Inductances of an Inductor

Loosen the coil a little - that should fix it. ;^)

Are you sure the inductor you're looking at is involved in this mysterious resonance, completely, partially or at all?

There is also lead/circuit inductance and circuit capacitance to earth, shield or other nearby structures.150MHz is probably high enough for these to have an effect.

Sniffers don't care what parts are involved.

RL (....VE3-UTE)

Yeah, at 0.05%, I'd be re-checking my maths, or looking for stray C/L.

uhhh.. not 100% sure... Perhaps 70% sure. Reactances everywhere! Arrrrghh!

When I put some ferrite near the inductor lead, the frequency drops a few Mhz down from 150Mhz. (Changing lead inductance changes fs.)

Applying a single secondary test winding on the power inductor (32:1) and scoping that shows the same 150Mhz as the sniffer probe.

I'll keep poking around. Maybe I'll find the net responsible for the

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

Hey I like that idea, How many turns on your 400uH iinductor? If it's 100 then the single turn should give something like 10^-4 of that...40nH.

George Herold

What else is attached to these leads, besides the inductor? Snubber circuit values at 150MHz can be sized to have negligeable effect on power efficiency.

If the inductor current does not reverse, lossy low-frequency beads can also help to decouple the inductor body from the source of the excitation. If it does reverse, a common-mode bead, though physically more impractical, should also have little effect on power transfer, but be nice and lossy at that frequency.

Large component bodies tend to serve more as radiators, than as tuned elements, above 10MHz. Local sheilding can redirect the unaltered (or even increased) current amplitudes in tighter, less radiative paths.

RL

RL

For example, I'm using chip capacitors, short conductors, some PCB structures for capacitance..

What I'm checking into (was posted) is the single turn that exists around the toroid when the interwinding reactance is low. As a rough calculation I used:

It's in the ballpark for my 'mystery missing inductance'.

Interesting...

Some RF newbie questions:

Will the smps PCB in a 0.5mm thick aluminum enclosure be effective in attenuating the radiating 150Mhz.?

And does the RF bounce around in the box and makes it way onto the AC power wires and the DC output wires?

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

kOhm?

iirc 32 turns..

Here's how I'm just learning this:

The windings on a toroid form a network. It's the network the forms a single loop. When the interwinding capacitance basically shorts out the network, there's one loop. Where there's a loop and AC, there's inductance.

A 32 loop inductor turns into 1 loop if the frequency is high enough. The 1 loop inductance will depend mostly on the radius from the center of the toroid.

Did I get it right?

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

That doesn't answer the question. The parts you mention will not produce noise. It's more likely to be a rectifier or a switch.

PCB structures make lousy intentional HF capacitors - their surface area is generally too large and self-inductive effects pop up at lower frequencies than discrete parts can produce. You will see this from simple shield, ground plane and tracking effects.

Lots of conductor or hardware shapes can produce the same magnitude of L, in-circuit.

One method is the same one your sniffer uses, and the Al case isn't as important as distance and internal loop areas and orientation in minimizing coupling. RF shorts and traps at I/O ports can reduce pickup that is not avoided.

The other is capacitive, and the box is pretty good with that, if grounded, really conductive, and allowed to act as a return path for these currents internally. Beware that the box then becomes part of an internal re-radiating loop for 'method one'. That's the 'lid on' effect that may sometimes be noticable.

It's better to keep HF radiation off larger part bodies before it gets a chance to radiate - or shifting the frequency of the interference lower (part of the bead and snubber effects). Lower frequencies will not radiate as easily.

RL

True.. Wasn't a good answer.. Best if I posted a schematic. But just looking for some quick hints to spark some thinking.

Oh crap.. But makes for a great puzzle. I'll check...everything..

I'll try it out. Thanks.

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

=20

I had a similar problem once. My SMPS was radiating at about 10.7 MHz though. Totally buried the IF. A clear station seemed like it went off the air. It was a second oscillation.

turns.

than

smps

keeping

they

self-capacitance,

I don't think so. Do not forget u(r) at that frequency.

Oops that's right.. Some added inductance will be from the iron powder core. iirc ur drops like a rock after the permeability cutoff frequency however there might be some ur left at 150Mhz to create some extra 1 turn inductance.

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