[USB +5V]-> charger-> battery-> regulator-> 3.3V

usb 5v 3.3v charger

Colleagues,

I need to build a circuit, which will charge a battery from the USB and then run digital logic with Vcc=3.3V from the battery. Size and EMI are most important to me. Efficiency of this whole ordeal is of secondary importance. So, I thought I would use a linear charger and a linear regulator: small, cheap, low EMI. I thought: “Perfect!” But… But that would require a battery that has a voltage between 3.6V and 5V. I couldn’t find such a battery. Battery packs are not an option, because of their size. The biggest battery I can work with, is probably AA; a big coin cell would be ideal. Unregulated Vcc is not an option either. Finally, the question: is it possible to get 3.3V out of this arrangement without a step-up (boost) switcher?

Cheers,
Nick

3.7v battery regulator

You can use MCP73855 for example, a single cell Li-Ion (3,7V typical, 4,1 or 4,2V fully charged), then a LDO regulator such as LF33CDT or similar. I use this combination without any problem, in automotive environment.

/pisoiu

3.7v 5v regulator

Hi

you can check

AS3603 of Austria microsystems

Salam
Hossam Alzomor
www.i-g.org

5v regulator, usb

pisoiu said:

You can use [...], a single cell Li-Ion (3,7V typical, 4,1 or 4,2V fully charged)...

Click to expand...

That would be great. Could you recommend some particular models of small Li-Ion cells?

Thanks,
Nick

Added after 1 minutes:

alzomor said:

AS3603 of Austria microsystems

Click to expand...

Hi Hossam,

Thanks for the tip. I think, AS3603 is hard to get in the US in prototyping quantities. Do you know of any other LDO+charger chips?

Thanks,
Nick

single li ion 3.3

You can search at uk.farnell.com or www.digikey.com for Li-Ion cells. On the other side, almost any accumulator for mobile phones, which is marked as "Li-Ion" will be good as well. Almost all are single cell, 3,7V type.

/pisoiu

3,6 battery regulator

pisoiu said:

You can search at uk.farnell.com or www.digikey.com for Li-Ion cells.

Click to expand...

Easy to say. If you go to DigiKey and navigate to the Battery->Lithuim section, there's no entry for 3.7V cells. In addition, all 3.6V cells are non-rechargeable Li-tionyl-chloride (made by Tadiran). I bet, there's not a single Li-Ion cell on DigiKey.

3.7v to 3.3v regulator

Try these:

h**tp://www.goldmine-elec.com/default.htm
They have Li-Ion cells on sale for $0.99USD
They are in the USA but ship international.

This website has 5-packs for $5.00USD
h**p://www.sciplus.com/
USA. Don't know about international

3.3v regulator charger

Kender,
From Farnell I've purchased Li-Ion cells. It was a guess that Digikey also may have, but it seems I was wrong, apologize for that. However, I think the easiest way is to search for those used in mobile phones, they should be available almost everywhere.

/pisoiu

Sourcing Li-Ion cells

pisoiu said:

From Farnell I've purchased Li-Ion cells.

Click to expand...

Could you post the part number, model and maker?
May be I'll be able to track them down in the US.

Thanks,
Nick

1188679 , this is what I've used. But you can browse uk.farnell.com in batteries&power/batteries/rechargeable lithium, then you can choose one suited to your needs.

/pisoiu