Inductors with powdered iron toroids.

[GK]

I need to build a variable 5V to 25V 13A (continuous), 20kHz PWM buck converter (from a 40V unregulated supply).

I’ve got everything sussed except for winding the inductor, which I’m having trouble finding good information on.

Due to the wide output operating voltage range of the supply and the need for stability into loads that draw 13mA as well as 13A (a power resistor as a minimum resistive load will be installed inside the supply to keep things under control) the buck converter will need have a relatively large inductance to keep the maximum ripple current within bounds.

A supplier local to me stocks these (which I assume are suitable for this kind of thing):


http://www.jaycar.com.au/productView...Max=&SUBCATID=

http://www.jaycar.com.au/productView...Max=&SUBCATID=

http://www.jaycar.com.au/productView...Max=&SUBCATID=


The only information I have found on these is:

Material = HY-2
Initial Permeability (ui) = 75
Frequency (kHz) = 0.05 - 50
Bs (kG) = 12
Hc (Oe) = 6


I’ve got a couple of SMPS design books but they say nothing on how to calculate and design a high current inductor from here.

Help!

Cheers,
Glen

[lumanauw]

13mA as well as 13A

There's toroid type with 2 different materials sandwiched top and bottom for such a wide output current range.

[GK]

Nevermind, I found the info I need.

Cheers,
Glen

[Eva]

Ouch, I arrived late. Anyway, this is a brief guide that I published some time ago:

http://www.diyaudio.com/forums/showt...03#post1393703

[GK]

Originally posted by Eva
Ouch, I arrived late. Anyway, this is a brief guide that I published some time ago:

http://www.diyaudio.com/forums/showt...03#post1393703

That's partly what I was referring to

[switchmodepower]

Why not do a synchronous buck? You don't have to worry about min load and it's more efficient,

[GK]

Oh, I'm not fussed about efficency. I was originally going to make a linear regulator out of the parts I have in my junk box, but then I decided that the complete unit would take up a bit too much room on my test bench.

Cheers,
Glen

[switchmodepower]

OK. But the synchronous buck always has continous inductor current even at 0 load regardless of inductor size. Transient response is great and it's easy to make it stable.

[GK]

Hmm.....

A slow transient response really isn't a problem for the intended application but I'll think about it.

[Tolik]

Just keep in mind that the looses in iron powder cores are very noticable at high values of ripple current, iron powder not the best choise for high values of Fsw. Molypermalloy (MPP) cores with u60...u125 are much better for your purpose.
Personally I tested u60,u125 MPP vs. 26 iron powder. The inductor was used in common mode. u60 MPP was a winner