Re: Electronics gurus please help

--- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> Scott,
>
> The reason for the transistor in the center-tap circuit is increase
> the rate of current removal from the winding at the end of a step.
> Without it, current decays at a very lesiurely rate and severely
> limits the maximum speed of the motor.
>
> Mariss
>
> --- In CAD_CAM_EDM_DRO@y..., "Scott M. Thomas" <scott@d...> wrote:
> > Hmmm. I suppose you could use 6 if you want to. I built one
using
> a PIC
> > and chopped the input to the 4 "end" transistors, worked very
> well. I also
> > used a common current sense resistor, so this simplified it even
> further.
> >
> > I'll have to check out the voltage doubling effect, hadn't
thought
> of that.
> > But this shouldn't have a huge effect on things depending upon
the
> power
> > supply voltage.
> >
> > Thanks
> >
> > Scott
> >
> >
> > -----Original Message-----
> > From: mariss92705 [mailto:mariss92705@y...]
> > Sent: Wednesday, September 11, 2002 3:38 PM
> > To: CAD_CAM_EDM_DRO@y...
> > Subject: [CAD_CAM_EDM_DRO] Re: Electronics gurus please help
> >
> >
> > Scott,
> >
> > If it were an R/L drive you would be correct. The center-tap of
the
> > motor coil would go to the + supply thru a large current limit
> > resistor and the winding ends would have the transistors.
> >
> > Since a unipolar chopping drive was mentioned, 6 transistors are
> > required; the current limit resistor is replaced with a
transistor
> to
> > which pulse width modulation (chopping) is applied. The end
> > transistors still would behave the same.
> >
> > A center-tapped (6-wire motor) winding is a 2:1 step-up
> transformer.
> > because the center tap goes to the + supply, pulling one end wire
> to
> > ground causes 2 times the supply voltage to appear on the other
end.
> >
> > Mariss
> >
> > --- In CAD_CAM_EDM_DRO@y..., "Scott M. Thomas" <scott@d...> wrote:
> > > I count 4 mosfets not 6 for a unipolar drive, did I miss
> > something? And,
> > > because there are half the parts and no high side drivers
> involved,
> > I would
> > > say that a unipolar drive is much simpler. I also don't
> understand
> > why the
> > > voltages would be different.
> > >
> > > Scott
> > >
> > > -----Original Message-----
> > > From: mariss92705 [mailto:mariss92705@y...]
> > > Sent: Wednesday, September 11, 2002 12:59 PM
> > > To: CAD_CAM_EDM_DRO@y...
> > > Subject: [CAD_CAM_EDM_DRO] Re: Electronics gurus please help
> > >
> > >
> > > Hi,
> > >
> > > It takes 6 power transistors and 6 high speed rectifiers to
build
> a
> > > unipolar "chopper", it takes 8 power transistors and 8 high
speed
> > > rectifiers to make a bipolar (full bridge) one.
> > >
> > > The power rectifiers are not across the power transistors in
the
> > > unipolar drive. If MOSFETs are used in a bipolar drive, the
> > > rectifiers are included in the transistors.
> > >
> > > The power transistors "see" twice the power supply voltage in a
> > > unipolar drive. In a bipolar drive, the maximum voltage "seen"
by
> > the
> > > power transistors is equal to the supply voltage.
> > >
> > > The performance of a unipolar drive is about equal to a bipolar
> > drive
> > > running a motor in a half-winding connection.
> > >
> > > A bipolar drive is prefered because it is simpler (when MOSFETs
> are
> > > used) and the circuit voltages are lower.
> > >
> > > Mariss
> > >
> > > --- In CAD_CAM_EDM_DRO@y..., Vajk Fekete <vajk.fekete@o...>
wrote:
> > > >
> > > > question1: is a chopper unipolar driver much worse than a
> chopper
> > > bipolar drive?
> > > >
> > >
> > >
> > >
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