GB1023950A - Improvements in electric circuits for controlling controllable single-phase rectifier elements - Google Patents

Abstract

1,023,950. Rectifying. KOEFOED, HAUBERG, MARSTRANDOG HELWEG A/S TITAN. Feb. 25, 1963 [Feb. 26, 1962], No. 7456/63. Heading H2F. In a rectifying circuit comprising a load 5 fed from a transformer 4 through a controllable rectifier 1, a control circuit for the rectifier includes a transistor 10 and a Zener diode 12. The collector electrode of the transistor is connected to the rectifier gate 13 and the emitter is held-during the positive half-cycle, but prior to firing-at the reference potential of the Zener diode 12 through the potential divider 11, 12. A capacitor 9 is charged during the negative half-cycle with current derived from a transformer 6, whose supply may be in phase with or phase displaced from the main supply. During the positive half-cycle the capacitor 9 discharges through the series combination of resistor 8 and Zener diode 12 (in its forward direction) which series combination is across the emitter-base circuit of transistor 10, the discharge being opposed by a D.C. control voltage at ab. During the discharge the potential of the base falls until it is below the emitter potential, at which point the transistor conducts firing the rectifier 2. Only a short firing pulse is produced since the conduction of the rectifier short circuits the control circuit. The firing angle thus depends on the level of the D.C. control voltage at ab. In modifications, this control voltage is connected directly to the emitter (Fig. 2, not shown) and a Zener diode is connected between the gate of the rectifier and the collector of the transistor (Fig. 3, not shown).