[sdiy] Buffer question

[Harry Bissell]

My vote as well... most COMS outputs will be full supply voltage (+15V in my case) so they could use some attenuation anyway,
the series resistor is plenty to protect them. It would be nearly impossible to hit them with such a high negative voltage
through a 1K (or larger) series resistor that you might blow them.  The 'output resistance' of the CMOS is much smaller than the
1K series resistor, in effect you would be trying to drive a voltage divider backwards.  If you feel nervous, add a small series
resistor (maybe 100 ohms) in series with the output, then use clamp diodes, then use the 1K resistor. This would be pretty much totally
bullet-proof0

OK if you are plugging into the mains by mistake, all bets are off...

H^) harry


----- Original Message -----
From: blacet at blacet.com
To: synthdiy diy <synth-diy at dropmix.xs4all.nl>
Sent: Tue, 31 Jan 2012 11:32:25 -0500 (EST)
Subject: Re: [sdiy] Buffer question

The only output protection I have ever used is a 1K resistor. Zero blown
CMOS in the last umpteen years. I'm sure this was arrived at by careful
consideration of the CMOS output structure. Most likey from info from the
manufacturer or Don Lancaster (" CMOS Cookbook").


> Ingo Debus wrote:
>
>> So the opamp would be killed instead of the CMOS chip, no? Is there
>> anything gained?
>
> Op-amps are more robust that CMOS logic gates.  Go look up "SCR Latchup".
>
> Cheers,
> Neil
> --
> Modules and more: http://www.cesyg.com
> Homepage: http://www.njohnson.co.uk
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-- 
Harry Bissell & Nora Abdullah 4eva