GB1117878A - Static relay - Google Patents

Abstract

1,117,878. Transistor switching circuits. VAPOR CORP. 24 Aug., 1966 [3 Jan., 1966], No. 37934/66. Heading H3T. A circuit 13 for performing switching operations in, for example, tele-type applications, comprises an oscillator 31 energized by input signals applied at 25, 27 and producing relatively high frequency (at least about 50 Mc/s) output signals in response thereto, a transistor 83 rendered conductive in response to the input signal, and an S.C.R. 87 in series with transistor 83 and rendered conductive a predetermined time after initiation of the input signal and rendered non-conductive a predetermined time after cessation of the input signal, so that during conduction of the S.C.R. 87 a path is completed between output terminals 17, 19. The oscillator is coupled to the input through a filter 41, 43, 45, 47 to prevent the high frequency oscillations affecting the input source. The signals produced in secondary 71 of transformer 63 are rectified at 73 and passed through a filter 77, 79, 81 to render transistor 83 conductive, and are also rectified at 91 and passed through a filter 95, 97, 99 to the gate of S.C.R. 87. The S.C.R. 87 does not conduct until capacitor 99 becomes sufficiently charged. On cessation of the input signal, transistor 83 cuts off immediately, causing the cathode potential of the S.C.R. to rise towards that of the anode. During this rise the anode-cathode current diverts to the gate of the S.C.R. and flows through resistor 100. The potential of the gate is limited by Zener 109. As the cathode potential of the S.C.R. continues to rise it becomes sufficiently positive with respect to the gate to cause the S.C.R. to out-off. This switch-off delay of the S.C.R. is made equal to the switch on delay. A diode bridge 103 ensures completion of the output circuit on conduction of the S.C.R. independently of the polarity of terminals 17, 19. A steady D.C. applied to terminals 25a, 27a of an identical circuit 13a produces a signal in windng 111a of transformer 63a, which signal is rectified at 113a and applied between the base and emitter of the transistor 83 of circuit 13 to reverse bias that transistor, so that an input signal to circuit 13 must exceed a level determined by this reverse bias before the switch operates. Circuits 13, 13a may be combined to produce a polar relay by connection of terminal 27 to 25a and of 19 to 17a and applying the input to terminals 25 and 27a. With an input of a first polarity, one circuit is rendered conductive whilst the other is inhibited by the signal from the tertiary winding of the one circuit, whilst with an input of the second polarity, the one circuit is inhibited and the other conducts.