hybridfree/eevblog-posts huggingface dataset:
current limiting is not happening in LM723??? - Page 1
Forum section: electronics / projects

author: Gurumurthy
author_rank: Regular Contributor
timestamp: June 13, 2017, 06:08:46 am
content: I designed a Lab power supply with LM723(for 0-30V @ 5Ampere),Initially I limited the current at .65 ampere(I limit=o.65V/1 ohm). But the problem is ,the IC is not performing the current limiting operation, eventhough it had potential difference is 5V across its base to emitter transistor which does this current limiting function.What could be the problem?1)is with current sense resistor precision?2) is it with Base emitter junction breakdown with transistor? Because of 5V across it?Totally confused . Help me in this regard...

author: Kleinstein
author_rank: Super Contributor
timestamp: June 13, 2017, 10:29:36 am
content: The current shunt precision should not be a problem. The current limit with the LM723 is not really accurate, as the reference voltage used is just the VBE of the internal transistors. Anyway the current limit should engage, even if maybe a few percent off.Once you get 5 V across the shunt, chances are very high that the internal transistor for the current limit is broken due way to much base current. However normally the circuit should prevent this. So maybe one of the power transistors of the regulator as a whole is broken too.

author: David Hess
author_rank: Super Contributor
timestamp: June 13, 2017, 12:43:04 pm
content: Without base-emitter shunt resistors, the output transistors may have responded too slowly to prevent damaged to the low impedance base-emitter junction of the current sense transistor. Even with the shunt resistors, a high current design might cause damage anyway. I would include a resistor in series with the base of the current limiting transistor which is pin 2 on the DIP package.Commercial high current power supplies based on the 723 do this in one form or another; either they add the series resistor or they implement foldback current limiting which includes it anyway. Foldback current limiting only requires adding two resistors and is well worth it in a high voltage or high current design.
Help with current limiting this AC circuit - Page 1
Forum section: electronics / projects

author: jwbrooks
author_rank: Contributor
timestamp: January 09, 2014, 03:19:59 am
content: Objective:I want a safe and simple way to current limit the below circuitSetup:I'm presently building the below circuit. For the source, I'm using a variac plugged into the wall (60Hz, not 50). My transformer is a 3000 V (or abouts) microwave oven transformer (MOT). My load, which looks just like it does in the diagram, is a set of electrodes, and I imagine that this ends up having a slight capacitive impedance and subsequently draws very little current.The circuit is a Paul Trap for any anyone curious.My question:How can I safely current limit the above circuit? I realize not knowing the impedance of the load makes this a tad bit more challenging.Here are my thoughts so far:Can I put a small capacitor in series between the variac and the MOT? Would this not limit the current if I size the capacitor correctly? Zcap=1/(2*pi*f*C) and I=V/Zcap? Would the capacitor and inductor (transformer) end up creating their own oscillatory frequency and voltage?Would a fuse be better? Or would even a fast blow fuse not be fast enough to keep the MOT from killing someone?I've read about people using light bulbs as ballasts, but maybe this would still be too much current? It's also easier to visualize the trap and trapped particles in near darkness, and a light wouldn't help.Is there a better way to do this? Is my idea about the capacitor correct or even a good idea?Thanks for your help!

author: skyler
author_rank: Regular Contributor
timestamp: January 09, 2014, 03:43:42 am
content: Another MOT with the secondary shorted in series with the AC in might work

author: johansen
author_rank: Super Contributor
timestamp: January 09, 2014, 04:04:34 am
content: the load is capacitive and very low current is it not?just use a small high voltage capacitor in series with the load.you might only need a few nanofarads.

author: peter.mitchell
author_rank: Super Contributor
timestamp: January 09, 2014, 08:16:46 am
content: just ballast the primary side of the transformer with a resistive load. How much current do you want to let through/what is the rating of the transformer?
current limting doesnt work only constant voltage - Page 1
Forum section: electronics / projects

author: ZeTeX
author_rank: Frequent Contributor
timestamp: December 21, 2015, 05:23:47 pm
content: Hi!I'm playing around in LTSPICE trying to create a CC\CV supply based around and NPN or darlington NPN and I'm trying to get current regulation working, but it seems like it doesnt want to work!the problem is that U3 keeps it negative voltage and doesnt try to make it so the inverting and non inverting stays the same. I tried swapping the non invert input to the inverting input but all it those is oscilate and I could not stop the osciliation and also it doesnt make any sense to me why swapping will help, it is almost im doing something completely stupid and I just cant figure it out.(the schematic is a quick copy from agilent 30W psu series)here is the schematic:

author: Kleinstein
author_rank: Super Contributor
timestamp: December 21, 2015, 07:04:28 pm
content: Having the current sensing high side is the fist stupid idea.It's much better to have the shunt low side, or alternatively the whole regulator floating high side like most of the HP power supplies did it. My gues is you got caught by the GND symbols.The LT1013 is a nice slow precicion OP especially at 10 fold amplification. For a first try I would change to a LT1037 or similar.The way it is drawn, the polarity is wrong - just swapping the inputs at U2 will also change the polarity at the reference.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: December 21, 2015, 07:30:00 pm
content: Quote from: Kleinstein on December 21, 2015, 07:04:28 pmthat workedthank you very much mr analog guy

