Big inductor

Multiple devices is right--Digikey has a 2.7 mH, 2.2A Bourns unit that woul d fit, but you'd need like 128 of them and they cost $7. You're asking for

How about a nice cap multiplier?

Cheers

Phil Hobbs

If you are trying to block differential mode signals then you could use a common mode choke (two windings) wound on a toroid. That way the DC cancels out and you're left with a relatively large series inductance in series with both sides of the 8A DC. Because the DC cancels out you can use a high permeability core and a relatively large number of turns without the core saturating.

Doesn't do you any good for normal mode though- the inductances cancel out almost perfectly.

--sp

uld fit, but you'd need like 128 of them and they cost $7. You're asking fo r 320 mJ of magnetic energy, which is a lot. At a 100 kHz switching frequen cy, that's a 30 kW class inductor.

I need to try your cap multiplier "backwards" idea. Have you done one with anything near 8 amps? (I did a ~1 amp one with a TIP31)

George H.

There's no switching frequency, it needs to pass current from a PSU but not allow signals between 10kHz and 100kHz to be significantly attenuated - 10mH is plenty.

I can do it (I think) with a couple of Kool Mu toroids, but winding two lots of >320 turns using over 30m of as-thick-as-will-fit wire doesn't thrill me.

Gyrator is ok, but the signals can be quite big as well as quite small, so it would need to be very power hungry.

Cheers

Normal mode, sadly.

I had considered using a common mode choke but connected in a single line with the windings in inverse serial to cancel the DC flux, and with a capacitor across one winding to pass AC into the other which would then block it.

Of course, once the drugs wore off I realised this can't work, and indeed simulations show it to be as much use a a chocolate teapot.

Cheers

Get a professional coil winder to wind the toroids. They've got special purpose machinery to do it, and, if they wind power transformers, which is more or less the ball-park you are in, heavy wire won't phase them.

If you say roughly where you are, somebody might come up with a name in your locality. My "local" coil winder in Nijmegen was actually in Horst

ACE Wikkeltechniek Nijverheidsstraat 2

half way to Venlo, about a half hour drive away.

Due to the frequency, you should consider an isolated wire bundle instead of single thick wire for the windings. The limit frequency falls down when the energy in the coil grows. Your power range is in the power electronics domain.

Sure. I was using the switching regulator to illustrate what a gigundo chunk of ferrite you're going to need.

A cap multiplier will cost you 0.8V or so, so about 6W maximum, but it'll be a lot cheaper than those toroids and will work much better at low-to-moderate frequency. Plus if you like you can run its base circuit off a little switched-cap filter and get the dropout voltage down to probably 0.3V.

Cheers

Phil Hobbs

I've tried to simulate a gyrator (is that the same thing?) and it works well at low amplitudes, but higher amplitudes (can be a few volts) break through.

My circuit is similar to the following, except using a Sziklai pair and different values...

... the line is at high voltage, so it's a convenient topology.

Do you have an example of what you have in mind?

Cheers

Thanks, yes I just asked a local firm how much. I'm sitting down waiting...

Cheers

Yes, you don't get something for nothing. You need enough dropout voltage to accommodate the largest negative-going peaks.

Another approach is to use a big audio amp part as a noninverting stage and capacitance-multiply that way. It's an old technique but somebody named Kanner named it after himself. Google "Kanner Kap".

It's similar to what you have, except without the B-E resistor. Normally I'm trying to minimize the dropout voltage. That extra resistor is convenient for setting the dropout voltage, of course.

Cheers

Phil Hobbs

One trick is to put a transformer secondary in series with the power rail, and actively drive the primary to cancel noise. That works best for small noise voltages.

How big might the noise be? Can you use an LC filter? Caps are cheaper than inductors.

It's signal, not noise, I want to isolate it from a DC power supply so it's not attenuated too much. I'm looking into active methods like your transfomer.

Cheers

Thanks for the pointer, I'd been thinking along similar lines but couldn't find anything online, and it's obviously not a new problem.

Cheers

Can you resonate an inductor, or several inductors in series? Sort of an elliptical inductor. That could save a bunch of iron.

I did a system for the C5A, that sent power and audio and supersonic control signals over a single wire, so remote handsets could talk and control the cargo loading winch. It used pseudo-inductors, sort of c-multiplier things, to pick off the DC without loading the audio. They were modulated in the transmit direction.

I guess you can't afford enough DC drop for an active solution.

Den torsdag den 11. august 2016 kl. 13.19.27 UTC+2 skrev Syd Rumpo:

loud speaker crossover inductors ?

-Lasse

Yes, I saw the Visaton 3613 which claims 10mH at 5.2A, but as it's only

Audio stuff specs combined with made in China makes me nervous.

Cheers

yeah cap multiplier is gyrator-like, but it tracks voltage, not current.

cap multiplier has the low capacitor end grounded. and no R2 between B and E.

The normal capacitance multiplier configation only allows for excusions of about 0.6V below mean voltage. to handle "a few volts" you need a lower voltage on the base. perhaps add a resistor, or zener across the capacitor. and consider a (bigger) heat-sink.

so the amplifier block pulls on the other end of a capacitor that's used to feed current to the positive rail in times of need... seems somewhat insane.