[sdiy] Temperature stable lin-exp converter with a CA3086 or CA3046

[Ian Fritz]

Hi Tim --

A couple of comments:

Putting insulation around the chip will decrease the power needed for 
temperature control, but it will also slow down the response rate of the 
controller, because the chip's cooling rate will be decreased.

A standard tempco resistor (with resistance proportional to absolute 
temerature over the operating range) will in fact give *exact* compensation 
(cancels the 1/kT factor in the exponent). The idea that compensation is 
correct at one temperature only is a common misconception, unfortunately 
promulgated by some people who should know better.  We've been over this 
point many times here.  :-)

Also remember that temperature stabilization of the converter does not 
correct for other sources of drift, so it only does part of the job.

   Ian


At 11:14 AM 5/27/2002, Tim Ressel wrote:
>Roman,
>
>The design only heats up the internal die of the part
>in question: CA3046 or MAT04. The temperature is not
>that great (40C). I use styrofoam arounf the IC to
>insulate it, increasing stability and further
>protecting outlying circuits.
>
>As for the method of using a tempco: the curves of
>tempco R's and diodes are not an exact match. So over
>temperature you'll still get drift. With the heater
>design, its stable across its entire temp design
>range.
>
>--TR