[sdiy] MIDI and ESD protection

[Steve Lenham]

On 06/02/2020 08:44, Julian wrote:
> The problem is not that there are no TVS diodes... there are plenty.
> But the clamping voltage is always too high with the low value resistor.
> 
> I just hoped somebody would have encountered the problem before, even if
> it is not really DIY relevant ;)

Clamp to your 3V3 rail (and Ground) with fat Schottky diodes on the 
inboard side of the current-limiting resistor. The Schottkys will 
conduct before the bipolar clamp diodes of your device.

You are only protecting against a small capacitance charged to 3 or 8kV 
(nothing could defend against continuous application of that!), so as 
long as there is a decent amount of reservoir capacitance on the power 
rail then it will be disturbed by a negligible amount.

To be thorough, you would need to specify your resistor so that it is 
capable of handling the energy/power of the ESD event without blowing 
apart. That is not the same as needing to specify it for a continuous 
3/8kV across its terminals though, which would require a big resistor 
indeed.

Hope this helps,

Steve L.
Benden Sound Technology