Constant current circuit using current mirror circuit

Abstract

In a source-type constant current driver circuit for driving an LED, a current of 1/β times a reference current is generated from a base current of a transistor Q2 for generating the reference current by means of the current mirror circuit composed of a transistor pair Q1a, Q1b. Further, the current generated by the current mirror circuit is amplified by a factor of n by means of a current mirror circuit composed of a transistor Q3 and one of transistors Q5a to Q5h. Then the amplified current is supplied to a base current of a transistor Q8. Thus, a base current of the transistor Q8 in a final stage is controlled.

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