Inductances of an Inductor

You mean you're seeing 400.045 uH?

Sylvia.

D from BC schrieb:

Hello,

you really want an inductance of 400 µH to be far more precise than about +- 4 µH? You expect a resistor of 400 kOhm to be better than 399.955 to 400.045 kOhm?

Bye

The total is not important me. The breakdown is.

After testing, my inductor seems to be composed of 4 inductances.

I suspect I'm getting some 'uncored' inductance (35nH?) from my winding technique. The inductor is hand wound.

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

It's not about precision, it's about power inductor modeling at >1Mhz. I'm doing some 1st time learning in how non-ideal inductors in an smps can generate EMI.

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

Huh? If all you have is a series connection of inductors (no parallel capacitances), then the terminal characteristics are equivalent to a single (total) inductance.

What are you measuring that "leads" you to seeing something more complicated?

As others have said, it had better be something more than a value tolerance issue.

I think the real question is... (Now that the coffee has kicked in.)

What factors contribute to an inductors series resonance?

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

Essay question, or multiple choice ?:-)

...Jim Thompson

You have not explained what you are measuring very well. Please explain your measuring techniques the frequencies and other parameters used how you get four values without any assumptions of where they come from. Also a description of the physical situation, core, how wound, size, number of turns, wire size, wire length, lead length, coil resistance, voltage, current, frequency and anything else you can think of, all would be helpful.

iirc as per textbook inductor model. the series resonance of an inductor would be just from (lead inductance + circuit conductor inductance) with the interwinding capacitance.

But on the bench, the inductor series resonance I get (frs=~150Mhz) suggests I have more lead inductance than what I can account for.

I've seen a few non-ideal inductor models but I don't recall what I'll call 'the core doesn't link everything' inductance.

Leakage inductance? But isn't that just for transformers.

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

How in Buddha's world are you accounting for 45 nH of mystry inductance out of 400 uH??? Obama couldn't even do the deficit calculations down to that precision. Are you measuring this?

A 400 uH inductor will probably have a self resonance pretty low in frequency, who knows, maybe even around 1 MHz. 400 uH in a 1 MHz switcher seems like something that won't work very well. The iron core will also be very lossy at 1 MHz. You want to use ferrite or powdered iron cores at those freqs.

As you start to approach resonance, you will see the inductance increase. Do you have access to an impedance analyzer like a HP4194 or HP4195? This will be very instructional, especially when you start to examine different winding geometries to increase the self resonant freq.

As well as the inductors spewing out a bunch of magnetic crap, how you lay out the circuit board and filtering will also have a huge effect on EMI issues.

Don't get the question. I don't know what you're subtracting from what.

Shifting windings on the toroid or heck, just moving the leads relative to the core (as you note not all the flux is in the core) will produce bigger changes in inductance that what you're asking about.

Tim.

Ugh...that'll take too long. But I'll mention that I used an EMI sniffer probe.

What I'm looking for is an explicit cored inductor model. Know any good links? I'd like to see if there's more than 2 types of inductances in the equivalent network..

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

I'm observating what looks like a ~150Mhz series resonance from my

Good estimate.. Fr parallel = 1.6Mhz. But my tests suggest I have a series resonance of Fs ~150Mhz. Besides using an oscilloscope...I turned on an FM radio.. Smps off-get static Smps on..no static.

Oops. I guess that was vague.. . I wrote iron to mean powdered iron.. I guess electromagnetics use iron.

Yup.. Had to rearrange parts twice now :(

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

It was a late night post.. Sorry..I could have d What contributes to an inductors series resonance? This is the resonance due to the lead inductance and the interwinding capacitance. But is there anything else?

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

electromagnets..

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

He's making about as much sense as he ever does.

John

kOhm?

You probably need to think about what your winding looks like to

If is a single-layer widing on a toroid the current might be running around the circumference of the toriod through the inter-winding capacitance, thus seeing the single loop around the periphery of the toroid as as your 45nH.

You could try and see what a "non-progressive" winding scheme did for you, though it might lower the first self-resonance frequncy below 1.6 MHz - they are essentially two-layer windings. Rayner and Kibble in "Coaxial AC Bridges" at Fig. 4.20 recommend winding half way around the toroid, then winding back over the top of that winding and keeping going back around the toroid to the point when you first turned around, then turning around again and winding back to the start - they claim that this minimises the external field and the self-capacitance, but it is still a two-layer winding.

-- Bill Sloman, Nijmegen

-- Bill Sloman, Nijmegen

How have you determined that the inductance of the core/winding combo is

Sylvia.

Used a function generator and a scope to determine Lcore=400uH. Created an RL circuit with f for 90 phase and measured Vl and did the math..

The tiny inductances I mentioned were determined by other methods.

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design