A friend and I are working on building a smartwatch on a budget, so it’s a (very) low power project, but we are currently having a problem with the power supplying.
We already chose this board, because of its size and the BLE chip: RFduino BLE SMT
For now on, we are planning to use this battery 500 mAh LiPo battery (approx. 4V at full charge) with this voltage regulator Micrel MIC5209-3.6YS (the board supports 3.6V max.).
But the problem is that the Voltage Regulator will apparently drain by itself too much energy from the battery (by heating), reducing drastically the autonomy.
What (type of) regulator would be the best or do we need to find another battery?
Best Answer
The battery you have chosen is a typical Lithium Poly with a maximum voltage of 4.2v, dropping to 3.7v according to the description linked to in the OP; however the datasheet says it can be discharged to 2.75v, which is more typical of these batteries..
The RFduino can operate with voltages from 1.9v to 3.6v, with a typical voltage of 3.0v. (It's too bad it can't operate up to 4.2v like a lot of cell modems do, then it could be connected directly to the battery.)
However if you put a silicon diode with a typical forward voltage drop (Vf) of around 0.7v in series with the battery, this will drop the battery voltage range to 3.5v down to 2.0v, which is just right for the RFduino. And diodes are much much cheaper than regulators.
The venerable 1N4148 has a forward drop Vf of 0.6v at 1 ma, and 0.8v at 20 ma.