Dissipation of transistor in zero degree temperature?!

example:- 2SC1971 has its Maximum Power Dissipation- 12 watt. Inside the datasheet there is a graph of ''Temperature Vs Power dissipation''. In this graph, at 150 degree temperature the transistor dissipates ZERO watt. And at zero degree temperature the transistor dissipates full 12 watt.
If so, can I get full 12 (or almost) watt output by puting my FM Tx (100MHz) into the refrigerator? Haha
(I think the friquency is also related to power dissipation.)

The maximum junction temperature of the 2SC1971 is 150C. This means that, if the ambient temperature is 150c, then the permitted disipation is zero watts, as any power in the junction will raise the temperature above 150C.

The junction to case thermal resistance is 10 degrees per watt. This means that, at 12 watts, the junction temperature will be 120 degrees hotter than the case.

So yes, if you can keep the case temperature below 30C (while it is pumping out 12 watts of heat) then this transistor can safely disipate 12 watts. Barely.

A good, reliable design will have a margin between the max permitted temp and the operating point. I would recomend at least 30 degrees. Of course, more margin is better.

Hi,


Just a quick note here...

You will find that modern CPU's used by overclockers get hotter than normal because they like to try to drive the CPU at a higher frequency that it was originally intended to operate at. This higher frequency means the CPU gets hotter, so they sometimes use a water cooler heat sink. The water cooler heat sink keeps water flowing through the heat sink block and uses a radiator to dissipate the heat in another location away from the CPU.

So the general rule is to try to keep the device as cool as possible meaning a refrigerator would help. As long as you keep the case temperature low enough it works ok.