I need to build a circuit that will charge the battery and also will make my system work.
while charging - the system will work on 220AC (the power from the charger, and not the battery)
and when I disconnect the charger - the system will continue working smoothly.
for example - like we have in the cellular phone \ any PC

how do I start?
the battery is LiPo Vnominal=11.1V 2000mAh Max charge 12.8V

Thanks ,

 

Here is a Lipo charger for different cells and capacities, what is the battery powering?

 

what do you mean ?
the use of it?
something like a DVR

 

Hmmm... nice project. I'm looking forward to it. I'm curious too....
Btw, maybe there are already some module which also has that feature....

You could just get the schematic from their web or reverse engineering it by yourself.
I think It's not a bad way to start..

Anyway, Good Luck..

 

Bad idea... Deleted.

 

Maybe something like this.

http://blog.zakkemble.co.uk/a-lithium-battery-charger-with-load-sharing/

 

nice IC but I don't think it will hep me
from what I have read
it can only be use for Vcharge of 5V
I need 12V

something else maybe?

I have found this page - maybe it can help
http://www.linear.com/parametric/Ba...Polymer!vmax_12.1!icharge_1!bat_bat!buck_buck

there are too many options there - how do I know what to look for?

 

I think this would work.

http://cds.linear.com/docs/en/datasheet/4412fa.pdf

 

just to see I understand
if I take -
Figure 1. Automatic Switchover of Load Between a Battery and a Wall Adapter

then :
Battery cell - I connect the battery
To-Load - connect to my device (DVR)
Wall adapter input - to my 220AC-12DC charger \or any other external battery
PIN4(stat) - I can put a simple LED the will let me know when the battery is charging ?

Thanks ,

 

Here is how I would do your thing....

I wouldn't use a LiPo. I would use a Sealed Lead Acid battery.

First, you need a well-regulated AC powered DC supply that can be set to the ideal float voltage (13.65V @ 25deg C) for Sealed Lead Acid batteries.

If you have that, you can simply parallel the supply, the battery and the load.

To tell if the system is running on AC or battery, either just use an AC indicator, or use the voltage detector circuit pictured. If the AC fails, and the system is being kept alive by the battery, the voltage will instantly drop from the float voltage (13.65V) to less than 13V (the intrinsic battery voltage). As the battery discharges, the voltage will drop slowly towards ~11.5V, which is a good ending point where the load needs to be disconnected.

 

I have only LiPo battery.this is what I have , can't change it
so what can I do?

 

LiPo is a very complex system. It is not suitable for floating in parallel with a continuous load.

It will take a commercial charger to charge the battery in isolation while a separate DC supply is connected to the load. The switch-over from AC to battery will happen when the AC drops. You need a low-voltage disconnect circuit to protect the LiPo if the AC stays off too long...

 

You also need a lipo charger, like fig. 3 in the data sheet.

 

I have search some more
and found this circuit\device
http://www.linear.com/product/LT3652

I will just have to change the RC part to make it work
for me (charge of 1A\12V)
what do you think?