[time-nuts] Low noise voltage regulators
magnus at rubidium.dyndns.org
Fri Feb 26 08:49:47 UTC 2010
Bruce Griffiths wrote:
> Garry Thorp wrote:
>> With the 723, you can make the reference noise as low as you want, by
>> heavy RC filtering. This applies whether you use its own reference or a
>> better external reference.
>> The 723 also seems to work quite happily with a feedback capacitor from
>> the output to the inverting input, reducing the AC gain to unity. The
>> output noise will then just be the buffer amplifier's input noise
>> voltage, ~5-6nV/rtHz. This is about 20dB better than most modern
>> 'low-noise' LDOs will do. (I can't remember what the amplifier's noise
>> was like at very low frequencies - it was many years ago at a
>> different company, and I don't have the results any more.)
> Using a capacitor from the output to the inverting input of the error
> amplifier to reduce the high frequency noise gain of the regulator is
> often used in high performance series regulators.
It also reduces the loop bandwidth of the loop and then it becomes
weaker for higher frequency variations, so keen detail in decoupling is
needed. To a certain limit it should work well for a particular design.
The great thing about the 723 is that it has sufficient support for a
number of things in one package, that you very easily can build a
complete PSU with it. None of the features is very unique, but the
combination allows for quick and sound designs for most peoples use.
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