At 12:25 AM 4/13/03 +1200, Russell McMahon wrote:
> > Does anyone have any good ideas for protecting a PC parallel port?
> >
> > Other than:
> > - Opto-isolators (need to keep cost and board space lower) or
> > - Series resistor, 5.1v zener to ground and reversed diode to Vcc
> >- ... tiny little T1 or T1.75 lamps in series with each pin...
>
>The lamps sound like a clever and reasonable idea.
>
>Consider using a pair of Schottky diodes per pin, one each to Vdd and
>ground. Similar parts count to zener plus diode but better protection.

The only problem with this is that a large positive over-voltage can raise
Vdd higher than the maximum allowable.

Note: I happen to agree with you.  I'm just pointing out that you may also
require a clamp to stop Vdd from rising.  All depends upon what the static
Vdd load is: if this is a PC and its always consuming 5V at 2A or greater -
no problem.  If its a PIC consuming 2 mA and there is no other load on Vdd
- big problem!

dwayne

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Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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