Power inductor checker


Drone refers us to this article from ELM-chaN:  Power inductor checker

Here is a nice write-up on a home-brew power inductor checker for use with an oscilloscope. This device is useful for characterizing inductors from the junk-box, or pulls from dead PSU’s.
The Author says he’s switching the tester at 50Hz. I suggest that switching at the frequency you plan to use in your SMPS will give better results. Inductors should be tested at their operating frequency in order to reveal material characteristics and stray parasitics.

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  1. Very nice to see, especially the results from different toroids, showing their performance. So much inductor design is theory, it’s good to see some practical info!

    “I suggest that switching at the frequency you plan to use in your SMPS will give better results. ”

    Not entirely correct – yes, SMPS will operate at tens or hundreds of kHz, but that isn’t how he’s driving the inductors in this circuit. He is just applying a constant voltage and looking at the rise of the current waveform. The 50Hz value is the frequency that the inductor is _tested_. It can be even lower, if you have a storage scope – I built a similar tester a while back, and my lowest frequency is 0.2Hz (used for very large inductors, to cut down on power loss in the MOSFET and freewheel diode).

    The voltage droop can be a problem, but the best way around is to operate at a higher voltage and shorter pulse times. I typically use 60V, but sometimes up to 200V if I have a really large, high-current inductor and I have trouble keeping a constant voltage throughout the pulse.

    Plug for my own page – I looked at how the gap affects things like inductance and saturation current, it might help make things clearer for people:


    1. Yeah! I have to wonder, though, just how flexible it is, and what sort of range of inductors it can test. With my own little lash-up, I find myself changing voltages, MOSFETs, smoothing capacitors a lot, in order to get the best measurement setup for the inductor under test.

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