So say you want to use transistors with your Arduino Nano to power components, which require greater than 12V. If your power supply is more than 12V, is there a way to safely use the same power supply to power the Arduino?
The voltage regulator (on the Vin pin) is supposed to be provided with 12V at max, since it is not cooled (it is a linear regulator, that dissipates the excess voltage as heat). If you have significantly more, you should at best buy a little switching regulator, to directly get a regulated 5V to feed to the 5V pin of the Arduino (that's what I suggest). Be sure to use a regulator, that can provide the needed current (which also depends on what else you provide over the Arduino).
If you really don't want to use an extra regulator and you don't have much more than 12V (maybe like 15V), you might get away by cooling the voltage regulator on the Arduino. The voltage regulator on a genuine Arduino will go into emergency shutdown, if it overheats, but it will not be damaged easily. Here you could try a bit. But be careful to not stress it too much. The clones from china often have different/cheaper regulators, that will mostly be fried if you overheat them. But they are very cheap.
If powered with 12V, do those output pins still output 5V?– BobaJFETJan 31, 2020 at 22:35
The output pins of the Arduino still use 5V, since the Arduino still works with 5V. The 12V only get regulated down, when you provide them to the Vin pin or the barrel jack. A dedicated voltage regulator takes the 12V and outputs 5V for the Arduino to run on. The only question is, if the voltage regulator can stand the power to dissipate, which depends on the provided input voltage and the drawn current.– chrislJan 31, 2020 at 23:52
Even the 5V Pin provides 5V only :) You should not connect load to it, if Vin is 12V or even higher. Jan 17 at 10:35
The recommended input voltage for the Arduino Nano is 7-12 V, the max. 20 V.
So you could use upto 20 V, but this is indeed not advisable.
What you can do, is to use a so-called step down/boost down converter which converts the voltage back to a voltage that your Arduino Nano can (easily) handle. The voltage drop will be changed into heat, but I guess considering you are using a higher voltage power supply, you are not using battery power.
Note: this is only true for some (cheap?) converters, see the comment of DataFiddler below.
1Recommendable step down converters do not turn the excess voltage into heat, but use a fast switching regulation mechanism with a better efficiency. Jan 17 at 10:25
@DataFiddler I didn't know that, thought it was not advised to have a too much difference between input/output voltage. Jan 17 at 17:50
1That's correct for linear regulators like the one onboard Arduino. Jan 17 at 18:43
If I understand your question you have external devices say lamp, motor, etc. There are several ways of doing it. My preferred way is to use a N-Channel MOSFET where the drain is the output, the source is ground (both the logic and power grounds need to be connected together) and the gate Is connected to the port pin that also has a 10K pull down resistor. You can use the 12V to power the Arduino via Vin as you suggested. Be sure the MOSFET is avalanche rated and will turn on at about 3V or less.
You can do the same thing with an NPN Transistor where the port pin connects to the base with a 300 Ohm resistor (you need to calculate this based on the load), emitter to the connected grounds and the collector is your output.
power components, which require greater than 12VMore specific info leads to better responses.