GB962503A - Electrical inverter - Google Patents

Abstract

962,503. Transistor oscillator circuits; impedance networks. WESTINGHOUSE ELECTRIC CORPORATION. April 3, 1962 [April 11, 1961], No. 12788/62. Headings H3T and H3U. A self-oscillating inverter comprises at least one pair of semi-conductor switching devices connected in push-pull so as to become conductive alternately under control of a transformer, the primary winding of the transformer being connected in series with a tuned circuit, the natural frequency of which is arranged to be different when the circuit is first energized from that when oscillations have built up to the normal operating level. Fig. 1 shows a known inverter in which the two pairs of transistors 16, 18 and 22, 24 have regenerative feedback via transformer 34 so as to become alternately conductive at a frequency determined by the series tuned circuit 40, 42. The starting current is reduced by substituting the circuit shown in Fig. 3 for the series tuned circuit 40, 42. Capacitor C3 is initially uncharged hence the effect of the charging current via rectifier R2 will be to by-pass the auxiliary series tuned circuit R2, C2 and hence increase the natural frequency of the circuit connected between terminals A, B. If the core of transformer 32 is initially unmagnetized the duration of the first half-cycle will thus be insufficient for the current to build up to saturation level. A resistor (not shown) may be connected between terminal 4 and the base of transistor 16 to ensure that the first half-cycle is of the appropriate polarity. The frequency becomes reduced to one-half when C3 is fully charged. Fig. 2 (not shown), relates to triangular shaped flux waves produced when the circuit is operating into a reactive load 12. Specifications 869,454 and 882,126 are referred to.