VOLTAGE CHANGE DETECTING CIRCUIT AND VOLTAGE CHANGE DETECTING METHOD

PROBLEM TO BE SOLVED: To provide a voltage change detecting circuit capable of simply detecting a gate leak of an insulated gate transistor irrespective of whether the device is in operation or not.SOLUTION: A voltage change detecting circuit 1 includes: a driving circuit 1a which applies a voltage Vg exceeding a gate threshold voltage of an insulated gate transistor 3 to a gate of the insulated gate transistor 3; a current source 1b which applies an amount of current for a prescribed time so that the gate voltage Vg of the insulated gate transistor 3 is less than the threshold voltage, during a cutoff period when voltage application is not being executed from the driving circuit 1a to the gate of the insulated gate transistor 3; and comparing means 1d for comparing a gate voltage change amount at the time of current application from the current source 1b to the gate of the insulated gate transistor 3 with a reference voltage change amount that is a reference value for determining whether a gate leak is generated or not, and then outputting a comparison result.