Expo conv. heater (tomg et al.)

[Tony Clark]

> I had five small pumps on a heatsink to keep my drinks cool in the
> summer. Now what would be rather good is to build one onto the substrate
> in an integrated VCO. Tony Clark was going to do some small VCO
> hybrids... perhaps this is the answer to drifting:-)

   Well I wasn't working with heaters though!  I wasn't happy with the 
current consumption (which everyone knows about) nor the stability of the 
whole temperature circuit in general.  So instead I tried different 
current mirror schemes to see if any of them were more temperature 
resistant.
   The idea was when I "discovered" that heating one side or the other of 
the mirror caused either an up or a down shift in frequency.  So in my 
limited knowledge, it seemd that if you added more transistors to the 
side that made the frequency go opposite of its normal drift (normally 
the frequency rises, I believe, so you'd add (in parallel) a few more 
transistors to the side that would decrease it) it'd balance out.  But it 
doesn't.  It seems to just shift the frequency point where the drift goes 
from positive to negative.
   BTW, when I did my temperature tests, I used a small toaster oven and 
put the whole circuit board inside.  The oven had holes drilled in it to 
place thermometers inside so that the temperature could be measured 
accurately (those ovens are hard to heat up slow!).
   Anyway, I won't even begin to try correlating anything with math.  
Someone else can do it.  :)
   I will most likely try Rene's method again and see if I have better 
luck.

   Tony

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I can't drive (my Moog) 55!         |     The E-Music DIY Archive
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Tony Clark -- clark at andrews.edu     | aupe.phys.andrews.edu/diy_archive
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