On Thu, Jan 26, 2012 at 04:53:45PM +0000, alan.b.pearce@stfc.ac.uk wrote:
> > Short of using Schottky diodes for the external diode, in order to guar=
antee they
> > conduct first, what else can be done?
>=20
> For the cost of another couple of diodes, a resistor, and slightly more c=
urrent draw, the clamp diodes could have their own power supply, with the t=
wo diodes forward biased, and the resistor between them.
>=20
> i.e.
> Vcc
> Forward biased diode
> Clamp voltage going to top protection diode
> Resistor (10k or so?)
> Clamp voltage to bottom protection diode
> Forward biased diode
> GND

So by doubling the diodes, it guarantees conduction within the power supply
range instead of allowing the input voltage to wander outside the rails.

I take it the resistor is still a series resistor between the unknown
voltage and the doubled diode pairs?

Looks like a safe bet for a nickels more worth of diodes.

BAJ

>=20
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--=20
Byron A. Jeff
Department Chair: IT/CS/CNET
College of Information and Mathematical Sciences
Clayton State University
http://cims.clayton.edu/bjeff
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