Designing 4u7 60A inductor - Page 1
Forum section: electronics / projects

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 27, 2023, 08:51:13 pm
content: Hi i need to design my own inductor 4.7uH and 60A saturate current, working current will be 40A with 20A ripple (so 50A peaks).I am using this catalogue to select cores:https://www.cosmoferrites.com/uploads/278efc4b-d053-4eee-a723-3d229e4646a7_CatalogueLatest_30102019.pdfI have found this smd inductor which will perform well but since its homemade its expensive for me.https://www.tme.eu/cz/en/details/hci2717-4r7/smd-power-inductors/ferrocore/I would like to know how they select their cores, to has such small chokes... I am just unable to make something small enough.At the moment i have designed my choke with this core:https://www.semic.info/lj-p36x22-cf139-class2/and i will add paper to make gap large enough to have effective permeability equal to 40, then i will make 5 turns.then (1,256*1E-6) *40*5*60/52 = 289mT (uo*ur*Turns*Isat/Le) so its not saturated yetand L = uo*ur*Ae*turns*turns/Le = (1,256*1E-6) *40*202*5*5/52 = around 5uHAlso how they choose current density in thise chokes? I bet its very high.

author: Benta
author_rank: Super Contributor
timestamp: August 27, 2023, 09:02:32 pm
content: Don't see a big difference in size.One is 30x30x19, the other is ø36x22Concerning current density in the copper, that's a pure power dissipation issue (current, resistance, skin effects). Relatively easy to calculate.

author: Slh
author_rank: Regular Contributor
timestamp: August 27, 2023, 09:36:50 pm
content: Also, your calculations suggest that you're still a way away from saturation at 60A. It's probably not going to saturate until 320-350mT at 100C and more like 400mT at 25C whereas the off the shelf is saturating 62A according to that page.From experience, you can get around 5uH at around 60A in a pq26/20 core without too much trouble. When I did it, it was a high frequency AC application and I couldn't use an off the shelf inductor as I couldn't find a litz wire one. It might need some cooling at that current level depending on what size wire you use.

author: dobsonr741
author_rank: Frequent Contributor
timestamp: August 27, 2023, 09:54:41 pm
content: Hope you know many companies, including Coilcraft, has a free sample program.

author: dmendesf
author_rank: Frequent Contributor
timestamp: August 27, 2023, 10:06:53 pm
content: If you want to design it go for it but if you want to buy there's always the Aliexpress option:https://a.aliexpress.com/_mre64XU

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 27, 2023, 10:26:11 pm
content: What frequency? What maximum loss?Tim

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 28, 2023, 06:26:33 am
content: switching frequency is 50khz, topology is fullbridge and this coil will be used in second stage LC filter. So current ripple will be at 100khz i guess.I dont care much about loss itself. Coil temperature should be around 75Celsius max.Yesteraday i discovered page frenetic.ai which has some simulators. I dont know any programs except excel =).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 28, 2023, 09:04:29 am
content: What do you mean "second stage"? "Fullbridge" isn't a topology, it's an inverter. What's attached to it?By "second stage", you mean there's a first LC, and this is L of a second LC?...Do you really need ripple that low?On the upside, if that's the case, it can be much cheaper powdered iron (usually #26 or #52, but Hi-Flux is probably worth it for the size reduction), or a ferrite rod core: core losses, or external fields (EMI hazard otherwise), are irrelevant that way.If instead you meant "second stage" in the sense of "it's the rectifier on a forward converter", that will be much more specific, and will have, more or less, the ripple you say it will. Uh, if it's around 12V output or something like that? I don't know.I don't know what you mean by coil temp: that tells me nothing about the component. I need to know the allowable temp rise and airflow. If that's above strictly ambient, that's typically about 50C, which is on the high side but within reason. But it's a rare thing indeed that a power supply is operated at precisely ambient. Especially in summers like these...Tim

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 28, 2023, 10:12:24 am
content: Fullbridge converter on primary, full bridge rectifier on secondaryby second stage i mean double lc filter: Bigger inductor is 20uH.http://ridleyengineering.com/images/phocadownload/1%20second%20stage%20filter%20design.pdfIts 100V 40A output. Designed to operate in ambient of 25 degrees celsius. So temp rise is 50C? I dont know airflow, but there will be definitely active cooling.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 28, 2023, 11:39:39 am
content: Wow, that's an old PDF. Those aren't millis, those were supposed to be micro via the Symbol font I bet. Which somehow didn't get embedded in the doc...Okay then, ripple is extremely small and any type will do. For design, find energy storage tables for standard core shapes/types. Compare with E = (1/2) L I^2 and select size accordingly. Pick turns based on A_L, preferably at Idc(max), preferably at a saturation level of -30% or better.Tim

author: Martinn
author_rank: Frequent Contributor
timestamp: August 28, 2023, 04:13:59 pm
content: If you still want to wind your own, TDK (former Epcos former Siemens) offers the ferrite magnetic design toolhttps://www.tdk-electronics.tdk.com/en/180490/design-support/design-tools/ferrite-magnetic-design-toolwhich helps with some of the calculations (but requires lots of background knowledge beforehand).

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 28, 2023, 04:45:53 pm
content: For that frequency, powder-iron cores will work fine and don’t require gapping.The micrometals web page has an inductor design tool:https://www.micrometals.com/