author: ZeTeX
author_rank: Frequent Contributor
timestamp: December 23, 2015, 07:06:22 pm
content: Quote from: Kleinstein on December 21, 2015, 07:04:28 pmwhat do you think about this? is there any problems?
Current Measurement Device - Page 1
Forum section: electronics / projects

author: fedimakni
author_rank: Regular Contributor
timestamp: June 29, 2020, 09:27:30 am
content: Hello,Currently I am doing a current measurement device based on ucurrent from Dave but i want it to be switched from a microcontroller. ( i chose a raspberry Pi for that - I know it's an overkill but don't take care about it )I attached the schematic below i am using an SSR to make switching CPC1705Y: Datasheet:http://www.ixysic.com/home/pdfs.nsf/www/CPC1705Y.pdf/$file/CPC1705Y.pdfI would like to have an idea if i will face any problem with this design?Is there any limitationWhat things i could improve?Looking forward for your feedback.Thanks.

author: Dave
author_rank: Super Contributor
timestamp: June 29, 2020, 10:51:44 am
content: Those SSRs are designed for unidirectional operation. The measurements are going to be skewed when you forward bias the substrate diodes in those.You might also want to check the leakage current through them as well, because they might pose a problem on the nanoampere range.Those are also rather fast amplifiers for feeding an 860 Sps ADC. You need image reject filters.

author: Ian.M
author_rank: Super Contributor
timestamp: June 29, 2020, 12:07:39 pm
content: Additionally, you've got insufficient drive to guarantee the SSRs get turned hard on, and even if you fix that, the on resistance of K2 is several times greater than the resistance of the shunt R1, so the high current range will be unusable, grossly overreading by anything up to an order of magnitude.
Current measurement question - Page 1
Forum section: electronics / projects

author: liquibyte
author_rank: Frequent Contributor
timestamp: April 14, 2014, 05:30:20 pm
content: I've got a dual power supply and have worked out a quick load using an old stove eye just to test that the current limit is working. The eye has a resistance of 38.5 ohms and the power supply outputs up to 30V @ 3A. Using an ohms law calculator on line, the max amps I should be drawing through this is 0.77922 and 23.37662 watts at 30V but when I put my meter in the circuit, I'm showing 8A draw. If I keep this thing hooked up it gets warm enough to the touch that it starts being uncomfortable to hold in my hand. Current has always mystified me even though I know the math behind it. Anyone have any idea of what's going on here or do I just have a crappy meter that can't measure current in a circuit realistically?Edit: Nevermind, I forgot to put the leads in the correct jacks. I'm showing .78A now, what a boob I am.
Current mode controller giving external  access to both PWM comparator  inputs? - Page 1
Forum section: electronics / projects

author: ocset
author_rank: Super Contributor
timestamp: November 19, 2017, 05:46:44 pm
content: Why is the MCP1630 the only current mode control chip in the world that allows one to directly set the voltage on the PWM comparator input?(ie so that one can set the peak inductor current).Chips like the UCC28C43 make this impossible as they have diodes in the way.MCP1630 datasheet:http://ww1.microchip.com/downloads/en/DeviceDoc/21896C.pdfI appreciate the HV9910B has an accessible PWM comparator input but the reference is fixed and set too low for us..being just 0.25V…we need it to be 0.5 to 1V….or externally adjustable.HV9910Bhttp://ww1.microchip.com/downloads/en/DeviceDoc/20005344A.pdf
Current Mode LED driver with different compensation circuit. - Page 1
Forum section: electronics / projects

author: Patrick66
author_rank: Regular Contributor
timestamp: April 29, 2024, 12:25:49 pm
content: Hello everyone, I'm trying to study the difference in the output response when using different compensation circuits using type 1 and type 2 compensator circuits. The question is when comparing the table of type 1 compensator test C the cross-over frequency is almost similar to the type 2 compensator test A. The problem is the overshoot and time to reach stable is much longer compared to type 2 compensators even though both have the same cross-over frequency. Wanted to ask if is this considered normal or if there is some issue with my simulation. The figures of the circuit and the table for type 1 and 2 compensator circuits is shown below. Noted that the table that has 4 different test is type 1 compensation table where as the table with 6 different test is type 2 compensation table. Thank you in advance for the help.
Current Probe with Aceinna Current Sensors for Scopes - Page 1
Forum section: electronics / projects

author: B0B45
author_rank: Contributor
timestamp: November 12, 2020, 08:29:20 am
content: Hey everyone,I'm planning to rebuild my old current probes, based on an LEM hall-sensor, with new Sensor ICs from Aceinna (https://www.aceinna.com/current-sensors/5V%20Current%20Sensors). The main reason for a change is a bad design of the powersupply. This time I would like to use a switching regulator for the dual-power-supply.The origin of the idea is the design fromhttps://www.elektormagazine.de/labs/potential-free-current-measurement-for-oscilloscopes-150170The new design is a first concept for the current probe. Feel free to comment, every advice is welcome at this pointLater on I can take some picture of the old probes and scope plots of the sensors.-B0B

author: B0B45
author_rank: Contributor
timestamp: November 12, 2020, 10:46:46 am
content: Here is a screenshot comparing the output of the MCA1101-5-5 (blue) vs LEM LTS 25-NP (yellow).

