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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 11.1volt 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

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    \$\begingroup\$ I honestly don't know, but if I were you I would add them. There is a $1.99 step down voltage regulator on eBay with free shipping. I would only do this for the 5v. The 3.3v has a voltage regulator that you can't bypass like you can to with the 5v one (put it in 5v instead of VIN or power jack), therefore wasting more electricity. Even if you just did the 5v one, it would save a ton of electricity. There is a 6.1v difference compared to a 1.7v difference. \$\endgroup\$ – Anonymous Penguin Apr 9 '13 at 21:28
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The Leonardo uses linear regulators fed off the Vin line.

  • A low drop-out (LDO) linear regulator (NCP1117) for the 5 volt rail
  • An ultra-low drop-out (ULDO) linear regulator (LP2985) for the 3.3 Volt rail

Of these, the 3.3 Volt regulator's efficiency is less of a concern, given that it needs to supply very little current. The LP2985 regulator itself is rated for just 150 mA.

Depending on the actual application, the overall current drawn may or may not make switching to a switching regulator for 5 Volts viable: For low current applications, the overall thermal dissipation of the rest of the board would be bigger than the dissipation (lost efficiency) at the regulator itself, so there is not much to be gained by buck regulation.

For higher current demands (say ~ 500 mA overall, picking a number for convenience):
Replacing the 5 Volt regulator with a well-filtered 5 Volt integrated buck regulator module (e.g. Murata OKI-78SR05) will improve efficiency at the cost of size.

The 3.3 Volt ULDO's input should then taken from this 5 Volt rail instead of directly from Vin.

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The Arduino Uno schematic shows usage of two linear regulators:

  • MC33269D-5.0 for 5.0 volts
  • LP2985-33DBVR for 3.3 volts

The Leonardo schematic you referenced shows two linear regulators:

  • NCP1117ST50T3G for 5.0 volts
  • LP2985-33DBVR for 3.3 volts

A switching step down regulator could definitely be more efficient, but pay attention to the current you are using as it affects the efficiency.

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