SMPS inductor question

Can some one please tell me what are the advantages and disadvantages of using a toroid inductor(hand made) for the inductor of buck or boost converter?
View attachment 63758

Or is inductor in a buck or boost converter must be a one like these?
View attachment 63759


thank you

A hand made toroidal inductor is fine. Toroids have high efficiency with good magnetic coupling and a small external magnetic field.

The main reasons toioids aren't used more is the difficulty and higher cost of winding the toroid.

Thank you very much crutschow

i was used to build smps with toroid inductors and few days back a man (who has more experience than me) told me toroid cores are not for SMPS as they cant deliver much current. for SMPS you should go with something with air gap, that is why i need to clarify the thing

Well certainly the inductor cannot be allowed to saturate at the maximum DC inductor current and that may be easier to prevent with a gaped core. But if you can wind the toroid to give sufficient inductance that will not saturate at your desired inductor current, then you are fine. It just means you may have to use a larger core, then you would with a gaped core.

The difference is this:
If you have a DC component, you will need an air-gap to prevent the DC saturating the core.
If you don't have a DC component you can use lapped core pieces and glue them with magnetic glue or a toroid.

Toroid cores are made in different materials for different purposes and frequencies. For high frequency buck or boost converters, the best choice is powdered iron. Those cores have thousands of tiny air gaps distributed between the particles of iron. This will help prevent saturation when there is a DC bias current present.

Best thing about toroid is very low radiated EMI because the magnetic flux is confined to the core. Cores with an air gap have high EM fields in the vicinity of the gap and spray EMI.

ChrisP58 said:

Toroid cores are made in different materials for different purposes and frequencies. For high frequency buck or boost converters, the best choice is powdered iron. Those cores have thousands of tiny air gaps distributed between the particles of iron. This will help prevent saturation when there is a DC bias current present.

Click to expand...

Is there anyway to identify core material just by looking at the toroid? i mean like color or something?
toroids available locally have no product number or any other details. we can buy them by the size of the toroid. and sometime with colour,

thank you

Not really. Some manufacturers stamp their name and part number on them.

aruna1 said:

Is there anyway to identify core material just by looking at the toroid? i mean like color or something?
toroids available locally have no product number or any other details. we can buy them by the size of the toroid. and sometime with colour,

thank you

Click to expand...

Sometimes. Micrometals uses a two color code to represent different permeabilities of their powdered iron cores. Other than those, I don't know of a way to know by color. Most powdered cores will be painted or coated in some way. But the details vary with each manufacturer.

Doesn't your distributor have any data to go with their products? There are a number of different ways where one toroid might differ from another of the same size. Choosing one just on size alone is a guaranteed path to failure. At the very least, you want to know that the part you buy next month will have the same characteristics as the one you bought yesterday.