Patent ID: 8159165

Claim:
A motor drive circuit, comprising: a first semiconductor switching element for use in motor control, that by being located on a high side of a motor that is driven based on an electric power supply from an electric power source, controls on and off states of the electric power supply and that includes a diode that is connected in a reverse direction and whose cathode faces toward the high side; a second semiconductor switching element that is located on a low side of the first semiconductor switching element and that includes a diode that is connected in a forward direction and whose anode faces toward the high side; a third semiconductor switching element for use as a fail-safe element, that is located on a low side of the motor, that turns off the electric power supply when a failure occurs in the first semiconductor switching element, and that includes a diode that is connected in a reverse direction and whose cathode faces toward the high side; a fourth semiconductor switching element that is connected in parallel to the motor and configures a return current circuit that includes a return current element and that causes a return current that is generated when the first semiconductor switching element is turned off to flow through the return current element; and a control portion that controls on and off states of the first to the fourth semiconductor switching elements, that uses an electric potential of a connecting point between the first semiconductor switching element and the motor as a first monitor voltage, that inputs a voltage that corresponds to the first monitor voltage, and that performs failure detection, based on the first monitor voltage, that checks whether the return current circuit is functioning properly.