negative impedance power supply...

[John Larkin]

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.

 

[Tabby]

On Sunday, 16 July 2023 at 21:24:43 UTC+1, John Larkin wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.

Ye olde swinging choke PSUs were a crude version of this.

 

[Lasse Langwadt Christensen]

søndag den 16. juli 2023 kl. 22.24.43 UTC+2 skrev John Larkin:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.

I seem to remember there was once a fad of making power amplifiers with negative output impedance
to compensate for wire and coil resistance

 

[Phil Hobbs]

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.

Might be okay if the negative resistance occurred only at low frequencies,
didn’t look inductive, and had a very limited voltage range.

If the first rule for warships is to stay afloat, for power supplies it’s
to not blow anything up.

It wouldn’t help with wiring inductance, of course.

Phil Hobbs

(Who recently prototyped a 3.3 V regulator that usually runs at about 1A,
but has to handle occasional 6 A transients with < 1 us edges, holding
excursions to <30 mV. )

--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

 

[Dave Platt]

In article <d2k8bidmgecfdko2ihp616h8nvt3fqa8m7@4ax.com>,
John Larkin <xx@yy.com> wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

They exist and they\'re often used to drive DC brush motors which are
intended to maintain a constant speed in the face of a varying load.
The output impedance of the supply is set to negate the DC resistance
of the motor windings.

The tricky bit is that if you get the negative impedance wrong, the
supply will either under-correct or over-correct for the current
demand. Put a load on the motor, and the motor speeds up!

 

[Fred Bloggs]

On Sunday, July 16, 2023 at 4:24:43 PM UTC-4, John Larkin wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.

A more systematic way would be to sense a scaled down mirror of the output current (DC), and apply that to a programmable resistance corresponding your hypothetical line loss to develop a voltage that is scaled and added to your regulator reference.

 

[Fred Bloggs]

On Sunday, July 16, 2023 at 4:24:43 PM UTC-4, John Larkin wrote:

I have seen some buck switchers that had native negative output
impedance but never explored why.

They were using a shit optocoupler to isolate the output voltage sense from the input side regulator.

 

[John Larkin]

On Sun, 16 Jul 2023 16:24:15 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Sunday, July 16, 2023 at 4:24:43?PM UTC-4, John Larkin wrote:


I have seen some buck switchers that had native negative output
impedance but never explored why.

They were using a shit optocoupler to isolate the output voltage sense from the input side regulator.

I\'ve seen it on simple non-isolated buck converters.

 

[John Larkin]

On Sun, 16 Jul 2023 22:00:42 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.



Might be okay if the negative resistance occurred only at low frequencies,
didn’t look inductive, and had a very limited voltage range.

If the first rule for warships is to stay afloat, for power supplies it’s
to not blow anything up.

It wouldn’t help with wiring inductance, of course.

Phil Hobbs

I can\'t predict the user loads. If their loads are resistive, it\'s
easy to compensate the wire resistance and still have net positive
resistance, which would be stable. If the customer load starts with a
big cap, the effective loop resistance could go negative and it will
run away if we over-correct the wire resistance. So we\'d need to limit
the -R bandwidth.

It can be made to work but might be hard to explain to users, how to
progam it. Maybe more trouble than it\'s worth.

(Who recently prototyped a 3.3 V regulator that usually runs at about 1A,
but has to handle occasional 6 A transients with < 1 us edges, holding
excursions to <30 mV. )

 

[whit3rd]

On Sunday, July 16, 2023 at 1:24:43 PM UTC-7, John Larkin wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

Not a great solution, though. If remote sensing is too expensive (wire cost)
just do point-of-load regulation instead. Negative resistance is annoying
if it hits frequencies where you can oscillate, and almost NEVER do people
know what those are.

 

[legg]

On Sun, 16 Jul 2023 13:24:24 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

What\'s expensive about remote sensing - the connex and harness?

RL

 

[Fred Bloggs]

On Sunday, July 16, 2023 at 7:31:08 PM UTC-4, John Larkin wrote:

On Sun, 16 Jul 2023 16:24:15 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Sunday, July 16, 2023 at 4:24:43?PM UTC-4, John Larkin wrote:


I have seen some buck switchers that had native negative output
impedance but never explored why.

They were using a shit optocoupler to isolate the output voltage sense from the input side regulator.
I\'ve seen it on simple non-isolated buck converters.

They had some kind of non-linearity in the voltage feedback with reduced gain at larger amplitude error correction voltages.

A big problem with very long runs of DC power is the power supply output can\'t be dialed up enough without tripping some internal OV protection.

Of course the same people who run into this have no clue beforehand that a 300 ft run might be problematic.

A power supply is \'just\' a simple \'system\' subelement in a \'box.\'

 

[John Larkin]

On Mon, 17 Jul 2023 09:04:12 -0400, legg <legg@nospam.magma.ca> wrote:

On Sun, 16 Jul 2023 13:24:24 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

What\'s expensive about remote sensing - the connex and harness?