author: trobbins
author_rank: Frequent Contributor
timestamp: November 13, 2020, 06:49:01 am
content: Hi Bob, you show two scope plots - can you elaborate on the circuit configurations used for each plot, and the test conditions? If that is the noise floor of each configuration, it may be more meaningful to show performance as a frequency spectrum plot (maybe your scope has that capability or you have a soundcard and software set up to do it).Is it the noise floor that is the concern, or did you think the Aceinna sensor would achieve a wider bandwidth, or better insulation, or DC accuracy ...?Ciao, Tim
Current protection help - Page 1
Forum section: electronics / projects

author: rex1232
author_rank: Contributor
timestamp: December 05, 2019, 03:54:42 pm
content: Hey everyoneThe circled part in question is what I need help understanding.Can anyone give me a run through of how it work.Thank you in advance

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 05, 2019, 04:56:23 pm
content: Keyword, foldback current limiting.The diodes appear to be intended to shape the curve, so that instead of a straight negative slope, it has a dual slope, I assume more closely approximating a constant-power curve. The aim would be limiting power dissipation in the output transistors, a valuable feature.Tim

author: David Hess
author_rank: Super Contributor
timestamp: December 06, 2019, 04:59:55 pm
content: This form of current limiting is often referred to as Vbe current limiting because the threshold for current limiting is set by the Vbe voltage of a transistor. This is distinct from using a differential pair for current limiting which allows the threshold voltage to be arbitrary, more precise, and usually lower.Ignoring the foldback part for the moment, when the voltage across emitter resistors R23 or R24 reaches the Vbe voltage of Q8 or Q9, about 0.6 volts, Q8 or Q9 turns on and removes base drive from Q12 or Q10 lowering the output current for that side.The foldback part lowers the current limit further when the voltage across the output transistors is higher. In audio amplifiers, this is desirable because the reactive load of the speakers would otherwise drive the output transistors into secondary breakdown with higher currents at higher voltages. A purely resistive load would only result in high currents at low voltages across the transistors. Adding this allows less derating of the output transistors so they can be less expensive.
Current Rebuild  - Page 1
Forum section: electronics / projects

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: November 16, 2012, 02:34:46 am
content: Today I picked up a beautiful AKAI LCT3201AD LCD tv but the problem is that the unit does not work... So I opened the unit up and found a crap load of Decon Caps blowing up.. I want to repair this unit but not sure if it's really worth fixingOh by the way what company of caps should I use?The main board pictured below (Not my board but a pic used for representation ) that I have has over 1/3 of the caps blow or the rubber piece is coming out and the power board has 8 more caps that need repaired too ..ThanksJAy

author: SeanB
author_rank: Super Contributor
timestamp: November 16, 2012, 04:46:19 am
content: Rubycon, Panasonic, any other aside from OHL and Samwha.

author: poorchava
author_rank: Super Contributor
timestamp: November 16, 2012, 11:51:30 am
content: Nichicon, Yageo and Vishay are also good

author: George_Race
author_rank: Regular Contributor
timestamp: November 16, 2012, 03:11:18 pm
content: One of the best places I have found to get information on TV replacement capacitors is here:http://www.badcaps.net/forum/They even have listings of TV set models that you can buy capacitors replacements kits for.A really neat place!Hope this helps,George

author: T4P
author_rank: Super Contributor
timestamp: November 16, 2012, 07:16:52 pm
content: Any TV with blown caps are mostly worth trying to repair it ...

author: Stephenniall
author_rank: Contributor
timestamp: November 17, 2012, 08:54:50 pm
content: A couple of $ worth of caps and an hours work, Its definetly worth replacing it even if your going to sell it !Try to use panasonic caps, Or ones that haven't been bought on Ebay from hong kong !
Current Regulator: Buck, High-Side Res, Op-Amp - Page 1
Forum section: electronics / projects

author: snoop33
author_rank: Contributor
timestamp: January 24, 2022, 06:50:54 pm
content: Hi,I've a requirement to regulate a 5v supplies current in about 20mA steps from 20mA (ideally) to 2A peak.I built a hysteresis mode current regulator but exhibited problems people warned about at low current where it fails to regulate and overshoots.I then built a buck based on Texas Instruments SLVA419d recommendations (in the screenshot you can see the adj on the neg rail, I've tried both).The second should be the optimal in terms of performance but testing it in TINA (files supplied) I am able to get it regulating fine until the adj voltage was attached. At this point the current will swing either all the way up or down with almost no adjustment. No matter what resistors are used it is the same.One assumption I have made is when there's little current the voltage at the LMV324's inputs is very close or nigh on at Vdd (5v). Typically this isn't a good thing and I'm wondering if that will work for low current. I do not however believe it is the main control issue.I should mention the DAC voltage is annoyingly 3.0v peak, so the sense resistor is going to be quite large to reduce the gain and allow the DAC to not always be a sink.Appreciate any help before it drives me mad.
current sense amplifier with different ground - Page 1
Forum section: electronics / projects

author: fedimakni
author_rank: Regular Contributor
timestamp: March 11, 2025, 03:28:11 pm
content: Hello,I would like to use a current sense amplifier IC to measure the current between 2 points in a circuit i don't have access to its ground.So the ground IC and the ground of the load will not be shared.Most of the datasheet i saw always mention in their typical application circuit that the shunt resistor and the IC will be referenced to the same ground.Could you suggest how i can overcome this issue?The expected current measured is about 1-10mAOperating voltage of the device is 24V.Thank you.

