Circuitry for providing a constant current to a load includes a source of current and a regulating circuit interposed between the current source and the load. The regulating circuit includes a current shunting transistor coupled to the output of the current source and a feedback transistor also coupled to the output of the current source and to the base of the current shunting transistor. A diode connected between the current shunting transistor and the current source is chosen to have a dynamic admittance substantially equal to the transconductance of the current shunting transistor to provide the latter with unity voltage gain. A variation in current output of the source is accommodated by the current shunting transistor so that a substantially constant voltage at the output thereof is maintained. An output circuit including a transistor, coupled to the output of the current shunting transistor and to the load, and controlled by the output voltage, provides a substantially constant current to the load despite current variations from the current source.
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