GB1176307A - Improvements in the control of the Switching of a Gate Controlled Rectifier Device - Google Patents

Abstract

1,176,307. Triggering controlled rectifiers. HEBERLEIN & CO. A.G. 20 Sept., 1968 [20 Sept., 1967], No. 44915/68. Heading H2F. [Also in Divisions G1 and H3] In an inductive proximity switch including a gate-controlled-rectifier (e.g. thyratron, thyristor or S.C.R.) the inductive sensor directly controls the rectifier by varying the amplitude of the triggering pulse. As shown the pulse is generated by capacitor 2 discharging through the sensor inductance 6 when trigger element 4 breaks-down. The resultant pulse fires trigger 7 and hence thyristor 1, (in the absence of a metal body). The presence of metal vane 40 near the inductor 6 reduces the amplitude of the pulse below firing level. Modificadions.-(i) Resistor 13 and capacitor 12 may be provided to fire-trigger 14 late in the half cycle of the A.C. so that the supply to load is regulated to one of two levels, (and not switched off entirely by the presence of vane 40). (ii) Fig. 2 (not shown) a D.C. BIAS may be added in series with the inductive pulse by a capacitor (2<SP>1</SP>) charged from a potentiometer (9), (10) across the capacitor 2. (iii) Fig. 3, the triggers may be replaced by TRANSISTOR SWITCHES. Normally cut-off transistors 15, 16 conduct rapidly on the breakdown of Zener diode 17, and the resultant pulse from inductor 6 switches-on a normally cut-off transistor pair 20, 24. (iv) Fig. 4 illustrates a modification of Fig. 2 (not shown), using UNIJUNCTION transistors 4<SP>1</SP>, 7<SP>1</SP> as trigger elements and added D.C. bias from capacitor 2<SP>1</SP>. The circuit may be arranged to operate as shown in Fig. 5, the threshold value of unijunction 7<SP>1</SP> rising to a substantially constant value 32 (due to regulation by Zener diode 17); the D.C. bias across capacitor 2<SP>1</SP> increasing slowly as indicated by curve 33 (due to the time constant of resistors 9, 10 and capacitor 2<SP>1</SP>); and a series of pulses 34 are provided by inductor 6 due to repeated firing of unjunction 4<SP>1</SP>, whereby the triggering point, in the A.C. half cycle, of thyristor 1 varies with the position of vane 4. (v) Fig. 6 (not shown), the circuit may operate on both half-cycles of the supply by using a full-wave bridge rectifier; an A.C. load may be connected in the supply to the rectifier. (vi) Fig. 7 (not shown), the output may be connected to a pulse transformer e.g. to control a triac. (vii) Fig. 8 (not shown), the inductance 6 may be replaced by a transformer whose MUTUAL INDUCTANCE is varied by the vane 40.