From Newsgroup: sci.electronics.design

john larkin <jl@glen--canyon.com>wrote:

On Sat, 25 Jul 2026 16:28:18 GMT, Jan Panteltje <alien@comet.invalid>

wrote:

john larkin <jl@glen--canyon.com>wrote:

On Sat, 25 Jul 2026 13:50:28 +0200, Lasse Langwadt <llc@fonz.dk>

wrote:

On 7/25/26 09:31, Jan Panteltje wrote:

john larkin <jl@htigct.com>wrote:

https://www.dropbox.com/scl/fi/s8by878zs7a7h4knhr7f4/R360_2V_rail.jpg?rlkey=wbkw49r4oxrute7iy6rmjy792&raw=1

What is wrong with using a LM317?

it'll only source

We could add a dump resistor to a vreg; the load is light.

But we have the opamp and resistors on the BOM already, and the opamp >>>thing is small and precise.

And a 317 is not c-load stable, so we still have a problem.

What do you mean by that, only loaded a by a capacitor?

317's and 1117's can ring or oscillate with all-ceramic cap loads.
They like some ESR.

I have always used tantalum caps, or electrolytic caps.

The output R to adjust input to make 2 V is already a load.

I have used the LM317 with very low AND with very high loads.

This circuit I once found online:
https://panteltje.nl/pub/LM317_switching-regulator-schematic.png

And then did some tests:
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_test_setup_img_2318.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_diagram_img_2316.jpg >> https://panteltje.nl/pub/LM317_switcher/LM317_switcher_no_100nF_img_2320.jpg >> https://panteltje.nl/pub/LM317_switcher/LM317_switcher_final_img_2312.jpg

Anyways never had some instability issues with that chip.

Your pics are unreadable.

Eyes?

It just ocurred to me that I can use a 2.048 volt shunt reg, an
LM4040, and one pullup resistor to make a nice +2V rail. LM4040 is
c-load stable. We have that part in stock.

Max 15 mA is that enough?

Microchip has some voltage reference chips too:
https://www.microchip.com/en-us/products/data-converters/voltage-references

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From Newsgroup: sci.electronics.design

On Sun, 26 Jul 2026 06:27:03 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

john larkin <jl@glen--canyon.com>wrote:

On Sat, 25 Jul 2026 16:28:18 GMT, Jan Panteltje <alien@comet.invalid> >>wrote:

john larkin <jl@glen--canyon.com>wrote:

On Sat, 25 Jul 2026 13:50:28 +0200, Lasse Langwadt <llc@fonz.dk> >>>>wrote:

On 7/25/26 09:31, Jan Panteltje wrote:

john larkin <jl@htigct.com>wrote:

https://www.dropbox.com/scl/fi/s8by878zs7a7h4knhr7f4/R360_2V_rail.jpg?rlkey=wbkw49r4oxrute7iy6rmjy792&raw=1

What is wrong with using a LM317?

it'll only source

We could add a dump resistor to a vreg; the load is light.

But we have the opamp and resistors on the BOM already, and the opamp >>>>thing is small and precise.

And a 317 is not c-load stable, so we still have a problem.

What do you mean by that, only loaded a by a capacitor?

317's and 1117's can ring or oscillate with all-ceramic cap loads.
They like some ESR.

I have always used tantalum caps, or electrolytic caps.

The output R to adjust input to make 2 V is already a load.

I have used the LM317 with very low AND with very high loads.

This circuit I once found online:
https://panteltje.nl/pub/LM317_switching-regulator-schematic.png

And then did some tests:
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_test_setup_img_2318.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_diagram_img_2316.jpg >>> https://panteltje.nl/pub/LM317_switcher/LM317_switcher_no_100nF_img_2320.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_final_img_2312.jpg >>>
Anyways never had some instability issues with that chip.

Your pics are unreadable.

Eyes?

It just ocurred to me that I can use a 2.048 volt shunt reg, an
LM4040, and one pullup resistor to make a nice +2V rail. LM4040 is
c-load stable. We have that part in stock.

Max 15 mA is that enough?

