#2 🚀 California, Magnetic Designer, Rac resistance Part II 🧵 and Beta Version

The Newsletter of High-Frequency people

👋 Hello! Dr. Molina here! 👨‍🔧

Thank you for reading and welcome to the jungle my Newsletter about my journey at Frenetic, expanding our business to the USA, and my favorite topic, High-Frequency Magnetics 🚀.

This is the Second edition of my Newsletter, which means, that I’m looking for your comments, suggestions of topics, and feedback to provide you with more interesting comments (High-level audience 😎).

🌵 Disclaimer! Before hurting anyone, I write ✍️ with a touch of humor, and I can make mistakes (I will, for sure), don’t take me too seriously 😉.

P.D. I have improved the previous edition, especially, the explanation of the skin effect, according to some comments from colleagues.

First of all…

We have incorporated a subsidiary of our company in the USA, called Frenetic USA Inc!!!

Visiting Apple and Virgin driving a Tesla

Two crazy weeks of meetings around California can´t be considered working at all. I’ve had a lot of fun!! I can confirm, the USA are open for business. Basically, we arrived at SF on Monday 15th, and then on Tuesday 16th, we already had 3 meetings in the SF area, EV chargers and Solar inverters around Newark, and finally, Apple 🍏 at Cupertino. Thanks to Frenetic, I’m working with Apple. Of course, I can´t tell you what are they doing

Later on that night, we took a flight to LA, where we have another apartment. On Wednesday, we rented a Tesla using Turo (It was one of the cheapest cars) and we drove through the LA area. One of our visits was Virgin Hyperloop!!

We stayed another 3 days in LA, visiting semiconductors companies, some of them are already users of Frenetic and some others are in their way 😍. In both cases, they have received us in their offices very kindly.

But I’m not facing this challenge alone, I have recruited a TOP businesswoman, Laura!! She is the boss here and also a very funny girl.🦸🏼‍♀️

Magnetic Designers’ feedback

Today I would also like to talk about what motivates me most today. We already have more than 120 paid users of Frenetic Online, our Online platform, for designing Magnetics 🚀. That means, 120 engineers with opinions, feelings and problems to be solved.

I’m very surprised how good feedback is we are receiving, even, when there are a lot of things to improve. For example, one customer made this comment in a meeting with some other companies (I didn´t ask for permission, then, I will keep him anonymous).

I love using Frenetic to design my magnetics, it’s the faster way to test some ideas. It has changed my work methodology.

I’m a user, but I’m very critical, everytime I find something that is not perfect, really makes me sad. Of course, statistically, we have around 5% of users, who are not happy. They are my main motivation, I’ll work to turn those unhappy users into happy engineers, creating amazing magnetics.

Of course, the expectations we have created in our users are huge and this is a challenge for us. We have been using old-style software for a long time, where no one was asked to verify their results, while I need to bring a calorimeter with me to prove the accuracy of our losses prediction. This is part of the game and I’m happy to be pushed to the real excellence.

We are creating a new understanding of what a simulator software should demonstrate. The simulation results need to be proved with experimental results.

In the coming weeks, we will be releasing new features which will mean a game-changer for the magnetic design process. Some of these features will be revealed at the Bodo Power Conference.

The Design

My next challenge is to improve the design of the user interface and the journey, to really create an experience that allows users (design engineers) and factories (our partners producing the pieces of our users) to talk in a similar language. As Joe Gebbia, from Airbnb, explains in this video, the design can help us to eliminate the differences between us and create relations based on trust. (My wife Natalia is great at design, I learn a lot from her and her book recommendations are amazing, thank you!!)

With the appropriate design of tools, the future of the power supplies will be totally different, and the next generations of engineers will create power supplies as today web platforms are created. The consultants will have a place to show their skills in Magnetic Design and the final customer will have much more data to make decisions. And as a final step, manufacturing would be just a bottom to push and not a long discussion.

I dream of a future of Power Supplies, solving hardware problems and logistics by software with a common vocabulary.

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Let’s start with the High-Frequency Magnetics technical stuff 👩🏽‍🏫.

