GB1028090A - Improvements in or relating to electronic switches - Google Patents

Abstract

1,028,090. Semi-conductor switching circuits. TELEPHONE MANUFACTURING CO. Ltd. March 24, 1964 [April 2, 1963], No. 12969/63. Heading H3T. [Also in Division H2] In an electronic switching arrangement, the output of an oscillator is switched between alternative circuits in dependence upon the polarity of a signal applied to an input stage so as to control operation of two switching devices respectively arranged to provide outputs of opposite sign, the oscillator also supplying power to the input stage. As shown in Fig. 1, telegraph pulses on a line connected to terminals 1, 2 or two lines connected respectively to terminals 1, 3; 2, 3, are fed to the gate electrodes of silicon controlled switches SCS1, SCS2 arranged so that the switch associated with the more positive line is turned on so as to feed the output of an oscillator via transformer T1 either to transformer T2 or T3. The outputs of T2 or T3 are rectified at D3 and D4, the rectified outputs being used to turn on either transistor TR1 or TR2 so as to feed either a positive potential to a line connected between terminals A, D or a negative potential to a line connected to terminals C, D in dependence of the polarity of the input terminals 1, 2. The minimum voltage required to turn on transistors TR1, TR2 is determined by Zener diodes Z1, Z2. The circuit may alternatively be used as a comparator, emitting positive or negative voltage outputs in dependence on the relative polarities of terminals 1, 2. Fig. 2 shows a further arrangement in which the conductive state of transistors V1, V2 of a bi-stable circuit is dependent on the relative polarity of input terminals 1, 2. The conductive states of transistors V3, V4 are in turn controlled by the bi-stable circuit so that the output of a self-oscillating inverter C is fed either to transformer T2 or T3 in dependence upon the relative polarities of terminals 1, 2. The outputs of transformers T2, T3 are rectified at D8 . . . D11 and the resulting D.C. voltage turning on either transistor V7 or V8 so as to feed a positive or negative voltage to output terminal B in dependence upon the polarity of input terminals 1, 2. The self-oscillating inverter C comprises series-connected transistors V5, V6, operating in push-pull and having feedback via the primary windings of transformer T1. The output from the secondary winding of T1 is rectified at D16 so as to provide power supply for the bi-stable circuit V1, V2 and, after stabilization by Zener diode D14 provides bias for transistors V3, V4. Fig. 3 (not shown), relates to an alternative circuit which may be connected to terminals XX, YY in Fig. 2 and comprises two silicon-controlled switches, one or other of which is turned on by the first pulse of a train switched from the inverter C (Fig. 2) so as to feed either a positive or a negative voltage to the output terminals. The respective switch is turned off by action of a capacitor (C7) and an inductor (L11) when the polarity of input terminals 1, 2 becomes reversed. The use of a train of pulses to trigger the switches ensures that if the incorrect switch is turned on by a spurious pulse, the correct switch is turned on by the next pulse of the train.