3 ma (1K from +5) will be plenty. It's the reference for a lot of
signals that ride on +2. There's hardly any DC load.

https://www.dropbox.com/scl/fi/cpduqesmn8v664asi9uiu/R360_Block_A14.jpg?rlkey=63ndt86o18mdgua92rdzx3nzi&raw=1

https://www.dropbox.com/scl/fi/dt09oeiay7ue2977gumqd/R360_Tach_A14.jpg?rlkey=ncthqnzpwum6udidum0kgqmht&raw=1

I scribbled the initial schematic and turned it over to an intern to
implement. The kid is so smart he scares us. He can code too!

There were so many things, like ADCs and DACs and analog switches,
that were inhernetly unpolar that it made sense to offset the signal
levels +2 volts.

Microchip has some voltage reference chips too:
https://www.microchip.com/en-us/products/data-converters/voltage-references

Somebody, TI I think, makes a "rail splitter" chip too, but we don't
have it in stock. Adding a new chip to inventory is a nuisance.

The LM4040 family of shunt regs is geat. Lots of people make them. And
you can float them most anywhere and flip ends.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
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From Newsgroup: sci.electronics.design

john larkin <jl@glen--canyon.com> wrote:

On Sun, 26 Jul 2026 06:27:03 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

john larkin <jl@glen--canyon.com>wrote:

On Sat, 25 Jul 2026 16:28:18 GMT, Jan Panteltje <alien@comet.invalid>

wrote:

john larkin <jl@glen--canyon.com>wrote:

On Sat, 25 Jul 2026 13:50:28 +0200, Lasse Langwadt <llc@fonz.dk>

wrote:

On 7/25/26 09:31, Jan Panteltje wrote:

john larkin <jl@htigct.com>wrote:

https://www.dropbox.com/scl/fi/s8by878zs7a7h4knhr7f4/R360_2V_rail.jpg?rlkey=wbkw49r4oxrute7iy6rmjy792&raw=1

What is wrong with using a LM317?

it'll only source

We could add a dump resistor to a vreg; the load is light.

But we have the opamp and resistors on the BOM already, and the opamp >>>>> thing is small and precise.

And a 317 is not c-load stable, so we still have a problem.

What do you mean by that, only loaded a by a capacitor?

317's and 1117's can ring or oscillate with all-ceramic cap loads.
They like some ESR.

I have always used tantalum caps, or electrolytic caps.

The output R to adjust input to make 2 V is already a load.

I have used the LM317 with very low AND with very high loads.

This circuit I once found online:
https://panteltje.nl/pub/LM317_switching-regulator-schematic.png

And then did some tests:
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_test_setup_img_2318.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_diagram_img_2316.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_no_100nF_img_2320.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_final_img_2312.jpg >>>>
Anyways never had some instability issues with that chip.

Your pics are unreadable.

Eyes?

It just ocurred to me that I can use a 2.048 volt shunt reg, an
LM4040, and one pullup resistor to make a nice +2V rail. LM4040 is
c-load stable. We have that part in stock.

Max 15 mA is that enough?

3 ma (1K from +5) will be plenty. It's the reference for a lot of
signals that ride on +2. There's hardly any DC load.

https://www.dropbox.com/scl/fi/cpduqesmn8v664asi9uiu/R360_Block_A14.jpg?rlkey=63ndt86o18mdgua92rdzx3nzi&raw=1

https://www.dropbox.com/scl/fi/dt09oeiay7ue2977gumqd/R360_Tach_A14.jpg?rlkey=ncthqnzpwum6udidum0kgqmht&raw=1

I scribbled the initial schematic and turned it over to an intern to implement. The kid is so smart he scares us. He can code too!

There were so many things, like ADCs and DACs and analog switches,
that were inhernetly unpolar that it made sense to offset the signal
levels +2 volts.

Microchip has some voltage reference chips too:
https://www.microchip.com/en-us/products/data-converters/voltage-references

Somebody, TI I think, makes a "rail splitter" chip too, but we don't
have it in stock. Adding a new chip to inventory is a nuisance.

The LM4040 family of shunt regs is geat. Lots of people make them. And
you can float them most anywhere and flip ends.

John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

The LM4041-ADJ is super useful too. Unlike any other reference except IIRC
the LM385, it looks like a PNP transistorrCoit senses the voltage between ADJ and anode, so to get minimum voltage you tie ADJ to anode. (The others
all work the other way up, so to get minimum voltage you tie ADJ to K.)

That makes it possible to use all the usual or unusual positive-rail shunt reference tricks on the negative rail.

