Thanks for replies so far. I'm reading references but have to admit
I've not got it yet. Doesn't help that manufacturers are inter-breeding
diodes to make many types of hybrids

> There's really no basis to say something like "Schottky is not
> suitable as a substitute ..." without more context

I believed the context of the OP was comparing a Schottky with
an ultrafast for spike suppression on a DC motor

For example, in some fast recovery diode datasheets, which often
include something like "These rectifier devices are suited for free-
wheeling function in converters and motor control circuits", there is
a "Turn-off switching characteristics" diagram, showing a diode
across an inductor. I've not yet found a Schottky datasheet with
such a diagram

But http://en.wikipedia.org/wiki/Flyback_diode claims

"Schottky diodes are preferred in flyback diode applications, because
they have the lowest forward drop (~0.2 V rather than >0.7 V for low
currents) and the fastest (but still "soft") reverse voltage recovery"

So I'm still none the wiser, unless it's perhaps something to do with
reverse voltage/current capability, which appears to me so far to be
generally less for Schottky than for silicon

Joe

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