high-side current sensor...

[Anthony William Sloman]

On Thursday, January 13, 2022 at 3:52:39 PM UTC+11, Flyguy wrote:

On Tuesday, January 11, 2022 at 5:19:34 PM UTC-8, lang...@fonz.dk wrote:
onsdag den 12. januar 2022 kl. 02.10.07 UTC+1 skrev Flyguy:
On Tuesday, January 11, 2022 at 4:25:45 PM UTC-8, jjhu...@gmail.com wrote:
On Monday, January 10, 2022 at 10:26:19 PM UTC-5, jla...@highlandsniptechnology.com wrote:
We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents so that we can
do some sorts of intelligent cutoffs if the eight boards threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.

I\'ve used the ina168 and ina219. Liked the results - easy to use. The ina168 seems to meet your specs.
https://www.digikey.com/catalog/en/partgroup/current-monitor/19066

Just to play with, get the breakout board with I2C interface and connect to arduino or RPI for testing.
J
The AD8479 handles up to 600V common mode. Couple this with a current shunt and you are good to go.
https://www.analog.com/media/en/technical-documentation/data-sheets/ad8479.pdf
also much much more expensive than a current sense amplifier.

Well, you might actually compare prices of a working circuit to the AD8479. I don\'t think you can.

Mouser Electronics in Australia sell the AD8479 for $A11.67, so that part is do-able. A \"working circuit\" is a trifle unspecific - Flyguy won\'t have a clue what that might be, but somebody who knew something about electronics could probably come up with something. I\'m not going to spend time trying - why do stuff for John Larkin for free - but anybody with more sense than Flyguy could probably manage it. It\'s not rocket science.

--
Bill Sloman, Sydney

 

[Three Jeeps]

On Wednesday, January 12, 2022 at 10:57:56 PM UTC-5, jla...@highlandsniptechnology.com wrote:

On Wed, 12 Jan 2022 14:33:48 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

onsdag den 12. januar 2022 kl. 23.20.21 UTC+1 skrev whit3rd:
On Wednesday, January 12, 2022 at 9:00:21 AM UTC-8, Phil Hobbs wrote:
Lasse Langwadt Christensen wrote:

also much much more expensive than a current sense amplifier

Of course five LM358As, five dual 2N3906es, one 24V zener dropper, and
nine quad pack resistors would do it too.
True; that\'s only the first step, though, it just makes a ground-referenced signal,
and next step is an ADC. Trouble is, this is a power signal, with surges expected,
so the sampling due to an ADC is problematic. Since low-power-using modules aren\'t the
most important to get accurate readings on, I\'d note that an eightpack of VCOs
can deliver pulse streams that don\'t ignore any of the abrupt changes in their inputs,
and at the ground-referenced end it just takes counter inputs to digitize the averages
over any convenient period. Ten kilohertz center frequency, half-second average period,
beats the precision of a 1% shunt resistor. Total the counts to get that ninth number...

A bunch of TLC555 with the INAxxx current doing the capacitor charge is the general scheme. You\'d
want the capacitors accurate, and/or adjust counter gate times after calibration, and a regulated
Vdd for the \'555.

Less elaborate, capacitors in parallel with the low-end receive resistors to do averaging.

the Zynq ADC is 1MSPS ...
And kinda nasty. But we can scan fast and do a bit of signal averaging
in the FPGA. I only need the current measurements every millisecond,
to do my shutdown protection logic.

Exponential smoothing (1st order lowpass) is easy

Vout = Vout + (Vin-Vout) * K with smallish K

but my FPGA kids will probably want to do something fancier.
--

I yam what I yam - Popeye

For situations like this I tend to like using a simple moving average filter with the window being variable. If so inclined, could be made adaptive.
First or second order biquads can also be effective. I usually chose direct form one implementations

 

[server]

On Thu, 13 Jan 2022 06:53:28 -0800 (PST), Three Jeeps
<jjhudak4@gmail.com> wrote:

On Wednesday, January 12, 2022 at 10:57:56 PM UTC-5, jla...@highlandsniptechnology.com wrote:
On Wed, 12 Jan 2022 14:33:48 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

onsdag den 12. januar 2022 kl. 23.20.21 UTC+1 skrev whit3rd:
On Wednesday, January 12, 2022 at 9:00:21 AM UTC-8, Phil Hobbs wrote:
Lasse Langwadt Christensen wrote:

also much much more expensive than a current sense amplifier

Of course five LM358As, five dual 2N3906es, one 24V zener dropper, and
nine quad pack resistors would do it too.
True; that\'s only the first step, though, it just makes a ground-referenced signal,
and next step is an ADC. Trouble is, this is a power signal, with surges expected,
so the sampling due to an ADC is problematic. Since low-power-using modules aren\'t the
most important to get accurate readings on, I\'d note that an eightpack of VCOs
can deliver pulse streams that don\'t ignore any of the abrupt changes in their inputs,
and at the ground-referenced end it just takes counter inputs to digitize the averages
over any convenient period. Ten kilohertz center frequency, half-second average period,
beats the precision of a 1% shunt resistor. Total the counts to get that ninth number...

A bunch of TLC555 with the INAxxx current doing the capacitor charge is the general scheme. You\'d
want the capacitors accurate, and/or adjust counter gate times after calibration, and a regulated
Vdd for the \'555.

Less elaborate, capacitors in parallel with the low-end receive resistors to do averaging.

the Zynq ADC is 1MSPS ...
And kinda nasty. But we can scan fast and do a bit of signal averaging
in the FPGA. I only need the current measurements every millisecond,
to do my shutdown protection logic.

