10% thru-hole air or phenolic inductors?

Change to the "Tawanda" style, and don't steal parking spaces from little ol' ladies ;-) ...Jim Thompson

Any chance of using two or four 1206 or 2010 surface-mount parts in series/parallel? You could heat sink the ends to some copper pours.

Yes, we could. Especially since we will re-layout this board anyhow on account of some more stuff the client wants to have on there. In the interim we could just solder wires to them. But IME those li'l SMT inductors blow into smithereens when lots of RF power waltzes through them.

The copper pours will suck the heat out; wires won't. The Gowanda axial won't get much cooling through its leads either.

We have run 0603 resistors at half a watt, with reasonable hot-spot temperatures. They don't get any hotter than a 1206 IF you keep the end caps cool.

Get an x-acto and some copperclad and try it. Hack a drop-in (drop-over?) replacement for that big axial thing.

The problem is the skin effect in the winding, makes it burn up locally. For now we'll just get bigger axial things, their 21M series. The 28M series is too long so if someone would know inductors that aren't much more than 0.500" long but thick instead, and ideally have 22AWG leads, that would be great.

I told the client already that we may have to roll our own. Not a big deal but since this is medical that comes with a lot of bureaucratic procedures.

Four inductors in parallel; skinny wire uses copper more efficiently. Think of it as distributed Litz wire. Power goes as i-squared, so 1/4 becomes 1/16.

Give it a try!

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Hi Joerg, If the SMD inductors are wound on some nice ceramic, (Al2O3 ?) then getting the heat out will certainly help the local heating.

But I don't know how the leads are connected in a SMD inductor... are the ends metal coated as the resistors? (Good thermal contact between pcb and ceramic)

George H. (Mind you I know very little about inductors.)

Good idea. One additional challenge is that most small inductors in the

I have no idea about those details. But I know that even SMT inductors with one side to a ground plane can become friggin' toasty. Part of it may have to do with the fact that they must use ferrite at lower inductances to get the sizes down.

Most of the time I can't sink into the board anyhow because everybody and their brother is already doing that with DPAK, D2PAK, SOT223 and so on.

a bit too small in value but:

-Lasse

Thanks, Lasse, those could work for the next layout. If they make custom ones with higher inductance. I have already maxed out the 90 degree rotations to decouple fields from consecutive filter stages.

Can't do that because several are decoupled via 90 degree rotation. Plus there's a chunk of metal above.

Too long? Will the fudge of vertical mounting be acceptable?

Hmm..take that array configuration and rotate maybe by 45 degrees along most useful axis?

Then they'd crash into other obstacles, like driving into the garage at too shallow an angle.

Well, get that pesky rowboat out of the garage first..

Something is... odd... if you feel the need to use 10% part in a lowpass pi filter. And Litz wire is completely obscure for such a low- Q application.

You have to think the completely other way around, and design FOR absorption, not against it. A ferrite or iron core inductor, or maybe even a snubber, may be entirely more appropriate for your application. Meaning that's what everybody else does.

A change in topology to a diplexer would allow you to direct the undesired HF components to a load to be dissipated, instead of hoping they get reflected and dissipated in the source or the filter's circulating currents. But 50W is just not that much.

Tim.

The filter also does slight impedance transformation. Right now we have

Well, this ain't my first filter of this kind. Believe me, it has been simulated ad nauseam :-)

One most previous onces we rolled our own inductors but that gets old and is nowadays not so desired anymore. The ferrite cores of the typical COTS inductor can get rather hot at 10MHz. Unless you wind you own and gear the material towards the frequency range at hand.

No diplexer here because that would really cook things out once we go to class C.

Sounds like a job for Micrometals #2 or #6 iron powder core toroid.

Can't escape conservation of energy. Any reject band stuff you put into the filter, must either be absorbed by the filter, or reflected back to the source.

Tim.