Differential exposure meter circuit

Published:2011/5/3 6:18:00 Author:Christina | Keyword: Differential, exposure meter | From:SeekIC

The BPX63 photodiode's sensitivityis 10mA/IX. This circuit ensures that the figure Location only affected by the useful light but not affected by the noise signal. When the circuit is under the low light condition, this circuit can collects a series of short pulse light rapidly. When the camera shutter is not open, K1, K2 closed, so the output of the operational amplifier tied back to its input port. At the beginning of the exposure, K1 and K2 open, the circuit produces more than 3000 times magnification. So the integration capacitor C1 charged by the photocurrent to make the output voltage changed by the time. When the output voltage is 1V, T3's base-emitter starts to conduct. When the C1 feeds back through T3, the RL stops, so the exposure stops, power supply is +/-3V.



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