Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
<stefan_trethan@g...> wrote:
...
> 
> For example, if you look at a relay, most wouldn't argue that a 400x
is  
> not ok.

Agreed. I use them for relays and haven't blown a driver yet (famous
last words).  I think the reason is because there is very little
mechanical energy in the relay.  A motor with permanent magnets acts
as a generator so you have both the field collapse emf and the rotor's
mechanical energy. Given a high speed stop, I'd bet there is more emf
from the mechanical energy than the field collapse.  Again, its not
just about switching speed but about the amount of energy that doesn't
get shunted off.

What I don't know is how to calculate when its safe to use slower
diodes and when not.  So I err on the side of safety.