author: jwet
author_rank: Frequent Contributor
timestamp: March 11, 2025, 03:45:45 pm
content: Current sense amps have a wide common mode range- they can measure a small drop at an arbitrary voltage away from ground. Voltages of 40 and 80v aren't unusual and some modern parts can have a 3V supply and can look at rails of way more (40V)- look at Ti or Maxim. This is called high side sensing and it very common.If you truly have no idea how far you are from ground or need isolation, there are a class of hall effect current sensor. LEM make modules and TI and Allegro among others make the chips. These can be used with unlimited (thousands of volts) of CM.

author: TimFox
author_rank: Super Contributor
timestamp: March 11, 2025, 04:13:46 pm
content: For lower-accuracy sensing, you could try a photoisolator, relying on the current-transfer ratio from the LED current (appropriately connected to your ungrounded current, a bit tricky) to the photo current connected to your grounded monitor.

author: fedimakni
author_rank: Regular Contributor
timestamp: March 12, 2025, 01:55:30 am
content: jwet:Thank you for your answer,The issue with hall effect sensor that they are very inaccurate at low current. It is true that the accuracy i am looking for is quite low but i would like at least to differentiate between 1mA and 5mA.Most hall effect sensor i saw are mainly for A or even few 100 of mA

author: fedimakni
author_rank: Regular Contributor
timestamp: March 12, 2025, 02:01:09 am
content: TimFox:It is a good idea to investigate so the opto will be in series with the system i would like to measure its current. but don't you think at that time the LED itself will disturb the current flow? Also it may require high resistor as the supplied voltage is 24V?

author: Smokey
author_rank: Super Contributor
timestamp: March 12, 2025, 04:07:28 am
content: Quote from: jwet on March 11, 2025, 03:45:45 pmMake sure you check the datasheet. The bandwidth usually goes down with higher common mode.

author: TimFox
author_rank: Super Contributor
timestamp: March 12, 2025, 02:13:49 pm
content: Quote from: fedimakni on March 12, 2025, 02:01:09 amIt’s tricky to apply, due to the voltage drop of the LED. If you can somehow drive the LED through a transistor or something connected to a shunt resistor in the ungrounded part of the system, then the opto allows a huge variable voltage difference to the grounded bits. The CTR is reasonably constant.
current sense and low ripple  - Page 1
Forum section: electronics / projects

author: navidrct
author_rank: Regular Contributor
timestamp: January 06, 2016, 11:17:28 am
content: hii want a IC that can sense from 0 to 3 amp with 10mA or better resolutionand i want a regulator that its output current max can be 5A and its max voltage is 13 V .the important thing is ripple should be lower than 20 mV ;please helpi failed one timeand i cant fail againhelp

author: AlxDroidDev
author_rank: Frequent Contributor
timestamp: January 06, 2016, 11:18:47 pm
content: Current sensor: TI. INA219Voltage regulator: TI LM338

author: AlxDroidDev
author_rank: Frequent Contributor
timestamp: January 07, 2016, 04:47:28 am
content: Complementing myself: the INA219 will report the current through an I2C interface, thus requiring you to use a uC.If you're not using a uC, please let us know.

author: navidrct
author_rank: Regular Contributor
timestamp: January 07, 2016, 07:19:40 am
content: thanks a loti use uCill read their datasheetthanks again
Current Sense circuit for Back EMF measurement for sensorless BLDC motor control - Page 1
Forum section: electronics / projects

author: gauravmp
author_rank: Regular Contributor
timestamp: March 31, 2020, 09:45:54 pm
content: Hi, I'm working on a sensorless BLDC motor controller and I intend to use the DRV8305 (http://www.ti.com/lit/ds/symlink/drv8305.pdf) for my FET drivers for the motor. I have been looking at their example application (page 45) as shown in the picture attached. I'm trying to figure out what the zener diode in this circuit is used for. Any help would be appreciated. The PVdd will be 12V and the Vcc will be 3.3V.[ Specified attachment is not available ]

author: KaneTW
author_rank: Frequent Contributor
timestamp: March 31, 2020, 09:51:19 pm
content: It's just input protection. Also a Schottky, not a Zener.

author: gauravmp
author_rank: Regular Contributor
timestamp: March 31, 2020, 10:43:20 pm
content: Oh thanks a lot!
Current sense resistor in-series with bulk capacitor? - Page 1
Forum section: electronics / projects

author: cRash1001
author_rank: Contributor
timestamp: June 02, 2022, 03:14:01 am
content: Hi,I am trying to understand how an LLC Resonant Power Converter based on UCC25600 works. The LLC is converting 24V inputs to 18V output.I am however a little confused about how the current sense measurement is being implemented here. Normally, the current-sense resistor is placed in series with the output and voltage drop across it measured.But in this circuit, the current sense resistor is placed in series with the bulk capacitor.Could someone please explain to me how this current sense would actually work in this configuration, and the pros/cons of using this vs the commonly used configuration where the current-sense resistor is in series with the output?Please referto the attached schematic.Thanks.

author: Phoenix
author_rank: Frequent Contributor
timestamp: June 02, 2022, 04:48:26 am
content: It looks very much like the current sense resistor is measuring the current being delivered out the 18V rail. Whatever returns on GND_18V goes through that resistor.