Exponential smoothing (1st order lowpass) is easy

Vout = Vout + (Vin-Vout) * K with smallish K

but my FPGA kids will probably want to do something fancier.
--

I yam what I yam - Popeye
For situations like this I tend to like using a simple moving average filter with the window being variable. If so inclined, could be made adaptive.
First or second order biquads can also be effective. I usually chose direct form one implementations

I\'m fond of making digital filters out of exponential lags or
integrators, starting with a classic analog filter and essentially
Spicing it inside the FPGA or uP. My fpga folk really don\'t like that
for some reason. Not enough Zs or something.

They like filters that have a constant of integration in the output,
and assume that nothing ever goes wrong to make it nonzero. A sinc3
filter terrifies me.



--

I yam what I yam - Popeye

 

[Phil Hobbs]

jlarkin@highlandsniptechnology.com wrote:

On Thu, 13 Jan 2022 06:53:28 -0800 (PST), Three Jeeps
jjhudak4@gmail.com> wrote:

On Wednesday, January 12, 2022 at 10:57:56 PM UTC-5,
jla...@highlandsniptechnology.com wrote:
On Wed, 12 Jan 2022 14:33:48 -0800 (PST), Lasse Langwadt
Christensen <lang...@fonz.dk> wrote:

onsdag den 12. januar 2022 kl. 23.20.21 UTC+1 skrev whit3rd:
On Wednesday, January 12, 2022 at 9:00:21 AM UTC-8, Phil
Hobbs wrote:
Lasse Langwadt Christensen wrote:

also much much more expensive than a current sense
amplifier

Of course five LM358As, five dual 2N3906es, one 24V zener
dropper, and nine quad pack resistors would do it too.
True; that\'s only the first step, though, it just makes a
ground-referenced signal, and next step is an ADC. Trouble
is, this is a power signal, with surges expected, so the
sampling due to an ADC is problematic. Since low-power-using
modules aren\'t the most important to get accurate readings
on, I\'d note that an eightpack of VCOs can deliver pulse
streams that don\'t ignore any of the abrupt changes in their
inputs, and at the ground-referenced end it just takes
counter inputs to digitize the averages over any convenient
period. Ten kilohertz center frequency, half-second average
period, beats the precision of a 1% shunt resistor. Total the
counts to get that ninth number...

A bunch of TLC555 with the INAxxx current doing the capacitor
charge is the general scheme. You\'d want the capacitors
accurate, and/or adjust counter gate times after calibration,
and a regulated Vdd for the \'555.

Less elaborate, capacitors in parallel with the low-end
receive resistors to do averaging.

the Zynq ADC is 1MSPS ...
And kinda nasty. But we can scan fast and do a bit of signal
averaging in the FPGA. I only need the current measurements every
millisecond, to do my shutdown protection logic.

Exponential smoothing (1st order lowpass) is easy

Vout = Vout + (Vin-Vout) * K with smallish K

but my FPGA kids will probably want to do something fancier. --

I yam what I yam - Popeye
For situations like this I tend to like using a simple moving
average filter with the window being variable. If so inclined,
could be made adaptive. First or second order biquads can also be
effective. I usually chose direct form one implementations

I\'m fond of making digital filters out of exponential lags or
integrators, starting with a classic analog filter and essentially
Spicing it inside the FPGA or uP. My fpga folk really don\'t like
that for some reason. Not enough Zs or something.

They like filters that have a constant of integration in the output,
and assume that nothing ever goes wrong to make it nonzero. A sinc3
filter terrifies me.

Recursive filters can exhibit limit cycles, though. For a simple
example, if you put a step function into a one-pole IIR lowpass
implemented in fixed point, with a decrement of 0.01 (say), it will get
stuck somewhere around 50 units away from the \'true\' value. That\'s DC,
but it\'s still a limit cycle. Fancier filters can have AC limit cycles.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

;

 

[Phil Hobbs]

John Larkin wrote:

On Wed, 12 Jan 2022 21:00:23 +0100, Klaus Vestergaard Kragelund
klauskvik@hotmail.com> wrote:

On 11/01/2022 17.49, jlarkin@highlandsniptechnology.com wrote:
On Tue, 11 Jan 2022 16:35:10 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

jlarkin@highlandsniptechnology.com> wrote:

We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents so that we can
do some sorts of intelligent cutoffs if the eight boards threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.

Current mirror using pairs of high voltage PNP transistors?

I just posted something like that. It should be good enough. If the
voltage drop across Q2 is pitched a little high, so there is a little
positive measurement offset, we can math that out.



A single current sense amp, but switched to the different sense
resistors with a 50V ana mux. Syncronized to the ADC sampling

We could mux on the high side, with a cheap 4051 type mux. We\'d need a
highside power supply, just a zener, and some way to translate the mux
address lines.

I still like an ordinary 36V dual or quad RRO op amp for this, running
off +26ish and ground, with a good quad pack such as an
ACASA1003S1003P100 (100k, 0.1% absolute, 0.05% relative), 37 cents.

That puts both inputs near +24V with the output near ground. There\'ll
be a little bit of offset, but nothing major, and since you can switch
off all the loads, you can measure it at POST. A little bit of
intentional imbalance will prevent the output from really going to zero,
so the op amp and ADC will both be on-scale at all times.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Thu, 13 Jan 2022 11:26:28 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 12 Jan 2022 21:00:23 +0100, Klaus Vestergaard Kragelund
klauskvik@hotmail.com> wrote:

On 11/01/2022 17.49, jlarkin@highlandsniptechnology.com wrote:
On Tue, 11 Jan 2022 16:35:10 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

jlarkin@highlandsniptechnology.com> wrote:

We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents so that we can
do some sorts of intelligent cutoffs if the eight boards threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.

