555_TIME_DELAY

Published:2009/7/14 19:38:00 Author:May | From:SeekIC

Many electronic circuits frequently require the brief delay of a pulse. Such a delay, here between 100μs and 100 seconds, is easily provided by a simple circuit based on the popular 555. That is more than adequate for most applications. The output of the 555 can go high only if the potential at pin 2 drops below a third of the level of the supply voltage, provided that the level at pin 4 is high. In quiescent operation, the level at pin 4 is low and C1 is charged via T1, so the output is low. When the input goes high, T1 is switched off and C1 is discharged via R1. In that condition, the REST state is cancelled and after a time delay that depends on the state of discharge of C1, the output of the 555 goes high .The time delay in seconds is calculated from r=0.69R1C1, where R1 must be greater than or equal to 10KΩ



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