USB / VIN power selection

Hi All,

I have been using what I assume are Arduino clones, and I'm using both the external power, and the USB power.

I am expecting for the external power to be the priority power source, however what I am finding is that the USB supply is dominant. Both sources are being used.

If I just power the Arduino on the USB input, then the 5v supply is providing ~40mA, however when I then add the extenal supply, the 5V drops to 39mA, and the external supply is only providing 1 mA.

Does anyone know why I might be getting this problem occur, or how to correct it?

Thanks, -Steve

Which Arduino?

What do you mean by “then the 5v supply is providing ~40mA”

If you power the Arduino via the Vin that voltage needs to be at least 7V. You need the extra for the regulator drop and only that way the USB power is turned off.