GB1510644A - Voltage stabilizers - Google Patents

Abstract

1510644 Automatic voltage control ROBAND ELECTRONICS Ltd 5 Dec 1975 [5 Dec 1974] 52719/74 Heading G3R [Also in Division H3] A voltage stabilizing circuit includes A.C. input and output terminals between which there is connected a compensating arrangement which introduces an alternating voltage component dependent on the difference between the circuit output voltage and a reference voltage. The arrangement includes a solid state switching circuit, operating at a high frequency compared with the supply, which connects voltages of opposite polarity with a variable duty cycle. As shown in Fig. 2, a compensating circuit 10 is connected between terminals X, Y in one supply lead between input terminals L, N and a load R. A transformer 30 measures the load voltage and supplies a rectified signal to a junction point 35 for comparison with an output from a reference source 36. If only RMS or mean voltage stabilization is required, the reference may be a D.C. voltage, but if waveform stabilization is required, the desired waveform must be produced by the source 36 which is phase-locked to the supply by a loop circuit 40, Fig. 5 (not shown), including NAND gate circuitry controlling a frequency determining FET (68). The output from junction 35 is passed through a feedback amplifier 41 to a comparator circuit 43 which also receives an input from a ramp generator circuit 44, Fig. 6 (not shown). The frequency of the ramp generator may be 200 kHz, and the output of the comparator 43 will be a series of width modulated pulses at this frequency. The pulses are passed through a NAND gate control circuit 45, Fig. 7 (not shown), producing signals for switching alternately transitions 16, 19 which connect transformer windings 11b, 11c respectively to the supply terminal X. The duty cycle of the pulses determines the magnitude of the compensating voltage which aids or opposes the supply from source terminals L, N. A circuit (46) responds to excessive current in the compensating circuit to inhibit the production of switching signals by the control circuit 45, Fig. 7 (not shown). An overvoltage protection circuit (48), Fig. 8 (not shown), including a triac (235) fired by an inverse pair of Zener diodes (231, 232) may short the terminals, X, Y. A clamping circuit 47 limits the voltage appearing between terminal Y and the common lead 20 so as to protect the switching transistors 16, 19. The circuit 47 includes parallel branches each formed by a diode and opposed Zener diode.