MCU application circuit for working while power loss?

[Nicholas]

work while power loss

Any reference for me about a circuit work for a short while when power lost? Of course It should backup power when alive. Anything about such a circuit will be appreciated. Thanks in advance.

 

[Ante]

Re: work while power loss

Nicholas,

Search for ” Uninterruptible Power Supply” on Google and you will find what you are looking for.

Ante :roll:

 

[Nicholas]

Re: work while power loss

thank you for ur reply.
But, actually, I don't mean UPS. Just an AC to DC convert mains voltage to about 24VDC to power a circuit, say some MCU application circuit. And problem is the line to mains will be cut for a while, say up to 1 sec. So, how can I keep the DC voltage alive while AC loss?
I know using CAPs will do. I try to find some circuits like this for reference.

 

[flatulent]

Re: work while power loss

The cheapest solution would be two 12V gel cell batteries in series. A capacitor large enough would be expensive.

 

[tR|GG3rX]

Re: work while power loss

i've read about one circuit that uses 2 battery cells but not in series. and there's a diode to protect the backup battery from conducting to the load. unless the main battery losses its power, the backup battery will be able to power-up the load.

 

[batdin]

Re: work while power loss

I wouldn't use batteries for just one second!
And there must be some charging circuit etc.
I would use large enough capacitors.
To avoid the very large charging current during power-on I would connect them through a Shottky diode and a resistor in parallel,so that the capacitors are charged slowly through the resistor and discharged when needed through the diode.

 

[nford]

Re: work while power loss

Its easy enough to get capacitors which have a very large capacitance. The only problem is that they often can't handle much more than about 2-3V max. If you got say a 1F aerogel or goldcap you could use a voltage pump to get the voltage you need when the power went out. I believe that you could use something like this only because you said that it was to power a MCU which I asume doesn't draw much more than a few milliamps.

**broken link removed** stocks some of these caps

I am a bit of a newbie to this stuff so if I'm completely wrong please don't hesitate to inform me of my mistake.

 

[Nicholas]

work while power loss

If the load will probably draw more than 20mA @ MAX. Is the use of battery the only choice?

 

[batdin]

Re: work while power loss

It is as simple as this:
deltaV=time*Imax/C; deltaV is the voltage drop during discharge time .
thus C=time*Imax/deltaV
If time=1s;Imax=50mA;deltaV=3V(for example) then
C=1*0.05/3=16000uF.(quite feasible)
If the voltage drop may be bigger(depends on the minimum voltage required) ,the capacitor could be smaller.