Flyback diode is missing

[sdparkes66]

First time I've seen this article, looks good apart from missing a vital diode to prevent the possibility of a Back EMF pulse causing component damage.

I would suggest using either a 1n4148 or 1n5187 across the fan Diode cathode ( the end with the stripe ) to the + of the fan, and the Anode to the - of the fan.

There is a case for using a MOV for this purpose, but maybe not worth going into for this

Ref : https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction

This fly-back diode should be used when switching any inductive load ( iron bar through coil of wire induces current )

[DurvalMenezes]

Thanks for the heads-up @sdparkes66. I was about to build the circuit and, while reviewing its software's issues, stumbled on this.

I brought this up on the Raspberry forum, got confirmation from another user that a flyback is indeed essential.

The only divergence is re:the appropriate diode, why did you suggest a 1N4148/1N5187 instead of a more common 1N400x? I compared their specs and it seems the main difference is their respective speeds (faster on the 1N5187); IIUTC, the diode's function in this is to short-out the back EMF pulse, thereby killing it before it reaches the RPi pins; is it important that it´s done quicker than a general diode would? And in fact, the Wikipedia page for the 1N400x even mentions that "they are commonly used [...] as freewheeling diodes to protect circuits from inductive loads".

So, is a 1N4148/1N5187 really necessary, or can one use a 1N400x without negative effects?