What is the difference between coupled inductors and fixed inductors? - Page 1
Forum section: electronics / beginners

author: Benjam
author_rank: Regular Contributor
timestamp: April 29, 2022, 07:05:53 am
content: What is the difference between coupled inductors and fixed inductors? What application scenarios are they used for? When should I use a coupled inductor and when should I use a fixed inductor?When I was studying some circuit schematics, I found that some DCDC circuits use coupled inductors and some use fixed inductors. Is this related to their different topologies? Because I see the coupled inductor is used on the flyback and the fixed inductor is used on the buck circuit. Is that right?So which one is better, flyback or buck? In what scenarios should you choose flyback and in what scenarios should you choose buck?Requirements: Bus voltage: 12V-60V, nominal: 48V, output 15V7A.Premise: Don't consider cost, but consider size.Which structure to choose is more suitable?

author: golden_labels
author_rank: Super Contributor
timestamp: April 29, 2022, 08:24:17 am
content: A request: provide context and tell us where your questions come from. Both here and in other threads you seem to build some mental model and expect a response within that model. But the models you develop are pretty weird and a good answer can’t really be given without first correcting those. Which is hard without knowing, how you came to such ideas. Even worse, you connect unrelated areas and want that connection to be explained.To start with: coupled and fixed inductors are not referring to two different, independent classifications of inductors. They are not disjoint sets, much less opposite of each other. The question is similar to asking, what car is better: a red one or a convertible. Fixed inductors are inductors with inductance that can’t be adjusted. Coupled inductors are multiple inductors that are magnetically coupled, so they affect each other.There is no “X or Y” between those. There is even no such “or” in those two categorizations, with regard to DC-DC converters. Almost all practical implementations will use fixed inductors. Whether inductors are coupled or not depends on how the circuit operates.Flyback and buck do different things, so there is no “which is better”. They have different purposes and characteristics, with flyback converters offering galvanic isolation, while buck do not. Also: they are not “opposite” in any way: those are just two specific topologies in an entire class ofswitched-mode power supplies, with buck converters being themselves a subclass of a class of such topologies, acting specifically as step-down converters (while flyback converters do not).

author: Benjam
author_rank: Regular Contributor
timestamp: April 29, 2022, 09:31:32 am
content: Quote from: golden_labels on April 29, 2022, 08:24:17 amthank you.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 29, 2022, 10:17:52 am
content: Fixed inductor just means inductor. Fixed just means it's not adjustable. Adjustable inductors are very special (for tuning analog signal circuitry) and not seen in power converters.Coupled means, there are at least two inductors, which share the magnetic flux. Coupled inductor is also known as transformer, although there are different nuances to the terms, but despite that, the terms get happily mixed up left and right, so let's not get into the details for now.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 29, 2022, 11:29:01 am
content: Coupled inductors are usually fixed as well... the adjectives are non-exclusive.The most common exception probably being RF/IF coils, with the threaded core piece to tune it, which can be made with single or multiple windings.Tim

author: tepalia02
author_rank: Regular Contributor
timestamp: April 29, 2022, 12:28:35 pm
content: You may like this write-up.https://www.electronicshub.org/types-of-inductors-and-applications/#Coupled_InductorsIt's about different types of inductors. Coupled inductors have also been covered here.