Current mirror using pairs of high voltage PNP transistors?

I just posted something like that. It should be good enough. If the
voltage drop across Q2 is pitched a little high, so there is a little
positive measurement offset, we can math that out.



A single current sense amp, but switched to the different sense
resistors with a 50V ana mux. Syncronized to the ADC sampling

We could mux on the high side, with a cheap 4051 type mux. We\'d need a
highside power supply, just a zener, and some way to translate the mux
address lines.


I still like an ordinary 36V dual or quad RRO op amp for this, running
off +26ish and ground, with a good quad pack such as an
ACASA1003S1003P100 (100k, 0.1% absolute, 0.05% relative), 37 cents.

That puts both inputs near +24V with the output near ground. There\'ll
be a little bit of offset, but nothing major, and since you can switch
off all the loads, you can measure it at POST. A little bit of
intentional imbalance will prevent the output from really going to zero,
so the op amp and ADC will both be on-scale at all times.

Cheers

Phil Hobbs

I could mux into a single official highside measurement chip. But we\'d
still need to control the mux without slowing down the scan much.

AC couple the mux selects? Or use a fast digital isolator, with
highside power.

If I can actually buy the highside sensor chips for 80 cents each, we
can just use 9 of them.

We plan to put a fuse on the +48 input to each of the power module
boards, to avoid internal forest fires.

Here\'s the box concept:

https://www.dropbox.com/s/8ubv5if7cbnsjzn/P940-8_front.jpg?raw=1






--

I yam what I yam - Popeye

 

[server]

On Thu, 13 Jan 2022 11:16:32 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Thu, 13 Jan 2022 06:53:28 -0800 (PST), Three Jeeps
jjhudak4@gmail.com> wrote:

On Wednesday, January 12, 2022 at 10:57:56 PM UTC-5,
jla...@highlandsniptechnology.com wrote:
On Wed, 12 Jan 2022 14:33:48 -0800 (PST), Lasse Langwadt
Christensen <lang...@fonz.dk> wrote:

onsdag den 12. januar 2022 kl. 23.20.21 UTC+1 skrev whit3rd:
On Wednesday, January 12, 2022 at 9:00:21 AM UTC-8, Phil
Hobbs wrote:
Lasse Langwadt Christensen wrote:

also much much more expensive than a current sense
amplifier

Of course five LM358As, five dual 2N3906es, one 24V zener
dropper, and nine quad pack resistors would do it too.
True; that\'s only the first step, though, it just makes a
ground-referenced signal, and next step is an ADC. Trouble
is, this is a power signal, with surges expected, so the
sampling due to an ADC is problematic. Since low-power-using
modules aren\'t the most important to get accurate readings
on, I\'d note that an eightpack of VCOs can deliver pulse
streams that don\'t ignore any of the abrupt changes in their
inputs, and at the ground-referenced end it just takes
counter inputs to digitize the averages over any convenient
period. Ten kilohertz center frequency, half-second average
period, beats the precision of a 1% shunt resistor. Total the
counts to get that ninth number...

A bunch of TLC555 with the INAxxx current doing the capacitor
charge is the general scheme. You\'d want the capacitors
accurate, and/or adjust counter gate times after calibration,
and a regulated Vdd for the \'555.

Less elaborate, capacitors in parallel with the low-end
receive resistors to do averaging.

the Zynq ADC is 1MSPS ...
And kinda nasty. But we can scan fast and do a bit of signal
averaging in the FPGA. I only need the current measurements every
millisecond, to do my shutdown protection logic.

Exponential smoothing (1st order lowpass) is easy

Vout = Vout + (Vin-Vout) * K with smallish K

but my FPGA kids will probably want to do something fancier. --

I yam what I yam - Popeye
For situations like this I tend to like using a simple moving
average filter with the window being variable. If so inclined,
could be made adaptive. First or second order biquads can also be
effective. I usually chose direct form one implementations

I\'m fond of making digital filters out of exponential lags or
integrators, starting with a classic analog filter and essentially
Spicing it inside the FPGA or uP. My fpga folk really don\'t like
that for some reason. Not enough Zs or something.

They like filters that have a constant of integration in the output,
and assume that nothing ever goes wrong to make it nonzero. A sinc3
filter terrifies me.

Recursive filters can exhibit limit cycles, though. For a simple
example, if you put a step function into a one-pole IIR lowpass
implemented in fixed point, with a decrement of 0.01 (say), it will get
stuck somewhere around 50 units away from the \'true\' value. That\'s DC,
but it\'s still a limit cycle. Fancier filters can have AC limit cycles.

Cheers

Phil Hobbs

If you do the exponential smoothing equation with K=0.01, in 32 bit
scaled integer math, it works fine.

In really dinky machines, the trick is to do

Out = Out + (In-Out)/2^n

which is just a right shift.



--

I yam what I yam - Popeye

 

[Phil Hobbs]

jlarkin@highlandsniptechnology.com wrote:

On Thu, 13 Jan 2022 11:26:28 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 12 Jan 2022 21:00:23 +0100, Klaus Vestergaard Kragelund
klauskvik@hotmail.com> wrote:

On 11/01/2022 17.49, jlarkin@highlandsniptechnology.com wrote:
On Tue, 11 Jan 2022 16:35:10 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

jlarkin@highlandsniptechnology.com> wrote:

We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents so that we can
do some sorts of intelligent cutoffs if the eight boards threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.

