is drawn from the gate electrode of the power transistor 1 so that the rise of the potential of the gate electrode is suppressed and the power transistor 1 is not turned on. Just control.

That is, when the power transistor 2 is switched from the cut-off state to the conductive state, as described above, the gate switching controller 8 changes the signal G2 from the “L” level to the “H” level. As a result, the gate current controller 9 outputs the signal C21 to the third current source 21, and simultaneously outputs C12 to the second current source 12 at this time. As a result, the power transistor 2 is switched from the cut-off state to the conductive state, while the second current source 12 outputs the third current value I12a and draws the current from the gate electrode of the power transistor 1. As a result, the potential of the gate electrode of the power transistor 1 can be prevented from rising due to the influence of the feedback capacitance, the power transistor 1 can be prevented from conducting, and a short circuit between the power supply terminals can be prevented. (Period of symbol (I) in FIG. 2)
Similarly, when the power transistor 1 is switched from the cut-off state to the conductive state, current is drawn from the gate electrode of the power transistor 2 so as not to make the power transistor 2 conductive, thereby preventing an increase in the potential of the gate electrode. Thus, the power transistor 2 may be prevented from conducting.

That is, when the power transistor 1 is switched from the cut-off state to the conductive state, the gate switching controller 8 changes the signal G1 from the “L” level to the “H” level as described above. As a result, the gate current controller 9 outputs the signal C11 to the first current source 11, and simultaneously outputs the signal C22 to the current source 22. As a result, while the power transistor 1 is switched from the cut-off state to the conductive state, the current source 22 outputs the current value I22a and draws the current from the gate electrode of the power transistor 2. As a result, an increase in the potential of the gate electrode of the power transistor 2 can be prevented, the power transistor 2 can be prevented from conducting, and a short circuit between the power supply terminals can be prevented. (Period of symbol (J) in Fig. 2)
Alternatively, in the gate driver 7 in which measures for preventing a short circuit between the power supply terminals are taken, the following does not depart from the gist of the present invention in order to simplify the control.

That is, when the power transistor 1 is switched from the conductive state to the cut-off state, the gate switching controller 8 changes the signal G1 from the “H” level to the “L” level as described above. The current value I22a may be output from the current source 22. (Period of symbol (L) in FIG. 2)
Conversely, when the power transistor 2 is switched from the conductive state to the cut-off state, the gate switching controller 8 changes the signal G2 from 'H' level to 'L' level as described above. At this time, the signal C12 is changed to the second level. The third current value I12a may be output from the second current source 12 by outputting to the current source 12. (Period of symbol (K) in FIG. 2)
As described above, in the gate driver shown in the first embodiment, the current value output to the current source (the first current value I11a in the symbol (A) period, the third current value I12a in the symbol (C) period, and the symbol (E) If the current value I21a in the period and the current value I22a in the symbol (G) period are set appropriately, the switching speed of the power transistor can be adjusted, and the time for the power transistor to change from the conductive state to the cut-off state Alternatively, it is possible to adjust the time for changing from the cutoff state to the conductive state with a few elements, and it is possible to reduce the size and cost of the gate driver.

  In addition, after the power transistor is switched to the conductive or cut-off state, the minimum necessary current value for maintaining the state (second current value I11b in the symbol (B) period, fourth in the symbol (D) period) By outputting the current value I12b, the current value I21b in the symbol (F) period, and the current value I22b in the symbol (H) period from the current source to the gate electrode, the power consumption of the gate driver can be suppressed.

  Further, in FIGS. 1 and 2, when the power transistor 2 is switched from the cut-off state to the conductive state by the current value I 21 a from the third current source 21, the third current value by the second current source 12 from the gate electrode of the power transistor 1. I12a can be extracted, and an increase in the potential of the gate electrode can be suppressed. As a result, it is possible to prevent the power transistor 1 from conducting due to the influence of the feedback capacitance between the gate and the drain and the like, and short circuiting between the power supply terminals due to the conduction of the power transistor 2 can be prevented.

  FIG. 3 is a schematic view of the motor driving apparatus of the present invention.

  In FIG. 3, power transistors 1 and 2, power transistors 3 and 4, and power transistors 5 and 6 are connected in series between power supply terminals, and the connection points are connected to motor drive windings 100, 200, and 300, respectively. All power transistors have gate electrodes insulated with oxide films, and in the present embodiment as well as the first embodiment, MOSFETs are described as specific examples.

