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Anyone using these 'W' material torroids?

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Dylan

Tue Aug 05 2008, 08:23AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Hi all,
Im looking at grabbing some of these torroids for my GDT's:

The FT44916-ZW ( second down on the left ).

They are a generous size (2"), and high permeability.
I'll be running around the 60 - 150Khz ranges on various coils.

Anyone have any experience with these ?

Tom540

Tue Aug 05 2008, 02:44PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Posts: 617

10,000 seems a little high. I use 5,000 but Ive never tried 10,000 so it might work. If I was you I would just try them out.

Steve Ward

Tue Aug 05 2008, 04:46PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

This brings up a good question (which i dont know the answer to). What is the trade-off for permeability? Is it simply saturation flux density is typically lower? Or are hysteresis losses worse?

The obvious benefit to higher permeability is the greater mutual inductance between the windings, which means the coupling coefficient is higher than it would be otherwise.

Sulaiman

Wed Aug 06 2008, 06:58PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Saturation flux density is only an issue for dc inductors
at high frequency the limitation for the core is dissipation
for the circuit it's in the limitation is usually 'Q' (as a result of dissipation in the core)

High permeability Mn-Zn cores are useful below about 500kHz, or less for the really high permeability cores
Ni-Zn cores are for the higher frequencies.
Powdered iron cores are for even higher frequencies (10's of MHz)

The best advice that I can give is to go to look here

first, then here

Click on the material that you think is most suitable and you will get a lot of data:
look at the graph for 'complex permeability vs. frequency',
u' is the normal inductive part, it will be fairly flat up to a certain frequency, u'' is effectively the resistive part.
Core "Q" is u' / u'' at the chosen frequency and if it's too low the core will get hot.

If you have a specific requirement I could suggest a suitable core size and material for you.
(Given transformer input volts, amps, frequency)
For a GDT for a medium/large TC (a few hundred kHz) the Mn_Zn cores found in common-mode line filters are ok
(the inductor with two windings found near the ac input to many electronic items)
For higher frequencies I'd probably go for a 'binocular' core like those found in TV baluns etc.

EDIT: Broken link fixed

Tom540

Wed Aug 06 2008, 08:01PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Interesting, So the 10,000 cores might be okay then huh?

Sulaiman, the second link you posted doesn't work.

-Tom

Dylan

Sun Aug 10 2008, 04:35AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Great , good info !
And Sulaiman , you are spot on there, I have found the cores in those little common mode filters you mention to be excellent so far, I'm using one now to drive a big IGBT brick half bridge!
I ended up with about 15 turns on it 1:1 of cat5 driven by 2 TC4421's, no gate resistor, around 180kHz, and even on that big brick the gate waveforms look great!
I was suprised at their performance as they are such skinny little cores.

But back to the torroids, it sounds like for the frequeny range I'm targeting of around the ballpark of about 60-150kHz ish, the high permiability is a good thing.

Will update when I get them and have some results.

Dylan

Sat Aug 16 2008, 04:09AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Double post , but resuts are in.

In short they work very well.
Im running with 15 turns of cat5 (so easy to wind on these big toroids) driving my new minibridge of to-247 IGBT's , and the waveforms on my test 177Khz rig are fantastic, very clean, very square.

Same setup driving a 10nF film cap as a load show excellent waveforms from over 1Mhz (didn't go much over this) right down to around 15Khz! where droop starts to appear.

So , I can highly reccomend them, they far outperform the various cores I have used to date.

I have ordered some simmilar sized cores ('J' material) with a lower permiability of 6000 (from memory) , I'll post some results on these when I get them.

I'll be posting some photos of the waveforms, and my test rig including my new minibridge and the wound torroid in a couple of days when I get my new camera.

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