[sdiy] "Substrate Oven" in VCO and VCF again

[Tim Ressel]

I have built two versions of the AN299 VCO: one with a 3046 and one with 
a MAT04. Both worked fine.


--tr


On 4/27/2016 4:23 PM, Nils Pipenbrinck wrote:
> Hi folks.
>
> We had the heated expo-pair topic recently, and since I still have 
> some CA3046 at hand I thought to give it a try.
>
> 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.
>
> Here is what I pulled from the CA3046 data-sheet:
>
>  - Max collector current: 50mA
>  - Max power dissipation per tranny: 300mW
>  - Max collector to substrate voltage: 20V
>
>
> Now let's start with the classic AN-299:
>
>  http://users.ece.gatech.edu/lanterma/sdiy/datasheets/opamp/AN-299.pdf
>
> Here, at an opamp output voltage of 10V I get (by simulation):
>
>   Base Voltage: 6.6V
>   Heater Collector current: 160mA (3 times as much as allowed)
>   Heater Power dissipation around 1.6W (5 times as much as allowed)
>
>
> Doepfer A-110:
>
>   http://www.doepfer.de/a110_s.gif
>
> 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.
>
>
> And then there is Moog Prodigy:
>
>
> http://www.emusic-diy.org/MoogManuals/Prodigy?action=AttachFile&do=get&target=prod9.gif 
>
>
> 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).
>
> Only good old Electronotes S-019 seems to be fine, albeit is is a bit 
> on the weak side with just about 200mW dissipation.
>
>   http://electronotes.netfirms.com/s019.pdf
>
>
> 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?
>
> Best,
>   Nils
>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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