USB Lithium battery charger PCB

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Hello, I need a little help this is driving me mad to work out..

I am either after a schematic or some help.. Im just trying to make a usb charger to be placed in my unit im making.

Basically, I need a 3.6v Lithium battery to run my circuit, but instead of batteries being changed, I just wanted to out a internal lithium battery inside.

So all I want to do is make a circuit so as I plug a usb cable in it, pretty much like the usb end of the cable which would go say into the printer,

It will charge the battery, when fully charged a LED lets me know it is, but at the same time whist charging the battery is still able to feed power to the unit..

Can anyone help?

Thanks in advance

 

[(*steve*)]

There are a plethora of small ICs that are designed to charge single lithium cells from USB.

Alternatively you could purchase a cheap USB LiPo charger and rip out the innards.

 

[subplay]

There are a plethora of small ICs that are designed to charge single lithium cells from USB.

Alternatively you could purchase a cheap USB LiPo charger and rip out the innards.

Thanks Steve, I have seen some charging IC`s but what I would like to know is how would I be able to draw and charge at the same time, for instance a mobile phone on charge whilst using it...

Once the circuit is made, and I have made the usb charger part of the pcb, is it as simple as connection the charger to the battery and at the same time the pcb via the battery?


Thanks

 

[(*steve*)]

I can't point to anything specifically.

However the general principle is that if the charge rate exceeds the current draw in operation then you can operate the device whilst on charge without further depleting the battery. There may be some issues about detecting end of charge though.

I would suggest going to digikey and searching for "PMIC", then selecting a likely looking subcategory (I think "PMIC - Battery Management" would be the one) and taking a look at some of the devices listed. Beware that an awful lot are quite small surface mount packages due to the nature of the devices in which they're used.

Digikey has a good parametric search, so you can narrow down the selection by things like battery chemistry, mounting type, case, etc. However it might be interesting to look at the various functions because what you want may be in one of these. Perhaps "Charge Management" may be one to start with.

Go through a selection of them and read their datasheets.