Expo conv. heater (tomg et al.)

[Bissell, Harry]

You don't need a separate heater power source, but it might put a strain on
the existing power supply, and the traces on the pcb might not like the
additional voltage drops. Decoupling might be a problem as the heater cycles
on and off. So, a separate power source might be a good thing. Keeping the
circiut under a styrofoam cup would isolate the chip from air movement,
which would be a very good thing because even a tiny breeze would change the
thermal environment drastically. The right temperature is above the highest
expected temperature, in use. About 120 degrees F. would be my best guess ?
Not letting the chip overshoot is more important than the actual temp.
Again, the styrofaom cup is a good idea. A not-obvious point is that for
stability and lack of overshoot you want to make the temp. loop faster in
response. (I tried slowing a similar circuit for along time before I
discovered what I was doing wrong.) Harry :-)

> -----Original Message-----
> From:	Steve Varner [SMTP:varner at k-online.com]
> Sent:	Wednesday, January 27, 1999 8:08 PM
> To:	synth-diy
> Subject:	Expo conv. heater (tomg et al.)
> 
> I haven't built a discrete VCO yet (just CEM chips in a kit VCO). I want
> to build a 3046/thermostat circuit, but I have a few questions.
> 
> 1. Do you really need a separate power source for the heater part?
> That's a real pain in the rear. You mentioned regulators and I've seen
> separate supplies mentioned on the web... so that's why I want to know.
> 
> 2. Barry Klein suggested putting the 3046 under a styrofoam cover to
> isolate the chip from heat loss or gain - sort of a chip calorimeter.
> Has anyone done this?
> 
> 3. How do you know where to set the temperature trim on the thermostat?
> I mean, how do you know where to set the temperature and how do you
> measure a silicon chip's temperature accurately anyway? Not having the
> temp too high or low was discussed, so this is important.
> 
> PS, if you folks lived in San Diego instead of 2 degrees from the Arctic
> Circle you might not worry so much about temperature   ;-)
> 
> SV