GB778635A - Improvements in or relating to electric control circuits, incorporating semiconductor devices - Google Patents

Abstract

778,635. Rectifying; control systems for consumption apparatus. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. March 30, 1955 [April 5, 1954], No. 9248/55. Classes 38 (2) and 38 (4). D.C. (Fig. 1) or A.C. (Fig. 2) is supplied to a load from an A.C. source through one or more controllable transistors. In Fig. 1 the load 104, the secondary winding of supply transformer 101 and a selenium or silicon rectifier 106 which relieves the transistor of reverse voltage in the non-conducting half-cycles, are connected in series between the emitter 110 and collector 112 of a P-N-P-type junction transistor 108. During the half-cycles when the transistor is to be rendered conducting the base electrode 114 is made negative with respect to emitter 110 while remaining positive to collector 112 by a pulse derived from supply source 100 and made rectangular by a circuit 120. The potential of the base electrode is so chosen that the emitter-collector current reaches saturation. The instant at which conduction begins is controlled by a variable resistor 126 in a phasechange circuit which also includes capacitor 124 and the two halves of the secondary winding 130 of transformer 128. Fig. 2 shows two transistors 208, 217 of the N-P-N- and P-N-P-types respectively, connected so as to supply controllable A.C. to a load 204 from A.C. terminals 202, 203. The control pulses are supplied from terminals 216, 218 between base electrodes and emitters of the transistors, being effective in the two transistors respectively in alternate half-cycles. In a modification the load is supplied with A.C. through two P-N-P transistors having their base-collector circuits in series with each other and the load, the control pulses being applied between the base and emitter electrodes.