A part we're using in a half-bridge LLC soft-switching DC-DC converter is getting hard to find (STW20NM60, 600 V, 20 A, 0.25 Ω, 192 W), and I need to find a replacement. What parameters do I need to care about?
The first thing to check is the voltage rating. The voltage supplying the converter is nominally 400 V, but can temporarily rise to 460 V or so. 600 V parts should be plenty, right?
According to Selection of MOSFETs in Switch Mode DC-DC Converters, it's probably dissipating around 10 W, so the >140 W power ratings of every TO-247 component I've found seem perfectly adequate.
So how about the current rating? I'm not sure how to calculate this. The AN2492 example circuit is for a 400 W supply, and they use a 14 A FET. I think the actual peak current through them is more like 3 A, though. Why such a big margin?
What other parameters are important? I think a "fast diode" version would be best for reliability and efficiency:
This revolutionary Power MOSFET associates a new vertical structure to the company's strip layout and associates all advantages of reduced on-resistance and fast switching with an intrinsic fast-recovery body diode. It is therefore strongly recommended for bridge topologies, in ZVS phase-shift converters.