[sdiy] Overdriving 4069UB

[René Schmitz]

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