[ARC5] DC-DC: Need a Receiver Bias Supply?

[Bruce Long]

Zener noise
My experience in using zeners in high performance receivers is that a bypass cap across the zener and maybe a rc or LC network between the zener and the load does the job.

It is also important to run the zener at or near its specified test current.  The trick to using zeners as a noise source is to run them current starved.







On Monday, December 23, 2013 11:34 AM, Dennis Monticelli <dennis.monticelli at gmail.com> wrote:
 
Zeners (actually avalanche breakdown diodes) can indeed be noisy.  The
noise varies by type, maker, date code, and phase of the moon.  One thing
they have in common is that the noise is greatest when they are barely
biased into breakdown.  For example a few 10's of uA.  I recommend 1mA and
that gets the bias point up beyond the worse of the noise.  Also, in most
zener diodes the noise really isn't bad at all.  You just need to keep them
away from the front end of a receiver or the pre-amp stage of a quality
audio PA.  And yes, an RC filter definitely helps; just insure you can
accept the extra effective series resistance in your circuit.

My former company made zeners and transistors at one time.

Dennis AE6C


On Mon, Dec 23, 2013 at 4:54 AM, David Stinson <arc5 at ix.netcom.com> wrote:

>
> ----- Original Message ----- From: "Bill Cromwell" <wrcromwell at gmail.com>
>
>  I haven't used zener diodes in a grid circuit as they are reported to be
>> excellent noise generators. I'm reluctant to put a noise generator on a
>> grid and degrade the receiver's noise performance. ...
>>
>> Are there some people who have used a zener diode in a grid circuit (bias
>> supply regulator) without noise problems? Maybe with a filter cap?
>> 73,
>> Bill  KU8H
>>
>
> That's an excellent point I hadn't thought of, Bill.
> One of the reasons I'm so glad to have access to people smarter than me
> :-).
>
> Since this is a little-to-no current bias supply, the small converters
> typically sourcing a Watt or two and already
> regulated, perhaps a simple resistive Voltage divider is a better answer.
>  I'm going to look into that.
>
> 73 and Best for Christmas, Dave AB5S
>
>
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