Hi All,

I'm running into an issue with an Arduino project. I have a power supply at 24V going into a DC DC converter (V7809-1000) which is supposed to have a 9V output. This 9V output is tied to the "Vin" pin on an Arduino Uno.

What I've noticed is that if I plug the Arduino Uno into my laptop USB port first, and then power on my 24V supply, the output of the DC DC converter is only 5V. Conversely, if I power on the 24V supply first and then plug the USB in, the output is 9V as expected.

I understand the Arduino has some type of automatic power source switching to determine when to use power from the USB and when to use power from an external source, but I don't think this is the issue here.

Does anyone have any suggestions on why this may be happening? Will a DC DC converter function improperly if it sees a voltage on its output without a voltage on its input?

 

Turns out this issue was solved after putting a reverse bias protection diode in series with the 9V output from the DC DC converter!

 

Thanks for the update. Love learning tips and tricks from other people's experiences. Glad you got it working.