Abstract: A control circuit is proposed, which can be used for the phase-shift control of an electric motor in an a.c. voltage supply line. The ground connector of the control circuit, together with the cathode of a semiconductor switch (triac), is directly connected with load current circuit. Because of this, it is possible to do without potential-separating means when it is intended to feed signals at the load current circuit directly into the control circuit. An auxiliary voltage source is connected between the synchronization input and the ground connector to maintain the function of the synchronization input.

Abstract: A direct current voltage controlled triggering circuit for triacs connected via a consumer resistor to an alternating current supply voltage uses the controllable channel resistance of a field effect rransistor to distribute loading current among a series connection of capacitors connected via a load resistor and the consumer resistor to the a.c. supply voltage. A connection point of the load resistor and a load capacitor in the series connection is connected via a diac to the gate electrode of the triac, and the remaining series connected capacitors have an approximately equal value to provide symmetrization of the current flow phase angle for the diac.