Overvoltage protection for Raspberry Pi with Zener Diode

Question

I am aiming to power 2 Raspberry Pis via their GPIO pins. As there is no protection on GPIO, I would like to add one on my PCB (that will deliver the 5 V thanks to a TRACO, which can deliver 6 A maximum).

I looked on the internet how to do it, but I am a bit lost in the dimensioning part. I am following this tutorial, and I don't know how to deal with point 2 in section 4 in my case:

Calculate the load current that is linked across the circuit of overvoltage safety. This is 50mA for our example discussed above. Other than the load current, biasing current is required by Zener diodes. Therefore, the total current, plus the Zener diode biasing current, should be equal to the load current. For the above-mentioned example, it can be total current=50mA+10mA=60mA.

How can I know the load current of my RPi? Should I use the maximum (2*3 A)? Here is the diagram of what I planning to do.

Thanks in advance.

Answer 1

I did it several years ago, using a Traco to power a Pi via the GPIO connector. There is no overvoltage protection, but I used a pair of power schottky diodes to protect against reverse polarity, like this:

^{simulate this circuit – Schematic created using CircuitLab}

In fact this was a nicety, as with a PCB it's pretty hard to reverse power. If I did it again I'd probably use a MOSFET to protect against reverse. But anyway that design has been in use for several years and survived multiple power cycles without a single RPi failure. The Traco seems to be quite well behaved when used like this (which you would expect it to be, given its intended function).