[sdiy] CA3046 Heater / Substrate Question

Nils Pipenbrinck n.pipenbrinck at hilbert-space.de
Thu May 5 20:29:17 CEST 2016

On 05/05/2016 08:08 PM, ASSI wrote:
> On Thursday 05 May 2016, 19:46:28, Nils Pipenbrinck wrote:
>> In my part I generate a small negative voltage using the LED and R5.
>> This puts the base of Q3 at -1.8V and the emitter at roughly -2.4V.
>> That's the most negative point in my circuit.
> Unless your schematics are for a different circuit, the most negative point
> in your circuit seems to be the emitter of Q1 at -15V and that is where the
> substrate should be connected to.

Hi Achim,

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.

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

 From the array I have one matched pair for the expo-converter, one 
diode junction as a temperature sensor and I want to use the remaining 
two as heaters for temperature compensation.

Maybe I should post the whole schematic next time :-)


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