[Amps] Regulated AB Bias schematic

[Will Matney]

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 at 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
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
>
>__________ NOD32 1.999 (20050215) Information __________
>
>This message was checked by NOD32 antivirus system.
>http://www.nod32.com