[sdiy] Overdriving 4069UB

[Harry Bissell Jr]

If he can truly reach 17V on a 15V supply... there is likely substantial
  current there. 18V is the max rating (ok some might say 20V)... so I'd still
  be very concerned.  I agree that raising the input resistor value is prudent...
  but the feedback has to go up as well to keep the same gain.
  
  I might want to let that one run for some weeks in overdrive...
  
  H^) harry

René Schmitz <uzs159 at uni-bonn.de> wrote:  Hi Harry, Seb and all,

Harry Bissell Jr wrote:
> with a 10K resistor in the inout you might be over the edge. I'd be
>   concerned. You might want to use shottky clamp diodes instead
>   of allowinng the CMOS input diodes to clip.

A few mA into the diodes won't hurt. There is a parasitic thyristor 
which might fire when a certain current is exceeded. No need for extra 
shottkys IMO, I'd rather make that resistor a little larger.
Ok, this is stretching the ratings in the datasheet a little, but does 
work.

Btw, this sort of overdrive is explicitly allowed for the 4049 and 4050, 
to be able to do a 15V to 5V crossvolt conversion. Check the datasheet 
on these.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159




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