GB1500444A - Voltage control apparatus - Google Patents

Abstract

1500444 Automatic voltage and current control FERRANTI Ltd 8 April 1976 [15 April 1975] 15592/75 Heading G3R A voltage regulating circuit has two AC inputs of the same frequency and phase, but different voltages. A control device responds to changes in the output voltage of the circuit to replace the lower input voltage by the higher input voltage over a part of each AC cycle. As shown in Fig. 4, a transformer 10 provides a rectified output voltage on lines 12, 13. Line 12 is connected directly to a centre tap, while line 13 can receive a low voltage from intermediate taps through diodes D1, D2 or a high voltage through thyristors TH 1, TH2 connected to the ends of the transformer secondary winding. The thyristors are turned on at times during the supply cycle determined by a control signal on line 14, and operation is synchronized with the AC input by a transistor T3 which produces negative pulses at zero crossings. The signal on line 14 is produced by a control circuit, Fig. 6 (not shown), including a monostable device (M) responsive to the output of an operational amplifier (A2) which compares the circuit output voltage with a reference voltage derived from a Zener diode. A conventional series regulating circuit, Fig. 5 (not shown), is connected between the transformer outpout line 12 and the circuit output terminal, and includes a series transistor (T4) controlled by a regulating module (VR) in dependence on measured output current and voltage. In other embodiments, Figs. 7 and 8 (not shown), the secondary side of the transformer 10 is connected through a single-phase or three-phase rectifier bridge circuit.