Patent ID: 7859229

Claim:
A discharge device for charging a main capacitor via a separately-excited DC/DC converter and discharging energy from the main capacitor, the discharge device comprising a pulse width control circuit for controlling a conduction pulse width on a primary side of the separately-excited DC/DC converter, wherein the pulse width control circuit is configured to perform a PWM soft start drive of stepwise increasing the conduction pulse width on the primary side of the separately-excited DC/DC converter up to a maximum pulse width when the main capacitor has a voltage less than a predetermined low voltage at the time of charging the main capacitor, to perform a PWM drive with the maximum pulse width when the main capacitor has a voltage not less than the predetermined low voltage at the time of charging the main capacitor, to perform the PWM drive with the maximum pulse width by detecting that the main capacitor reaches a predetermined voltage and terminating the PWM soft start drive in course of performing the PWM soft start drive of stepwise increasing the conduction pulse width on the primary side of the separately-excited DC/DC converter up to a maximum pulse width when the main capacitor has a voltage less than the predetermined low voltage at the time of charging the main capacitor, and to determine that the separately-excited DC/DC converter is in an overload condition and to perform the pulse width control by the use of an intermittent drive of alternately performing a charging operation and a no-charging operation on the main capacitor at a predetermined time ratio when a charging voltage of the main capacitor does not reach a predetermined voltage with the lapse of a predetermined time after starting the charging operation.