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My current project will be sitting next to a 12VDC power line. It seems a waste no to tap it to power into the Arduino board too. Now I read everywhere that with 12V input quite a lot power gets dissipated by the voltage regulator. Wouldn't it then a wise move to use the board 's own PWM capabilities to throttle the input voltage?

Nother point is whether it is sensible at all when the board is using little current (in this case less than 5mA over the pins for 0.1 sec every few seconds, plus the board in deep sleep mode).

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    You could use a 12V to 5V or 3.3V Buck Converter Module ($0.84CDN) aliexpress.com/item/… – VE7JRO Dec 31 '18 at 21:17
  • If there isn't a lot connected to the Arduino, that is not a lot of current is used, then the loss will also be minimal. (12-5)*current. Let's say the Arduino Uno uses 50ma. You'd end up with a loss of 0.350Watt. Not a lot, so the regulator will only get a bit warm. The problem is that some people will connect a 12V power supply, and then run a string of leds from the regulated 5V pin. Resulting in a lot of wasted power in the form of heat. So much heat that the regulator burns out. – Gerben Jan 1 at 16:16
  • Thanks @Gerben, this is reassuring. I thought so, but wasn't too confident about it. VE7JRO: at the moment the price is no issue with the Chinese parts, but shipping times have increased to well over a month. If I could take a shortcut as outlined here, I would prefer that. But not yet in this project, so. – user508402 Jan 1 at 17:46
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How did you measure that it's going to be 5mA? Because if that's really the case, the regulator dropping 7V (I'm assuming it's a regular 5V arduino) will need to dissipate ~35mW of heat which is not much and it should not cause a lot of problems for your board.

Another option would be using a step-down power supply module, there are tons of available dc-dc converters, mostly based on LM2596 (search for LM2596 DC-DC module) which will handle your 12 power rail with ease.

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There are some models of clone boards that have a DC-DC switching regulator instead of linear regulators to do just that. The extra cost for the regulator chip, inductor, diode, etc. are probably not worthwhile in the majority of applications tho.

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