NANOAMPERE_SENSING_CIRCUIT_WITH_100_MEGOHM_INPUT_IMPEDANCE

Published:2009/6/25 3:29:00 Author:Jessie | From:SeekIC

Circuit Notes The circuit may be used as a sensitive current detector or as a voltage detector having high input impedance. RI is set so that the voltage at point (A) is Vz to 3A volts below the level that fires the 2N494C. A small input cur-rent (Iin) of only 40 nanoamperes will charge C2 and raise the voltage at the emitter to the firing level. When the 2N494C fires, both capacitors, C1 and C2, are discharged through the 27 ohm resistor, which generates a positive pulse with sufficient amplitude to trigger a con-trolled rectifier (SCR), or other pulse sensitive circuitry.



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