On Tue, 08 Feb 2011 17:39 -0700, "Vitaliy" wrote:
> Olin Lathrop wrote:
> > Bob Blick wrote:
> >> Anode to positive supply. It points away from the positive supply
> >> toward the base of the transistor.
> >> Resistor is chosen for a milliamp or so, if you can afford that much
> >> wasted current. So figure 4k3 in a five volt circuit.
> >> The amount of current you can absorb is the current through the
> >> resistor multiplied by the gain of the transistor, or about 100
> >> milliamps with
> >> your typical PN2907.
> >> If you share one diode and resistor among several clamp transistors
> >> then one pin or the total of all can clamp 100 milliamps.
> >=20
> > Also add a capacitor to ground at the transistor base.  This will let i=
t
> > clamp short transients to higher currents.
>=20
> Cool. I'll add this to my bag of electronic tricks.

It's especially good for protecting A/D inputs because it isn't as
sloppy as a zener diode - your A/D values don't get compressed as much
when the signal gets near the supply rail.

Bob=20

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