PURPOSE: To obtain the sharp rising and falling waveforms of a low-voltage/ large-current pulse power supply by connecting an auxiliary DC power source having a voltage level higher than a main DC power source to each arm middle point of a bridge circuit connected to a line.

CONSTITUTION: The ON signals are simultaneously produced by the control circuits 4 and 10 and therefore the switching elements 5 and 11 and a thyristor 35 are turned on. The voltage of an auxiliary power source 9 is higher than the voltage of a main DC power source 3. Therefore the voltage e0 set between the output terminals 21 and 23 is controlled by the voltage of the power source 9. Thus the overvoltage is applied and at the same time a current rising curve becomes sharp. When the level of the current i1 reaches a set level, the circuit 10 stops the drive signal with the signal of a current detector 20. Then the circuit 4 stops the drive signal. Thus the current energy stored in an inductance 27 flows to successively a load resistance 29, the terminal 23, the detector 20, a diode 31 and a capacitor 37. As a result, the capacitor 37 is charged by the voltage e9 and the energy is quickly eliminated.