a couple of highside current sensors...

[legg]

On Thu, 20 Aug 2020 14:06:32 -0500, \"Tim Williams\"
<tiwill@seventransistorlabs.com> wrote:

If you\'re going to brag, at least do it in a hand stand with a friend:
https://www.seventransistorlabs.com/Images/BidirectionalCurrentLimiter.png

Tim

Backwards, reverse polarty, and wrong connections, all in
one fell swoop.

RL

 

[John Larkin]

On Thu, 20 Aug 2020 18:05:25 -0400, legg <legg@nospam.magma.ca> wrote:

On Thu, 20 Aug 2020 14:06:32 -0500, \"Tim Williams\"
tiwill@seventransistorlabs.com> wrote:

If you\'re going to brag, at least do it in a hand stand with a friend:
https://www.seventransistorlabs.com/Images/BidirectionalCurrentLimiter.png

Tim

Backwards, reverse polarty, and wrong connections, all in
one fell swoop.

RL

We call that one swell foop.

 

[whit3rd]

On Thursday, August 20, 2020 at 12:06:35 PM UTC-7, Tim Williams wrote:

If you\'re going to brag, at least do it in a hand stand with a friend:
https://www.seventransistorlabs.com/Images/BidirectionalCurrentLimiter.png

Yeah, well that\'s a little TOO elaborate for me; the use-another-power-supply
route seems less of a problem when some of the solutions are seen.

Jim Thompson\'s two-transistor solution (with input through the low-Z emitters
instead of bases) has some interesting features, too

<https://web.archive.org/web/20150212042754/http://www.analog-innovations.com/SED/CurrentSense.pdf>

It\'s another variant of handstand...

What I\'d really like to see, is a logarithm-of-I scale, so I could make a lab supply
that had good-ish resolution but didn\'t need range switching. My first way to
do that, though, was to compare analog current monitor voltage against a triangle
wave, and sample/hold the exponential decay of the asociated square wave into
an RC circuit, to present to the meter. Or, to thermostat-control a well-characterized
base-emitter voltage against the scaled current into the colledtor, and display BE voltage.

Both are slightly too elaborate to get past my laziness, so I just continue to range-switch
the silly (only ONE meter, but two voltage and two current ranges) supply on my bench
It gets pegged, a lot, because the white paint stripe on the knob is kinda... dirty.

 

[bitrex]

On 8/20/2020 3:07 PM, legg wrote:

On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL

LT1001AM maybe, guaranteed < 15uV offset, < 0.6uV / degree C drift, < 2
nA bias current

OP07A is a cheaper alternative

 

[server]

On Thu, 20 Aug 2020 15:07:31 -0400, legg <legg@nospam.magma.ca> wrote:

On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL

Needs to be RRIO and fairly low power. I like OPA197 lately, but it\'s
fairly expensive.

It has to handle the bus voltage too, but that could be fudged.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[legg]

On Thu, 20 Aug 2020 21:05:39 -0400, bitrex <user@example.net> wrote:

On 8/20/2020 3:07 PM, legg wrote:
On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL


LT1001AM maybe, guaranteed < 15uV offset, < 0.6uV / degree C drift, < 2
nA bias current

OP07A is a cheaper alternative

it\'s not bias current, but Icc that has to be low and controlled.

Stick an LT1001A in the sim to see the issue.

RL

 

[legg]

On Thu, 20 Aug 2020 19:11:48 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Thu, 20 Aug 2020 15:07:31 -0400, legg <legg@nospam.magma.ca> wrote:

On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL

Needs to be RRIO and fairly low power. I like OPA197 lately, but it\'s
fairly expensive.

It has to handle the bus voltage too, but that could be fudged.

The models do a lousy job in simulation. Somebody forgot to cap Icc.

RL

 

[bitrex]

On 8/20/2020 11:16 PM, legg wrote:

On Thu, 20 Aug 2020 21:05:39 -0400, bitrex <user@example.net> wrote:

On 8/20/2020 3:07 PM, legg wrote:
On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL


LT1001AM maybe, guaranteed < 15uV offset, < 0.6uV / degree C drift, < 2
nA bias current

OP07A is a cheaper alternative

it\'s not bias current, but Icc that has to be low and controlled.

Stick an LT1001A in the sim to see the issue.

RL

Ah yea I see that.

With that in mind the most appropriate device in Analog Device\'s stable
looks to be the LT1637, like a lot of things AD they slam you for small
quantity but it\'s about $1.80 in 100s.

