Patent ID: 8686694

Claim:
A discharge circuit for a DC power supply smoothing capacitor that is used in a power conversion device that is supplied with electrical power from a DC power supply via a contactor, the discharge circuit comprising: a resistor that discharges charge in the capacitor; a switch connected in series with the resistor, that either passes or intercepts discharge current flowing from the capacitor to the resistor; a measurement circuit that measures a terminal voltage of the capacitor; and a control circuit that controls continuity and discontinuity of the switch; wherein: the control circuit, after having made the switch continuous and starting discharge of the capacitor by the resistor, in predetermined time intervals repeatedly executes comparisons between the terminal voltage of the capacitor as measured by the measurement circuit and a predetermined voltage decrease characteristic, and when the terminal voltage of the capacitor becomes less than or equal to the predetermined voltage decrease characteristic: the control circuit determines the contactor to be normal, a decision is made as to whether or not the terminal voltage of the capacitor has reached a target discharge voltage that is set in advance, and if the target discharge voltage has been reached: the discharge circuit turns off the switch such that discharge is stopped, the discharge circuit waits for a predetermined inactive period of time (T intv ) corresponding to an amount of time necessary for a temperature of the resistor to decrease by a given amount, and after T intv has elapsed, the control circuit restarts discharge.