Electronics > Beginners
zener reference instability
nnills:
Hi all, I just built a zener driver/reference(much like for a LTZ1000) with a 5V zener and a LM358(on a breadboard). It is powered from a 12V plug pack so ignore the top part of the schematic(and the bnc...). I would expect some instability but it varies around 3mV in 2-3 minutes, and the ripple is around 5mV RMS! What could be the problem(of both DC and AC)?
* The cheap zener
* The 12V supply
* The LM358
* The breadboard
* long-ish leads
Conditions: Temp: 22C Vin: 12.225V VinAC: 130uV
Schematic: PDF attachment
Kleinstein:
The filter cap at the input could be rather small, even for just a few mA cold be too small. from 12 V to 9 V is not much to spare for the 7809 and also the LM358 has not much reserves to get some 6 V from a 9 V supply. So maybe power the LM358 directly from the raw 12 V.
The 100 nF cap at the output is not helping the OP and may lead to oscillation
alex-sh:
Power LM358 directly from 12V. How noisy is your 12V PSU? You may need some additionally filtering
LM358 - According to the datasheet - Single Supply: 3V to 32V
nnills:
Firstly, The AC/ripple is now negligible(<1uV). Secondly, on the breadboard there is a 100u cap. But the DC instability is still quite horrible(~3mV).
nnills:
--- Quote ---Power LM358 directly from 12V.
--- End quote ---
It is. I have a plug pack directly connected to the breadboard
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