Abstract: A driver circuit for a semiconductor power switch. The driver circuit supplies a high voltage pulse to the gate of an IGBT. The driver circuit also monitors the voltage on the collector of the IGBT with respect to the emitter. If the voltage at the collector of the IGBT does not drop when the IQBT is turned on, the IGBT driver circuit detects a short circuit and triggers a linear integrator within the driver circuit. The linear integrator gently ramps down the voltage on the gate of the IGBT.

Abstract: A gate drive circuit for a silicon controlled rectifier (SCR) connected in an a-c power circuit includes a voltage divider network connected between a d-c voltage source and the SCR for developing a varying voltage on a control node, depending upon whether the anode-to-cathode a-c voltage of the SCR is positive or negative. A first switching transistor, responsive to the control node voltage, controls conduction of a second switching transistor connected between the d-c voltage source and a voltage regulated driver circuit. In this way, a constant drive current is applied to the SCR gate only while the anode-to-cathode voltage of the SCR is positive.

Abstract: The load currents, supplied by a three-phase AC power source to a three-phase load, are established and maintained at a preset desired level by sensing those currents and producing a feedback voltage which is compared with a reference potential. Anytime the load currents differ from the desired level the comparison produces a difference or error signal which causes an adjustment of the amplitudes of the three load currents such that they automatically return to the desired level, thereby regulating the current flow to the load. At start-up, the feedback arrangement is also effective in preventing instant current build-up to avoid sudden power surges. When the load is a three-phase motor, limiting the current flow facilitates a soft start with the motor gradually accelerating to full operating speed. Two overload protection circuits shut the system down in response to different overload or overcurrent conditions.