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.

Also add a capacitor to ground at the transistor base.  This will let it
clamp short transients to higher currents.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.