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Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
Ha. I like it. I imagine lowering RDSon is a pretty hard task, similar to getting down to 32nm transistors. Putting two switches in parallel seems the clever and cost effective thing to do. I have seem a common MOSFET that can handle almost 700A pulsed, either.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
That's a whole lot of MOSFET! :O I'll check them out for an experiment I have just now that could benefit from the very low Rds(on).
I've seen it done before, though. I built my first hi-fi amp using dual die lateral MOSFETs from Semelab.
The datasheet claimed double the power dissipation, but the case-to-heatsink thermal resistance means that the real world improvement is more like 50%. Probably not so much of an issue in a switched mode design.
Registered Member #816
Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156
What I don’t understand is how or why they put like 100+ amp rated devices in TO-247 packages? The leads or PCB traces will surly get hot enough to melt the solder or fail themselves wont they? Unless there’s typically another way of mounting them that I’m not aware of, unless they expect nobody will use them at more than a third of their maximum rating or something, or perhaps it’s just for repetitive pulse rating.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The legs of a TO220 or TO247 can carry a surprisingly high current density, because they're short, and can lose heat into the PCB (or whatever they're soldered/clamped to)
Also as pointed out, the maximum current listed on the datasheet is thermally limited with a case temperature of 25c and can't be sustained in the real world with a sensibly sized heatsink. For reliable and efficient running, you would use those "100 amp" MOSFETs at maybe 30A RMS.
Registered Member #1334
Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
Alex1M6 wrote ...
Dat gate capacitance...
What do you expect ? its all about compromise - the raw physics involved in getting a low RDSon means a big gate (or two). Gate drivers are well understood and cheap, so Qg should not be a problem if driven "stiffly" by an appropriate chip.
Not very expensive though - about USD 3.60 from Digikey - RS & Farnell don't seem to have them...
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What does a $1,600,000,000 corporation do when it can't figure out how to lower RDSon?
