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Diode and zener-diode as voltage divider?

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exe:
May be the diode is for temperature compensation of the zener.

ArthurDent:
It’s somewhat hard to tell with the little given because we can’t see where these pins go, but here is my S.W.A.G..

The -17 VDC is a rail and that is fixed. In the relay's de-energized state there is the series zener/rectifier for about 5.6 VDC to pin 29 (which I think is a control line to another part of the circuit), so pin 29 can be no more positive than -11.4 VDC or the zener/rectifier will clamp the voltage at that level. If pin 29 tries to go more negative, the 1N4448 will be reverse biased, the zener can not act like a regular rectifier, and the clamp is then effectively out of the circuit.

There is another zener/rectifier for about 15.6 VDC between the -24 VDC rail to pin 29 with the relay de-energized so pin 29 can't go more positive than about -8.4 VDC with the relay de-energized. This means that when the relay is de-energized, pin 29 is held between -11.4 and -8.4 volts.

When the relay is energized the 15 VDC zener is shorted out and pin 29 can't go more negative than -24.6 VDC or more positive than -8.4 VDC.

https://www.eevblog.com/forum/beginners/diode-and-zener-diode-as-voltage-divider/?action=dlattach;attach=722169

madires:
The rails are referenced to different grounds (S COM != DAC COM), and S COM is connected to DAC COM via a 422k and a 10k resistor in series.

ArthurDent:
I realize that there are multiple commons, grounds, or reference points but that doesn’t mean my explanation is incorrect. The zener/rectifier in series is used as a clamp in one direction only. Whether the reference is ‘R’ or ‘A’ or ‘FG’ may be important for operation of the reference but that is what those diodes are used for. The relay contacts show are on K2 and it is energized for negative outputs and de-energized for positive outputs.

After a search of the service manual I found this chart of voltages at various test points and the point in question above is marked as V1(FH) and is shown to have a nominal value of -11.3 VDC and a limit of -8.6 VDC which is pretty close to my guess of  -11.4 to -8.4.

Psi:

--- Quote from: voltampere on May 01, 2019, 03:19:41 pm ---Okay, i did not expect the inductor to have much impact.
2k ohm would definitely help here.
But your datasheet reference gives 1910 typ. and 2380 max, but that is milliohms!

--- End quote ---
Lol digikey are listing spec wrong.
 Says 2.38kOhm

In any case, 6 turns wont have any real resistance.
It would need to be 1000s of turns

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