QT PY 5V input diode requirement

[yzfoot]

Pinout blurb says it's important to place a diode between external power and 5V input pin. What is the purpose of this ? Backfeed protector ? Voltage drop ? Other ?

[rpiloverbd]

To protect the board from sudden spikes maybe?

[dastels]

The reason for the diode is to protect against the problem of having an external supply connected when you plug in USB. There's a diode onboard between the 5v line on the USB connector and the 5v pin. By putting one on an external supply you guarantee that only one is providing 5v to the board: whichever is higher.

Dave

[yzfoot]

Dave
Thank you. That explanation of why would be welcomed by many along with the statement that the diode is needed.