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2SC1947
Neil:
Attached is a link to the Mitsubishi datasheet for the 2SC1947. Regarding the thermal specifications, the maximum junction temperature is 175C. The thermal impedance is 15C-per-watt junction-to-case, and 150C-per-watt junction-to-ambient. What this means is that the junction temperature will be hotter than the case temperature by 15C times the numer of watts dissipated. For example, if the transistor is dissipating 4 watts, the junction will be 60C hotter than the case temperature. Thus the maximum case temperature should be limited to 175-60 = 115C (pretty darn hot). There will be some thermal impedance between the heatsink and the case, but if well designed, and well attached, it should be only 1 or 2 C/watt, almost negligible in this example. The 150C/watt junction-to-ambient spec means that the metal case of the transistor is not too effective at rediating heat by itself. Without any heatsink, and assuming 1 watt dissipation, the ambient temp would have to be limited to 175-150 = 25C (room temperature). http://www.mitsubishichips.com/data/.../ds/sc1947.pdf -- Tom, N5EG "Neil" wrote in message ... How safe is it to run these without forced air cooling? I've got one as a 1 - 4w driver (feeding a BLW60C) and although has a finned TO5 heatsink, it gets up to 70+ degrees Celsius when running. The Mitsubishi spec says it is safe up to 175 degrees Celsius but am not sure if what I'm doing will do the device damage? Any thoughts anyone? Neil |