Abstract: In an electrically driven vehicle which is controlled by a thyristor chopper circuit having a main thyristor in series with the traction motor and a commutating thyristor for turning the main thyristor off, demand means is provided for setting a required current through the motor and firing the commutating thyristor when the required current is attained. An overriding control permits firing of the commutating thyristor when the main thyristor has been on for a predetermined period, and timing means operates when the overriding control is operative for setting the minimum off period of the main thyristor.

Abstract: In a control circuit for an electrically driven vehicle, there is a main thyristor in series with a traction motor and a commutating thyristor for turning the main thyristor off. Firing pulses for the thyristors are provided by an operational amplifier having two states in which it fires the main thyristor and commutating thyristor respectively, and delay means operates when the main thyristor is fired to drive the operational amplifier to its other state after a predetermined delay.