> Short of using Schottky diodes for the external diode, in order to guaran=
tee they
> conduct first, what else can be done?

For the cost of another couple of diodes, a resistor, and slightly more cur=
rent draw, the clamp diodes could have their own power supply, with the two=
 diodes forward biased, and the resistor between them.

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


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