Jim Manzari wrote:


>Regarding the comments on MOSFETs...Can anyone tell me if there is a
>MOSFET that can control say 100 Amps?  I would like to replace a
>mechanical battery switch with a MOSFET one.  For this I would like a
>minimum of on-resistance, say less than 0.1 ohms if possible.  Of
>course, I realize that careful attention will have to be paid to the
>thermal design aspect.  Does any such device exist?  If so, please
>point me to its data sheet.
>
>TIA
>
>Jim Manzari

Yes, although I do not have any references near by. These typically are
modules which mount several MOSFET die onto a metal back plate and then
provide a sealed package. I have typically just use several parallel
MOSFETs separately strapped to a heat sink. When doing this use separate
gate drive resistors and do not attempt to use the parallel combination
in a linear mode -- it will fail at a much lower than expected current
as current is not shared well unless the parts are fully on.

One project I did had an H-bridge which switch currents on the order of
400Amps at 24VDC at around 24KHz PWM. BTW it is very easy to release the
factory installed smoke from these devices. Make sure the heat sink is
adequate and make sure that the source to drain voltage does not get
exceeded when you open the circuit. Typically this requires good bypass
on the power supply and possibly external catch diodes (the parasitic
MOSFET reverse diodes do fairly well in most cases) and typically double
the source to drain voltage over the voltage you are switching.

Chip Weller