I am designing my first "permanent" Arduino application, and I would like to know if the voltage regulator is linear or step down.
The reason I would like to know is because I am currently powering the prototype with an 11.1V 1300mAh LiPo battery. If it uses a linear regulator the efficiency would be, best case, 30% and 46% for the 3.3V and 5V regulators respectively.
I would much rather add my own step down converter to drop the voltage to 5V and power via USB port if that would be much more efficient.
I'm not sure if the different Arduino models have different parts or not, but for this application I am using an Arduino Leonardo.
Here is the schematic of the Leonardo.
Best Answer
Arduino Leonardo, like the Uno, uses an NCP1117 linear regulator (LDO), which can supply 800 mA, but at 11.1 V input that would be 4.88 W, so thermal protection will set in much earlier.
Using USB is a possible solution, but keep in mind that USB doesn't have to supply more than 100 mA, you'll have to negotiate for 500 mA. And Arduino is not designed for low-power, I don't know what the Leonardo consumes, but I guesstimate the Uno's supply current at 50 mA, so powered from USB that may leave too little for for instance a series of LEDs.
Your own switching power supply looks like the best solution. Bypass the NCP1117 and supply it directly with 5 V. A 12 V to 5 V buck converter should be able to have a near 90 % efficiency. If the dingus would need 50 mA it can run for more than 48 hours on the LiPo battery.
Further information
Arduino Leonardo schematic