Patent ID: 8159166

Claim:
A motor drive circuit, comprising: an inverter that is placed between and connected to a positive electrode and a negative electrode of a direct-current power source; a pair of nonuse-time interrupting MOSFETs connected in series and arranged in a feed line that connects the positive electrode of the direct-current power source and the inverter circuit in such a manner that paired parasitic diodes are in opposite orientations; a pair of main drive circuits which are formed by connecting voltage divider circuits and drive MOSFETs in series in this order in a direction from sources of the nonuse-time interrupting MOSFETs toward the negative electrode of the direct-current power source, and connecting outputs of the voltage divider circuits to gates of the nonuse-time interrupting MOSFETs; a control circuit that transmits gate signals to the pair of drive MOSFETs to keep the pair of nonuse-time interrupting MOSFETs on in a normal situation, and that stops transmission of the gate signals to the pair of drive MOSFETs to turn off the pair of nonuse-time interrupting MOSFETs in an abnormal situation where the inverter circuit is not able to be used; a compensation switch element that is connected in parallel to a resistance that forms the voltage divider circuit between the source and the gate of the nonuse-time interrupting MOSFET that has the parasitic diode in which an anode is arranged on a positive electrode side of the direct-current power source; and a compensation drive circuit that is connected to the compensation switch element and the negative electrode of the direct-current power source, wherein when the positive electrode and the negative electrode of the direct-current power source are connected to the motor drive circuit properly, the compensation drive circuit turns off the compensation switch element, and in an abnormal situation where the positive electrode and the negative electrode of the direct-current power source are connected in reverse to the motor drive circuit, the compensation drive circuit turns on the compensation switch element using an output from the direct-current power source connected to the motor drive circuit in reverse.