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From: Tim Williams on 16 Feb 2010 22:40
<oparr(a)hotmail.com> wrote in message
news:46b86706-7a79-4d41-a104-a443f64785f0(a)b18g2000vba.googlegroups.com...
> What are high power MOSFETs in DPAK and D2PAK packages good for when
> one can get the TO-220 equivalent? Why pay for capability that you
> will never realize? I can see these packages being useful in low power
> applications where the pad on the PCB is a sufficient heatsink and the
> board consists of mainly SMT components.

Because, you aren't paying for the power dissipation. Power ratings are
lies anyway, and the manufacturers admit it. Either IR or Fairchild obtains
the measurement by submerging the device in a nucleated boiling liquid, like
stirred freon, so it will it boil at the slightest increase in temperature,
carrying away a tremendous amount of power. This is BS for three reasons:
1., the case (plastic) generally isn't cooled; 2., the leads are infinite
heatsinks; 3., the heatsink tab itself is never so well thermally coupled.

What you *are* paying for is a really low Rds(on). You can't ever use the
thing at more than 1/3 - 1/4 times rated current, but by doing so, you get
awesome efficiency.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


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