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Old 28th January 2005, 05:03 PM   #1
claudio is offline claudio  Italy
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Default Reference zener in Series regulator

Hello,
I am building a PSU, series regulator, and I would like to know if there is any advantage in using a multiple zener in series as reference instead of just one. for example: I need a 33v reference, I can use one 33v zener or three 11v in series zeners. Will it make any difference?

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Claudio
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Old 28th January 2005, 05:52 PM   #2
AndrewT is online now AndrewT  Scotland
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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.
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Old 28th January 2005, 09:53 PM   #3
claudio is offline claudio  Italy
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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)?

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Claudio
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Old 29th January 2005, 07:45 AM   #4
AndrewT is online now AndrewT  Scotland
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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.
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Old 29th January 2005, 02:03 PM   #5
claudio is offline claudio  Italy
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Hi,
I read this on TL431: http://www.tnt-audio.com/clinica/reg..._noise1_e.html

I prefer to stay with the zener.

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Claudio
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Old 31st January 2005, 05:36 PM   #6
AndrewT is online now AndrewT  Scotland
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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.
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Old 4th February 2005, 06:38 AM   #7
d3imlay is offline d3imlay  United States
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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.
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Old 4th February 2005, 12:32 PM   #8
claudio is offline claudio  Italy
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Thanks for the infos, d3imlay.

Andrew, I was reading the Super Reg thread, and is it right that the max Vout you can get is 30 V ? At least this is what specified in Peranders super reg. I was thinking in giving a try on the original Jung super reg. II, but I will need 33-36 Vout.

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Claudio
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Old 4th February 2005, 12:55 PM   #9
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Quote:
Originally posted by AndrewT
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.
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Old 4th February 2005, 01:03 PM   #10
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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.
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