Russell McMahon wrote:
> 
> >Will a ULN 2803 (8 darlington drivers) protect its inputs from
> back-EMF?
> >In the case of a PIC driving a 2803 which drives the stepper motor
> coils,
> >is there any danger of hurting the pic?
> 
> Careful!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> 
> Yes, the ULN2803 has protection diodes and they all connect to a
> single pin. The normal and simple approach is to connect this to V+.
> However, this is the WRONG thing to do when driving certain loads
> including certain stepper motors. Consdier, when any output tries to
> rise above V+ the diode internal will conduct and clamp that pin to a
>

Tying V+ to Vdd (or Vcc) effectively dumps all the spikes on the 
output of your regulator. I agree - bad idea. A better approach 
is to keep the GND connection, but connect the V+ to a 1.5kE 
tranzorb. (almost) No spike will break it.

-- 
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