Current mirror using pairs of high voltage PNP transistors?

I just posted something like that. It should be good enough. If the
voltage drop across Q2 is pitched a little high, so there is a little
positive measurement offset, we can math that out.



A single current sense amp, but switched to the different sense
resistors with a 50V ana mux. Syncronized to the ADC sampling

We could mux on the high side, with a cheap 4051 type mux. We\'d need a
highside power supply, just a zener, and some way to translate the mux
address lines.


I still like an ordinary 36V dual or quad RRO op amp for this, running
off +26ish and ground, with a good quad pack such as an
ACASA1003S1003P100 (100k, 0.1% absolute, 0.05% relative), 37 cents.

That puts both inputs near +24V with the output near ground. There\'ll
be a little bit of offset, but nothing major, and since you can switch
off all the loads, you can measure it at POST. A little bit of
intentional imbalance will prevent the output from really going to zero,
so the op amp and ADC will both be on-scale at all times.


I could mux into a single official highside measurement chip. But we\'d
still need to control the mux without slowing down the scan much.

AC couple the mux selects? Or use a fast digital isolator, with
highside power.

Run the logic outputs into the emitters of a quad PNP via resistors, and
use the same resistance on the high side. Hang the bases on the logic
supply. Works better at 3.3 or 5 V than lower rails--the logic threshold
is 30% to 70% of VDD.

If I can actually buy the highside sensor chips for 80 cents each, we
can just use 9 of them.

Sure. Press on, next problem.

We plan to put a fuse on the +48 input to each of the power module
boards, to avoid internal forest fires.

Good idea.

Here\'s the box concept:

https://www.dropbox.com/s/8ubv5if7cbnsjzn/P940-8_front.jpg?raw=1

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Lasse Langwadt Christensen]

torsdag den 13. januar 2022 kl. 17.49.33 UTC+1 skrev jla...@highlandsniptechnology.com:

On Thu, 13 Jan 2022 11:26:28 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 12 Jan 2022 21:00:23 +0100, Klaus Vestergaard Kragelund
klau...@hotmail.com> wrote:

On 11/01/2022 17.49, jla...@highlandsniptechnology.com wrote:
On Tue, 11 Jan 2022 16:35:10 +0000, l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

jla...@highlandsniptechnology.com> wrote:

We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents so that we can
do some sorts of intelligent cutoffs if the eight boards threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.

Current mirror using pairs of high voltage PNP transistors?

I just posted something like that. It should be good enough. If the
voltage drop across Q2 is pitched a little high, so there is a little
positive measurement offset, we can math that out.



A single current sense amp, but switched to the different sense
resistors with a 50V ana mux. Syncronized to the ADC sampling

We could mux on the high side, with a cheap 4051 type mux. We\'d need a
highside power supply, just a zener, and some way to translate the mux
address lines.


I still like an ordinary 36V dual or quad RRO op amp for this, running
off +26ish and ground, with a good quad pack such as an
ACASA1003S1003P100 (100k, 0.1% absolute, 0.05% relative), 37 cents.

That puts both inputs near +24V with the output near ground. There\'ll
be a little bit of offset, but nothing major, and since you can switch
off all the loads, you can measure it at POST. A little bit of
intentional imbalance will prevent the output from really going to zero,
so the op amp and ADC will both be on-scale at all times.

Cheers

Phil Hobbs
I could mux into a single official highside measurement chip. But we\'d
still need to control the mux without slowing down the scan much.

AC couple the mux selects? Or use a fast digital isolator, with
highside power.

If I can actually buy the highside sensor chips for 80 cents each, we
can just use 9 of them.

https://lcsc.com/product-detail/span-style-background-color-ff0-Current-span-Sensing-Amplifiers_Diodes-Incorporated-ZXCT1080E5TA_C151589.html

$0.5803 if you buy 100

 

[Lasse Langwadt Christensen]

torsdag den 13. januar 2022 kl. 05.52.39 UTC+1 skrev Flyguy:

On Tuesday, January 11, 2022 at 5:19:34 PM UTC-8, lang...@fonz.dk wrote:
onsdag den 12. januar 2022 kl. 02.10.07 UTC+1 skrev Flyguy:
On Tuesday, January 11, 2022 at 4:25:45 PM UTC-8, jjhu...@gmail.com wrote:
On Monday, January 10, 2022 at 10:26:19 PM UTC-5, jla...@highlandsniptechnology.com wrote:
We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents so that we can
do some sorts of intelligent cutoffs if the eight boards threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.



--

I yam what I yam - Popeye
I\'ve used the ina168 and ina219. Liked the results - easy to use. The ina168 seems to meet your specs.
https://www.digikey.com/catalog/en/partgroup/current-monitor/19066

Just to play with, get the breakout board with I2C interface and connect to arduino or RPI for testing.
J
The AD8479 handles up to 600V common mode. Couple this with a current shunt and you are good to go.
https://www.analog.com/media/en/technical-documentation/data-sheets/ad8479.pdf
also much much more expensive than a current sense amplifier
Well, you might actually compare prices of a working circuit to the AD8479. I don\'t think you can.

the AD8479 is about 10x the price of a part made for the purpose

 

[Phil Hobbs]

jlarkin@highlandsniptechnology.com wrote:

On Thu, 13 Jan 2022 11:16:32 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Thu, 13 Jan 2022 06:53:28 -0800 (PST), Three Jeeps
jjhudak4@gmail.com> wrote:

