555 timer for large signal delay

[vimalkhanna]

I need to delay the switch ON of my converters by a 60secs /90sec/120sec after recpt of a shutdown data thru a 5VDC /100uA input .
The time delay enables hiccup mode of the converters so that the holding charges in the ckt capacitance are neutralized .
I want a very small /economical design.
Designers kindly help...

 

[KerimF]

The formula is:
T = 1.1 * Ra * C
C could be 470uF or 220uF in your case.

I already used 555 for such long time to control my 3 refrigerators so that they start one after another when mains voltage returns after cut-off.

Kerim

PS: The leakeage current of C will affect the time, by making it longer. But if it is relatively high then time will be infinite ;-)

 

[dick_freebird]

There's 555s, and there's 555s. Some versions are proud of
low current and ability to do long delays. Some, not so much.

 

[KerimF]

I think you mean:
bipolar 555 (old standard)
CMOS 555 newer one, low current

 

[IanP]

I wouldn't use 555, instead consider (also 8-pin-DIP) PICAXE-08.
Delay can be set by programming this IC (command WAIT 60 => 60s delay), there is no problem in triggering it on power-on, and input can read transitions from 0-to-1 and from 1-to-0 ..
Cost - $1.
And the most important thing is that there is no dependence on any external components such as capacitors ..

:wink:
IanP

https://www.picaxe.com/docs/picaxe_manual1.pdf