On Wed, 9 Feb 2000 13:34:03 -0000 Michael Rigby-Jones
<mrjones@NORTELNETWORKS.COM> writes:
>         Fansler, David [DFANSLER@AUTOCYTE.COM] wrote:
>
> > After reviewing the circuit mounted to the motor, I did find an
> error - so
> > here is the revised schematic.
> >
> >                       Red
> >                        |
> >             27 ohm     |     .3 ohm power resistor
> > Yel -----/\/\/\/\/\----|----/\/\/\/\/\/--|
> >       |                                  |
> >       |      220 ohm                     |
> >       |----/\/\/\/\/\/----|---Motor------|
> >                           |              |
> >                           |              |
> >                           |              |
> >                         Blue           Green
> >
> > Just in case the ASCII art gets distorted,  there is a yellow wire
> that
> > feeds a 27 ohm and a 220 ohm resistor.
> > The other end of the 27 ohm goes to a red wire and a .3 ohm power
> > resistor.
> > The other end of the 220 resistor goes
> > to one terminal of the motor, and to a Blue wire.  The
> > other end of the .3 ohm power resistor goes to the 2nd terminal of
> the
> > motor and a Green wire.
> >
> >
> This is more than likely a protection scheme to limit the current to
> the
> motor.  The 27R and 220R resistor provide a reference to the control
> circuitry.  By placing these devices in close proximity to the
> motor, any
> voltage drops in supply cables are ignored.  The current limit will
> probably
> become active when the voltage drop across the 0.3R resistor exceeds
> that
> accross the 27R resistor.
>
> I=(V*(27/247))/0.3  where V is the supply voltage.
>
> Your original post asked if this was some kind of feedback circuit.
> Well it
> is in a sense, but it dosen't feedback positional information, only
> current
> draw
>
> Cheers
>
> Mike.

If it does feed back current...then the chip probably calculates the
speed from it..

Andrew
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