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I once discussed this circuit with a friend. He was thinking of using an R/C series n/work that'll create a delay equal to its charging time≈5RC. There was also to be a zener diode to give further delay.
A 555 timer, theoretically I think would do the job, but being a low power device might be a problem, especially if you're going to power the cct from the mains.
Whichever circuit you choose, think about how it will respond to a momentary power dip.
Many products in the world don't reset properly under such conditions.
how do i calculate the delay time??? i tried using this formula T=RC but then my calculated time is not equal to my actual delay time when i tested my power on delay.i did not use transistor only capacitor and resistor.do you know any method to ccompute time daly???
T=RC is the time constant. It will give you the time taken to reach a value of 63% of the final value. For every additional time constant after the value reaches 63% of whatever remained at the previous time constant.
So after 2 time constants value will be 63 + 36*0.63=85%.
After 3 time constants the value is 85 + 15*0.63=94% etc.
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