Planar/PCB inductors, any good starting place/realistic specifications? - Page 1
Forum section: electronics / projects

author: DutchGert
author_rank: Frequent Contributor
timestamp: December 01, 2024, 05:35:33 pm
content: Hi,I recently did a project at work where I designed a 2-phase, 54V to 12V at 115A (58A/phase)/1400W DC-DC converter based on GaN fet's.It runs at 200kHz and for the inductors I am using 2x TDK ERU series, 1.5uH coils.All is working great and will be in production shortly but since the inductors are relatively lossy and bulky, I was thinking of investigating the use of planar inductors. Be it integrated into the current PCB or as some separate component mounted as SMT/THT.However, planar inductors are completely outside of my field of expertise and I have no idea if this idea actually makes sense and where to start in terms of app-notes and/or design software?Rough specification would be:1-2.2uH60A Ir~80A Isat<1mOhm Rdc<500mm2 footprintLink to current inductors:https://www.tdk-electronics.tdk.com/en/529778/products/product-catalog/inductors-coils/high-current-flat-wire-inductors]https://www.tdk-electronics.tdk.com/en/529778/products/product-catalog/inductors-coils/high-current-flat-wire-inductors] https://www.tdk-electronics.tdk.com/en/529778/products/product-catalog/inductors-coils/high-current-flat-wire-inductors

author: selcuk
author_rank: Frequent Contributor
timestamp: December 01, 2024, 08:20:53 pm
content: I designed many PCB inductors in the past. They were for inductive sensing and not for power electronics. So I cannot say I'm experienced in this topic. There is a tool called "spiki" to generate parametric inductors. I used that one and then imported the structures into KiCad. They were pretty consistent with the simulation data.https://github.com/in3otd/spiki

author: Slh
author_rank: Regular Contributor
timestamp: December 01, 2024, 08:40:24 pm
content: I think that the problem you'll have with integrating into the PCB it is getting a decent fill factor and you may want a different higher temperature PCB material. At that current you want as much copper as possible and want as little other material in the gap.Designing planar inductors isn't really too different to standard ones except the construction of the winding is different. Same sort of magnetic circuits etc.I've never tried to get custom flat wound inductors but it's not as common as round winding. If you've got the volume then you could talk to Wurth Electronics about custom inductors as they do flat wound pq26/20 inductors already.Perhaps I'm looking at at the wrong inductors but it looks like the ones you currently have are planar.

author: mtwieg
author_rank: Frequent Contributor
timestamp: December 02, 2024, 12:44:34 pm
content: IME there are three good reasons to consider planar magnetics:1. Need for a very low profile2. Need excellent repeatability of parasitics (especially for transformers)3. Need very low costYou said your current inductor is relatively lossy, I think you should investigate that first. Could be that changing inductance or core material could resolve that. I doubt a planar design would reduce losses (for the same core material and footprint size, that is).

author: Someone
author_rank: Super Contributor
timestamp: December 02, 2024, 09:00:27 pm
content: Quote from: DutchGert on December 01, 2024, 05:35:33 pmYou'd need to run through some relatively obscure and painful calculations even for an approximation:https://www.ti.com/download/trng/docs/seminar/Topic4LD.pdfQuote from: DutchGert on December 01, 2024, 05:35:33 pmWithout running the numbers exactly I'm feeling your requirements are many multiples away from what's realisable in a planar core.