coil for SMPS

Thunderchild

New Member

• May 29, 2007

• #1

I'm thinking of making a 1.5 A smps and it uses a large looking 75 uH 0.0023 ohm coil, can stuff like this be bought fairly easily or perhaps home made ?

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• May 29, 2007

• #2

You usually have to wind them yourself, projects usually give full details? - you normally need the exact core specified, and the correct gauge of wire.

 

Papabravo

Well-Known Member

• May 29, 2007

• #3

Without the winding details and the core material, you have to have some test equipment to sweep the inductor over the frequency range of interest to get the inductance right. You need to be able to measure small DC resistances, and you need to recognize what core saturation looks like if it happens to you. Other than that its like any other piece of engineering, it helps to know what you are doing, and trial and error actually works pretty well in this regard.

 

Thunderchild

New Member

• May 29, 2007

• #4

hm I'm not after complicated things this is a design by national semiconductor i suppose I best order the inductor from them as they give no details as to how it is made

 

ericgibbs

Well-Known Member

Most Helpful Member

• May 29, 2007

• #5

hi,

Perhaps this link will help if you decide to wind your own inductor.

Have a look at the RM10 range 250/400 of ferrite cores, they are supplied with a centre former for winding.
Use some old enamelled copper wire off an old transformer etc.

Follow the calculation instructions in the RM10 datasheets, they are easy to wind in the < 100microH range.


https://www.electro-tech-online.com/custompdfs/2007/05/sfappl.pdf

 

Hero999

Banned

• May 30, 2007

• #6

Most datasheets suggest part numbers and suppliers for the coils so it normally isn't a problem.

What IC are you planning to use?

What are you using it for?

 

S

Speakerguy

Active Member

• Jun 3, 2007

• #7

I wound a 50uH .04ohm multilayer air core inductor by hand. It was easy, and I found an online calculator that was very accurate. If you were to use an iron or steel laminate core it would be very easy to get that low DCR but you'd have to know the relative permeability of the core exactly.

 

Hero999

Banned

• Jun 3, 2007

• #8

You also need to make sure that the core is suitable for the frequency you're using. An iron or steel laminate coil might be perfect at 1kHz but totally useless at 1MHz.

 

S

Speakerguy

Active Member

• Jun 3, 2007

• #9

Also ceramic/ferrite cores are a cheap way to get higher relative permeability than air but you have to worry about saturating the core with it. Also it is no where near as good as iron or steel laminate in terms of relative permeability (mu-r ~1000 for ferromagnetic stuff vs. mu-r ~2 for ceramic/ferrite IIRC). I believe beyond saturation it behaves as it was just an air core inductor (mu-r = 1).