[Re: thermal tips re expo converters:]

[terry michaels]

Message text written by "Bissell, Harry"
>Correct, no doubt. The techniques I'm suggesting serve to decouple the
external temp changes from reaching or disturbing the expo converter. If we
change ambient and the converter takes a half hour to notice, we win. With
high heat loss, or low heat loss the circuits will achieve steady state.
You
could even turn the heater power down and still stabilize the loop. Which
factor is more significant, good thermal isolation, or ability to bleed off
excess heat ?  Beats me... what does anybody think ? :-)  Harry Bissell
<

Hi Harry:

My vote is for good thermal isolation as the more important parameter.  If
the error loop is designed with the proper gain and frequency constants,
you can achieve a critically damped feedback response, which means the
temperature rise will increase smoothly upon power-up, and upon approaching
the temperature setpoint will quickly slow to a steady state temperature
with no overshoot.  Good thermal isolation will isolate the tranny from
changes in ambient temperature, and also reduce the amount of current
needed to maintain thermal equilibrium.  There is no need to bleed off
excess heat: if the feedback circuit is done right, there is no way the
tranny can get hotter than the setpoint.

Terry Michaels