Hi!
I'm trying to figure out a way to have a 3.7v single cell Lipo charged by a Lipo charger controller while the Moteino is connected to USB cable, and when the cable is removed, I want to use the same Lipo to now feed the Moteino trough the same Vin pin. If the Moteino is connected to the USB cable, it is always on, as normally it is not possible to cut the power from the USB port without cutting something on the PCB. But when the USB is disconnected, it should only power up when a SPST switch is ON.
Any ideas?
Something like this?
(http://www.linhadafrente.net/Moteino/IMG_1880.JPG)
or like this:
(http://www.linhadafrente.net/Moteino/IMG_1882.JPG)
However, using diodes will clip the useful charge due to the dropdown on the diodes. Even if a Schottky is used. Maybe a Mosfet?
Anyone?
The lipo charger is this one:
(http://www.baaqii.com/promanage/productimage/Baaqii/A/A866-1.jpg)
, but with the USB connector removed
Sorry I missed this thread. I think you're looking for a load shared charger circuit, see this link (http://blog.zakkemble.co.uk/a-lithium-battery-charger-with-load-sharing/) for an example.
You can always cut current with a mosfet rather than cutting the PCB trace :)
Well, the last schematic ended up working very well, using the lipo charger. The problem I was trying to solve was to be able to charge the 3.7v Lipo battery when the circuit was not in use. The diode should be a schotky to avoid a large voltage drop. If the switch is ON, the battery connects trough the schotky diode to the Moteino VIn. If the switch if OFF, the battery connects directly to the Lipo charger. And now, connecting the Moteino to an USB port charges the battery, and also turns the Moteino ON. I guess I could have a double switch and break the 5v supply from the USB to the Moteino, but for the circuit I use it was not required.