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Ferrite transfomer what do you varables do you use for a core

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Andy

Thu Jan 30 2014, 01:05AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Finn Hammer

Thu Jan 30 2014, 10:31AM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
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Posts: 741

Andy,

It is not entirely clear what you are hoping to acheive, by boldly hooking this humongous toroid, wound with whichever turns of wire, across whatever circuit.
Magnetics has always been considered, to some point, a "black art", and you have to start somewhere, so could you please start with a full schematic of your circuit, a clear statement of what you intend to acheive with that circuit, and a full account of what you have wound around that, I admit, wonderfull toroid.
Meanwhile, read this:

,d.bGE
And in general, peruse the Mag-inc site, not only are they the experts, their attitude towards the budding wannabee magnetics designer is much more benign than that exercised by Epcos. And donÂ´t forget, Google is your friend, there is a full set of magnetics tuitions if you only care to dig for them.

Cheers, Finn Hammer

Ash Small

Thu Jan 30 2014, 11:09AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
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From memory, I think N87 is generally used at higher frequencies (around 100-500kHz), N27 is usually used below 100kHz.

Sulaiman

Thu Jan 30 2014, 04:48PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

With this core I'd operate at about 20 Amp.turns peak at 32 kHz as an inductor,
N.I = B . (Ae/Al) and at 32 kHz, B= 0.2T is a reasonable peak flux density.
e.g. 10 turns=288uh,2A peak, 20t=1.15mH,1Apk, 100t=28.8mH,0.2A etc.

= 576 uJ energy storage = 18 W throughput as a flyback at 32 kHz.

As a normal transformer or forward converter MUCH higher power throughput.

High permeability toroidal cores are rarely useful as inductors
because the magnetic path is closed and easily saturated.

For inductors at 32 kHz use ferrite with an air gap
or powdered iron toroids for best results.(or MPP & $$$materials)

As above, use the Magnetics site,
I learned many times more about magnetics there than I did at Uni.
Many manufacturers succeed by helping their customers succeed
Almost all electronics related manufacturers have useful websites
some more useful than others.
Application Notes can be so good that exact copies are used in some of the equipment that we repair at work, makes diagnosis/repair so much easier!

Andy

Thu Jan 30 2014, 10:47PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Mattski

Fri Jan 31 2014, 12:04AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

If you want to learn more about transformer design, Fundamentals of Power Electronics by Robert W. Erickson and Dragan Maksimovic is a power electronics book I've heard good things about which covers magnetics design.

wrote ...
a inductor across the primary terminals to make it run at dc current, that is pulsating at 32khz.

No transformer runs at DC, but "pulsating" (what waveform?) isn't DC so that's probably okay. Your circuit actually looks like a flyback converter though it depends what you put on the secondary of the transformer, which can work. The design of a flyback transformer is quite different from other types of transformers since you're deliberately storing flux in the core while the switching device is turned on.

Andy

Fri Jan 31 2014, 12:30AM

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Ash Small

Fri Jan 31 2014, 12:51AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Andy wrote ...

Hi Ash Small
I just wondering how you worked out what type of core is used at what frequency, core cross section, inductance,permeability,etc

EPCOS application notes. I'll provide some links tomorrow when I'm sober

Andy

Fri Jan 31 2014, 07:19AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Finn Hammer

Fri Jan 31 2014, 10:18AM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

Andy wrote ...

@Finn Hammer
The document has Np = (V*10^8)/(4*B*Ac*f), using 2000guess for B and cross section of 2.672cm2 at 38khz, and 12volt makes 1.5 turns, Is that right?
What would the effect be if you have to many turns?

Cheers

Andy,

Yes, I get the same result. More turns leads to a lower flux density, which may not be a bad thing. If you use 2 turns, then you will get ~1500Gauss.

Cheers, Finn Hammer

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