GB1331512A - Constant voltage regulators - Google Patents

Abstract

1331512 Automatic voltage control THORN AUTOMATION Ltd 13 Jan 1971 [28 Jan 1970] 4165/70 Heading G3R [Also in Division H3] A regulator for maintaining a constant voltage at output terminals 4, 4 supplied, via input terminals 2, 2, by an alternating voltage or a uni-directional periodic voltage having a zero potential in each period, comprises an impedance 6 which limits the current in each half cycle or period until a Triac T5 is fired to short circuit the terminals 4, 4 for the remainder of that half cycle or period, the Triac being fired when the time integral of the output voltage, taken from the zero condition at the start of the half cycle or period, reaches a predetermined magnitude. The firing circuit 8 for the Triac is shown in Fig.2 and comprises a full wave rectifier D1---D4 whose voltage is integrated by an RC circuit RV 1 , R1 and C1, the voltage across the latter being applied to the base of a transistor T2 whose emitter receives a voltage from a resistor Zener diode chain R3, ZD1 representative of the predetermined magnitude. When the voltage of capacitor C1 reaches this magnitude, transistor T2 conducts to cause transistors T3, T4 of a regenerative switch arrangement to conduct. Initially the current therethrough passes through a capacitor C2 until voltage build-up thereon diverts the current through a Zener diode ZD2. The current divides through a resistor R6 and the primary winding of a transformer TR1 whose secondary winding produces a pulse which fires the Triac T5. The current also causes a transistor T1 to conduct to discharge the capacitor C1. To ensure there is a sufficiently low impedance voltage source for the above operations to occur, even towards the end of a half cycle or period with diminishing voltage, a capacitor C3 is connected across the switch arrangement T3, T4 and is charged during each half cycle or period from divider R7, R8, D6 to a voltage limited by a Zener diode ZD3. When the voltage across terminals A, B has reduced sufficiently for a diode D5 to be forward biased, the capacitor C3 discharges through this diode and the parallel path of resistor R4 and emitter-base junction of a transistor T3 until it reaches a voltage lower than that on the capacitor C2, whereupon the switch T3, T4 turns off. If the output voltage is not high enough to cause the capacitor C1 to charge sufficiently to trigger the Triac, when capacitor C3 begins to discharge through members R4, D5 the volt drop across R4 biases the transistor T3 to cause the switch T3, T4 to conduct, so firing the Triac and turning on transistor T1 to discharge the capacitor C1. As before switch T3, T4 turns off when the voltage of capacitor C3 falls below that of C2. Triac T5 may be replaced by a pair of anti-parallel connected controlled rectifiers.