GB1179449A - Improvements in or relating to Regulated Electrical Power Supplies - Google Patents

Abstract

1,179,449. Automatic voltage control. MULLARD Ltd. June 13, 1967, No.27152/67. Heading G3R. A power supply arrangement comprises two regulated supplies having one output terminal of each commoned at B and providing outputs of opposite polarity at terminals A and C, at least one of the regulated supplies being rendered operative at switch on by a voltage applied through a diode D9 from its associated unregulated supply, and the diode D9 being rendered non-conducting during the normal operation of the arrangement by a voltage applied thereto from the other of said supplies. As shown, the unregulated supplies are constituted by bridge rectifiers D1-D4 and D5-D8 which are connected to respective secondary windings of a transformer T. The respective regulating elements are series transistors VT1, VT2 and VT3, VT4 connected as Darlington pairs, with associated control transistors VT5, VT6. In the absence of diode D9 transistors VT2 and VT3 would not conduct at switch on and no output would appear at terminals A and C; the diode D9, however, allows the voltage at rectifier D5-D8 to be applied to the base of transistor VT4 whereby transistor VT3 is reduced conductive, and the voltage then available at terminal C is applied over resistor R10 to the base of transistor VT1. Thus, transistor VT2 is also rendered conductive so that an output voltage is them available at terminal A; this latter voltage is applied to diode D9 over a resistor R9 to render the diode non-conductive, and the regulating elements then operate in conventional manner to maintain constant the output voltages between terminals A, B and B, C. A second diode may be provided so that both regulated supplies are rendered operative at switch on, and such a modification is described with reference to Fig. 2 (not shown).