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power supply interruption

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garg29

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hi friends,
i'm facing a small problem. i have designed a 4 digit counter using 89c51. sometimes when the counter is busy counting the external pulses and there's a power supply interruption (just for a fraction of a second), the micro-controller hangs up. how can i prevent the problem to occur. i tried adding big condensors (4700uF + 2200uF0 in power supply but nothing helped. what can i do?

Thanks,

With best regards.
 

One of the immediate solution is to use an external circuit, a wellknown brownout detect. It will monitor your +5v power supply and firmly reset your microcontroller each time when a power fail occurs.
It's more suitable than the RC pair fitted on Reset pin. This way your micro won't hangup anymore, but will start fetching clean from 0000. If you can't provide a continous power supply and don't like to reset your micro then use an UPS or try to split the current between the micro and your power hungry LED display (if that is what are you using for your counter).
 

how long does interrupt last? Perhaps you should isolate your micro power from other circuitity and secure it with caps. Can try :
- put 2 regulators (let say 7805) - one to micro , second to rest of circuits
- put forward biased diode to firs regulator input and capacitors after this diode .

Or you can use rechargeable battery also connected through diode . Pay attention to current limiting resistors connected to output ports. They define how big current is throughn from micro . you can use transistor based drivers to reduce output current (if you drive LED indicators directly from micro).
 

Thanks silvio and artem for your great ideas. Silvio, i've heard about brown out circuits before also but was never able to find satisfactory details on the same, if you can please provide me a circuit for the same i'll be really very thankful to u.

With best regards.
 

Hi Garg29,

Well there a lot of manufacturers of this kind of circuit. I'll mention Maxim among them for the simple reason that can offer you some free samples.

Read first this introduction :
**broken link removed**

then choose one according to this narrowest table search:
**broken link removed**
 

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