MACHINE MOTOR DRIVER

PURPOSE:To protect a discharge circuit against overvoltage without depending on a fuse by stopping discharge until output voltage of a DC power supply drops below a predetermined level and sustaining power supply to conducting phase windings. CONSTITUTION:When the voltage of an AC power supply 3 exceeds a rated voltage and thereby a source voltage VDC exceeds a voltage limit Vref, a remarkably larger amount of charge is stored in a capacitor 5b as compared with regenerative charges and several mS to several seconds may be required for the source voltage VDC to drop below the limit voltage Vref through discharge of capacitor. When the discharge time exceeds a time limit, logic signal S3 of a flipflop FF goes Low thus pulling the stop signal Sstop of an AND circuit Low. Consequently, a transistor Trd is turned OFF to stop discharge. At the same time, output signals S3 from the flipflop FF are fed to a conduction control circuit 20 and a latch circuit 30 and a phase winding current 1 having maximum current level is fed to phase windings Lu-Lw thus protecting a discharge circuit 9 without blowing a fuse F.