Importance

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Abstract

Disclosed is a variable output-type constant current source circuit capable of varying its output current in a stepwise manner without the complication in circuit configuration and the increase in size of a semiconductor circuit board for incorporating the circuit therein. The constant current source circuit comprises a first self-biasing type constant current circuit 3a configured such that transistors M1, M2 are operable to cooperatively supply a given voltage across a resistor RS to generate a stabilized current I.sub.R1. In order to vary the output current, the constant current source circuit includes a switching circuit 5 (transistor M5) connected in series to a series circuit connecting in series the transistor M1 and the resistor RS, and a second constant current circuit 4 connected in parallel to a series circuit connecting in series the transistor M1, the resistor RS and the transistor M5. The second constant current circuit 4 is also configured to serve as an activation circuit for the first constant current circuit 3a.

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First Claim