Trying to determine which inductore core to buy, making sence of it all.

[David_]

I am trying to find a core to be wound into a 100µH inductor(toroidal), it need to carry a DC bias voltage of 40V in a buck converter which outputs up to 3A but the current peaks at 5A so I would like saturation not happening until perhaps 6-7A and with saturation I mean a inductance value drop of 10%.

I have found company's that guide you from start to end but I can't find the cores to buy and know I am checking if any one of the series sold on digikey will suite my needs.

But I don't get how I determine saturation when given the core dimensions, AL, le, Ae, Σl/A and µi?

Also I'm kind of lost in that I know that saturation has to do with the highest flux density to field strength but in some cases they talk about saturation current and in others saturation flux density. And sometimes they give you a Amperage and other times a Gauss value...
Please advice on how I can solve this problem.

Regards

 

[chemelec]

Shouldn't be too difficult.

At What Frequency?
You might need Litz Wire, if its High Frequency.

Most important to help prevent Saturation is to have a Small Gap (.002 of a inch) between the two core halves.

 

[David_]

Sorry for taking so long to respond.
I'm not sure jet, I can control the converters frequency between 50kHz and 850kHz but I would think that I will use between 100kHz and 500kHz IF its possible to cover such a large range when winding the coil.

I had thought to use a single-core magnet wire with a really thick diameter at least 1,5mm on a toroidal core with distributed air-gap, I don't know how much difference it makes if I went with a unshielded two part core but the main concern in this design is ripple/noise.
I could probably get away with ~47µH coil but I want lower current ripple.

 

[chemelec]

What Buck Converter Circuit are you using?

Is This the Coil you are using in the Buck Converter, Or is this for a Ripple Filter?

Ripple Current is mostly a function of the Filtering.

1.5mm is 15 AWG (17 SWG) That Should be OK.
At 100 Khz, a single Strand wire might be OK, But at 500 Khz, you will need Litz Wire.

 

[David_]

I have a almost finished design based on LTC3864 which has a input voltage up to 60V and should be able to output almost 60V though I only need to output 3-33V. But I have not jet gotten through figuring out the loop compensation components.
Here it is anyway:


Yes it is the coil for the converter, but after figuring this out I am going to design a dampened input filter and a secondary output filter(I think at least)

But I have just found out about synchronous buck converters and am thinking I might change converter all together.

OK, I did not know that.
I might have some litz at home somewhere.