Toroid shape vs square shape?

[gary350]

I know the round toroid can be high KHz depending on the material but what about the square shape in the center made with the black color material? I know metal laminates will be low Hz but will it work same as a toroid shape as a transformer?

 

[rjenkinsgb]

If it's the same material with the same cross-section, it should work pretty much the same, as long as the parts are properly clamped together.

 

[ZipZapOuch]

The black color material is a magnetizable ceramic known as Ferrite. There are different ferrite formulations. They are the highest frequency transformers.

The toroids shown are typically iron powder (atomized iron powder by high pressure air or water jets hittin a molten droplet of iron. These can handle up to 200kHz. Iron powder made from superheated iron pentacarbonyl forms spheres and can be insulated really well with very thin oxide layers so you can get good efficiency up to 400kHz transformers. All of these are formed in hydraulic presses with about 2% epoxy to hold everything together. Then baked to cure epoxy, then painted to show the type or grade of iron used to make the inductor (or permiability of the inductor. Color really depends on manufacturer. Micrometals has a trademarked set of colors to indicate grade of iron and insulation.

The silicon-steel plates of the laminated transformer can go up to 100kHz (depending on quality of alloy, insulation and stamping.

 

[MrAl]

I know the round toroid can be high KHz depending on the material but what about the square shape in the center made with the black color material? I know metal laminates will be low Hz but will it work same as a toroid shape as a transformer?


View attachment 147337

Hi,

There are different aspects of this problem to think about because for a good comparison you have to specify what is the same for the two as well as what is different.
For example, the magnetic path length affects the inductance so you have to specify the relationship between the dimensions of each core. For an example of that, say the magnetic paths were the same length so that the inductance factor due to that alone was not that different. Then you have to figure in the winding factors and winding methods and window area as to how many turns of the same diameter wire can be put on the two cores, and also how much physical material is involved to make the core volume.
In the past toroids were used for a number of reasons, one being that there are toroid winding machines that can place the turns on the core without much human intervention. Also, since for a rectangular core the cross section in the corners is different than in the straight sections, some of that core material sort of goes to waste.
Toroid constructions are a little more efficient than EI constructions so that may allow a project to have a higher efficiency.
Probably the most significant factor is that magnetic path length difference vs window area or another way of looking at it is just the number of turns that can fit on the cores vs the magnetic path lengths. With the rectangular core if the window area is smaller than less turns will fit on the core.

There are some advantages for rectangular cores though too when it comes to the construction. For one, most of them come apart into two halves which makes winding simpler, and you can use bobbins. It's also much easier to gap rectangular cores if you need to provide variable inductance for different projects with the same core sizes. In fact, it's very hard to do a custom gap on a toroid while for most rectangular cores it's very common.

So there are different ways to compare the two. The best one for your project depends on a number of requirements.

 

[ZipZapOuch]

The story behind is a bunch of trade-offs.
Manufacturing costs, winding costs, benefit or detriment of requiring a bobbin, size, stray magnetic signals, Eddie current losses at the required frequency, current density, coupling efficiency. Also, the various designs can be executed in multiple geometries so the "black material" is not limited to the square shape or E-core design. Once you start looking, there are many innovative designs to achieve cost effective coil winding, mounting and controlling EMI.

 

[MrAl]

The story behind is a bunch of trade-offs.
Manufacturing costs, winding costs, benefit or detriment of requiring a bobbin, size, stray magnetic signals, Eddie current losses at the required frequency, current density, coupling efficiency. Also, the various designs can be executed in multiple geometries so the "black material" is not limited to the square shape or E-core design. Once you start looking, there are many innovative designs to achieve cost effective coil winding, mounting and controlling EMI.

Hi there,

Yes, this area is very varied. One older design I saw used a very unique core design it was for a very expensive product. They wanted it to work well all the time as it involved money and the accounting of money transfers.

That's why the simpler question of donut vs square is hard to address without more information, or setting some criterion such as the same amount of material for each core, or same window area, stuff like that.
It is interesting though that when it comes to the amount of material, a rectangular construction has wasted material at the corners because there we see an excess of material that is not needed to form the magnetic path. That means the flux density varies between the straight sections and the corners, and the corners do not need that excess of material. Rounded corners are different, and maybe that's how the "C" cores came about; they are oblong and with no sharp corners.

There are some issues that are dead set, pretty much anyway, like the fact that it is very hard to gap a toroid without expensive machining. The usual approach is to order the cores with the right specifications for a given product. That way they are ready to go right from the manufacturer.

 

[gary350]

That is about what I expected.

What is the frequency range of the black color ferrite material?

 

[ZipZapOuch]

That is about what I expected.

What is the frequency range of the black color ferrite material?

For power transformers, up to 200kHz.
And up to 300MHz for inductor cores (according to Wikipedia) but I've seen some GHz applications.

 

[ChrisP58]

That is about what I expected.

What is the frequency range of the black color ferrite material?

Depends on the material. This one goes up to 3MHz. But this is only of a few material from one manufacturer.
https://www.mag-inc.com/Products/Ferrite-Cores/L-Material
Their other materials can be linked from here: https://www.mag-inc.com/Products/Ferrite-Cores

There are a dozen or more different manufacturers out there.

Also, it's not a simple question. There are other factors that affect the usable frequency of a material.