[sdiy] CA3046 Heater / Substrate Question

[Rick Jansen]

The idea is that the chip is at a constant temperature, i.e. That the ambient temperature does not influence the circuit. You can only increase temperature by heating the array. As long as the chip temperature is above ambient you should be fine. I'd say 40-ish is fine, as long as you don't run the circuit in the Sahara.

rick

> On 06 May 2016, at 15:32, Bert Vermeulen <bl.vermeulen at gmail.com> wrote:
> 
> see datasheet 3046
> Operating Temperature Range −40°C to +85°C 
> 
> 2016-05-06 14:14 GMT+02:00 Steve <sleepy_dog at gmx.de>:
>> I've never done this, but do you really need 65°C?
>> Wouldn't 40..45°C suffice? And you could perhaps put some thermally isolating foam around the IC, if the layout allows it? Then you'd not need to heat so much to be stronger than the surrounding heat I guess.
>> Also... if the thing takes a minute to be operational, I personally couldn't care less, the guitarist also needs to heat up his gear :-)
>>  
>> Steve
>>  
>>  
>> 
>> Von: "Nils Pipenbrinck" <n.pipenbrinck at hilbert-space.de>
>> An: synth-diy at dropmix.xs4all.nl
>> Betreff: Re: [sdiy] CA3046 Heater / Substrate Question
>> [...]
>> 
>> > BTW, "better" is an enemy of "good". What is wrong with just 1
>> > transistor heater?
>> 
>> There is nothing wrong with it, but it's not ideal because the 1
>> transistor heater can only dissipate 300mW. The cooling of the package
>> takes away a big chunk of the energy we put into heating. So reaching
>> tuning stability is slower than it could be.
>> 
>> 
>> I did some measurements yesterday, measuring the Vbe drop directly while
>> heating with two different target temperatures. I faked a bit, left the
>> substrate transistor connected as usual and used one of the matched pair
>> transistors as my second heater:
>> 
>> http://torus.untergrund.net/synth/heater_65deg.png
>> 
>> Here I aim at 65°C. You'll see that the two transistor circuit reaches
>> stability after 4 seconds while the one transistor circuit needs about
>> 100 seconds:
>> 
>> http://torus.untergrund.net/synth/heater_90deg.png
>> 
>> Here I aim at about 90°C. The two trannie method reaches stability after
>> half a minute while the single transistor never reaches it's target
>> temperature and asymptotically drifts to somewhere around 70°
>> 
>> 
>> I think this is a great improvement over the one transistor circuit, and
>> the substrate transistor is unused, so why not use it as a second heater?
>> 
>> 
>> Best,
>> Nils
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