GB1061688A - Constant current power supply - Google Patents

Abstract

1,061,688. Automatic current control. BECKMAN INSTRUMENTS Inc. June 22, 1965 [July 1, 1964], No. 26283/65. Heading G3R. A load 14, e.g. a chronopotentiometer, is supplied with constant current from input terminals 10, 11 by way of a regulating transistor 12 controlled by an error signal derived from an amplifier 22 and a current sensing circuit 21 which has a pair of parallel connected branches; the first branch includes a selector switch 36 associated with resistors 32, 33, 34, 35 for selecting one of a plurality of maximum load currents; the second branch includes a variable voltage source, constituted by a battery 25 and a potentiometer 24, and resistors 28 and 29 connected as shown, the signal at junction 31 between resistors 28, 29 being an error signal which is applied to the input of amplifier 22 which controls transistor 12 in a manner to maintain the error signal at zero. A desired load current, having any value from zero to a maximum determined by the setting of switch 36, may be selected by adjustment of the variable voltage source 24, 25, and this desired current is maintained constant by the action of the circuit 21, the amplifier 22 and the regulating transistor 12. To compensate for leakage current through the transistor 12, the transistor is arranged in a bridge circuit together with resistors 39, 41 and 42, the supply 10, 11 being connected across one diagonal of the bridge and the load being taken across the other diagonal.