GB902751A - Improvements in or relating to electronic relay devices - Google Patents

Abstract

902,751. Diode-switching circuits. TELEFONAKTIEBOLAGET L. M. ERICSSON. May 7, 1959 [May 9, 1958], No. 15734/59. Class 40 (6). In a switch or gate in which a signal is controlled by a D.C. control voltage two rectifiers are connected in parallel with the control voltage and directed so as to conduct in the same direction. The rectifiers have a sharp " knee " in their characteristics at a predetermined voltage, so that the switch has a high attenuation when the control voltage is not applied to it provided that the voltage of the signal to be switched is below that corresponding to the " knee " of the characteristic of the rectifiers. Fig. 1 shows a circuit for switching a signal from a generator 1 to a load 9 in dependence upon a D.C. control voltage applied between terminals 14, 15. Rectifiers 5, 6 are constituted by Zener diodes having a sharp " knee " in their voltage current characteristics, Fig. 2 (not shown). When terminal 14 is positive with respect to terminal 15 diodes 5 and 6 are conductive and diodes 10 and 11 cut-off so that the signal 1 is connected to load 9. When the D.C. voltage has the opposite polarity diodes 5 and 6 are blocked and 10 and 11 conductive so that the switch is open. When the D.C. circuit is broken so that the rectifiers are unbiased, provided that the voltage of signal source 1 is below the potential of the " knee," the switch presents a high attenuation to the signal source 1. In the modification shown in Fig. 3 the rectifiers 10, 11 are replaced by a resistor 16 and the combination of a resistor 17 and rectifier 18 across the D.C. control supply removes the value of the input resistance from that of the control circuit. In a further modification of Fig. 1, the terminal 15 of the control source is applied to the mid-point of a resistive potential divider connected across the primary of transformer 4, Fig. 4 (not shown).