A measurement technique -- you don't need a Bode-100 VNA to do it -- uses a current controlled DC power supply with low output voltage (500mV) to bias inductors. A diode bridge is used to protect the input of the VNA. Will have to try it with a center-tapped audio transformer for the two inductors as DUT1, DUT2
https://www.omicron-lab.com/fileadm...kose/Inductance_measurement_under_DC_bias.pdf
https://www.omicron-lab.com/fileadm...kose/Inductance_measurement_under_DC_bias.pdf
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Will use his methodology and report back! He used a pair of 32uH inductors, for audio output trafo the inductance is orders of mag larger.
Great find! Thanks for sharing. I will have to try this with my Analog Discovery set up. Not professional level like the Bode-100, but good enough for me as a retired professional, because nobody cares!
BTW, the author's suggestion to use a bunch of ceramics in parallel with the electrolytic may or not be a good idea. Generally, if you parallel different value caps the ESL of one type will resonate with the C of the other, and vice versa. Better to use all the same values. You can simulate or measure this.
I've been measuring some caps for another project and found that the newer generations of hybrid aluminum electrolytic polymer caps are pretty darn good. Here's a well regarded Nichicon aluminum electrolytic for comparison. 470 uF @ 35 VDC:
Now, here is a Nichicon hybrid cap, only 150 uF @ 35 VDC:
I bet a higher value (can be lower voltage) hybrid cap would do fine by itself in the test fixture. Several in parallel would be even more betterer.
BTW, the author's suggestion to use a bunch of ceramics in parallel with the electrolytic may or not be a good idea. Generally, if you parallel different value caps the ESL of one type will resonate with the C of the other, and vice versa. Better to use all the same values. You can simulate or measure this.
I've been measuring some caps for another project and found that the newer generations of hybrid aluminum electrolytic polymer caps are pretty darn good. Here's a well regarded Nichicon aluminum electrolytic for comparison. 470 uF @ 35 VDC:
Now, here is a Nichicon hybrid cap, only 150 uF @ 35 VDC:
I bet a higher value (can be lower voltage) hybrid cap would do fine by itself in the test fixture. Several in parallel would be even more betterer.