Patent ID: 8243009

Claim:
A separately-excited inverter circuit, comprising: a transformer having a primary coil and a secondary coil; a switching circuit that is coupled with the primary coil of the transformer, converts a direct current (DC) input voltage into an alternate current (AC) output voltage, and applies the AC output voltage to the primary coil of the transformer; a control circuit that performs a switch control of the switching circuit when receiving a command signal from a command signal transmission line; a feedback circuit that is coupled with a feedback voltage transmission line for transmitting a direct current feedback voltage and converts an alternate current voltage of the secondary coil of the transformer into the feedback voltage; an output voltage monitor circuit that is coupled with the feedback voltage transmission line; and a thyristor that is coupled with the command signal transmission line; wherein the output voltage monitor circuit has a comparator, a CR time constant circuit and a hysteresis resistance; the comparator has a non-inverted input terminal, an inverted input terminal and an output terminal; a divided voltage of a DC input voltage is input to the non-inverted input terminal; a voltage corresponding to the feedback voltage on the feedback voltage transmission line is input to the inverted input terminal; the output terminal of the comparator outputs a reference voltage to a gate of the thyristor when the feedback voltage is higher than a predetermined voltage; the CR time constant circuit has a resistance connected between the feedback voltage transmission line and a ground; the CR time constant circuit has a capacitor connected between the feedback voltage transmission line and the ground; the CR time constant circuit forms a predetermined decay in the feedback voltage; the hysteresis resistance is connected between the output terminal of the comparator and the non-inverted input terminal of the comparator; when the reference voltage from the output terminal of the comparator is input to the gate of the thyristor, a gate current flows through the thyristor, and the thyristor turns on and impedes the command signal on the command signal transmission line to thereby stop the oscillation of the control circuit; and the hysteresis resistance exerts a hysteresis to the comparator to make a time width of the reference voltage sufficient to turn the thyristor on.