From: jl@glen--canyon.com   
      
   On Thu, 19 Feb 2026 13:50:52 -0500, Phil Hobbs   
    wrote:   
      
   >On 2026-02-18 22:34, john larkin wrote:   
   >> On Wed, 18 Feb 2026 22:12:12 -0000 (UTC), Phil Hobbs   
   >>  wrote:   
   >>   
   >>> Is generally the pits.   
   >>>   
   >>> Anybody got a fave negative regulator with decent PSR?  I need a few rails   
   >>> at no more than 150 mA, and the landscape is bleak.   
   >>>   
   >>> The 337-style ones seem to rule the roost, and they stink.   
   >>>   
   >>> I’m thinking of using TCA0372s, but they don’t have a PSR spec at all.   
   >>>   
   >>> Cheers   
   >>>   
   >>> Phil Hobbs   
   >>   
   >> TPS723xx claims ultra low noise and high PSRR.   
   >>   
   >> I like to put an RC at the input of a lin reg. That improves hf psrr,   
   >> shares some power dissipation, and gives me a way to measure the   
   >> current.   
   >>   
   >> I like to bypass the top resistor in a feedback divider too.   
   >>   
   >>   
   >> John Larkin   
   >> Highland Tech Glen Canyon Design Center   
   >> Lunatic Fringe Electronics   
   >>   
   >   
   >About 20 dB at 10 kHz. :(  They're almost all like that.   
      
   I guess that the substrate is the unreg input on a negative regulator,   
   so it couples into everything.   
      
      
      
      
   >   
   >I've got a four-pole RLC LPF on each input that's -3 dB at 12 kHz and   
   >(theoretically) -100 dB at 300 kHz, before veering off into spherical   
   >meadows of -150 to -220 dB from 1  to 50 MHz. ;)   Simulation shows no   
   >peaking and no overshoot.   
   >   
   >       1 ohm        2 ohm    47u   
   >Supply 0---POLYSWITCH--*--RRRR--*--LLLLLL---*--0  --> vregs   
   >                        |        |           |   
   >        4.7 uF (about  CCC      CCC 4.7uF   CCC   
   >        3.3 @ 15V)     CCC      CCC         CCC 2x 4.7uF   
   >                        |        |           |   
   >                       GND      GND         GND   
   >   
      
   Maybe get some 150 uF polymer caps?   
      
      
   >The caps are all CL31B475KAHNNNE (1206, X7R, 5 cents) and the inductor   
   >is ANR6045T470M (6mm x 6mm, 0.25 ohm ESR, also 5 cents). I'm splurging   
   >on the polyswitch (RXEF030, about 12 cents).  That's seven parts on each   
   >polarity, amortized over all the rails, not counting the RF bypass cap   
   >and TVS (SMBJ15A, about 8 cents).   
   >   
   >The regulators typically have 50 dB-ish rejection near DC, some   
   >considerably less, but then go into the tank above 1 kHz or so, like   
   >20-25 dB at 10 kHz.  (Lasse's one is about 20 dB better there, for an   
   >extra buck per rail).  Discrete front ends have no PSR to speak of, so I   
   >really need > 60 dB from hum frequencies to 10 kHz, and much better   
   >above there.   
   >   
   >So it's looking like a cap multiplier supervised by an LM4041 shunt   
   >reference as the next stage.  That's about a dozen parts per rail, which   
   >isn't brilliant.  It's hard to share them, because two of the rails need   
   >to be near the negative input supply.   
   >   
   >Humph.   
   >   
   >Cheers   
   >   
   >Phil Hobbs   
      
   Maybe make a regulator with an opamp and a mosfet or bipolar follower?   
      
   I'm lucky, I guess, that I don't have to sweat over pennies. Our   
   selling price over parts cost ratio is pretty high. I'd hate to be   
   making stuff where a gang of competitors are battling over price.   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
   --- SoupGate-Win32 v1.05   
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