Another thing, the power dissipation is going to be big.  At half current,
say 5 amps, you'll be dropping  half of the supply voltage accross the
MOSFET giving 55 * 5 =275 watts.  This will probably be too much for one
device, unless it is some hugely expensive ultra high power item.

In actual fact the resistance of most motor windings is so low I guess
you'll still need the power resistor to limit maximum current so this will
add to the dissipation.

Regards

Mike Rigby-Jones
mrjones@nortelnetworks.com

> ----------
> From:         Jochen Feldhaar[SMTP:jfeldhaa@DETEKTOR.DE]
> Sent:         23 February 1999 12:17
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: MOSFET as a current limiter?
>
> Hi Harrison,
>
> this sounds just like an application for a VMOS FET device. I do not know
> if any of your Drain or source leads will be tied to a fixed potential. If
> this is so, look at the HV082 (also called STHV82...and so on) in the
> Thomson website. These guys do more than 10 Amps and more than 400 Volts
> (but not at the same time...;-).
> Another thing to observe: The gate capacitance of such a device is above 1
> nanofarad, take care when switching, it needs current to alter the
> potential of the gate. The electrode the gate is referenced to is the
> Source!
> There are some other devices available, their codes begin with IRF....
>
> Greetings, hope this was some help,
>
> Jochen DH6FAZ
> jf@detektor.de
>