Homebrew PCBs

why do most hbridges and stepper controllers use schottkys?

--- In Homebrew_PCBs@yahoogroups.com, KD5NWA <KD5NWA@c...> wrote:
> Those puppies are faster than grease lightning, they use the
structure used 
> by pin diodes. I use the 1N4007 to switch rf signals by controlling
the bias.
> 
> At 05:31 PM 6/20/2005, you wrote:
> >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
> > > :)
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > What are you using for driver transistors there?
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > Be sure to visit the group home and check for new Links, Files, and
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> >
> >
> >
> >
> >Be sure to visit the group home and check for new Links, Files, and
Photos:
> >http://groups.yahoo.com/group/Homebrew_PCBs
> >
> >If Files or Photos are running short of space, post them here:
> >http://groups.yahoo.com/group/Homebrew_PCBs_Archives/
> >Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >
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> 
> Cecil Bayona
> KD5NWA
> www.qrpradio.com
> 
> 'Never argue with an idiot. They drag you down to their level then
beat you 
> with experience.'