The inputs are over-the-top up to 44 volts so could run it off a lower
supply voltage and cut the bias current down even further. works good in
the sim

 

[Jasen Betts]

On 2020-08-20, bitrex <user@example.net> wrote:

On 8/20/2020 1:06 PM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 20 Aug 2020 11:35:57 -0500, John S <Sophi.2@invalid.org
wrote:

On 8/20/2020 11:17 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 20 Aug 2020 11:07:12 -0500, John S <Sophi.2@invalid.org
wrote:

On 8/20/2020 9:28 AM, jlarkin@highlandsniptechnology.com wrote:

Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

There is a 53mV offset. Why is that?

The opamp version? That\'s the supply current of the opamp. Use a lower
current amp, or calibrate it out.

I just used the default universalopamp2

It\'s an idea. It\'s free.

I like it. Thank you!


I designed a functional but clumsy highside current sensor into an EOM
driver recently, to protect a $200 distributed amplifier chip. I
should have done this!




Zetex IIRC used to make a high-side current-sense IC; basically a Wilson
CM on a chip. It worked good and was cheaper than a quad transistor array.

EOL-ed, naturally

TI does some ADC equipped volatge and current sensors INA3221 is a triple

--
Jasen.

 

[bitrex]

On 8/20/2020 11:24 PM, legg wrote:

On Thu, 20 Aug 2020 19:11:48 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Thu, 20 Aug 2020 15:07:31 -0400, legg <legg@nospam.magma.ca> wrote:

On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL

Needs to be RRIO and fairly low power. I like OPA197 lately, but it\'s
fairly expensive.

It has to handle the bus voltage too, but that could be fudged.

The models do a lousy job in simulation. Somebody forgot to cap Icc.

RL

Oddly if you use the LTC1637 \"over-the-top\" amp and configure its supply
rail in the same circuit like this:

<https://imgur.com/a/eEMqHrk>

the sim claims the amp draws no Icc thru the positive supply. At all.

The current sense feature still works fine at least down until the
current thru the 100 ohm resistor becomes on the order of the normal
supply current, then it craps out.

That\'s weird...

 

[bitrex]

On 8/21/2020 2:34 AM, bitrex wrote:

On 8/20/2020 11:24 PM, legg wrote:
On Thu, 20 Aug 2020 19:11:48 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Thu, 20 Aug 2020 15:07:31 -0400, legg <legg@nospam.magma.ca> wrote:

On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0


Which non-ideal op amp models are suitable, do you think?

RL

Needs to be RRIO and fairly low power. I like OPA197 lately, but it\'s
fairly expensive.

It has to handle the bus voltage too, but that could be fudged.

The models do a lousy job in simulation. Somebody forgot to cap Icc.

RL


Oddly if you use the LTC1637 \"over-the-top\" amp and configure its supply
rail in the same circuit like this:

https://imgur.com/a/eEMqHrk

the sim claims the amp draws no Icc thru the positive supply. At all.

The current sense feature still works fine at least down until the
current thru the 100 ohm resistor becomes on the order of the normal
supply current, then it craps out.

That\'s weird...

Definitely something to do with the model, the voltages on the
transistor Q2 don\'t even make sense.

 

[Klaus Kragelund]

On Thursday, August 20, 2020 at 4:29:03 PM UTC+2, jla...@highlandsniptechnology.com wrote:

Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

A very nice idea

But, isn\'t difficult to find a high voltage positive rail opamp that has low operation current?

Cheers

Klaus

 

[Ricketty C]

On Thursday, August 20, 2020 at 12:09:40 PM UTC-4, George Herold wrote:

On Thursday, August 20, 2020 at 10:29:03 AM UTC-4, jla...@highlandsniptechnology.com wrote:
Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0


Huh... (you\'re a wild man, but I\'m missing something.)
For the first one with the opamp. With one amp through R1
there\'s a 1 volt drop.
Which gives 23 volts for U1 output. A 1 volt drop across
R3 or 10 mA of current... that 10 mA must go through the
negative rail resistor R2. ... Which then gives me 10V on your
output.
What did I do wrong?

Maybe trying to use this circuit that has limitations? The voltage across R1 at 1 amp is 0.1 volts, it\'s a 0.1 ohm resistor with nearly no current in the amp input, how could it be anything else?

