GB691245A - Improvements in direct current power supply systems - Google Patents

Abstract

691,245. Protective cut-out arrangements. GENERAL MOTORS CORPORATION. Nov. 22, 1949 [Dec. 1, 1948], No. 29821/49. Class 38 (v) A direct current power supply system comprises an electronic oscillator adapted to cease the generation of oscillations upon excessive loading of its tuned circuit, a relay in the plate circuit of the oscillator adapted on the passage of plate current to deenergise said oscillator, and a rectifier circuit adapted to be connected to said apparatus and coupled to said tuned circuit and responsive on the passage of excess currents in said rectifier circuit to load said tuned circuit thus causing cessation of the generation of oscillations with resultant flow of plate current and the actuation of said relay to de-energise said oscillator. Referring to the drawing, an alternating current source 141 is connected across transformer winding 82 whose centre-tapped secondary 84 produces an alternating plate voltage for tubes 86, 88 which form a push-pull oscillator with common output circuit of condenser 90 and inductance 92, which is fitted to provide a feed-back voltage to grids of tubes 86, 88 in condensers 94 and 96 respectively to produce self oscillation. Condenser 98 and resistance 100 form a self-biasing circuit forthe grids of these two tubes. Of the lifter coils 102 and 104, the latter acts as overload relay 106. The output circuit 90, 92 has a resonant frequency of several kilocycles, and the critically coupled coil 108 and condenser 110 have the same resonant frequency. The rectifier 112 connected to the high voltage sid of the circuit supplies a steady high voltage to the contact 31. Under normal operating conditions the current is of the order of a few milliamperes, but under short circuiting conditions sparking may occur and consequent loading of the secondary tuned circuit 108, 110 causes a loading of the tuned circuit 90, 92 and stops oscillation. The tubes 86, 88 then pass a current large enough to energise the manually reset relay 106. This de-energises the oscillator circuit and thus quenches the arc formed at the short circuit.