GB915979A - Improvements in or relating to electric inverter circuits - Google Patents

Abstract

915,979. Inverting. GENERAL ELECTRIC CO. Ltd. May 18, 1961 [May 23, 1960; Jan. 6, 1961], Nos. 18107/60 and 653/61. Class 38 (2). An inverter circuit giving a substantially sinusoidal output includes an inductive element 7 which with the capacitor 11 forms a parallel tuned circuit, a smoothing choke 9 and a pair of semi-conductor controlled rectifiers 4,5 triggered alternately by pulses from a D.C. operated blocking oscillator at intervals less than the half-periods of the resonant frequency of the tuned circuit. In the arrangement shown, the inductive element 7 is an autotransformer having primary tappings B, D, a centre tap C and output tappings A, E supplying the load 12. The D.C. voltage 3 stabilized across the capacitor 24 by the Zener diodes 25, 26 supplies the self-excited oscillator comprising transistor 13, transformer 15, capacitor 18 and resistors 19 and 20. The pulse frequency, adjustable by the resistor 20, is arranged to be just less than one-half of the natural frequency of the tuned circuit. The semi-conductor rectifiers 4, 5 are arranged to have slightly differing characteristics such that when the switch 10 is closed one or other of them strikes first. Assuming rectifier 5 strikes, the terminal D is short-circuited to the supply terminal 2 and due to the tuned circuit the voltage across the rectifier 4 varies sinusoidally. When the pulse amplitude is sufficient to fire both rectifiers simultaneously the rectifier 5 which was conducting is immediately rendered quiescent by the sinusoidal variations across the winding BD, the rectifiers then conducting cyclically (Figs. 2 and 3, not shown). The capacitor 30 reduces variations in the tuned circuit frequency caused by the load 12. In an alternative arrangement (not shown) the choke 9 is connected in the negative supply line between the resistor 16 and the transformer winding 21.