author: CMTan
author_rank: Contributor
timestamp: June 02, 2022, 02:48:04 pm
content: Current Sense resistor can be placed anywhere in the current loop, since the current in the loop will be the same. It does not matter if it is on the ground side or +V side.If you placed it on the +V side, you will need differential measurement which is more complicated, since you need 2 connectionsIf you placed on the ground side, you only need one wire, since the other connection is on the ground connection.If most typical current measurement, you will notice that it is almost always on the ground side because the ground is used a a reference.You concern might be if it cause a ground bounce since the resistor is in series with the capacitor ground. Yes, there will be a slight disturbance to the ground in this case. but if the resistor is chosen to be very small, the effect is too small to affect the supply.In the case mentioned, the resistor is 0.05 ohm, if your output has a change of current of 1A, the effect is 0.05V. In most case, the current change is small, say a few milliampere or a few hundred milliampere in the worst case, which will not cause a voltage fluctuation of less than 50mV. Of course if the current sense resistor is on the V+ side, voltage fluctuation will also happen but on the V+ supply but not the the ground, which will be less of a concern, but V+ fluctuation happens nonetheless. In the end, it is a design decision.

author: ajb
author_rank: Super Contributor
timestamp: June 02, 2022, 04:04:20 pm
content: It may help to flip the schematic around a bit and look at it like the below. This is exactly the same circuit, just rearranged to show the power flow more conventionally and make the polarity of the sense resistor look a little more sensible.
Current Sense Resistor Specs - Page 1
Forum section: electronics / projects

author: raptor1956
author_rank: Frequent Contributor
timestamp: February 05, 2018, 08:41:21 pm
content: I'm adding the final touches to a Peltier module testing rig and the last thing I want to add is current sense for the Peltier power and for the heater circuit -- two circuits. So I go to Digikey and look up current sense resistors and have found several resistors that look to be a good fit but there's something in the specifications that has me a bit puzzled.In the linked PDF for a Bourns current resistor there's a specification called "Load Life" that I don't quite understand. I would not have expected a limited lifespan so long as you don't exceed the ratings so seeing a 1000hr life at 70C and a limit of 1000 cycles just doesn't add up for me. See link.http://www.bourns.com/docs/Product-Datasheets/PWR4412-2S.pdfIn my application the two circuits are at 2A-5A and 12VDC (Peltier power) and the heater circuit is less than 2A at about 16VDC and I plan to use 50mOhm 1% 3W resistors for current sense with the Peltier circuit using one and the heater circuit using two in series so the voltage drop in large enough to get reasonable resolution with a 12-bit ADC. So, the max power the resistor will see is about 1.25W but that's at 5A and most of the modules are running under 4A -- the heater circuit is much less and spread over two resistors so heating will not be an issue.So, could someone illuminate me as to what the load life and cycle limit is about -- I suspect that running them below rating as I plan will avoid lifespan limits.Brian

author: Paul Price
author_rank: Super Contributor
timestamp: February 05, 2018, 11:53:52 pm
content: What "load life" refers to is the maximum change in resistance over time at a given temperature and this means the value of the shunt might age after sustained high temperature. The shunt wouldn't fail, but the change in resistance will affect the accuracy of current sensing by the time the load life (1000-hrs) has been reached, so you might expect up to additional 2.5% error if it is in use for a sustained 1000 hours at 70-C, but since the error drift direction is not specified, this is a worse-case spec and the sense resistance might even drift up and down from its specified value and also drift back towards its specified value again over time.

author: raptor1956
author_rank: Frequent Contributor
timestamp: February 06, 2018, 12:49:44 am
content: Thanks Paul, that's kind of what I thought it meant but wanted a second opinion. At the lower power dissipation I expect to operate at I doubt I'll get anywhere near 70C. I may add a small fan, of which I have many, to make sure they stay relatively cool.Brian
Current sensing noise consideration in FoC capable BLDC Motor driver - Page 1
Forum section: electronics / projects

author: satyamfifa
author_rank: Regular Contributor
timestamp: November 16, 2021, 09:37:18 pm
content: Hey Guys,I am designing a 48V, 30A continuous current FoC capable BLDC motor driver. I want to do in-line current and voltage sensing in all three phases plus total current sensing. For this I was to use shunt resistor about 0.001each connected to INA240 current sense amplifier which is connected ADS7947 (12 bits 2MSPS) ADCs which has SPI interface, each ADC has two channels therefore I am thinking of using one channel for measuring phase current and other for phase voltage. I am thinking of placing one shunt resistor, amplifier and ADC close together for each phase.However, the thing I am really considering now is the impact noise generated by MOSFETs switching high current on current sensing circuit and how can it be minimized. I am considering using separate ground planes for the sensing circuit, I have been doing quite some research on separating ground planes and I have heard argument both for and against doing so, and because I am measuring frequencies below 20 kHz, I am thinking this could be good idea. I understand that ADCs and Amplifiers referencing should be tightly coupled together since any noise / offset with affects them both will be cancelled out.Another design decision that I am not really sure about is weather to power the analog circuit from 3.3V directly from the logic board, to power it with 5V requiring me to add a LDO which is sourced from 48 V input.Finally, I am also concerned about the signal integrity of the SPI signals if the ADCs are placed close to amplifiers which mean they might be placed further away from the logic board. I assume that SPI clock frequency will be a typical of 34 MHz.I think the right component placement will be key to achieving the most optimal design. I would really appreciate any suggestions, tips, possible solutions, considerations etc.Kind Regards,Sparsh

author: Benta
author_rank: Super Contributor
timestamp: November 16, 2021, 09:52:53 pm
content: The most ambitious and problematic point in your post is using 1 m\$\Omega\$ resistors for current sensing.