Its max voltage is sort of low, but a cascode fixes that.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
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From Newsgroup: sci.electronics.design

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

john larkin <jl@glen--canyon.com> wrote:

On Sun, 26 Jul 2026 06:27:03 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

john larkin <jl@glen--canyon.com>wrote:

On Sat, 25 Jul 2026 16:28:18 GMT, Jan Panteltje <alien@comet.invalid> >>>> wrote:

john larkin <jl@glen--canyon.com>wrote:

On Sat, 25 Jul 2026 13:50:28 +0200, Lasse Langwadt <llc@fonz.dk>

wrote:

On 7/25/26 09:31, Jan Panteltje wrote:

john larkin <jl@htigct.com>wrote:

https://www.dropbox.com/scl/fi/s8by878zs7a7h4knhr7f4/R360_2V_rail.jpg?rlkey=wbkw49r4oxrute7iy6rmjy792&raw=1

What is wrong with using a LM317?

it'll only source

We could add a dump resistor to a vreg; the load is light.

But we have the opamp and resistors on the BOM already, and the opamp >>>>>> thing is small and precise.

And a 317 is not c-load stable, so we still have a problem.

What do you mean by that, only loaded a by a capacitor?

317's and 1117's can ring or oscillate with all-ceramic cap loads.
They like some ESR.

I have always used tantalum caps, or electrolytic caps.

The output R to adjust input to make 2 V is already a load.

I have used the LM317 with very low AND with very high loads.

This circuit I once found online:
https://panteltje.nl/pub/LM317_switching-regulator-schematic.png

And then did some tests:
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_test_setup_img_2318.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_diagram_img_2316.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_no_100nF_img_2320.jpg
https://panteltje.nl/pub/LM317_switcher/LM317_switcher_final_img_2312.jpg >>>>>
Anyways never had some instability issues with that chip.

Your pics are unreadable.

Eyes?

It just ocurred to me that I can use a 2.048 volt shunt reg, an
LM4040, and one pullup resistor to make a nice +2V rail. LM4040 is
c-load stable. We have that part in stock.

Max 15 mA is that enough?

3 ma (1K from +5) will be plenty. It's the reference for a lot of
signals that ride on +2. There's hardly any DC load.

https://www.dropbox.com/scl/fi/cpduqesmn8v664asi9uiu/R360_Block_A14.jpg?rlkey=63ndt86o18mdgua92rdzx3nzi&raw=1

https://www.dropbox.com/scl/fi/dt09oeiay7ue2977gumqd/R360_Tach_A14.jpg?rlkey=ncthqnzpwum6udidum0kgqmht&raw=1

I scribbled the initial schematic and turned it over to an intern to
implement. The kid is so smart he scares us. He can code too!

There were so many things, like ADCs and DACs and analog switches,
that were inhernetly unpolar that it made sense to offset the signal
levels +2 volts.

Microchip has some voltage reference chips too:
https://www.microchip.com/en-us/products/data-converters/voltage-references >>

Somebody, TI I think, makes a "rail splitter" chip too, but we don't
have it in stock. Adding a new chip to inventory is a nuisance.

The LM4040 family of shunt regs is geat. Lots of people make them. And
you can float them most anywhere and flip ends.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

The LM4041-ADJ is super useful too. Unlike any other reference except IIRC the LM385, it looks like a PNP transistorrCoit senses the voltage between ADJ and

cathode,

so to get minimum voltage you tie ADJ to anode. (The others
all work the other way up, so to get minimum voltage you tie ADJ to K.)

That makes it possible to use all the usual or unusual positive-rail shunt reference tricks on the negative rail.

Its max voltage is sort of low, but a cascode fixes that.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
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From Newsgroup: sci.electronics.design

The circuit is from Fig.9 Low Cost 3A Switching Regulator, Nat Semi App Note 181. It's a sort of 60ish design, hysteretic switcher, relatively low frequency 10-30 kHz range, load dependent of course, noisy and ripply output, no overcurrent protection since it bypasses the '317. It's not a very good candidate for a reference rail.


LM4040 is the answer for the application. You can use enough bypass to get 80dB attenuation of worst-case load-step voltage coupling onto your rail, at which point the shunt regulator can take it down even more. You can bias it with enough current to handle light loads. Main thing is low parts count, especially versus the double differential feedback required to stabilize capacitive loaded OAs.
--
For full context, visit https://www.electrondepot.com/electrodesign/2v-rail-with-an-opamp-4407115-.htm

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