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questions on zener diode selection (for noise generation project)

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kubuni:
I found the following link for generating a random signal from a reverse bais zener diode.
http://www.ciphersbyritter.com/NOISE/NOISRC.HTM

How can  I calculate or get the min current going through a zener diode for an apply voltage (e.g 9V)?

Also, would there happen to be any zener diodes with a smaller max reverse voltage bais?

Benta:
IIRC, 6.2 V Zeners are preferred for noise generation, as there exists a 'sweet spot" here between Zener and avalanche operation, which provides the most linear noise spectrum.

Your link is a bit strange, as an LM336 is used as "zener", which it is not (it's a bandgap reference). The LM336 is not known for being noisy, exactly the opposite, in fact. The circuit would probably operate just as well measuring the noise from a resistor...

kubuni:
Would there happen to be a better example of a noisy zener circuit I could use?

Benta:
Lots of them around the web, search for "zener noise source".

Here's an example:
http://www.radiohobbyist.org/blog/?p=1884

Zero999:
I was under the impression that higher voltage zener diodes are generally more noisy than lower voltage ones. I know that 6.2V is best for temperature drift but wasn't aware that it gave a better noise spectrum too.

There is a sweet spot, as far as reverse current vs noise is concerned. At very low currents, there will hardly be any nose and a much higher currents there's less noise too. Perhaps someone else here will know more about this?

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