author: jonathan_nadar
author_rank: Contributor
timestamp: November 17, 2021, 03:53:54 am
content: You can refer to this document from TI.
Current sensor datasheet ACS 715 - Page 1
Forum section: electronics / projects

author: sandy
author_rank: Contributor
timestamp: August 03, 2014, 04:26:11 pm
content: Hi, The datasheet for ACS 715 current sensor from allegro, shows a vout from 1.5V to 4.3V for input current of 5A to 20A (page7 of datasheet). If we want to measure from 0A-20A , then is it possible to measure below 5A? . It is stated in datasheet that it can measure from 0-20A , them why the spec , can someone help me with this. Rgds

author: nctnico
author_rank: Super Contributor
timestamp: August 03, 2014, 04:42:24 pm
content: The swing of the output amp is limited. If you need to measure from 0 then you need a bipolar device.

author: dannyf
author_rank: Super Contributor
timestamp: August 03, 2014, 05:00:11 pm
content: QuoteSure. Though measuring very low current (ma for example) is likely difficult.QuoteLikely due to reduced accuracy. Same thing with other high side sensors (different beast).

author: Asim
author_rank: Regular Contributor
timestamp: August 03, 2014, 05:24:01 pm
content: If you check page 9 you will find the full scale graph.The graph in page 7 is probably showing the linear region? ( this is what it looks like for me )

author: mij59
author_rank: Frequent Contributor
timestamp: August 03, 2014, 05:28:54 pm
content: The sensor is kind a noisy, take a look at page 10 of the data sheet.
Current sensor MPQ8113 - any good? - Page 1
Forum section: electronics / projects

author: eTobey
author_rank: Super Contributor
timestamp: March 09, 2023, 09:23:29 am
content: Hi,i found this current sensor:https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MPQ8113AGJ-AEC1/Im thinking of using it in my brushless motorcontroller to sense current in the phases of the motor. I am wonder if this chip/brand is one of the good ones.Also, would it be better to use hall sensors for this? What about current sensing with rdson?Any tipps would be much appreciated.CheersToby
Current sensor sampling - Page 1
Forum section: electronics / projects

author: XaviPacheco
author_rank: Regular Contributor
timestamp: September 28, 2018, 07:35:25 pm
content: Hello,I'm using thiscurrent sensor TLI4970located at the emitter leg of a power IGBT, which is being switched at 10 kHz. I'm reading the sensor every 10 ms. However, sometimes I get expected values, and sometimes I get strange values. Does this have to do with the sampling frequency? Is this behavior normal? I know that I'm measuring current on a switching element, which is why I'm probably not getting a "constant current value". What are your thoughts?

author: aheid
author_rank: Regular Contributor
timestamp: September 28, 2018, 07:49:28 pm
content: You probably should define what you mean with "strange values". I notice the thing has a max bandwidth of 18kHz, which is quite low assuming you're switching rather fast, ie square wave-ish.

author: XaviPacheco
author_rank: Regular Contributor
timestamp: September 28, 2018, 07:54:45 pm
content: Quote from: aheid on September 28, 2018, 07:49:28 pmLet's say I'm getting 6A (what I expect), in the next measurements I get values around 0A. Then I get 6A again and so on.

author: Gribo
author_rank: Frequent Contributor
timestamp: September 28, 2018, 07:55:27 pm
content: What are your filter settings? Not all settings support a 10KHz signal.

author: XaviPacheco
author_rank: Regular Contributor
timestamp: September 28, 2018, 08:01:03 pm
content: I'm using the default settings as I don't have how to program the sensor for now.

author: aheid
author_rank: Regular Contributor
timestamp: September 28, 2018, 09:32:13 pm
content: Quote from: XaviPacheco on September 28, 2018, 07:54:45 pmWhat's strange about that? You have a (roughly) square wave signal at 10kHz, and you're sampling it at 0.1 kHz, so your samples will essentially be randomly distributed in the waveform. Sometimes you will sample when the transistor is on, sometimes you will sample when it's off.
Current sensor with LM324 Single supply - Page 1
Forum section: electronics / projects

author: panoss
author_rank: Frequent Contributor
timestamp: August 28, 2023, 11:13:13 am
content: I 'm trying tosimulate in falstad online simulatora current sensor built arount an LM324, powered by 5V (single supply).It will sense current of 2.5A(load=1.8 Ohm) to 1.5A(load=3 Ohm) using the R sense.(Rf=50k R1=10k)RL=3 Ohm I=1.563A 312mV Out=0.123VRL=1.8 Ohm I=2.5A 500mV Out 1VSo, the range of output is from 0.123V up to 1V.I want awider range of output, something like from 0.123V up to 3,5V.I have tried different values of Rf but no improvement in the range.Maybe the whole circuit is not correct, you can freely try the simulation on the link above.Any help is welcome.

author: pqass
author_rank: Super Contributor
timestamp: August 28, 2023, 01:20:55 pm
content: The LM324 can't produce an output close to the positive rail. If you need the output to be at most +3.5V and if the simulation is correct, then it would need a min. +5.5V supply. Anything below that would affect the output. Also, the output can get close to the negative rail but not quite 0V; 123mV in my simulation. Seeherefor a modified version using a diff-amp configuration. You can change the supply voltages; see right margin sliders.