The rest of the circuit is the typical balanced voltages on different value resistors, R1 and R3, resulting in currents in the ratio of the resistors. This is normally done with a FET which means the same current in R3 matches the current in R2 resulting in another gain step. So the voltage at the output should be I*R1*R2/R3. However, in order to save one transistor Larkin uses the negative rail connection of the op amp for the current sense which pollutes the signal with the op amp operating current.

In the circuit with the transistors it fails to work further by introducing unequal offsets in the BE junctions due to unequal currents. For the currents in the two BE junctions to be equal, the resistor currents and voltages should be equal. You can only make the claim that the two resistor voltages are equal if you can show the BE junction voltages to be equal, i.e. circular reasoning. That\'s only a reasonable approximation if the voltages on the resistors are the lion\'s share of the total voltage drop meaning significantly more than 0.7 volts. This can also be approximated if the beta of the two transistors are equal, but that requires a matched pair. Is that really any better than just using an op amp and a FET in the standard circuit that doesn\'t have any of these issues?

Here\'s one with the FET included, SOT23, under a buck, just add two resistors!

https://www.ti.com/product/INA138

--

Rick C.

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

 

[legg]

On Fri, 21 Aug 2020 01:28:52 -0400, bitrex <user@example.net> wrote:

On 8/20/2020 11:16 PM, legg wrote:
On Thu, 20 Aug 2020 21:05:39 -0400, bitrex <user@example.net> wrote:

On 8/20/2020 3:07 PM, legg wrote:
On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL


LT1001AM maybe, guaranteed < 15uV offset, < 0.6uV / degree C drift, < 2
nA bias current

OP07A is a cheaper alternative

it\'s not bias current, but Icc that has to be low and controlled.

Stick an LT1001A in the sim to see the issue.

RL


Ah yea I see that.

With that in mind the most appropriate device in Analog Device\'s stable
looks to be the LT1637, like a lot of things AD they slam you for small
quantity but it\'s about $1.80 in 100s.

The inputs are over-the-top up to 44 volts so could run it off a lower
supply voltage and cut the bias current down even further. works good in
the sim

Got to be problems with the model. LT1001A draws the typical 1mA,
not enough to get the abysmal results of the sim.

Perhaps it\'s input offset voltages reacting to the low source
impedance. Input pin currents are off the wall.

RL

 

[server]

On Fri, 21 Aug 2020 00:23:51 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

On Thursday, August 20, 2020 at 4:29:03 PM UTC+2, jla...@highlandsniptechnology.com wrote:
Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0


A very nice idea

But, isn\'t difficult to find a high voltage positive rail opamp that has low operation current?

Cheers

Klaus

Opamp max supply voltages keep creeping down. That\'s annoying. A lot
of our stuff runs off a +24 supply, and some recent boxes use a 48
volt wart. High voltage opamps are rare.

Of course highside current sensor chips are common, but I\'m a circuit
designer. And I don\'t like to add new parts to stock (parts that will
eventually go EOL) when I can make something from what we have
already.

My current gumdrop is OPA197, but its supply current is about 1 mA. So
one might add a transistor. At that point, there are better circuits.

This adds the transistor and deletes the opamp!

https://www.dropbox.com/s/5upvl9e0aurjkwt/28S131A_sh5.pdf?dl=0






--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[bitrex]

On 8/21/2020 8:20 AM, legg wrote:

On Fri, 21 Aug 2020 01:28:52 -0400, bitrex <user@example.net> wrote:

On 8/20/2020 11:16 PM, legg wrote:
On Thu, 20 Aug 2020 21:05:39 -0400, bitrex <user@example.net> wrote:

On 8/20/2020 3:07 PM, legg wrote:
On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL


LT1001AM maybe, guaranteed < 15uV offset, < 0.6uV / degree C drift, < 2
nA bias current

OP07A is a cheaper alternative

it\'s not bias current, but Icc that has to be low and controlled.

Stick an LT1001A in the sim to see the issue.

RL


Ah yea I see that.

With that in mind the most appropriate device in Analog Device\'s stable
looks to be the LT1637, like a lot of things AD they slam you for small
quantity but it\'s about $1.80 in 100s.

The inputs are over-the-top up to 44 volts so could run it off a lower
supply voltage and cut the bias current down even further. works good in
the sim

Got to be problems with the model. LT1001A draws the typical 1mA,
not enough to get the abysmal results of the sim.

Perhaps it\'s input offset voltages reacting to the low source
impedance. Input pin currents are off the wall.

RL

A problem with the LT1001 etc. is it\'s not rail-to-rail IO; the inputs
have to be at least 1 volt below the V+ AFAICT

Frustratingly AD makes a lot of high-voltage precision op amps with
rail-to-rail outputs but not that many with rail-to-rail inputs.

