Dwayne Reid wrote:
> He's currently using a IRF1405 N-channel Mosfet with a data-sheet
> rating of RDSon = 5.3 Milli-Ohms.

That sounds pretty good already.

> He's finding that the temperature rise is higher than he likes and is
> therefore looking for a Mosfet with lower RDSon.

So go look, what's the problem?  If I was looking for this I'd check the
usual suspects like IR, Fairchild, and other transistor manufacturers.  I'm
not sure what you're expecting from us short of doing the search for you.

The other thing to consider is paralleling two or more FETs.  5.3mOhms
already sounds pretty good.  To get much better than that probably requires
multiple devices.

> The circuit operates at less than 30 Vdc and he has at least 10V of
> gate drive available.
>
> He'd prefer to stay with the current TO-220 package if possible.

30V at 5.3mOhms is 4.8W, which a TO-220 with reasonable heat sink should be
able to handle well enough.  The real cause is likely not the on resistance
of the FET, but slow switching edges or inadequate heat handling.  Having
something that deals with 30V and 30A dissipate 5W doesn't sound out of
line, so a better description of what exactly the limiting factor is and how
much heat he can really handle is required.  At first glance, things don't
add up.


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