On Wednesday, January 12, 2022 at 10:57:56 PM UTC-5,
jla...@highlandsniptechnology.com wrote:
On Wed, 12 Jan 2022 14:33:48 -0800 (PST), Lasse Langwadt
Christensen <lang...@fonz.dk> wrote:

onsdag den 12. januar 2022 kl. 23.20.21 UTC+1 skrev whit3rd:
On Wednesday, January 12, 2022 at 9:00:21 AM UTC-8, Phil
Hobbs wrote:
Lasse Langwadt Christensen wrote:

also much much more expensive than a current sense
amplifier

Of course five LM358As, five dual 2N3906es, one 24V zener
dropper, and nine quad pack resistors would do it too.
True; that\'s only the first step, though, it just makes a
ground-referenced signal, and next step is an ADC. Trouble
is, this is a power signal, with surges expected, so the
sampling due to an ADC is problematic. Since low-power-using
modules aren\'t the most important to get accurate readings
on, I\'d note that an eightpack of VCOs can deliver pulse
streams that don\'t ignore any of the abrupt changes in their
inputs, and at the ground-referenced end it just takes
counter inputs to digitize the averages over any convenient
period. Ten kilohertz center frequency, half-second average
period, beats the precision of a 1% shunt resistor. Total the
counts to get that ninth number...

A bunch of TLC555 with the INAxxx current doing the capacitor
charge is the general scheme. You\'d want the capacitors
accurate, and/or adjust counter gate times after calibration,
and a regulated Vdd for the \'555.

Less elaborate, capacitors in parallel with the low-end
receive resistors to do averaging.

the Zynq ADC is 1MSPS ...
And kinda nasty. But we can scan fast and do a bit of signal
averaging in the FPGA. I only need the current measurements every
millisecond, to do my shutdown protection logic.

Exponential smoothing (1st order lowpass) is easy

Vout = Vout + (Vin-Vout) * K with smallish K

but my FPGA kids will probably want to do something fancier. --

I yam what I yam - Popeye
For situations like this I tend to like using a simple moving
average filter with the window being variable. If so inclined,
could be made adaptive. First or second order biquads can also be
effective. I usually chose direct form one implementations

I\'m fond of making digital filters out of exponential lags or
integrators, starting with a classic analog filter and essentially
Spicing it inside the FPGA or uP. My fpga folk really don\'t like
that for some reason. Not enough Zs or something.

They like filters that have a constant of integration in the output,
and assume that nothing ever goes wrong to make it nonzero. A sinc3
filter terrifies me.

Recursive filters can exhibit limit cycles, though. For a simple
example, if you put a step function into a one-pole IIR lowpass
implemented in fixed point, with a decrement of 0.01 (say), it will get
stuck somewhere around 50 units away from the \'true\' value. That\'s DC,
but it\'s still a limit cycle. Fancier filters can have AC limit cycles.

Cheers

Phil Hobbs

If you do the exponential smoothing equation with K=0.01, in 32 bit
scaled integer math, it works fine.

But Vout - Vin doesn\'t decay all the way to zero. With lots of bits and
intelligent scaling, you may not care, of course.

In really dinky machines, the trick is to do

Out = Out + (In-Out)/2^n

which is just a right shift.

Sure.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Thu, 13 Jan 2022 09:15:01 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

torsdag den 13. januar 2022 kl. 17.49.33 UTC+1 skrev jla...@highlandsniptechnology.com:
On Thu, 13 Jan 2022 11:26:28 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 12 Jan 2022 21:00:23 +0100, Klaus Vestergaard Kragelund
klau...@hotmail.com> wrote:

On 11/01/2022 17.49, jla...@highlandsniptechnology.com wrote:
On Tue, 11 Jan 2022 16:35:10 +0000, l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

jla...@highlandsniptechnology.com> wrote:

We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents so that we can
do some sorts of intelligent cutoffs if the eight boards threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.

Current mirror using pairs of high voltage PNP transistors?

I just posted something like that. It should be good enough. If the
voltage drop across Q2 is pitched a little high, so there is a little
positive measurement offset, we can math that out.



A single current sense amp, but switched to the different sense
resistors with a 50V ana mux. Syncronized to the ADC sampling

We could mux on the high side, with a cheap 4051 type mux. We\'d need a
highside power supply, just a zener, and some way to translate the mux
address lines.


I still like an ordinary 36V dual or quad RRO op amp for this, running
off +26ish and ground, with a good quad pack such as an
ACASA1003S1003P100 (100k, 0.1% absolute, 0.05% relative), 37 cents.

That puts both inputs near +24V with the output near ground. There\'ll
be a little bit of offset, but nothing major, and since you can switch
off all the loads, you can measure it at POST. A little bit of
intentional imbalance will prevent the output from really going to zero,
so the op amp and ADC will both be on-scale at all times.

Cheers

Phil Hobbs
I could mux into a single official highside measurement chip. But we\'d
still need to control the mux without slowing down the scan much.

AC couple the mux selects? Or use a fast digital isolator, with
highside power.

If I can actually buy the highside sensor chips for 80 cents each, we
can just use 9 of them.

https://lcsc.com/product-detail/span-style-background-color-ff0-Current-span-Sensing-Amplifiers_Diodes-Incorporated-ZXCT1080E5TA_C151589.html

$0.5803 if you buy 100

Nice. We could buy 1000.

We could do the dual layout to have a stuffing option. That\'s life
these days.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon

 

[whit3rd]

On Wednesday, January 12, 2022 at 11:13:36 PM UTC-8, bill....@ieee.org wrote:

On Thursday, January 13, 2022 at 3:52:39 PM UTC+11, Flyguy wrote:

The AD8479 handles up to 600V common mode. Couple this with a current shunt and you are good to go.
https://www.analog.com/media/en/technical-documentation/data-sheets/ad8479.pdf
also much much more expensive than a current sense amplifier.