 

[Jan Panteltje]

On a sunny day (Fri, 21 Aug 2020 07:44:29 -0700) it happened
jlarkin@highlandsniptechnology.com wrote in
<4kmvjfhc7mjkgbaqg0msb4fa9co71nfvlo@4ax.com>:

This adds the transistor and deletes the opamp!

https://www.dropbox.com/s/5upvl9e0aurjkwt/28S131A_sh5.pdf?dl=0

Long time ago I bought some Hall sensor modules to measure high current
(well what is high?) DC:
https://www.lem.com/en/hx-03p
datasheet:
https://www.lem.com/sites/default/files/products_datasheets/hx_03_50-p_ver15.pdf

For AC I like current transformers like this:
http://panteltje.com/panteltje/pic/pwr_pic/power_box_internals_top_img_1810.jpg
here used in the drain of a power MOSFET used for cycle by cycle current limiting..
secondary terminated with 10 Ohms gives you a nice waveform directly into a PIC comparator.

 

[server]

On Fri, 21 Aug 2020 17:03:47 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Fri, 21 Aug 2020 07:44:29 -0700) it happened
jlarkin@highlandsniptechnology.com wrote in
4kmvjfhc7mjkgbaqg0msb4fa9co71nfvlo@4ax.com>:

This adds the transistor and deletes the opamp!

https://www.dropbox.com/s/5upvl9e0aurjkwt/28S131A_sh5.pdf?dl=0

Long time ago I bought some Hall sensor modules to measure high current
(well what is high?) DC:
https://www.lem.com/en/hx-03p
datasheet:
https://www.lem.com/sites/default/files/products_datasheets/hx_03_50-p_ver15.pdf

For AC I like current transformers like this:
http://panteltje.com/panteltje/pic/pwr_pic/power_box_internals_top_img_1810.jpg
here used in the drain of a power MOSFET used for cycle by cycle current limiting..
secondary terminated with 10 Ohms gives you a nice waveform directly into a PIC comparator.

There are surface-mount Hall current sensor chips. One of them just
sits above a big PCB trace that carries the current.

Instead of a current transformer, you can use a surface-mount shunt
resistor and a signal transformer, standard small cheap parts. The
dual-winding inductors are good. An advanced trick is to add a
resistor in series with the primary and drive the secondary into a
summing point, essentially run the transformer zero-flux.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[legg]

On Fri, 21 Aug 2020 12:05:10 -0400, bitrex <user@example.net> wrote:

On 8/21/2020 8:20 AM, legg wrote:
On Fri, 21 Aug 2020 01:28:52 -0400, bitrex <user@example.net> wrote:

On 8/20/2020 11:16 PM, legg wrote:
On Thu, 20 Aug 2020 21:05:39 -0400, bitrex <user@example.net> wrote:

On 8/20/2020 3:07 PM, legg wrote:
On Thu, 20 Aug 2020 07:28:52 -0700, jlarkin@highlandsniptechnology.com
wrote:


Just woke up and these were there.

https://www.dropbox.com/sh/3snkyafrejh23xf/AACNN0tBc1oMV0kJX-rVNMICa?dl=0

Which non-ideal op amp models are suitable, do you think?

RL


LT1001AM maybe, guaranteed < 15uV offset, < 0.6uV / degree C drift, < 2
nA bias current

OP07A is a cheaper alternative

it\'s not bias current, but Icc that has to be low and controlled.

Stick an LT1001A in the sim to see the issue.

RL


Ah yea I see that.

With that in mind the most appropriate device in Analog Device\'s stable
looks to be the LT1637, like a lot of things AD they slam you for small
quantity but it\'s about $1.80 in 100s.

The inputs are over-the-top up to 44 volts so could run it off a lower
supply voltage and cut the bias current down even further. works good in
the sim

Got to be problems with the model. LT1001A draws the typical 1mA,
not enough to get the abysmal results of the sim.

Perhaps it\'s input offset voltages reacting to the low source
impedance. Input pin currents are off the wall.

RL


A problem with the LT1001 etc. is it\'s not rail-to-rail IO; the inputs
have to be at least 1 volt below the V+ AFAICT

Frustratingly AD makes a lot of high-voltage precision op amps with
rail-to-rail outputs but not that many with rail-to-rail inputs.

I can confirm that the model for LT1637 does work in the sim.

RL