Proximity Effect

The proximity effect appears between conductors of different layers but at an external scale. The Magnetic and the Electric fields are feeding each other in a very romantic way and today we will talk about this special love.

This effect is very similar to the skin effect but on an external scale. A variable current through one conductor generates a magnetic field, which generates induced currents in nearby conductors, causing power losses. The skin effect, induce eddy currents in the own conductor, while the proximity effect refers to the eddy currents that one conductor produces over the other conductors.

The proximity effect is very complex to be described mathematically, especially complex in the work of Ziwei Ouyang, but we will talk about him in another edition.

In this edition, I have selected the pictures of Marian Kazimierczuk and the examples of Colonel. Kazimierczuk describes in his book this effect with very mathematical detail and I use some of his images here to illustrate the explanation. In the following picture of his book, the effect of one conductor over the closer conductor is observed in two cases: a) Currents in opposite directions and b) in the same direction.

Some highlights to consider from his book where I have nothing to clarify.

Eddy currents are induced in a conductor by a time-varying magnetic field whether or not the conductor carries current.

This is especially relevant in Center Tap structures or Flyback, where windings could not carry current during some intervals of the period.

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Let’s analyze how the proximity effect impacts transformers and inductors

This effect appears in transformers and inductors with a non-negligible effect, between layers of windings. Components with a single layer have neglectable losses due to this effect. However, components with winding layers, based on conductors occupying most of the coil former window and having space between layers (Which is the most common) seeing increased the H field and the losses.

The problem is when there are more than two layers because the H field inducted grows and the current is needed to compensate for the losses growth until destroying the component 🔥.

As you can see in the picture (from Colonel McLyman’s book [2]), there are 3 layers of primary consecutively and the other 3 layers of secondary: Primary consecutive layers increment the H field, while the secondary layers decrement the H field.

The right graph of the picture shows the magneto-motive force (mmf = Fm) potentials, where Fm=NxI, where N is the number of conductors per layer, and I is the current. Considering 1A and 8 turns per layer, we have Fm=24 AxN.

The eddy currents induced in one wire, decrease the net current through that conductor, but contribute to the losses and force the system to increase the currents to get the desired net value.

In the following picture of Colonel [2], we can appreciate the current load current (Io), the current induced (Ig), and the current created to compensate for the induced current (Ic).

If we calculate the losses due to the currents, assuming Io=1 A and being the losses calculation Plosses=R x I^2, we need to calculate the real current I, which is affecting the losses. The effective current which generates the losses is 19 times higher than the net current.

Imagine the surprise 🤯 of a designer who doesn´t consider the proximity effect, finding 19 times more losses than expected!!

Yes, it’s hard to assume that magnetic fields and electric currents are feeding back constantly as a couple of lovers.

We started the previous edition, talking about the Rac. Here is a good point to find the Rac concept.

The Rdc is a physical concept, the resistance of the wire that you can measure:

• 1 Ohm wire, conducting 2 A, will produce 4 W of losses.

The Rac concept is not due to the physical wires, there are a lot of other factors that impact; The Rac is the resistance at high frequencies due to proximity effect and skin effect, as you can see in the previous example, the ratio Rac/Rdc is 19.

Since the Rdc is a physical value, a standard design process to minimize the losses is using the ratio Rac/Rdc.

I don´t want to bother all of you with equations, but, depending on the type of conductor, the specific position of the conductors, and the current nature, the mathematical models can be extremely complex.

Dowell, the first

I’m satisfied with the length of this edition, and if you have reached here, you might be a bit tired of me already, therefore, we will talk about this in the next edition. Also, I’m doing a design for a Flyback multi-output with requirements of cross-regulation at Frenetic Online and I need to work on it 😜. Next week, we will be back with Dowell!!.

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I love the magnetic world, and this is the reason why I work at Frenetic. We are preparing some news and a close Beta version for those customers who are bold enough to test our crazy ideas, before anyone. If you know any crazy engineer interested, please tell him!! (This is only for paid customers, it’s beta, but also has access to the current stable release). You can contact me anytime at my LinkedIn.

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