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Author Topic: 555 square wave help  (Read 1957 times)

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Offline electron_misfireTopic starter

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555 square wave help
« on: April 05, 2014, 06:13:50 am »
I'm designing a simple square wave generator.
I'm using a 555 timer in astable mode.
My problem is that whenever I power the circuit it turns on the after a few seconds turns off and never goes back on again.
Would anyone have some advice or help?
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Offline Simon

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Re: 555 square wave help
« Reply #1 on: April 05, 2014, 06:18:12 am »
Is the top resistor value 1R ?

1000uF ? you need to read the datasheet thoroughly, there is a limit to the discharge current allowed in pin 7
« Last Edit: April 05, 2014, 06:22:53 am by Simon »
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Offline electron_misfireTopic starter

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Re: 555 square wave help
« Reply #2 on: April 05, 2014, 06:48:43 am »
Ok I've swapped the 1r resistor and 1000uf cap. It's working now thanks
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Offline Simon

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Re: 555 square wave help
« Reply #3 on: April 05, 2014, 07:00:38 am »
I think that 1R needs to be 1K minimum (check the allowed discharge current) and with 1000uF and 4K that would have given a 4s discharge time.

Datasheets have all the formulas, give it a thorough read.
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