[time-nuts] Linear voltage regulator hints...
kb8tq at n1k.org
Thu Dec 11 19:16:18 EST 2014
Most OCXO’s will meet all spec’s with 1 to 10 mV RMS on the supply lead. That’s mV not uV.
If the noise is flat in a 100 Hz to 100 KHz bandwidth, most will meet their ADEV specs with a mV RMS on the EFC line. Again mV not uV.
The issue is pretty simple:
Things like an EFC or supply FM modulate the OCXO. Phase / time (= what you care about) drops off as 1/f. It’s actually pretty hard to find a reference or DAC that is noisy enough to bother a typical OCXO.
> On Dec 11, 2014, at 6:26 PM, Neil Schroeder <gigneil at gmail.com> wrote:
> So I've done a lot of work in power lately and I can summarize some of this
> The lowest noise LDOs today are the TI TPSa4700/01 up to 36v/1a and about 4
> uVRms noise, and the ADP7154/55 up to 5.5v and 600ma with only *0.9* uVRms
> above 100hz.
> Both feature great PSRR -and in the case of the ADI part don't even
> recommend filter caps at all.
> The TI however does still recommend some capacitance.
> Now most people's next question is how to get their ruby or their
> septuple-oven homebrew design powered by one. The quick answer is an error
> amplifier based ldo balancer for the most accurate distribution of current.
> Also helps with heat.
> Will share a sketch when at my desk next.
> On Thursday, December 11, 2014, Hal Murray <hmurray at megapathdsl.net> wrote:
>>> If the plan is to use a three-terminal regulator after all, I'd suggest
>>> using a low-dropout (LDO) type if the raw input supply is noisy - the
>>> usually have PNP output transistors (for positive regulators), so may
>>> to have poorer HF input ripple rejection than equivalent ones with NPN
>> In this context, what is "high"?
>> Why don't filter caps solve that end of the spectrum?
>> These are my opinions. I hate spam.
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