Abstract: A system for detecting an output of a controllable semiconductor device includes a controllable semiconductor device, a magnetic amplifier to which an output of the semiconductor device is fedback to control the semiconductor device, and a monitor device for monitoring an output of the magnetic amplifier. The monitor device serves for determining that the output of said semiconductor device exceeds a predetermined level, when the output of the magnetic amplifier is in a remanent output region of the magnetic amplifier.

Abstract: A protective circuit for protecting a main d.c. circuit of the kind comprising a d.c. power source, a d.c. load, a contactor and a chopper. In the protective circuit, a resistor is connected in parallel with the series-connected contactor and load to permit continuous application of power supply voltage across the chopper. A circuit is connected to the connection point of the load and chopper to provide a signal synchronous with on-off of the chopper, and the output signal of this circuit and a signal corresponding to a chopper-on signal are applied to a logic circuit which provides the logical sum of these inputs for the detection of commutation failure of the chopper. The output of the logic circuit turns on a thyristor for deenergizing the contactor thereby disconnecting the load from the power source.

Abstract: In cases of subjecting an electric motor operated vehicle to electric braking, regenerative braking is performed during the first stage of the braking operation thereby supplying the armature current to the battery as a load, and a plugging operation is performed during the last stage thereof to complete the braking operation, whereby the efficiency of operation is enhanced by conserving the armature current to extend the traveling distance of the vehicle per charge of the vehicle battery, and the generation of excessive heat in the motor is suppressed.

Abstract: In a semiconductor device which includes a main thyristor and an auxiliary thyristor for turning off the main thyristor and controls conduction period of the main thyristor according to a given duty factor, a gate control apparatus comprising a phase shifter for producing a square wave output corresponding to the duty factor, an integrator for integrating the output of the phase shifter, a relay circuit having two level settings and receiving the output from the integrator to produce an output which exhibits a hysterisis characteristic corresponding to the two level settings, and an amplifier for turning on the main thyristor in response to the output from the relay circuit and turning on the auxiliary thyristor upon the termination of the output from the relay circuit.

Abstract: In a chopper control device in which a magnetic phase shifter is used for providing chopper turn-on and turn-off signals, an external magnetic field is applied to the core of the magnetic phase shifter so as to carry out the notching control of a motor by regulating the residual phase angle of the output of the magnetic phase shifter.