Constant Current Regulator Circuit Diagram

Constant Current Regulator Circuit Diagram

This fixed 1-mA current source delivers a fixed current to a load connected between Q1's collector and ground; the load can be anywhere in the range from 0 n to 14 n. The circuit is powered from a regulated 15-V supply , and the R1/R2 voltage divider applies a 14-V reference to R3. The op amp's output automatically adjusts to provide an identical voltage at the junction of R4 and R5. That produces 1 V across R5 ,r esulting in an R5 current ofl rnA. Because that current is derived from Q1's emitter, and the emitter and collector currents of a transistor are almost identical, the circuit provides a fixed-current source. The output current can be doubled by halving the value of R5.