Homebrew PCBs

maybe this has been discussed but why not use mosfets instead of the
NPNs?  If you can turn them fully on they will run a lot cooler with
little voltage drop. 

Also, how are you limiting current?  

Will the 1N400x be fast enough to supress the spikes?  I thought one
needed to have schottkys for that.

Reasons to use a PIC (or other micros) is so you can do microstepping
which makes for a much smoother running stepper and you can use PWM
(aka chopping) on the coils to allow higher voltage and thus more
power.  But I'm sure that's all been discussed before.  by the way,
some of the newer 8 pin Z8s have a tansimpedance amp build in for
current sense - perfect for a stepper controller.  I'm thinking of
prototyping with one.

The allegro chips do this pretty well also and allegro is very easy
when it comes to samples.  I'd look at the A3982, it's new and comes
in a soic package which is much easier to solder than the older A3977.
 They'll send 3 units if you ask nice.

Phil

--- In Homebrew_PCBs@yahoogroups.com, Robert Hedan <robert.hedan@v...>
wrote:
> TIP31, I've included a parts list on the schematic in the CNC folder
of the
> Files Section.
> 
> Transformer 24V 1.5A
> 4070 XOR
> 4027 Flip-flop
> MCT6 opto-coupler
> 1K 1/4W resistor
> TIP31 100V 3A
> 1N4002 100V 1A
> Steppers 24V, 36/72ohms, unknown amperage, obsolete model SP57B by
COPAL.
> 
> Robert
> :)
> 
> 
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> 
> 
> 
> What are you using for driver transistors there?
> 
> 
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> 
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