7 Nov
2014
7 Nov
'14
10:10 a.m.
On 11/07/2014 09:41 AM, drlegendre . wrote:
Say, one quick question... this has been bugging me.
Exactly how is it that one little TO-220 device can have a Pt (total power
dissipated, right?) of like 75W, when a plain 75W power resistor is
physically many, many times larger and more massive? Does that Pt imply
some serious heat-sinking or something?
And if so, then why aren't all TO-220 power devices in the same range? Why
would some be rated as low as 5-10W, if it's really a matter of sufficient
cooling?
Well, in the first place, it is cooling--a "naked" heatsink-less TO220
isn't going to last very long dissipating 75W--simple thermodynamics
tells you that.
But any transistor is a compromise when it comes to geometry vs.
performance and characteristics. Here's a good paper on power
transistor structure that goes into pretty good detail:
http://elearning.vtu.ac.in/P2/EC42/1.pdf
--Chuck