Low noise higher voltage reference?

[Onvinyl]

Hi,
for an open loop regulator I'm still looking for a simple but silent voltage reference for voltages around 18 - 24 V.
I tried a fet as cCS and a resistor but it's a pain to spot the zero tempco of the fet to avoid drift. Still it's not stable enough once it is found. Chaining LED's adds their noise, and it's hard to predict the noise figure of a given LED.
I tried a TL431 which is an option but is there something simpler with lowest possible/reasonable noise for a MC input stage?
Rüdiger

[lineup]

I think TL431 is simple.
It is reasonably good, regarding temp & noise.
For lowest noise, I would use a basic RC filter at output of TL431.

There are 10 Volt precision references from several manufacturers.
Like from www.analog.com & www.ti.com
Ultraprecise 5 Volt there are plenty of


If I needed a precision 18-24 Volt reference
I would take a good 5 Volt ( or 10 Volt reference )
and use a transistor VBE-Multiplier or an Opamp to get the higher voltage.

A basic Op-Amp circuit with gain = x3.6
.. would give you 18.0 Volt from a 5 Volt precision reference.
You could add a filter in this circuit, for reduced noise.

[Christer]

For such high voltages, zeners are probably a very good choice.
http://www.diyaudio.com/forums/showt...008#post417008

[Onvinyl]

Hi Christer,
I recall this thread and your comprehensive measurements, but it slipped my memory that the zener noise was so widley varying between different zeners. You did not measure higher voltage zeners than 12V, I guess? This looks promising.

This was an exceptional input! (and lots of work, I guess...)

thanks,
Rüdiger

[Christer]

I didn't measure higher than 12 V, unfortunately. However, given the noise peak around 6 V and the knowledge about zener and avalanche breakdowns respectively and their relationships to zener voltage, I think it is fairly safe to assume that higher voltage zeners are even less noisy, or at least not worse then 12 V ones. It would be good to verify by measurements, though.