Well, you might actually compare prices of a working circuit to the AD8479. I don\'t think you can.
Mouser Electronics in Australia sell the AD8479 for $A11.67, so that part is do-able.

Something like LM331 is half the price, and doesn\'t tie up ADCs, because frequency counting
is already logic-level info. If overhead counts, I\'ve always liked frequency conversion because
it allows the CPU to tailor the resolution and response, with minimal latency at each status
check. Think of a motor-bearing analysis, accumulating the harmonics of the rumble
of rotating machines, for days... a big digital accumulator and phase-locking works great
with voltage-frequency conversion.

 

[piglet]

On 13/01/2022 18:38, John Larkin wrote:

On Thu, 13 Jan 2022 09:15:01 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

torsdag den 13. januar 2022 kl. 17.49.33 UTC+1 skrev jla...@highlandsniptechnology.com:
On Thu, 13 Jan 2022 11:26:28 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 12 Jan 2022 21:00:23 +0100, Klaus Vestergaard Kragelund
klau...@hotmail.com> wrote:

On 11/01/2022 17.49, jla...@highlandsniptechnology.com wrote:
On Tue, 11 Jan 2022 16:35:10 +0000, l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

jla...@highlandsniptechnology.com> wrote:

We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents so that we can
do some sorts of intelligent cutoffs if the eight boards threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.

Current mirror using pairs of high voltage PNP transistors?

I just posted something like that. It should be good enough. If the
voltage drop across Q2 is pitched a little high, so there is a little
positive measurement offset, we can math that out.



A single current sense amp, but switched to the different sense
resistors with a 50V ana mux. Syncronized to the ADC sampling

We could mux on the high side, with a cheap 4051 type mux. We\'d need a
highside power supply, just a zener, and some way to translate the mux
address lines.


I still like an ordinary 36V dual or quad RRO op amp for this, running
off +26ish and ground, with a good quad pack such as an
ACASA1003S1003P100 (100k, 0.1% absolute, 0.05% relative), 37 cents.

That puts both inputs near +24V with the output near ground. There\'ll
be a little bit of offset, but nothing major, and since you can switch
off all the loads, you can measure it at POST. A little bit of
intentional imbalance will prevent the output from really going to zero,
so the op amp and ADC will both be on-scale at all times.

Cheers

Phil Hobbs
I could mux into a single official highside measurement chip. But we\'d
still need to control the mux without slowing down the scan much.

AC couple the mux selects? Or use a fast digital isolator, with
highside power.

If I can actually buy the highside sensor chips for 80 cents each, we
can just use 9 of them.

https://lcsc.com/product-detail/span-style-background-color-ff0-Current-span-Sensing-Amplifiers_Diodes-Incorporated-ZXCT1080E5TA_C151589.html

$0.5803 if you buy 100

Nice. We could buy 1000.

We could do the dual layout to have a stuffing option. That\'s life
these days.

Yes, I suggested the related ZXCT1084 up thread a while back.

If you\'re in the mood to mux then you could take your 2xPNP current
mirrors and parallel all the measuring collectors into one resistor/ADC
and selectively enable each mirror with a HV open collector driver
(thinking old school ULNxxxx or discretes) ?

piglet

 

[piglet]

On 14/01/2022 07:45, piglet wrote:

On 13/01/2022 18:38, John Larkin wrote:
On Thu, 13 Jan 2022 09:15:01 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

torsdag den 13. januar 2022 kl. 17.49.33 UTC+1 skrev
jla...@highlandsniptechnology.com:
On Thu, 13 Jan 2022 11:26:28 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:
On Wed, 12 Jan 2022 21:00:23 +0100, Klaus Vestergaard Kragelund
klau...@hotmail.com> wrote:

On 11/01/2022 17.49, jla...@highlandsniptechnology.com wrote:
On Tue, 11 Jan 2022 16:35:10 +0000,
l...@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

jla...@highlandsniptechnology.com> wrote:

We\'ll have a 48 volt, 20 amp power supply that feeds eight
plug-in
modular load boards. We want to measure all 9 currents so that
we can
do some sorts of intelligent cutoffs if the eight boards
threaten to
cave in the big supply.

So we want nine mediocre-accuracy unipolar high-side current
sensors
so we can digitize the currents with a grounded mux/adc.

Does anyone have a favorite but cheap high-side current sense IC?

We can add shunts, or I guess it could be some Hall thing.

Current mirror using pairs of high voltage PNP transistors?

I just posted something like that. It should be good enough. If the
voltage drop across Q2 is pitched a little high, so there is a
little
positive measurement offset, we can math that out.



A single current sense amp, but switched to the different sense
resistors with a 50V ana mux. Syncronized to the ADC sampling

We could mux on the high side, with a cheap 4051 type mux. We\'d
need a
highside power supply, just a zener, and some way to translate the
mux
address lines.


I still like an ordinary 36V dual or quad RRO op amp for this, running
off +26ish and ground, with a good quad pack such as an
ACASA1003S1003P100 (100k, 0.1% absolute, 0.05% relative), 37 cents.

That puts both inputs near +24V with the output near ground. There\'ll
be a little bit of offset, but nothing major, and since you can switch
off all the loads, you can measure it at POST. A little bit of
intentional imbalance will prevent the output from really going to
zero,
so the op amp and ADC will both be on-scale at all times.

Cheers

Phil Hobbs
I could mux into a single official highside measurement chip. But we\'d
still need to control the mux without slowing down the scan much.

