TL431 based rogowski coil current sensor - Page 1
Forum section: electronics / projects

author: Slh
author_rank: Regular Contributor
timestamp: May 25, 2023, 05:08:54 am
content: Here's my latest project:https://hackaday.io/project/190985-tl431-rogowski-coil-current-sensorI wanted to see if I could abuse some TL431 shunt regulators to make a Rogowski coil for measuring current. Turns out that it works quite well.I used one as the integrator (good idea, seems to work really well) and another for a X20 amplifier (not such a good idea, <100kHz bandwidth). All in all, pretty good for around £1.00 in dodgy, unbranded silicon and passives.Now I need to make some sort of high frequency current source for calibration... I suspect that will be a lot more effort that the coil itself.

author: daisizhou
author_rank: Super Contributor
timestamp: May 25, 2023, 05:30:33 am
content: What is the difference between this and pearson current probe?https://www.pearsonelectronics.com/

author: Weston
author_rank: Regular Contributor
timestamp: May 25, 2023, 08:11:33 am
content: Cool work! Nice (ab)use of the TL431. I think its a really handy and under-appreciated chip.I made a rogowski coil + amplifier that is pretty similar to the CWT ultra mini and optimized for JLC assembly service. I just need to get around to document it. There is a really endless path of optimizations you can make.What is your noise level? Thats a big design challenge in designing the integrator.

author: moffy
author_rank: Super Contributor
timestamp: May 25, 2023, 09:47:28 am
content: Quote from: daisizhou on May 25, 2023, 05:30:33 amCost.

author: daisizhou
author_rank: Super Contributor
timestamp: May 25, 2023, 09:51:22 am
content: How much frequency AC current measurement can the Rogowski coil support? 800Khz?

author: moffy
author_rank: Super Contributor
timestamp: May 25, 2023, 10:03:05 am
content: Quote from: daisizhou on May 25, 2023, 09:51:22 amUp to 20Mhz fairly readily, see:https://www.ti.com/tool/TIDA-01063

author: daisizhou
author_rank: Super Contributor
timestamp: May 25, 2023, 10:16:23 am
content: Pearson current probes seem to be recognized by more people.I see a lot of people measuring high frequency induced currents using Pearson probesTIDA-01063 I don't know how it works in practice，Looking forward to the actual use experience

author: Slh
author_rank: Regular Contributor
timestamp: May 25, 2023, 03:50:02 pm
content: Quote from: Weston on May 25, 2023, 08:11:33 amThat sounds like something that I should look into. So far I've just been content with feeling smug that it worked so I haven't properly measured it's performance in any way other than eyeballing the difference between it and a LEM hall effect sensor.Interestingly, the output noise appears to be a lot better than a classic opamp based integrator that I used on a previous probe. It might just be because of the low high frequency cut off though.I think I'll probably wait until I get the assembled PCB before measuring it properly as my homemade one doesn't have space for good probing. I was also lazy with the ground as well so it doesn't have a proper ground plane. I was a good boy when I designed the assembled PCB. It has a ground plane and test points. I also snuck in some mods so that I can fit an NPN common emitter amplifier instead of the TL431 x20 amplifier to hopefully get better high frequency performance.The main useful differences with the pearson probe are:1) no core losses,2) can't saturate the coil (can saturate the integrator but that's ok).3) very low insertion loss4) thin flexible sensor that can be opened to feed around cables, bus bars and potentially MOSFET legs.5) requires power supply.

author: Slh
author_rank: Regular Contributor
timestamp: June 17, 2023, 06:35:16 am
content: PCBWay were kind enough to sponsor me with some assembled PCBs so I whipped up a quick design. They're a bit larger than the original but that's mainly to fit them in an off the shelf box.Only two issues that were fixed by resistor value changes. The bias resistors on the integrator were the wrong way round and the 5B regulator had too little resistance so it was burning 100mA all the time (getting rid of the 100R did the job). Ah, the importance of reviews...So far it looks like genuine TI TL431 regulators are faster than random junk TL431.

author: magic
author_rank: Super Contributor
timestamp: June 17, 2023, 09:24:44 am
content: If MMBT3904 works better for the 20x amp then it might also work better in the integrator

author: Slh
author_rank: Regular Contributor
timestamp: June 17, 2023, 12:37:36 pm
content: I'll look into it. It would be nice to make it even simplerThe original design was entered into the Hackaday opamp competition so I felt obliged to abuse the TL431 regulators as opamps as much as possible. Now, however, I can play and I have 10 populated PCBs to play with.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 17, 2023, 01:40:40 pm
content: Congratulations on your project.I also believe that the 431 is a versatile little chip which, with a little imagination, may be used in pretty creative ways.Now, that your project has been validated and have a nice PWBA for it, could you clean the schematic?

author: Slh
author_rank: Regular Contributor
timestamp: June 17, 2023, 04:26:44 pm
content: Sure. Here's the circuit as intended. I've also uploaded it to the project page.Having looked into using a single BJT as the integrator I've come to the conclusion that, while it's possible, the TL431 makes a much better one. The gain from a single BJT won't be anywhere near the 270 (~50dB) that I can get from the TL431. Probably only around 20dB. Also, the high frequency performance of the TL431 as an integrator is pretty good. I guess it will be limited by any higher up poles which aren't visible on the small signal voltage gain plots. I ought to hook the circuit up to my NanoVNA and see how it goes but first I need a load of attenuators so might need a bit of time to sort it out.

author: LukeW
author_rank: Frequent Contributor
timestamp: June 18, 2023, 03:37:08 am
content: Nice design.Good old 431. There should be a 431 hack challenge or something where people can show off the most creative or unusual ways to use or abuse the 431. You can do a lot of different things with it!

author: magic
author_rank: Super Contributor
timestamp: June 18, 2023, 07:39:47 am
content: With a few hundred of those bugs one could likely build a power amplifier even.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 18, 2023, 07:42:44 am
content: For a BJT, try putting a CCS load on top instead of a collector resistor. At AC, this can also be a gyrator, which doubles as emitter follower.Tim