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The RasPi requires a steady 5V and to this end I build a power regulator circuit using a LM2576T, similar to the one on page nine of the latest MagPi magazine.

This works great with an external battery pack but does not provide a way to charge the batteries directly. I have to charge the batteries first before using them with my Pi. Ideally I'd like a circuit that can run the RasPi from the mains power adapter while charging the batteries and run off battery when disconnected from the mains.

I have 4x 3.7V 4200mAh 18650 Ultracells batteries and a battery holder with PCM

These batteries have a full charge voltage of 4.2V and cut off discharge of 2.75V

I've done a lot of Google searches looking for examples of both a power regulator and li-ion charger but so far not found what I'm looking for...

Is there a specific name for this type of circuit? Does anyone have experience building a circuit like this? Is there any reference documentation or example circuit diagrams you could point me to?

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You're looking for a power management IC.

Here's an example of one

http://www.linear.com/product/LTC3553-2

it includes a LiIon charger, linear and switching regulators to charge from USB and then switch back and forth between USB and the LiIon battery. Possibly not the part you want, but it's a start.

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I been looking for same thing and I notices sites selling RC/Airsoft and (vacuumcleaner) robot batteries offer complete solutions at fairly reasonable prices. http://www.batteryspace.com/5vand6vregulatedli-ionpackmodules.aspx

And I found out they are selling battery packs with voltage regulators and power management (separare charging wires).

And there are even more complete solutions out there with even intergrated charger like: http://www.usledsupply.com/shop/12v-battery-pack-12v-3800mah-5v-5600mah.html

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