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 28, 2023, 01:26:29 pm
content: You are also exceeding the LM324 input’s common mode range.If the load *must* be referred to +5V, then you require an opamp with a common mode range that includes the supply voltage.

author: Psi
author_rank: Super Contributor
timestamp: August 28, 2023, 01:27:00 pm
content: ah the joys of opamps and rail to rail issues.

author: ledtester
author_rank: Super Contributor
timestamp: August 28, 2023, 01:43:24 pm
content: The LM324 has a common-mode voltage range of V- to V+ minus 2 volts and so when it is used for current sensing it is usually used in a low-side configuration.Have a look at OP1B in the attached schematic. Like in pqass's circuit it is used in a diff-amp configuration but the op-amp's inverting input is at ground (through R9). R6 is the current shunt, R7, R8 R9 and R10 are the diff-amp resistors.Update: Here's a TechNote from TI on low-side current sensing which discusses a bit about the LM321 (the single device version of the LM324).Low-Side Current Sense Circuit Integration - SBOA190https://www.ti.com/lit/an/sboa190/sboa190.pdf

author: panoss
author_rank: Frequent Contributor
timestamp: August 28, 2023, 02:42:41 pm
content: Unforunatelly I can' go up to 6V (would work nice with 6V), I have to use a 5V power supply.I ended up to the circuit from SBOA190 - Figure 2.Thank you all.
current sensors - Page 1
Forum section: electronics / projects

author: noobita
author_rank: Newbie
timestamp: January 19, 2016, 10:19:15 am
content: can any allegro current sensor sense current from 100mA to 10amps?

author: leonerd
author_rank: Regular Contributor
timestamp: January 19, 2016, 01:49:31 pm
content: They probably could, but less accurately. The Hall-effect sensors aren't so good much below about 1 amp.For smaller currents (1 to 100mA) I typically use a small shunt resistor and a current-sense amp. to amplify the voltage drop across it. These are good to tune down to smaller currents, though of course you lose the advantage of galvanic isolation from the measured source, so they aren't always a good replacement for what you can do with an Allegro Hall.
Current sharing / Ideal Diode ORing on 1.1V rail - Page 1
Forum section: electronics / projects

author: veryevil
author_rank: Unknown
timestamp: October 20, 2021, 07:10:04 pm
content: I'm trying to come up with a way to current share a 1.1V rail. I have a design with up to 6 plug in cards each which generate a 1.1V supply which I would like to use on the backplane the 6 cards are plugged into.This would be for fault tolerance and also reduced loading of all the individual cards.This is easy at higher voltages but I'm struggling to come up with a way to do it at such a low input voltageCoupled with the lack of available chips this is really got me stumpedI do have 5v and 3v3 available too if there is a chip I can use with vcc higher but 1.1v as the pass throughAny thoughts?Output current would only be an 1A at 1.1V

author: David Hess
author_rank: Super Contributor
timestamp: October 21, 2021, 10:57:19 pm
content: So each card generates a 1.1 volt supply, and you want to interconnect it between cards so that if power is lost to one of the cards, the other cards will power it?The forward voltage drop of diodes is obviously a problem at such low voltage. At such low voltages, bipolar transistors can be used to sort of make diodes with no forward voltage drop by biasing the base with sufficient current, and there is probably some way to improve that. This only works at low voltages because the reverse breakdown voltage of the base-emitter junction is only like 5 volts.1 amp is not all that much. If the 1.1 volt supplies are regulated closely enough, then they can be connected directly in parallel and rough current sharing will be enforced by the series resistance between the sources, or 10s of milliohms of series resistance can be added at each output.I am dubious about sharing such a low voltage between cards. Better might be to share a slightly higher and not as tightly regulated voltage, and implement 1.1 volt regulation on each card.
Current shunt temperature coefficient - Page 1
Forum section: electronics / projects

author: splin
author_rank: Frequent Contributor
timestamp: May 22, 2016, 07:11:35 pm
content: Searching on Digikey finds some surprisingly cheap Stackpole BR series (< $0.2) 5mohm 3W 20ppm/ºC shunts. Cheap for 20ppm/ºC that is. But the datasheet actually says:"±20 ppm/ºC element wire±200 ppm/ºC at lead stops"Hmm so does that mean you use the 200ppm/C figure as an overall TCR? That seems very pessimistic. TT electroncs OAR series shunts are similar and also cheap. The OAR data sheet only states 20ppm/ºC for the wire - it doesn't provide an overall TCR value.I guess its complicated by the relative heating of the resistance wire and the leads - the OAR datasheet shows some pictures of the temperatures of the resistive elements and the copper leads under load. E.g. the 3W, 5mohm version running @ 3W shows the element at 160C and the solder joint at 70C.So what TCR would you use? I assume that the overall TCR varies with power levels so what if it's running much below its rated power, say less than 10% with a temperature rise of perhaps only 20 or 30C above ambient? Yes I know there is no substitute for actually measuring some in your own circuit usage but I assume someone is familiar with these type of shunts and their characteristics.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 22, 2016, 09:10:40 pm
content: If what matters is the total voltage dropped across it, you're kind of stuck.If what matters is the voltage drop across the Kelvin sensed section (assuming it comes with wires, or you can add them), then you're fine.Tim

