A.C. REGULATOR CIRCUIT

1,201,120. Control circuit for domestic heating equipment. STANDARD TELEPHONES & CABLES Ltd. 21 Aug., 1968, No. 39923/68. Heading H2H. A circuit arrangement for regulating A.C. supply to a load includes a trigger circuit which delivers a control signal to a controlled switching element, and a variable element which can inhibit the trigger circuit for one or more whole cycles of the supply. As shown a transistor T1 receives negative to positive zerocrossing pulses through a capacitor C 1 and conducts to fire a second transistor T2 so that potential from P is applied through resistor R1 to charge a capacitor C biasing T 1 and thus T 2 to become hard turned on. Resistor R 1 and capacitor C are such that C is fully charged in one half cycle and the transistor T 1 , and thus transistor T 2 ceases to conduct. When T 2 conducts the potential P is also applied to a circuit including a transformer L whose secondaries 5, 6 are pulsed to switch controlled rectifiers S 1 , S 2 whenever the transistor T 2 starts or ceases to conduct. A variable resistor R v in circuit with diodes D 1 and D 2 and capacitor C controls the discharge of the capacitor to inhibit whole cycles of operation. R v may be controlled by heat or light or may be connected to a Zener diode for voltage setting (Fig. 3, not shown). The transformer L may have its two secondary windings connected to control a single thyristor which forms the diagonal element of a rectifier bridge in series with the load (Fig. 4, not shown).