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PostPosted: Mon Aug 15, 2022 9:34 pm 
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Joined: Tue Jul 05, 2005 7:08 pm
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Location: near Heidelberg, Germany
Hi there,

I am trying to make my design a bit more resilient by adding ESD protection to the VGA output.

The best I could find was the SMS05C like https://www.mouser.de/ProductDetail/Sem ... IgbA%3D%3D
It has 5 protection diodes in a single package, just good for VGA RGB an H/V-sync.

However it's not totally VGA spec (~1V on RGB) but that does not affect my circuit. And I haven't in fact seen any ESD protection circuit for discrete VGA output circuits ...

So, what's your take, is that IC a good choice?

Thanks
André

PS I might even use it for USB even if there are only two lines needed...

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PostPosted: Tue Aug 16, 2022 1:30 am 
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Is this for your '157? Have you ever heard of CMOS outputs getting damaged by static discharge? Certainly it's possible, but far less likely than damaging the inputs with static discharge. I've never heard of it myself. Maybe I haven't been paying close enough attention.

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PostPosted: Tue Aug 16, 2022 2:32 am 
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GARTHWILSON wrote:
Is this for your '157? Have you ever heard of CMOS outputs getting damaged by static discharge? Certainly it's possible, but far less likely than damaging the inputs with static discharge. I've never heard of it myself. Maybe I haven't been paying close enough attention.

A cursory read of that product’s data sheet suggests to me it is intended for use in consumer products, in which things get unplugged and plugged with no thought of avoiding static discharge. Apparently, someone felt there was a need for it, although I've not seen any examples in which such a device would be used to protect a VGA output.

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PostPosted: Tue Aug 16, 2022 5:25 am 
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It's for this VGA output circuit. I thought I'd at least have it there as an option.
https://github.com/fachat/csa_ultracpu/ ... -sch-4.png

I haven't had any damage plugging VGA myself, and mostly heard about the - NMOS - joystick ports of the C64 being damaged. But that may just be because of the protection circuit in the VGA path

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PostPosted: Tue Aug 16, 2022 12:01 pm 
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fachat wrote:
It's for this VGA output circuit. I thought I'd at least have it there as an option.
https://github.com/fachat/csa_ultracpu/ ... -sch-4.png

Sorry, I can’t quite read it. My vision is not able to distinguish some colors on a white background.

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I haven't had any damage plugging VGA myself, and mostly heard about the - NMOS - joystick ports of the C64 being damaged. But that may just be because of the protection circuit in the VGA path

The C-64 and C-128 joystick ports are connected directly to one of the CIAs, which have no ESD protection whatsoever. Adding insult to injury, Commodore, in their cheapness, didn’t place any reverse-biased Schottky diodes on those inputs, making a joystick port zap one of the most frequent causes of C-64 and C-128 failure.

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