GB983519A - Improvements in or relating to automatic voltage regulator circuits - Google Patents

Abstract

983,519. Automatic voltage control. MULLARD Ltd. Sept. 30, 1963 [July 6, 1962], No. 26037/62. Heading G3R. Regulation of the output voltage of a generator is effected by controlling the field current by the on-off control of a semi-conductor switch in series with the field winding, the switch having thyratron-type characteristics. In a self-excited alternator, the alternator field Lf is connected in series with a silicon controlled rectifier D8 across the alternator output L, N. Firing pulses for the rectifier D8 are obtained from a blocking oscillator comprising a transistor VT1 and a transformer T1, the base of the transistor having applied thereto a voltage which is the difference between a reference voltage developed by a Zener diode D4 and a hold off bias voltage developed by the resistor R3 and capacitor C2. The transistor collector voltage is developed across Zener diodes D5, D6, D7 whilst the voltage applied to the emitter of the transistor is dependent upon the alternator output and is derived by way of diode D1 and resistors R1, RV1. This signal is smoothed by capacitor C1 and applied to the emitter by way of a feedback winding S2 of the transformer T1 from a secondary winding S1 of which is taken the firing pulses for the rectifier D8. Temperature compensation may be provided by using a Zener diode D4 having a temperature responsive characteristic. For higher power alternators two or more silicon controlled rectifiers may be used in series and alternatively the field winding Lf may be the field of an auxiliary alternator acting as an exciter for the main alternator or the field may be energized from an external A.C. supply. At starting a low voltage rectified A.C. may be applied to the field winding by way of diodes D9, D10 to assist the residual magnetism thereof.