Cheap protection...

[Mike (Perth, Western Australia)]

At 11:04 PM 26/3/2000 -0800, you wrote:

>GM uses the 4049 in their older ECMs to buffer "switch" type inputs. 
>They also use a 100K series resistor, a signal diode to VCC, and a small
>filter capacitor (perhaps 1000pF).  The switch inputs also have a 1200
>ohm resistor to either ground or the 12V battery voltage.  The 1200 ohm
>is before the 100K series resistor.  Look at:
>  http://www.cruzers.com/~ludis/1227170sheet3.gif

OK, its good to know there are CMOS devices which diverge a little and
sidestep that particular latchup problem, lets hope all the variants from
different manufacturer's share that feature,

Thanks but, I still don't feel comfortable using Vcc as a sink, a 'dirty'
dedicated sink which bleeds back to Vcc via the reg should be OK though.
Used that on an inverter where we drove the core with a heap of noise to
get maximum efficiency - sometime before EMC issues became a problem...

Tah for that feedback,

Rgds


:) Mike

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