UNDERVOLTAGE_INDICATOR_FOR_SINGLE_CELL

Published:2009/6/22 22:22:00 Author:May | From:SeekIC

When operating with a single cell，it is necessary to incorporate switching circuitry to developsufficient voltage to drive the LED，A circuit that accomplishes this IS drawn In the figure shown Basically， it IS a voltage-cqntrolled asymmetrical multivibrator with a minimum operating thresholdgtven by∶ Above this threshold，the flash frequency increases with voltage This is a far more noticeable indication of a deteriorating battery than merely dimming the LED In addition，the indicator can bemade visible with considerably less power drain With the values shown，the flash rate is 1.4 sec -1at 1.2V with 300-μA drain and 5.5 sec-1 at 1.55V with 800-μA drain Equivalent visibility for continuous operation would require more than 5-mA drain.



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