Speed controlled DC motor protection circuit - has diode switching in ballast resistor when motor acts as generator

摘要

The protection circuit, for a speed-controlled dc motor supplied via a thyristor rectifier with energy return, has a diode (2) connected between the motor (3) and the rectifier (1) and forward biased when the motor is acting as a motor. The ballast resistor (4) used when the motor is working as a generator is therefore only effective when the motor is actually generating current. The rectifier consists of two antiparallel thyristors and is coupled to the ac supply. The ballast resistor, shunted by the diode, protects the generator from short circuit currents.