From: jl@glen--canyon.com
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.
>>>>>>
>>>>>> 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.
>>>>>
>>>>>
>>>>
>>>> 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
>
>PSR = 20*log(p-p ripple/200 mV)
>
>Verdict: Awesome.
>
>Freq Ripple PSR
>
>1 kHz 3 uV 96 dB
>10 kHz 5 uV 92 dB
>20 kHz 14 uV 83 dB
>50 kHz 12 uV 84 dB
>100 kHz 40 uV 74 dB
>200 kHz 500 uV 52 dB
>
>This is a lot better than an LM317.
>
>My 25-cent RLC filter is 100 dB down at 300 kHz, so I should be laughing
>as far as the positive rails are concerned.
>
>Cheers
>
>Phil Hobbs
Are you planning to use the TCA power opamp as the voltage regulator?
That makes sense, since I think you want two regs anyhow.
We did some testing on that amp. The current limiting mostly doesn't
work so you can blow it up. It can be made c-load stable.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
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