MULTIPLE_FIXED_CURRENT_SOURCE

Published:2009/6/18 2:21:00 Author:May | From:SeekIC

A multiple fixed current source is provided by the circuit. A reference voltage (1 Vdc) is established across resistor R3 by the resistive divider (R3 and R4). Negative feedback is used to cause the voltage drop across RI to also be 1 Vdc.This controls the emitter current of transistor Q1 and if we neglect the small current diverted into the (-) input via the 1-MQ input resistor (13.5μA) and the base current of Q1 and Q2 (an additional 2% loss if the β of these transistors is 100),essentially this same current is available out of the collector of Q1.Larger input resistors can be used to reduce current loss and a Darlington connection can be used to reduce errors caused by the β of Q1.The resistor, R2, can be used to scale the col- lector current of Q2 either above or below the 1-22-4 mA reference value.



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