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<p>I have built two versions of the AN299 VCO: one with a 3046 and
one with a MAT04. Both worked fine.</p>
<p><br>
</p>
<p>--tr<br>
</p>
<br>
<div class="moz-cite-prefix">On 4/27/2016 4:23 PM, Nils Pipenbrinck
wrote:<br>
</div>
<blockquote cite="mid:572149D4.6060602@hilbert-space.de" type="cite">Hi
folks.
<br>
<br>
We had the heated expo-pair topic recently, and since I still have
some CA3046 at hand I thought to give it a try.
<br>
<br>
First I checked a bunch of schematics and I am confused: Pretty
much all of them violate the maximum specs of the CA3046 in one
way or another.
<br>
<br>
Here is what I pulled from the CA3046 data-sheet:
<br>
<br>
- Max collector current: 50mA
<br>
- Max power dissipation per tranny: 300mW
<br>
- Max collector to substrate voltage: 20V
<br>
<br>
<br>
Now let's start with the classic AN-299:
<br>
<br>
<a class="moz-txt-link-freetext" href="http://users.ece.gatech.edu/lanterma/sdiy/datasheets/opamp/AN-299.pdf">http://users.ece.gatech.edu/lanterma/sdiy/datasheets/opamp/AN-299.pdf</a>
<br>
<br>
Here, at an opamp output voltage of 10V I get (by simulation):
<br>
<br>
Base Voltage: 6.6V
<br>
Heater Collector current: 160mA (3 times as much as allowed)
<br>
Heater Power dissipation around 1.6W (5 times as much as
allowed)
<br>
<br>
<br>
Doepfer A-110:
<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.doepfer.de/a110_s.gif">http://www.doepfer.de/a110_s.gif</a>
<br>
<br>
There is no voltage divider in front of the base of the heater
transistor, but the high base resistor somewhat limits the
current. This is of course dependent on the hFE of the transistor.
With simulation I still see the transistor dissipating about 1W
and the current is out of spec as well.
<br>
<br>
<br>
And then there is Moog Prodigy:
<br>
<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.emusic-diy.org/MoogManuals/Prodigy?action=AttachFile&do=get&target=prod9.gif">http://www.emusic-diy.org/MoogManuals/Prodigy?action=AttachFile&do=get&target=prod9.gif</a>
<br>
<br>
I haven't estimated the power dissipation or collector current
(will do so later), but the way Moog connects the substrate would
violate the maximum collector to substrate voltage (24 instead of
20V).
<br>
<br>
Only good old Electronotes S-019 seems to be fine, albeit is is a
bit on the weak side with just about 200mW dissipation.
<br>
<br>
<a class="moz-txt-link-freetext" href="http://electronotes.netfirms.com/s019.pdf">http://electronotes.netfirms.com/s019.pdf</a>
<br>
<br>
<br>
So with all these maximum spec violations these circuits still
work fine in practice. Have I done something stupid while
calculating the collector currents and dissipation or are the
transistors really operated that much out of their spec?
<br>
<br>
Best,
<br>
Nils
<br>
<br>
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<br>
<br>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
--Tim Ressel
Circuit Abbey
<a class="moz-txt-link-abbreviated" href="mailto:timr@circuitabbey.com">timr@circuitabbey.com</a></pre>
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