Patent ID: 8432116

Claim:
A toque motor driving device for wire cut electrical discharge machines that drives a torque motor using an AC power source, the toque motor driving device comprising: a bridge circuit connected between a rectification output of the full-wave rectifying circuit and the torque motor; a polarity determination signal generating circuit that detects a period during which an absolute value of a power voltage of the AC power source exceeds a first reference voltage in a period during which a polarity of the power voltage of the AC power source is positive and outputs a detection result as a first polarity determination signal and detects a period during which the absolute value of the power voltage of the AC power source exceeds a second reference voltage in a period during which the polarity of the power voltage of the AC power source is negative; a PWM signal generating circuit that generates a PWM signal whose duty is adjusted according to a physical quantity corresponding to a torque of the torque motor; and a logical AND circuit that obtains a logical AND between the PWM signal output from the PWM signal generating circuit and the first and second polarity determination signals output from the polarity determination signal generating circuit; wherein the bridge circuit includes a positive polarity switch group including two or more semiconductor switches that applies a positive voltage to the torque motor and a negative polarity switch group including two or more semiconductor switches that applies a negative voltage to the torque motor; wherein at least one of the semiconductor switches included in the positive polarity switch group operates according to a signal of a logical AND between the first or second polarity determination signal and the PWM signal and the other semiconductor switches operate according the first or second polarity determination signal; wherein at least one of the semiconductor switches included in the negative polarity switch group operates according to a signal of a logical AND between the second or first polarity determination signal and the PWM signal and the other semiconductor switches operate according the second or first polarity determination signal.