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Brians256 · 07-31-2003, 01:07 PM

I have no idea what the specs are on the MOSFETs for this cheapo MSI mobo on my work desktop (I didn't buy it!). They are labeled as BC240. Any ideas?

The DC-DC converter chip on my mobo at work is the Intersil HIP6302 (see PDF spec sheet for details). It runs at about 275KHz, which means that the MOSFETs are being turned on and off (two operations!) 275,000 times a second.

In order to spend at least 90% of the time in a fully on or off state, you have to switch the MOSFET on and then off 20x faster than your PWM frequency (using PWM to generate DC is what the mobo DC-DC chip does). That works out to be about 1/6 of a microsecond (1.8e-7 to be more exact).

Anyway, there are a couple of datasheets out there talking about how to optimize the MOSFETs for these things. The Intersil PDF focuses mostly on RDSon, but other papers talk about the Miller effect, transconductance, and other parameters.

Also, the inductors get hot too. Anyone think I could change them out for higher efficiency?

07-31-2003, 01:07 PM	#6
Brians256 Pro/Staff Join Date: Oct 2001 Location: Klamath Falls, OR Posts: 1,439	I have no idea what the specs are on the MOSFETs for this cheapo MSI mobo on my work desktop (I didn't buy it!). They are labeled as BC240. Any ideas? The DC-DC converter chip on my mobo at work is the Intersil HIP6302 (see PDF spec sheet for details). It runs at about 275KHz, which means that the MOSFETs are being turned on and off (two operations!) 275,000 times a second. In order to spend at least 90% of the time in a fully on or off state, you have to switch the MOSFET on and then off 20x faster than your PWM frequency (using PWM to generate DC is what the mobo DC-DC chip does). That works out to be about 1/6 of a microsecond (1.8e-7 to be more exact). Anyway, there are a couple of datasheets out there talking about how to optimize the MOSFETs for these things. The Intersil PDF focuses mostly on RDSon, but other papers talk about the Miller effect, transconductance, and other parameters. Also, the inductors get hot too. Anyone think I could change them out for higher efficiency?