[sdiy] MIDI and ESD protection

Richie Burnett rburnett at richieburnett.co.uk
Thu Feb 6 13:49:25 CET 2020


You could always take a look inside some recent commercial synths from reputable manufacturers that are CE marked, and see what protection components they use at their ports.

I suspect that ferrite beads in series and small value ceramic caps to ground are what you will find. Like in the schematics in that document that Neil linked to. The series inductance slows the rate of rise of the ESD pulse and reduces the peak current. The capacitor then absorbs the energy.

The same LC filter is coincidently also good at stopping RF that's picked up on cables from getting into your piece of kit. So it helps with RI and CI compliance testing too.

I'd second the suggestion to seek professional advice early on during the design stage if this is for a product that needs formal standards compliance. It's much cheaper to design for EMC from the outset than trying to retrofit it later!

-Richie,

Sent from my Xperia SP on O2

---- Julian wrote ----

>
>
>Am 06.02.20 um 11:29 schrieb Neil Johnson:
>> Hi,
>>
>>> I wonder how I should go about protecting a 3.3V MIDI out circuit
>>> against 8kV contact ESD.
>> So HBM @ 8kV then?
>Nope IEC_61000-4-2 Level 4 8kV contact/15kV air discharge
>>> When I use a TVS with 5V working voltage, most of the time I still have
>>> 16-20V clamping voltage over the diode for 8kV contact pulses.
>> Have you measured this?
>This is from the TVS diode datasheets TLP diagrams and some spice
>simulations I did.
>>> With the 3.3V setup I only have a 10Ohm resistor limiting the current to
>>> my UART TX pin.
>>> with a 74hc14 as driver/buffer I can sink +/-20mA, but with 16V at 10 ohm I
>>> have much more to sink.
>> Which make of 74HC14 are you using?  Most versions of the 74HC14 I can
>> find online are designed to cope with HBM ESD strike at 2kV.
>yes thats tru. But a 2kV HBM strike has a peak current of 1.33A, while a
>IEC 2kV strike has 7.5A and the 8kV has 30A.
>So there is a difference.
>See here:
>https://www.onsemi.com/pub/Collateral/TND410-D.PDF
>>> I'm new to ESD. So do I miss something? Is the short pulse time not
>>> enough to fry the internal clamping diodes of a 74HC chip?
>> Are you designing a commercial product?  If so, get proper advice.  If
>> this is just a home synth-diy project I wouldn't worry about it.
>I wouldn't bother for SDIY as well. Never had problems in the last 10 years.
>This is more in the commercial direction, but I want to understand it, too.
>
>cheers,
>Julian
>
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