Digital_system_ac_dc_dropout_detector

Published:2009/7/23 22:17:00 Author:Jessie | From:SeekIC

This circuit provides an indication if either or both the ac (line) or dc power to a digital system has dropped out. Fast ac-line dropout detection allows a memory-store command to be issued before dc power fails. Typically, the digital system regulators will continue to supply hold-up power for about 50 to 100 ms after ac-line dropout. This hold-up period (which should be verified in any individual application) permits adequate time to execute a memory-store operation. C1B serves as a final warning that power failure is imminent, by going low when the 5-V regulator drops below the threshold set by the selected resistors. These resistor values should be chosen so that C1B trips when the regulator input approaches the specified dropout voltage.



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