Drive device

1. A drive device for controlling a power switching element to turn on and off, the drive device comprising:

an on-side circuit that performs an on operation of the power switching element;

an off-side circuit that performs an off operation of the power switching element; and

a temperature detector that detects a temperature of the power switching element, wherein:

at least one of the on-side circuit or the off-side circuit includes a current path for supplying or drawing a gate current of the power switching element and a switch circuit for switching the gate current of the power switching element;

the switch circuit transitionally changes the gate current based on the temperature of the power switching element detected by the temperature detector when the switching circuit switches the gate current;

the off-side circuit includes:

a plurality of main MOS transistors as output transistors that provide the current path;

a sense MOS transistor that includes a gate in common with the main MOS transistors, and provides a current mirror with respect to the main MOS transistors to define a drain current of each main MOS transistor; and

a sense current control circuit that controls a drain current of the sense MOS transistor to be constant;

the switch circuit is connected to the gate of each of the main MOS transistors, and controls each of the main MOS transistors to turn on and off so as to switch the gate current in the power switching element; and

the switch circuit controls an on-resistance of each of the main MOS transistors based on the temperature of the power switching element to transitionally change the gate current when the switching circuit switches the gate current.

2. The drive device according to claim 1 , wherein:

the current path includes at least two passages; and

the gate current varies by switching between the at least two passages with the switching circuit.

3. The drive device according to claim 1 , wherein:

the sense current control circuit includes:

a reference power supply that generates a reference potential;

a reference resistor connected in series to the sense MOS transistor; and

an operational amplifier that generates an output at the gate of the sense MOS transistor so that a potential between the reference resistor and the sense MOS transistor approaches the reference potential; and

the sense current control circuit flows a current, determined by a resistance value of the reference resistor and the reference potential, as the drain current of the sense MOS transistor.

4. The drive device according to claim 1 , wherein:

the sense current control circuit includes:

an operational amplifier that generates an output at the gate of the sense MOS transistor;

a current source that supplies a predetermined current to one input terminal of the operational amplifier; and

a temperature sensitive element connected to the operational amplifier in parallel to the current source; and

the sense current control circuit changes the drain current of the sense MOS transistor based on a voltage drop in the temperature sensitive element that depends on temperature.

5. The drive device according to claim 1 , wherein:

the plurality of main MOS transistors include at least three transistors connected to each other so as to reduce the gate current in a stepwise manner; and

the switch circuit transitionally changes the gate current when the switch circuit switches the gate current.

6. A drive device for controlling a power switching element to turn on and off, the drive device comprising:

an on-side circuit that performs an on operation of the power switching element;

an off-side circuit that performs an off operation of the power switching element; and

a temperature detector that detects a temperature of the power switching element, wherein:

at least one of the on-side circuit or the off-side circuit includes a current path for supplying or drawing a gate current of the power switching element and a switch circuit for switching the gate current of the power switching element;

the switch circuit transitionally changes the gate current based on the temperature of the power switching element detected by the temperature detector when the switching circuit switches the gate current;

the on-side circuit includes:

a plurality of main MOS transistors as output transistors that provide the current path;

a sense MOS transistor that includes a gate in common with the main MOS transistors, and provides a current mirror with respect to the main MOS transistors to define a drain current of each main MOS transistor; and

a sense current control circuit that controls a drain current of the sense MOS transistor to be constant;

the switch circuit is connected to the gate of each of the main MOS transistors, and controls each of the main MOS transistors to turn on and off so as to switch the gate current in the power switching element; and

the switch circuit controls an on-resistance of each of the main MOS transistors based on the temperature of the power switching element to transitionally change the gate current when the switch circuit switches the gate current.

7. The drive device according to claim 6 , wherein:

the sense current control circuit includes:

a reference power supply that generates a reference potential;

a reference resistor connected in series to the sense MOS transistor; and

an operational amplifier that generates an output at the gate of the sense MOS transistor so that a potential between the reference resistor and the sense MOS transistor approaches the reference potential; and

the sense current control circuit flows a current, determined by a resistance value of the reference resistor and the reference potential, as the drain current of the sense MOS transistor.

8. The drive device according to claim 6 , wherein:

the sense current control circuit includes:

an operational amplifier that generates an output at the gate of the sense MOS transistor;

a current source that supplies a predetermined current to one input terminal of the operational amplifier; and

a temperature sensitive element connected to the operational amplifier in parallel to the current source; and

the sense current control circuit changes the drain current of the sense MOS transistor based on a voltage drop in the temperature sensitive element that depends on temperature.

9. The drive device according to claim 6 , wherein:

the plurality of main MOS transistors include at least three transistors connected to each other so as to reduce the gate current in a stepwise manner; and

the switch circuit transitionally changes the gate current when the switch circuit switches the gate current.

10. The drive device according to claim 6 , wherein:

the current path includes at least two passages; and

the gate current varies by switching between the at least two passages with the switching circuit.