Patent ID: 8648275

Claim:
A power supply device for sinker electric discharge machining for supplying current pulses to a machining gap formed between a tool electrode and a workpiece comprising: a DC power supply; a current sensor for detecting gap current flowing through the machining gap; a first switching element connected in series between the DC power supply and the tool electrode; a first reverse current prevention diode connected in parallel with the DC power supply and connected in series with the machining gap and the first switching element; a second switching element connected in series between the DC power supply and the workpiece; a second reverse current prevention diode connected in parallel with the DC power supply and connected in series with the machining gap and the second switching element; and a pulse controller for controlling the first and second switching elements in response to the gap current, the pulse controller having ON time and peak current; wherein from a first time when electric discharge is generated across the machining gap, until a second time when the gap current reaches the peak current during the ON time, both of the first and second switching elements are on; wherein only one of the first and second switching elements is turned off at the second time; wherein both of the first and second switching elements are on at a third time when a specified time period elapses during the ON time from the second time; wherein only the other of the first and second switching elements is turned off at a fourth time when the gap current reaches the peak current during the ON time after rising from the third time; and wherein when the ON time is completed both of the first and second switching elements are off.