From: pcdhSpamMeSenseless@electrooptical.net
john larkin wrote:
> On Fri, 20 Feb 2026 17:24:39 -0500, Phil Hobbs
> wrote:
>
>> On 2026-02-20 16:21, john larkin wrote:
>>> e`On Fri, 20 Feb 2026 16:05:26 -0500, Phil Hobbs
>>> wrote:
>>>
>>>> On 2026-02-19 21:57, Phil Hobbs wrote:
>>>>> On 2026-02-19 14:16, john larkin wrote:
>>>>>> 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.
>>>>>>>>>
>>>>>>>>> Im thinking of using TCA0372s, but they dont 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.
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> 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.
>>>>>
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>
>>>>> I think that's right. N-type Si substrates certainly exist, but IIRC
>>>>> they aren't common except for some photodiodes. One might wish that the
>>>>> old saying "reverse polarity and use PNPs" were more applicable to
>>>>> low-cost bipolar processes. ;)
>>>>>
>>>>> Re: Regulator
>>>>>
>>>>> After doing something fancier, and then Muntzing it down, I managed to
>>>>> make a reasonable regulator (60ish dB near DC, 70ish from a few
>>>>> kilohertz up) with only 10 cheap parts. No current limit, but oh
>>>>> well--the quiet supply doesn't have to run any external outputs. It
>>>>> piggybacks a bit from a -5V rail generated by an LM337L, which saves a
>>>>> zener diode for biasing the cascode transistor on the LM4041-Adj.
>>>>>
>>>>> I had to fudge the modeal a bit, because none of the LM4041-Adj models I
>>>>> can find actually work in LTspice. (Dunno about pspice.) Even the
>>>>> TLV431 models don't seem to work in AC mode--they don't sink any current
>>>>> for some reason.
>>>>>
>>>>> The LM4041 and LM385 adjustable refs look like a PNP
>>>>> transistor--feedback makes the reference voltage appear between ADJ and
>>>>> cathode, so if you want 1.2V, you connect ADJ to anode. That's super
>>>>> useful for negative supplies, because you can ground the anode and
>>>>> connect the feedback divider between output and ground.
>>>>>
>>>>> The more common TLV431 and its ilk are NPN-style, where the reference
>>>>> voltage appears between ADJ and anode, and connecting ADJ to cathode
>>>>> makes a 1.2V reference.
>>>>>
>>>>> To make the NPN-style work like a PNP, there's a voltage-controlled
>>>>> voltage (e) source to effectively move the reference terminals.
>>>>> Hopefully the AC characteristics of the two chips are similar
>>>>> enough--the mid- and high-frequency behavior is mostly determined by the
>>>>> BJT and passives anyway.
>>>>>
>>>>> Here's the current iteration, including a screen shot. Unfortunately
>>>>> the LM4041 model doesn't seem to work in .ac mode, so it's several .tran
>>>>> simulations instead.
>>>>>
>>>>>
>>>>>
>>>>
>>>> I just did some positive PSR measurements on a TCA0372. Conditions were
>>>> a single +10V supply with 200 mV p-p sinusoidal ripple, courtesy of my
>>>> trusty Siglent arb. I had to use one of our LA-22 100x precision low
>>>> noise lab amps to be able to see the feedthrough on a scope. (I could
>>>> also have broken out the lock-in, of course.)
>>>>
>>>> Amp is wired as a follower, with a 3.3V lithium battery providing its
>>>> input. PSR is calculated as
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