Arduino nano 7V VIN or direct 5V?

Official Hardware Nano Family Classic Nano
1

Hello, I have a project: an Arduino Nano project that controls a 6V submersible pump. In the project I use a 12V 2A adapter, one Arduino Nano, two buck converters, and one IRLZ44N MOSFET.

What I want to ask is this: I feed the 12V 2A power supply into two buck converters via their VIN inputs. One is set to 6V and the other to 7V. The 6V regulator powers the pump, and the pump’s signal control is connected through a MOSFET to the Arduino Nano. The 7V regulator is used to power the Arduino Nano through its VIN pin.

My question is: instead of setting the second regulator to 7V and feeding the Nano via VIN, would it be more reasonable to set it to 5V and power the Nano directly through the 5V pin?
(to reduce heating caused by using VIN during long-term operation)

2

If you think about it, when the Nano is powered from USB, it's putting 5V in through the 5V pin. Okay, there's a diode in the way, but you get the idea. In both cases, just make sure there's nothing that could be a load on the Vin pin so that you don't get voltage flowing backwards through the regulator.

If you wanted to go whole hog, you could unsolder the 5V regulator from the board.

3

I think that 5V pin is an output pin. You are fine with your current setup.

4

should I use a 1N4007 diode?

5

the reason I am using an adapter is that it will be connected to the adapter and remain continuously on. My main concern is about that: after long-term operation, will heating become a problem and cause issues?

6

Not a concern but if you want look up the minimum VIN and set it from 0.5 to 1.0 V above.

7

I wouldn't want to eat the 700mV voltage drop, myself. And if you're thinking "I'll just up the voltage until I get 5V on the output", you're right back where you were feeding 7V in Vin.

8

Does a buck regulator cause a voltage drop of about 700 mV? I also used 470 µF capacitors on both regulators, and additionally there is a 100 nF capacitor between the Arduino 5V and GND pins.

9

No, the 1N4007.

10

For now I did not use a diode on the 5V pin; I was just wondering in case there might be something related to polarity.

11

You can certainly take a look at the Nano schematics and see how they handle 5V from Vusb.

12

I definitely need to focus on this and learn it. Thanks.

13

Do you think your buck will generate less heat than the Nano regulator?
Does your buck meet the same specificaions as a USB power supply?

14

The official Classic Nano has a protection diode in the power circuit to prevent "external" 5V flowing back into the PC.

Powering with 7V is fine and you can still use the USB port.
I have understood from previous topics that the 78M05 on the board does not care about reverse voltage if one powers the Nano on its 5V pin with 5V.

15

It uses the LM1117 and there is no reverse voltage protection

16

I did look at a schematic for the 3.0 version and it specifies the UA78M05.
I've now verified against version 3.2 and it indeed uses the LM1117.

Thanks for the correction.

17

Reverse voltage is also a problem