[sdiy] CA3046 Heater / Substrate Question

[ASSI]

On Thursday 05 May 2016, 20:29:17, Nils Pipenbrinck wrote:
> Q1 is a single NPN. It does not care about the substrate of the array so
> it can be more negative than any array transistor.

Yes, I missed that.

> Q2 and Q3 are part of a 5 NPN transistor array where one emitter is tied
> to the substrate.

In any case, I don't understand why you do not simply put the bases of the 
two array transistors on the same potential or even why you need to produce 
the negative bias voltage with the LED at all (but you said there's an expo 
pair somewhere that may explain it).

Back to your original problem, I think that when Q1 shuts off the potential 
on the substrate just doesn't stay where you think it should be as all the 
current will flow through Q1 - R3 - R4 - R6 anyway the way you have biased 
things.  The actual failure then happens somewhere else in the circuit.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Wavetables for the Terratec KOMPLEXER:
http://Synth.Stromeko.net/Downloads.html#KomplexerWaves