Reference zener in Series regulator

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Hi,
yes, you should aim for a minimum dissipation in each zener of about 10% of maximum. This means all should be about the same voltage and if you use many then the total current will be that much higher. You could use a constant current source to help fix your zener voltage and additional filtering to ensure minimum hum and noise from your reference.
regards Andrew T.
 
Thanks Andrew,
since it is a PSU for a pre-amplifier, the current needed will be low. Do you suggest any specific type of zener? Besides the variations with temperature and current, is there something to look specifically in the datasheet of the zeners that indicates its quality (for example less noisy)?

Regards
Claudio
 
Hi,
I would use 400 or 500mW zeners.
If you need more power then you can add a medium power transistor.
Many suppliers sell 1.3W zeners.
All produce noise and most have tempco, I think the zero tempco is around 5v6 but check yourself.
Have you considered a tl431, it is a shunt regulator that has gained a good reputation for being fairly low noise and better performance than a zener. It is also adjustable. There is a thread here somewhere.
regards Andrew T.
 
I seem to recall that absolute temperature stability is acheived with a 4.7v zener. Zeners on either side of this value could drift. so that being true, multiple zeners could provide better temp stability. Regardles, I'd suggest running a hair dryer over it to check for temp stability.
 
AndrewT said:
Hi,
thanks for the reference. Not read it yet but a quick browse was surprising.
See the super reg thread. This achieves noise and hum below -120db and yet uses tl431 as a reference.
So the difference must be in the implementation.
regards Andrew T.
I think that the Super Regulators use the LM329DZ -- the TL431 is a very, very good device, however, and iwll be quieter and more stable than the garden variety zener. Don't view it as simply a voltage reference -- it is actually reference and error amplifier -- and they cost about $0.25.
 
A TL431 will be MUCH lower noise than a straight Zener.

BTW, so-called 'Zener' diodes above approx 5.6V are actually avalanche diodes which have the opposite temperature co-efficient to true Zeners. The crossover between Zener and avalanche action occurs at around 5.6V, so this voltage diode has the lowest temperature drift.

Avalanche diodes have well-defined breakover voltages but generate lots of broadband noise. TL431s and similar use internal 'band-gap' references which are quieter.
 
Hi Peranders,
the pre is a single stage cascode, so the lower the noise the better. The schematic is here: cascode thread

I have to choose between the Jung SR II (the one presented in 2000) that uses the LM329 as you said, or a classic series regulator. I don't need a negative voltage, but 33-36 Vout is needed.
Is the Jung SR II limited to 30 Vout, as your version of it (JSR 01) ?

Regards
Claudio
 
peranders said:
The Jung Regulator itself is limited by max voltage for the used opamp, 36 volt normallly.


if you need really, really low noise you can put 4 references in parallel --there was an application of this in Sep/Oct 2001 QEX in which 3 Thaler VRE305A references and chopper amplifiers were used to create an ultra low noise ref for a DVM --

Maxim has an application note where they use 4 voltage references in series, sum the outputs and divide.
 

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