RL

Connector pins, circuits in the power supplies, accomodating
connection errors, cable requirements.

 

[Anthony William Sloman]

On Monday, July 17, 2023 at 6:24:43 AM UTC+10, John Larkin wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.

Philips had a standard circuit for running their little DC (brushed) motors at constant rpm more or less independent of load, that did depends on setting it up to offer a negative output impedance to the motor, over a limited range of currents.

The feedback arrangement was frequency limited so that it didn\'t oscillate.

I set one up once, and it worked fine, but we didn\'t put it into production - we ended up going for a vibrating stirrer which was even more of a pest to drive, but was neater and more compact.

--
Bill Sloman, Sydney

 

[Jasen Betts]

On 2023-07-16, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

I did one to control the speed of a DC motor. it worked surprisingly
well. It was a linear regulator as the motor was small and the energy
supply plentiful.

I didn\'t invent this Philips did a similar thing for a portable record
player, I think they used two transistors, I used an op-amp and a
transistor.




--
Jasen.
🇺🇦 Слава Україні

 

[Fred Bloggs]

On Sunday, July 16, 2023 at 4:24:43 PM UTC-4, John Larkin wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.

Write-up linked below describes product line from XP Power PLS600 series. See section on \'addressing remote sensing and calibration\' . Seems much more practical with better performance than a negative impedance approach. Set-up couldn\'t be simpler, and is a good idea. I would be interested in knowing how they sense current without taking too much of hit to efficiency. Maybe efficiency is not a consideration for them. Whatever- they most likely use the more systematic approach previously described.

https://www.digikey.com/en/articles/apply-benchtop-power-supplies-programmability

 

[Clive Arthur]

On 16/07/2023 21:24, John Larkin wrote:

Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.

I haven\'t, but it\'s one technique for powering things at the end of very
long, lossy lines, think oilwell. Only one conductor plus armour, so
remote sensing would need pretty complex telemetry.

As the current drawn increases, so does the supply voltage in an attempt
to keep the downhole voltage within some range.

--
Cheers
Clive

 

[Fred Bloggs]

On Tuesday, July 18, 2023 at 9:04:14 AM UTC-4, Clive Arthur wrote:

On 16/07/2023 21:24, John Larkin wrote:
Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.
I haven\'t, but it\'s one technique for powering things at the end of very
long, lossy lines, think oilwell. Only one conductor plus armour, so
remote sensing would need pretty complex telemetry.

As the current drawn increases, so does the supply voltage in an attempt
to keep the downhole voltage within some range.

I would think they use Power Line Communications (PLC), of which there are bunches of protocols, to transmit a reading of the load voltage back to the source through the DC power cable.

https://www.sciencedirect.com/science/article/pii/S2352484722001421

This should be off-the-shelf availability.

--
Cheers
Clive

 

[John Larkin]

On Tue, 18 Jul 2023 11:17:53 -0000 (UTC), Jasen Betts
<usenet@revmaps.no-ip.org> wrote:

On 2023-07-16, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

I did one to control the speed of a DC motor. it worked surprisingly
well. It was a linear regulator as the motor was small and the energy
supply plentiful.

I didn\'t invent this Philips did a similar thing for a portable record
player, I think they used two transistors, I used an op-amp and a
transistor.

I\'ve done it with motor drivers too. Over-compensate, and the motor
starts a surge-stall cycle a few times a second. I\'d have a similar
problem if the load were low impedance, specifically very capacitive.

It might be interesting to simulate.

 

[Clive Arthur]

On 18/07/2023 15:04, Fred Bloggs wrote:

On Tuesday, July 18, 2023 at 9:04:14 AM UTC-4, Clive Arthur wrote:
On 16/07/2023 21:24, John Larkin wrote:
Has anyone designed a power supply with a negative output impedance?
That could be a viable (ie sellable) low-cost alternative to remote
sensing.

There could be a user-settable parameter, output impedance, that could
be signed. Positive values are \"droop\" and negatives are wire
compensation. Users could take out a few ohms of wire drop without
getting extreme and unstable. The dynamics could get interesting.

I have seen some buck switchers that had native negative output
impedance but never explored why.
I haven\'t, but it\'s one technique for powering things at the end of very
long, lossy lines, think oilwell. Only one conductor plus armour, so
remote sensing would need pretty complex telemetry.

As the current drawn increases, so does the supply voltage in an attempt
to keep the downhole voltage within some range.

I would think they use Power Line Communications (PLC), of which there are bunches of protocols, to transmit a reading of the load voltage back to the source through the DC power cable.

https://www.sciencedirect.com/science/article/pii/S2352484722001421

This should be off-the-shelf availability.

Expensive and vulnerable to shock and high temperatures, to be avoided
unless you need telemetry for some other reasons.

--
Cheers
Clive