Mosfet: best value for money...

[TroelsM]

Hi.

I'm designing some electronic loads in the 250W+ category based on mosfets. I'll need to isolate the heatsink from the mosfets.

The question is: Whats the cheapest way to dissipate 250W?

If a standard TO247 safely can dissipate ~50W then I'll need 5 of these and 5 driver-circuits. (For different reasons I'll need to use a separate driver for each mosfet).

Looking at ISOTOP's (TO-227) it seems that the Tjc, and Tch (case-heatsink) are much lower. As an bonus most (all?) ISOTOP/TO227 cases are isolated, and therefore doesn't need any silicone-pads.

The Questions are:

1) Whats to cheapest way to "buy 250W" as mosfests (250W including de-rating, thermal resistance and all other factors.)

2) Are all ISOTOP/TO227 cases isolated from the mounting-plate?

3) In general: how much more will a TO227 dissipate than a TO247 (including isolation-pads, grease and so on)?

I'm capable of all the basic thermal calculations, but I have no experience designing with TO227, and I'll be grateful for all the help I can get.

I'll be buying all parts new and from big "reliable" dealers, and therefore I'm not interested in offers on your old mosfets...

Give me all your ideas and inputs please.

Regards TroelsM

[mzzj]

1. My guesstimate goes for TO-247. TO247 is a high-volume product and it helps to keep costs down.
2. Yeah, as you can even guess from name ISOtop
3. Depends on what kind of like insulators you use and so on, should be pretty straightforwad to calculate.