Patent ID: 6876531

Claim:
A device for detecting failure of a field effect transistor (FET) comprising: a field effect transistor (FET) with a current input terminal and a current output terminal connected in series as well as a motor between a power source terminal and ground; a motor control unit for turning on and off a voltage to be applied to said motor to set a normal/reverse rotation; a gate control unit for turning on and off a gate voltage to be applied to the FET to control a motor driving; a voltage applying means for applying a positive voltage at a prescribed voltage level to the current input terminal of the FET; a voltage detecting means for detecting the voltage level of the positive voltage thus applied when said gate voltage is off; and a failure detecting means for detecting short-circuiting failure of the FET on the basis of a change in the voltage level detected by said voltage detecting means when said gate voltage is off while said motor stops, wherein it is determined that said FET is faulty due to short-circuiting when the voltage level at the current input terminal of the FET has fallen to ground potential while the gate voltage is off.