GB1120637A - Power control circuit - Google Patents

Abstract

1,120,637. Control systems for consuming apparatus; rectifying. GENERAL ELECTRIC CO. 15 Oct., 1965 [18 Nov., 1964], No. 43714/65. Headings H2F and H2H. [Also in Division H3] Power is switched to a load through a seriesconnected three-terminal bidirectionally conducting semi-conductor device which is fired by a signal on its gate derived from an energy storage means through another bidirectionally conducting semi-conductor device. In Fig. 3 a capacitor 55 charges up from an A.C. supply 35, 45 until its voltage is sufficient to break down a bidirectional diode 57, when current flows into the gate of a bidirectional triode 33 to turn it on. Current than passes from the source through the load 43 and a saturable reactor 41. The change in voltage at 39 causes an LC circuit 47, 49 to ring and when the reactor 41 is saturated the voltage across the triode 33 is reversed to turn it off. This operation may occur several times in each half-cycle of the supply. The circuit of Fig. 4 (not shown) fires only once during each half-cycle as the triode 33 has no ringing circuit to turn it off and is extinguished when the A.C. supply voltage reverses. Operation is controlled by a transistor (77) which when turned on by a voltage (at 83) shunts the capacitor (61) through a diode bridge (69, 71, 73, 75) and prevents it from charging. In a modification of this (Fig. 5, not shown) the transistor (99) is turned on and off by pulses at a frequency higher than that of the supply. The capacitor then charges in steps through the diode bridge until its voltage is high enough to fire the bidirectionally conducting devices. In another circuit (Fig. 6) the capacitor 113 is charged in alternate half-cycles through diodes 104 and 111, but as resistors 117 and 119 are unequal in value the capacitor voltage is greater in one half-cycle than the other and the bidirectionally conducting devices fire only once per cycle to pass D.C. through the load. Fig. 8 shows a snap-action circuit firing once per cycle, using a double Zener diode 137 in series with a D.C. control voltage applied at 150 so that the capacitor 133 is charged to a voltage which is the algebraic sum of the Zener voltage and the control voltage. Reversal of the polarity of the control voltage causes the bidirectionally conductive devices to fire on the other half-cycle.