AC couple the mux selects? Or use a fast digital isolator, with
highside power.

If I can actually buy the highside sensor chips for 80 cents each, we
can just use 9 of them.

https://lcsc.com/product-detail/span-style-background-color-ff0-Current-span-Sensing-Amplifiers_Diodes-Incorporated-ZXCT1080E5TA_C151589.html


$0.5803 if you buy 100

Nice. We could buy 1000.

We could do the dual layout to have a stuffing option. That\'s life
these days.


Yes, I suggested the related ZXCT1084 up thread a while back.

If you\'re in the mood to mux then you could take your 2xPNP current
mirrors and parallel all the measuring collectors into one resistor/ADC
and selectively enable each mirror with a HV open collector driver
(thinking old school ULNxxxx or discretes) ?

piglet

Maybe you don\'t even need the open collector enables, a 1/8 or 1/9 drive
should AC couple OK. I guess it depends whether a 60V capacitor is going
to cost more than a 2N7002?

piglet

 

[Anthony William Sloman]

On Friday, January 14, 2022 at 9:41:59 AM UTC+11, whit3rd wrote:

On Wednesday, January 12, 2022 at 11:13:36 PM UTC-8, bill....@ieee.org wrote:
On Thursday, January 13, 2022 at 3:52:39 PM UTC+11, Flyguy wrote:

The AD8479 handles up to 600V common mode. Couple this with a current shunt and you are good to go.
https://www.analog.com/media/en/technical-documentation/data-sheets/ad8479.pdf
also much much more expensive than a current sense amplifier.

Well, you might actually compare prices of a working circuit to the AD8479. I don\'t think you can.
Mouser Electronics in Australia sell the AD8479 for $A11.67, so that part is do-able.

Something like LM331 is half the price, and doesn\'t tie up ADCs, because frequency counting
is already logic-level info. If overhead counts, I\'ve always liked frequency conversion because
it allows the CPU to tailor the resolution and response, with minimal latency at each status
check. Think of a motor-bearing analysis, accumulating the harmonics of the rumble
of rotating machines, for days... a big digital accumulator and phase-locking works great
with voltage-frequency conversion.

Me too. But the charm of the AD8479 is in the four closely matched resistors.

Getting precisely calibrated frequency generators depends on getting precisely calibrated reactive components as well as resistors, so it is piling Pelion upon Ossa.

Precision resistors aren\'t cheap, but you can buy them. Equally precise capacitors don\'t exist. Precision inductors are even less precise. You can get stable parts, and calibrate them, but it\'s a good idea to recalibrate frequently and automatically.

--
Bill Sloman, Sydney

 

[whit3rd]

On Friday, January 14, 2022 at 7:05:45 PM UTC-8, bill....@ieee.org wrote:

On Friday, January 14, 2022 at 9:41:59 AM UTC+11, whit3rd wrote:
On Wednesday, January 12, 2022 at 11:13:36 PM UTC-8, bill....@ieee.org wrote:

Mouser Electronics in Australia sell the AD8479 for $A11.67, so that part is do-able.

Something like LM331 is half the price, and doesn\'t tie up ADCs, because frequency counting
is already logic-level info. If overhead counts, I\'ve always liked frequency conversion...

Me too. But the charm of the AD8479 is in the four closely matched resistors.

Getting precisely calibrated frequency generators depends on getting precisely calibrated reactive components as well as resistors, so it is piling Pelion upon Ossa.

The frequency generation is driven by the sensed signal, but the AD8479 and its ilk
use 100:1(?) pre-attenuation and that requires roughly 100x the precision of
those matched components. Only the 3 -terminal current monitor chips
like ZXCT1009F are actually amplifying straight off the sense resistor.

1% capacitors are plenty good enough (unless a 1 kW power supply cannot
be derated to 990W plus/minus 10W). For the AD8479 gain/offset, you
need resistors better than that, .01% or so.

> Precision resistors aren\'t cheap, but you can buy them. Equally precise capacitors don\'t exist.

It\'s mainly about aging, and for the resistors, also matching a quad. Either can be
calibrated, and neither should drift much. There\'s some auto-zero instrument amps, just
in case you want extra security.

 

[piglet]

On 15/01/2022 3:05 am, Anthony William Sloman wrote:

On Friday, January 14, 2022 at 9:41:59 AM UTC+11, whit3rd wrote:
On Wednesday, January 12, 2022 at 11:13:36 PM UTC-8, bill....@ieee.org wrote:
On Thursday, January 13, 2022 at 3:52:39 PM UTC+11, Flyguy wrote:

The AD8479 handles up to 600V common mode. Couple this with a current shunt and you are good to go.
https://www.analog.com/media/en/technical-documentation/data-sheets/ad8479.pdf
also much much more expensive than a current sense amplifier.

Well, you might actually compare prices of a working circuit to the AD8479. I don\'t think you can.
Mouser Electronics in Australia sell the AD8479 for $A11.67, so that part is do-able.

Something like LM331 is half the price, and doesn\'t tie up ADCs, because frequency counting
is already logic-level info. If overhead counts, I\'ve always liked frequency conversion because
it allows the CPU to tailor the resolution and response, with minimal latency at each status
check. Think of a motor-bearing analysis, accumulating the harmonics of the rumble
of rotating machines, for days... a big digital accumulator and phase-locking works great
with voltage-frequency conversion.

Me too. But the charm of the AD8479 is in the four closely matched resistors.

Getting precisely calibrated frequency generators depends on getting precisely calibrated reactive components as well as resistors, so it is piling Pelion upon Ossa.