author: Zeranin
author_rank: Regular Contributor
timestamp: May 23, 2016, 01:19:29 am
content: I haven’t looked up this Digikey part, but I presume these are 2 terminal resistors, in which case you will never achieve anything like 20ppm for a 5mohm shunt. Why so?Copper has a TCR of ~3900 ppm/K, As a 2-terminal device, this resistor must have some ‘lead resistance’. Let’s assume that the copper ‘leads’ contribute only 0.25 mohms, that’s a very small resistance indeed, but it’s still 5% of the total resistance of 5 mohms, so the copper will contribute (5%x3900) =195ppm of TCR! Enough said? If you repeat the calculation for a 10K or 1K resistor then you find that the TCR effect of the leads is rarely an issue, but for 5 mohms it’s a different story, and you will never get decent TCR without going to 4-terminal construction.

author: Marco
author_rank: Super Contributor
timestamp: May 23, 2016, 01:52:29 am
content: I think you are meant to solder separate wires if you want a Kelvin connection,the pinched legsmake it awkward to drop it on the PCB, not very convenient.
Current signal passive HPF - Page 1
Forum section: electronics / projects

author: Gerharddc
author_rank: Newbie
timestamp: August 26, 2022, 07:12:53 am
content: I want to passively filter out short pulses from a current source (photodiode). For a voltage signal, a typical RC high-pass filter works fine, but for a current signal that circuit obviously just doesn't work. A simple solution of course is to add a resistor after the current source to obtain a voltage signal that can then be filtered. (Something like in the attached image)This works, but I feel like a simple two component arrangement should also be possible for filtering current signals however I am struggling to think of one. Any ideas?

author: Terry Bites
author_rank: Super Contributor
timestamp: September 05, 2022, 05:39:35 pm
content: The signal source has a very high output impedance- 10kThis will not drive an hp section with a low impedance 100R in the passband. The passband attenuation will be ~100/10000 !For a passive hp response you want R2>>R1 typically 10x at least. You could reduce C1 and raise R1 proportionally. This would lead to silly values of course.There's no passive network that's going to work well.The simple solution is to buffer the input to the C1 R2 section from R1. Note that this buffer needs an input impedance >> R1 again typically 10x at least.Seehttps://www.analog.com/en/technical-articles/how-to-effectively-design-and-optimize-tia-interfaces-of-lidar-systems.htmlon AC coupling moansTo get a decent hf response you need a photodiode "transimpedance" preamp to turn output current into a useful voltage.Load of tools for that, eghttps://tools.analog.com/en/photodiode/. Low frequency rejection can be added post preamp or by adding an integrator loop . The integrator is a preferable solution.This might sound complicated but its not. Ambient light rejection circuits have a high pass effect. You just tune the integrator time constant to get the hp corner.
Current Sink/Source DAC - Page 1
Forum section: electronics / projects

author: luky315
author_rank: Regular Contributor
timestamp: May 08, 2014, 12:45:35 pm
content: I am using PSoCs with the incredibly useful IDAC8s. They can sink and source up to 2 mA (with limitations of course). Unfortunately there are only 2 of them and to get more than 8Bit resolution you have to combine them.For a new project I need more than the 2 available DACs. There is the DS4412 from Maxim with similar capabilities but with only 7Bit and a relatively high price.What would be a good way to get 8 current sink/sources with selectable range and high output impedance on power up? Accuracy is not a problem (+-5% is ok) but more resolution would be great.
Current-source drive Amplitude-tracking detector - Page 1
Forum section: electronics / projects

author: Mr. Coffee
author_rank: Regular Contributor
timestamp: March 11, 2014, 03:05:57 am
content: I’m not seeing it. How does driving a diode from a current source (practically) eliminate the forward voltage drop?Sure, I understand how more and more amplification of a low level input signal makes the forward drop and non-linearity of a diode's turn-on point become less and significant at the output of that amplifier...I just built one of those types of RF level meters--but I don't think that is what the author is describing here--not exactly.RobCan anyone dumb this down for me?From The Art of Electronics, second edition:“Current-source drive Amplitude-tracking detectorAnother solution to the problem of rectifierdiode nonlinearity is to drive the rectifier circuitwith a current, rather than a voltage;the output is then loaded resistively, to producea proportional output voltage (Fig. 13.29). Figure 13.30 shows a goodimplementation with voltage-controlledtransistor current source; the performanceis shown in Figure 13.3 1. You can understandthis circuit in another way: Withno input signal, the amplifier's output isdecoupled from the rectifier network, producingvery high voltage gain (with itscurrent-sink load); thus, only a very smallinput signal is needed to turn on the diodes.At that point the voltage gain drops toGv = &/(RE + re) (in this case, Gv x3), preventing saturation. With a widebandamplifier and fast diodes, this circuitdesign will operate to 100 MHz or more.”

author: Mr. Coffee
author_rank: Regular Contributor
timestamp: March 12, 2014, 02:28:16 am
content: Nevermind...I got it.