Power_fail_warning_and_power_up_power_down_reset

Published:2009/7/24 5:01:00 Author:Jessie | From:SeekIC

When the unregulated dc input of this circuit is above the trip point, OUT1 is low. When the dc input drops below the trip point, OUT1 shuts off and the power-fail warning goes high. The voltage on the input of the 7805 decays at a rate of IOUT/C. Because the 7805 continues to provide a 5-V output at 1 A until VIN is less than 7.3v, this circuit provides a certain amount of warning before the 5-V output begins to drop. The ICL7665S OUT2 (Fig. 9-15B) is used to prevent a microprocessor from writing spurious data to a CMOS battery-backup memory by causing OUT2 to go low when the 7805 5-V output drops below the ICL7665S trip point.



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