Precision resistors aren\'t cheap, but you can buy them. Equally precise capacitors don\'t exist. Precision inductors are even less precise. You can get stable parts, and calibrate them, but it\'s a good idea to recalibrate frequently and automatically.

All very true and can be great when precision is needed. However the
OP\'s need is for a low precision sensor for fault detection not exacting
metrology. And one that has to be simple cheap enough to be replicated
eight times. Since it only operates over a limited lab temperature range
the discrete PNP mirror may well be adequate.

piglet

 

[Klaus Vestergaard Kragelund]

On 12/01/2022 03.44, jlarkin@highlandsniptechnology.com wrote:

On Tue, 11 Jan 2022 14:44:57 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 11. januar 2022 kl. 23.31.35 UTC+1 skrev John Larkin:
On Tue, 11 Jan 2022 12:12:37 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

tirsdag den 11. januar 2022 kl. 18.09.07 UTC+1 skrev jla...@highlandsniptechnology.com:
On Mon, 10 Jan 2022 22:34:08 -0800 (PST), whit3rd <whi...@gmail.com
wrote:
On Monday, January 10, 2022 at 7:26:19 PM UTC-8, jla...@highlandsniptechnology.com wrote:
We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents ...

So, is this regulated voltages, nine of \'em, and you want the output currents
from nine low-V regulators, or is it input to the regulators, and is that input somewhere
in the vicinity of 48VDC? Are these nine currents going to include initial
charging of filter capacitors? How big are those capacitors? Are some of the
regulators switchers?

As for \'intelligent cutoffs\', do you want to do that at the high-side? A secondary
low-current power supply grounded at the high rail might be economic, if
you want to have nine sensors and nine cutoffs all near the +48V source.
There will be eight user-programmable power supplies, each running off
+48, all off a common +48 bus fed from a kilowatt bulk power supply.
Users can potentially install modules and program and load the
supplies such as to cave in the main source, which would be really
ugly. That\'s against the rules in the manual, but we need to protect
things if they do it.

there is quite a few high side load switches with short circuit protection
and a combined current monitor / error output , but I think most of them
are limited to a ~24V supply
The c code can shut down supply modules as needed. Each power supply
module has its own FPGA that the main controller can address. There\'s
no need to actually remove 48v power from the baby boards. The master
controller just needs to know the currents and have some reasonable
rules.

check.

depending on how good the ADC is, maybe just a resistivity divider on the 48V and after each shunt is good enough?





Looks like we can use the XADC in the Zynq, the main controller FPGA.
That\'s a 1-volt full-scale, pretty terrible ADC. The voltage drop
across a shunt might be 50 mV with a common-mode of 48 volts. So we
need some sort of high-side amp.

Maybe use the idea with the resistive divider, but then don\'t use the
ADC, use a slope converter for increased precision.
That can be done with one cheap comparator, and a loop from the FPGA/Micro

Add a resistor with known drop, to calibrate

 

[Rick C]

On Monday, January 17, 2022 at 5:59:38 PM UTC-5, Klaus Kragelund wrote:

On 12/01/2022 03.44, jla...@highlandsniptechnology.com wrote:
On Tue, 11 Jan 2022 14:44:57 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

tirsdag den 11. januar 2022 kl. 23.31.35 UTC+1 skrev John Larkin:
On Tue, 11 Jan 2022 12:12:37 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

tirsdag den 11. januar 2022 kl. 18.09.07 UTC+1 skrev jla...@highlandsniptechnology.com:
On Mon, 10 Jan 2022 22:34:08 -0800 (PST), whit3rd <whi...@gmail.com
wrote:
On Monday, January 10, 2022 at 7:26:19 PM UTC-8, jla...@highlandsniptechnology.com wrote:
We\'ll have a 48 volt, 20 amp power supply that feeds eight plug-in
modular load boards. We want to measure all 9 currents ...

So, is this regulated voltages, nine of \'em, and you want the output currents
from nine low-V regulators, or is it input to the regulators, and is that input somewhere
in the vicinity of 48VDC? Are these nine currents going to include initial
charging of filter capacitors? How big are those capacitors? Are some of the
regulators switchers?

As for \'intelligent cutoffs\', do you want to do that at the high-side? A secondary
low-current power supply grounded at the high rail might be economic, if
you want to have nine sensors and nine cutoffs all near the +48V source.
There will be eight user-programmable power supplies, each running off
+48, all off a common +48 bus fed from a kilowatt bulk power supply.
Users can potentially install modules and program and load the
supplies such as to cave in the main source, which would be really
ugly. That\'s against the rules in the manual, but we need to protect
things if they do it.

there is quite a few high side load switches with short circuit protection
and a combined current monitor / error output , but I think most of them
are limited to a ~24V supply
The c code can shut down supply modules as needed. Each power supply
module has its own FPGA that the main controller can address. There\'s
no need to actually remove 48v power from the baby boards. The master
controller just needs to know the currents and have some reasonable
rules.

check.

depending on how good the ADC is, maybe just a resistivity divider on the 48V and after each shunt is good enough?





Looks like we can use the XADC in the Zynq, the main controller FPGA.
That\'s a 1-volt full-scale, pretty terrible ADC. The voltage drop
across a shunt might be 50 mV with a common-mode of 48 volts. So we
need some sort of high-side amp.

Maybe use the idea with the resistive divider, but then don\'t use the
ADC, use a slope converter for increased precision.
That can be done with one cheap comparator, and a loop from the FPGA/Micro

Add a resistor with known drop, to calibrate

If the voltage range is not excessive you can use a differential input on the FPGA as a comparator. If it is excessive you can scale it down.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209