In a message dated 10/03/2005 01:23:29 GMT Standard Time, craxd1@ezwv.com
writes:
What they did for sensing the heat was use the base to emitter junction of a
transistor as a diode. They mount the tab of the transistor as close to the
finals as possible onto the heatsink. As the heatsink gets hotter, the heat
is transfered into the diode junction thus changing its resistance. This
changing resistance then is used to control the regulator and control thermal
runaway.
The original RCA circuit used a transistor with an extra diode actually on
chip for the sensing. Never quite understood why that didn't become a more
common practice.
73
Peter G3RZP
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