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Seeking tips on using J2121A High Power Line Injector to measure boost PFC inductors with bias current

Seeking tips on using J2121A High Power Line Injector to measure boost PFC inductors inductance with bias currents up to 20Apk and in the frequency range of 100kHz-500kHz. From what I have found there is not much published on using this particular injector in this manor and what needs to be done to make the measurements as accurate as possible. Also looking for information on if the current limit (20A) and voltage limits (400V) can be slightly exceeded without damage when measuring converter input & output impedances. As it is common for PFC output voltages / Isolation stage input voltages to be in the 390-450V range.

4 answers3 replies

7 Comments

steve

Aug 04, 2021

yes, please email me at Steve@picotest.com

steve

Aug 04, 2021

I don't know how much higher you want to go in current, but I believe you can probably push it to 450V. It would exceed our derating guidelines, but the capacitors are rated for 500V. At some point you'll thermally kill it, but if you wanted to go to 25Amp I would say maybe, especially if you don't run it there continuously. As a controlled experiment, I think it would be ok...

ben

Aug 04, 2021

Replying to

Thanks for the answer. On the current measurement side is it the pass device of the current sensor that is the limiting factor? Also can take offline.

steve

Aug 02, 2021

We do have some application info and also did some videos and webinars I can send, but they won't be all that helpful for you. We typically show step down regulator inductors, which are much lower value, since we don't get many requests for higher inductances. At high inductance, you will run into the noise limitations of the internal hall sensor as you have seen.

The voltage drop of the J2121A is only 700mV, so realistically, you can't modulate more than about 500mVpk, that's why increasing the signal level doesn't really help at some point.

I think you have 4 options to improve your measurements.

Try reducing the RBW from 100 Hz to 10Hz

Try trace averaging, which I admit, I haven't used myself

Use an external current probe. That will be lower noise than the internal hall sensor

Use a current sense resistor

This is a great application, so we'll help as much as you need and maybe end up with an app note for PFC inductors in the end. Can you send us an inductor we can try to measure here? What is the bias current?

ben

Aug 04, 2021

Replying to

Thanks for the response. Please contact me directly to discuss details and arrange for shipment.

steve

Jul 31, 2021

We have two methods that will work for you. Here is an app note for the J2121A and I also did a presentation at PSMA2020. You can find the video presentation here https://www.dropbox.com/s/0485cltxclli3ws/PSMA%202020.mp4?dl=0

ben

Aug 02, 2021

Replying to

Thanks for the presentation. Can you point me to the application note on the J2121A, as I am only finding the 2 page brochure and manual?

Since my initial post I have been able to work on the setup and measure several inductors.

The setup is working, but I have ran into a couple challenges:

The PFC inductors are in the range of 100uH to 1000uH, which is much larger than you typically demonstrate. At impedances above 50-100 Ohms it looks the measured current drops to the noise floor. Measuring a lower value 40uH inductor looks similar but with the measurement noise coming in at a higher frequency. Turning the drive level up seems to help, but this is limited as increasing it too far the test signal starts to intersect 0V which brings about other challenges.

The setup is using 3 P9610A in parallel as described, in the manual to deliver the required current. When in constant current mode the supplies are not stable testing inductors of this value range. Moving back to constant voltage mode is stable and the static sharing is pretty good. Dynamically there is some imbalance (trace 1 is the voltage into the P2121A and traces 2-4 is the current being delivered by each supply). No problems have been noted yet from this, but I have not investigated the sharing yet at 20A currents. Is there an alternate compensation network option for these supply to improve their operation in this configuration and these loads?

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