A Good Fet

[Bill]

I ordered a bunch of different fets that had seemed like good candidates after spending a few hours going over various datasheets. I am currently using this fet in my new HH and it has pretty good results. Its the FQU4N50. I was a little concerned about the size (its basically a SMT device with leads) and it's somewhat low current capability. I used an overkill cpu heatsink and it does not even get warm. Rds is kind of high but it helps limit the current. Right now I am at 2.5A going through the coil and all seems well. The Coss curve looks pretty good at 12V VDS. Its only a $1.50 to boot. Here is the datasheet:


http://www.fairchildsemi.com/ds/FQ/FQU4N50.pdf

What do you guys think?

Bill

[Carl-NC]

Looks fine. Current ratings are usually for continuous current, possibly with proper heat sinking. Pulsed current, when time-averaged (or RMS'd), presents a very low equivalent current, so it's usually not an issue even without a heat sink.

- Carl

[Bill]

I am now running it without a sink and there is no problem at all.

[bbsailor]

MOSFETS?

Bill,

What is the value of the damping resistor, R11 using the FQU4N50 MOSFET?

What is the inductance and resistance of your coil?

It looks like this FQU4N50 MOSFET has about 75pf at 12V so your damping resistance value should be a bit higher than when using the IRF740.

Which MOSFET, of the bunch you ordered, worked the best?

bbsailor