On Thu, Jun 2, 2011 at 5:03 PM, Dwayne Reid wrote: > At 03:06 PM 6/2/2011, Oli Glaser wrote: > >>You have probably already seen it, but is this one any good? Seems to be >>about the only option I could find on there that meets your specs. >>http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=3DIRFIB7= N50APBF-ND >> >> > > Yeah - that was the first part I ran across. =A0Then I found these: > > > > and > > > > This last device is in a plastic TO-247 package but I don't know if > there is exposed metal at the back of the device. =A0Unfortunately, the > datasheet doesn't say. > > Part of the problem is that this is the front end of the project - > now I'm told that I may need as much as 150W dissipation. =A0So - now > I'm looking for larger parts. > > The device will be operated in the linear region for use as a heating > device on a flat aluminum plate. =A0Thus the large dissipation > requirement. =A0Max temperature will be somewhere near 15C or so - this > device is simply used to keep the internal temperature of an outdoor > piece of equipment warm enough to stop it from failing because of > extreme cold. =A0I plan to use a thermistor tightly coupled to the > aluminum plate to avoid excessive transistor temperature. > > Simple project, except for finding the insulated transistor! Why not PWM power to a aluminum-housed resistor? Power FETs designed for linear use are not terribly cheap. For example, look at the SOA graph for your SiHG20N50C. It is for pulsed power, not DC, but extrapolating from 10ms towards DC, it's not at all clear that continuous 150W is OK at any combination of drain current and Vds. Use PWM and you can use a much smaller transistor. Regards, Mark markrages@gmail --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .