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.
Best,
Will
*********** REPLY SEPARATOR ***********
On 3/9/05 at 7:26 PM G3rzp@aol.com wrote:
>There was quite a good one in the old RCA app notes. The problem is that
>you
>need a zero impedance supply pushing a constant base current into the
>devices, possibly even reducing slightly, as the temperature goes up and
>the Vbe
>goes down, while the Hfe goes up. The best practical approach is a
>constant
>voltage supply that decreases as temperature goes up and so tracks the
>drop in
>Vbe.
>
>73
>
>Peter G3RZP
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