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<div class="moz-cite-prefix"><font face="Helvetica, Arial,
sans-serif">Well, talking about a blast from the past :-)<br>
<br>
It's hardly my circuit though, it's from the AN-299 application
note.<br>
<br>
Heating up the 3046 does not cost much power, it's mass is just
a few grams, and the chip is not hot to the touch.<br>
<br>
This is what I wrote in my documentation:<br>
<br>
1. Heater adjustment<br>
<br>
First make sure the heater is switched off by shorting D2. This
way the base of the heater is grounded and Q5 switched off. Now
measure the voltage present at the +-input of A1. This must be
done with a digital voltmeter (DVM) or another voltmeter with
high input impedance. A regular multimeter will not do. The
voltage measured must be about 650 to 700mV, being the Ube of
the sensor Q3. <br>
<br>
Do not apply power unless the heater is adjusted or switched
off!<br>
<br>
With every degree temperature rise this be drops 1.9mV. In
operation A1 will make Q5 heat up the 3046 array until the
voltage at the plus-input is the same as the (set) voltage at
the minus input of A1. So, you now need to adjust P1 so that the
minus-input of A1 is fed with the voltage that goes with the
elevated temperature. should with the elevated temperature. To
compute this set voltage subtract the temperature rise (in
Celcius) times 1.9mV from the measured voltage. <br>
Example: you want a 30 degrees temperature rise and the measured
Ube is 695mV. The desired drop in Ube therefore is 30x1.9=57mV.
The minus-input of A1 must be set (with P1) to 695-57=638mV. </font><br>
<br>
rick<br>
<br>
On 29/02/2016 01:33, <a class="moz-txt-link-abbreviated" href="mailto:sleepy_dog@gmx.de">sleepy_dog@gmx.de</a> wrote:<br>
</div>
<blockquote cite="mid:56D391EF.4010301@gmx.de" type="cite">
<pre wrap="">Hey there,
first a question about thermistors (this is what "tempco" are, correct?)
In circuits for voltage control of a VCO or VCF which use a tempco, how
much could one deviate with the coefficient, say for instance in Thomay
Henry's newest VCO based on the TLC555 timer? I think it was spec'd at
3500 - what if I could get one with 3470 or 3600 more easily?
Also, I find Rick Jansen's Moog VCF schematic interesting, which uses 3
remaining transistors in a 3046 transistor array as a controlled "oven"
for the NPN matched pair, to get rid of temperature sensitivity.
How come I don't see this kind of solution more often? Is the tempco
solution "better"?
How much current will the "oven" draw, and does this reduce the lifetime
of the IC?
Regards,
Steve
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