GB1474071A - Constant-voltage circuit - Google Patents

Abstract

1474071 Automatic voltage control HITACHI Ltd 11 June 1974 [13 June 1973] 25932/74 Heading G3R A power supply circuit, suitable for construction as an integrated circuit in a television receiver, includes a series transistor controlled by a drive transistor in response to a control signal from an output voltage sensing and error amplifying circuit. One electrode of the drive transistor is connected to the output terminal of the series transistor through a constant voltage element so as to minimize the voltage drop across the series transistor at the operating threshold of the circuit. As shown, a transistor 3 is biased by an output voltage divider 4, 5, 6 and a Zener diode 7 so as to produce an amplified error signal which is fed to the base of a drive transistor 2 which in turn controls the conduction of a series transistor 1 in order to regulate the output voltage V 0 . The collector of transistor 2 is connected to output terminal 13 by diodes 17, 18 connected in the forward direction, so that the junction of the collector of transistor 2 and a resistor 15 is maintained at a fixed voltage below the collector voltage of the series transistor 1. In this way, the lower limit of circuit operation occurs when transistor 1 saturates, minimizing the voltage drop between input terminal 11 and output terminal 13. A similar embodiment, using transistors of opposite conductivity types, is described with reference to Fig.4 (not shown).