Tiny intensity light control switch circuit

Published:2011/5/2 6:32:00 Author:Nicole | Keyword: light control switch | From:SeekIC

When the light intensity is tiny, it is unfit for adopting photosensitive resistance or general photodiode, it should use special photodiode BPX63 with small cut-off current. In the circuit, the light constantly shines diode D1, if switches S1 and S2 is closed, then the photocurrent is short-circuited, the source emitter follower is composed of FETs T1 and T2, resistances R1 and R2. When switch S2 is closed, opertional amplifier output is connected to its inverting input terminal by FET T1. If switches S1 and S2 are all open, then the strong negative feedback is cut off, but the work point of FET T2 is changed. Main technique target: work voltage: ±3V; illuminance: 0.01lx; the exposure time of 0.02lx: 12s; the measurement error of 0.01lx: < ±20%; temperature condition: -30~+50℃.



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