Osborne Vixen - Zenith 7" display t-shooting issues

[Chuck Guzis]

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