A Rogowski coil is a device for measuring AC current that differs from a conventional current transformer in that it has no need to encircle the conductor whose current it measures. They’re by no means cheap though, so over time we’ve seen some interesting variations on making one without the pain in the wallet. We particularly like [Stephen]’s one, because he eschews exotic devices for an interesting hack on a familiar chip. He’s taken the venerable TL431 voltage reference chip and turned it into an op-amp.
We had to look at the TL431 data sheet for this one and shamefacedly admit that since we’d only ever used the chip as a voltage reference, we hadn’t appreciated this capability. In this mode, it’s a op-amp with the inverting input connected to a fixed rail, so it can accept a feedback network to its non-inverting input just like any other. He’s using it as both integrator and amplifier, as well as, of course, in a more conventional power supply.
We like the instrument, and the use of the TL431 in an unexpected manner is the cherry on the cake. Here’s a previous Rogowski circuit using more conventional parts. You can dive a bit more into the theory, too.
I’d love to read the actual article, but there’s no link to it….
https://hackaday.io/project/190985-tl431-rogowski-coil-current-sensor
https://hackaday.io/project/190985-tl431-rogowski-coil-current-sensor
In circuits like this, it is helpful to think of the TL431 as a weird NPN transistor with a 2.5V base voltage and a super-sharp corner in its I-V graph.
“He’s taken the venerable TL431 voltage reference chip and turned it into an op-amp.”
The TL431 is an op-amp by design, or more specifically, an op-amp with a reference voltage tied to one of it’s inputs, just like most linear voltage regulators. Probably the majority of all ‘431 ever produced are not used as “precision zeners”, but as error amplifiers in the feedback loop of switched mode power supplies.
Yay a feedback oscillator! I guess this is a win somehow. You can do the same thing with a wide array of devices…
So do it a different way and right an article about it. Do you not understand how articles work? I swear, the hackaday article comments are more toxic than Arduino forums.
Seconding Paul, yes TerryMatthews, please share more examples with the “wide array of devices” and additionally please tell us how to do it with an Arduino and a 555 Timer.
So I learned two things. The other thing is that you can print a block diagram on the back of a circuit board so you don’t have to hunt for it.
thought this was neat too!
The datasheet from Onsemi: TL431CLPRPG.pdf has some other applications such as an SMPS circuit in their examples section.