----- Original Message ----- From: "Bruce Griffiths" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <[email protected]> Sent: Friday, December 14, 2007 4:36 PM Subject: Re: [time-nuts] Super Regulator links
> John Miles wrote: >> What are some of your favorite low-noise regulators? When I made >> the remark >> about the uA723, I was specifically thinking of its performance >> compared to >> the LT1762. With Cref=5 uF, the uA723's output noise voltage is >> rated at >> 2.5 uV from 100 Hz to 10 kHz. The LT1762, which seems to be among >> Linear's >> quietest parts, is rated at 20 uV from 100 Hz to 100 kHz, with >> external >> bypassing that places most of the noise at lower frequencies. >> Snake oil or >> not, that's 18 dB less noise from the 723. >> >> > This is perhaps a result of using the apparently inherently noisier > bandgap style references which offer significant advantages (lower > minimum input voltage, lower dropout but not necessarily lower > noise) in > lower voltage systems. >> There are various hacks like Wenzel's that can clean up after a >> noisy >> regulator > That particular circuit is only effective over the 100Hz to 10kHz > range. > The brute force darlington buffered RC filter favoured by NIST is > far > more effective when the accompanying disadvantages are acceptable. >> , but if there are quieter fully-integrated solutions out there I'd >> like to hear about them. Posted back to the list in case there are >> other >> views on the subject... >> >> -- john, KE5FX >> > > I havent yet come across any IC that seems to approach the > performance > achievable with a 723. > The next step up without adding too much complexity is perhaps to > use a > 723 with a low pass filtered LM329 reference powered from its > regulated > output. > To improve the ripple rejection you can add an LM317 tracking > preregulator. > Beyond that a well designed discrete regulator is the only way to > improve performance. > Off course if you are building hundreds of circuits and dont want to > take the risk of occasionally striking noisy parts then you either > need > to prescreen parts or buy noisier parts with guaranteed noise specs. > > Lots of so called low noise regulators pop up from time to time but > when > you actually read the datasheet and calculate the output noise for a > 12V > supply and not the 1V or so supply to which the noise specs apply > they > all seem to fall short of the 723's performance. > > Bruce > If the prime energy source is a car battery - or indeed any battery based system - then what other options are there than to use a switcher - at least in the first instance- when generating +5, and plus/minus 12, etc. for precision timing equipment? In this case, I assume the use of separate linear regulators based on the 723, would be the best way to clean up the dc supply rails? DaveB, NZ _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