  The gate electrodes of the power transistors 1, 2, 3, 4, 5 and 6 are connected to the gate driver 7.

  The gate driver 7 includes current sources 11, 12, 21, 22, 31, 32, 41, 42, 51, 52, 61, 62, a gate switching controller 8, and a gate current controller 9.

  Current sources 11 and 12 are connected in series, and the connection point is connected to the gate electrode of power transistor 1.

  Current sources 21 and 22 are also connected in series, and the connection point is connected to the gate electrode of power transistor 2.

Similarly, the current sources 31 and 32 are connected in series, the connection point is connected to the gate electrode of the power transistor 3, the current sources 41 and 42 are connected in series, and the connection point is connected to the gate electrode of the power transistor 4. The current sources 51 and 52 are connected in series, the connection point is connected to the gate electrode of the power transistor 5, the current sources 61 and 62 are connected in series, and the connection point is connected to the gate electrode of the power transistor 6. .

  The gate driver 7 has the same function as the gate driver of the first embodiment, and the gate driver in the first embodiment of FIG. 1 shows a gate driver that drives only one phase of the motor. Is the same.

  With this configuration, the motor driving apparatus shown in the second embodiment can realize noise reduction associated with switching of the power transistor at the time of PWM driving with a few elements, and the motor driving apparatus can be reduced in size and cost. .

  In addition, after the power transistor during PWM driving is switched to the conductive or cut-off state, the power consumption of the motor drive device is suppressed by outputting only the minimum current necessary to maintain the state. Can do.

  Further, in the power transistor connected in series between the power supply terminals, the power transistor connected to the positive power supply line is switched while the power transistor connected to the negative power supply line during PWM driving is switched from the cut-off state to the conductive state. By drawing the current from the gate electrode to the current source, it is possible to prevent the power transistor connected to the positive power supply line from conducting and short-circuiting between the power supply terminals.

  The gate driver according to the present invention can be applied not only to a PWM drive system motor drive device but also widely applicable to other motor drive systems and uses using a power transistor as a switching element. Furthermore, the motor drive device including the gate driver of the present invention can be incorporated into various devices, and the device can be reduced in size, cost, noise, and power saving.

Schematic of the gate driver in Embodiment 1 of the present invention Operational diagram of output current of gate driver in Embodiment 1 of the present invention Schematic of the motor drive device in Embodiment 2 of the present invention Schematic diagram of conventional gate driver Another schematic diagram of the gate driver in the conventional example Schematic diagram of motor drive device in conventional example Schematic diagram of gate driver configured with constant current source of the present invention

Explanation of symbols

1, 3, 5 First power transistor 2, 4, 6 Second power transistor 7 Gate driver 8 Gate switching controller 9 Gate current controller 11, 31, 51 First current source 12, 32, 52 Second current source 21 , 41, 61 Third current source 22, 42, 62 Fourth current source 100, 200, 300 Motor drive winding

Claims (2)

A gate driver for controlling a first power transistor and a second power transistor having gate electrodes insulated in series between power supply terminals, and when the first power transistor is turned on, the gate electrode A first current source that causes a current to flow in to increase the gate potential, a second current source that pulls out a current from the gate electrode when the first power transistor is shut off, and lowers the gate potential; and the second power When the transistor is turned on, a current is supplied to the gate electrode to raise the gate potential, and when the second power transistor is shut off, the current is drawn from the gate electrode to lower the gate potential. And a fourth current source, wherein the first current source is the first power. When the transistor is switched from the cut-off state to the conductive state, the first current value is output, and after switching to the conductive state, the second current value for maintaining the state is output. When the first power transistor is switched from the conductive state to the cut-off state, a third current value is output, and after the switch to the cut-off state, a fourth current value that maintains the state is output. The second and fourth current values are smaller than the first and third current values. When the second power transistor is switched from the cut-off state to the conductive state by the third current source, the second current value is A gate driver characterized in that an increase in potential of the gate electrode of the first power transistor is prevented by causing the current source to output the third current value. The first and second powers, wherein the gate driver according to claim 1, a single-phase or multiple-phase motor drive winding, and a power source terminal are connected in series, and one end of the drive winding is connected to the series connection point. A plurality of the first and second power transistors are provided according to the number of phases of the drive winding, and all have a gate electrode that is oxide-insulated,
A plurality of gate drivers are provided corresponding to each of the plurality of first and second power transistors.