I'm hoping to power my device with a 3.7V (2x 18650) rechargeable battery which can be recharged within the device using USB (like in a phone, laptop, etc.). I believe some kind of power selector is needed if the device is to be operational during charging. Is there a module out there that enables this?



Changed question to consider 3.7V (2x 18650).

  • \$\begingroup\$ I am not aware of any 5V battery system. Can you please specify exactly what type and quantity of batteries you are talking about? Maybe draw a conceptual diagram showing the jacks and cables and batteries and what they power? You may be looking for a USB charger with power path management. I think "power path" may be a TI trademark, and I am not trying to endorse them over any other vendor. But if you google power path charger, I think it may help you figure out how to describe what you want more clearly. \$\endgroup\$ – mkeith May 12 '15 at 3:45
  • \$\begingroup\$ @mkeith After giving it some more thought, I think 2x 18650 might fit the purpose better. So, rather than 5V, I'm looking at 3.7V. \$\endgroup\$ – Kar May 12 '15 at 8:06

You can use a load sharing circuit like this one:

enter image description here

When no USB is connected, the PMOS transistor Q1 will be on (through the pull-down resistor R2) and the battery will power your circuit. When the USB is connected, the input voltage will bring the gate of Q1 up disconnecting it, and the MCP73831 will be charging the battery, while at the same time the usb will be providing power to your load through the D1 diode. You can use any battery charger chip (this one is very simple), but the principle and load sharing circuit can be the same.


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