[106] Custom Transformers – ONE Design Equation

As with inductors, the design of a transformer is governed by a single design equation. Obey this, and the path to creation of new designs is clear 

I have observed over the years that people fall into one of two categories when it comes to designing magnetics. First, you have those who know how to build something. They are usually seasoned engineers, or technicians, who know that there are simple and straightforward design methodologies to ensure success. Secondly, you have the rest of the engineering world who are deeply intimidated by the magnetics. There seem to be endless intractable equations, obscuring the elegant simplicity of ‘how to start a design’. 

Theory is great for exercising the mind. However, there is no substitute for building magnetics and iterating the design. It is the only way to truly gain knowledge and experience. We have seen this applied to inductor design, and now we are going to turn our attention to the second magnetic element – the transformer. 

 

Two Types of Magnetic Circuit Elements

There are just two types of magnetics available in circuit theory – a simple inductor, and an ideal transformer. If you have one winding on a core, you have an inductor. If you have two or more windings, or even just a tap on the single winding, you have a transformer. It won’t be an ideal transformer, that is only possible in a simulation, but we still call it a transformer.

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Figure 1: The Two Types of Magnetics Components

As we will see, when you try to build an ideal transformer, there are extra inductive components that must be added to fully explain its operation. That is what makes magnetics so interesting – proper control of these extra components differentiates the expert from the novice. Detailed construction techniques lead to very advanced designs without the need for endless equations. 

But let’s start at the beginning. As we learned in previous articles, most publications on magnetics make the design process appear unnecessarily complex. For the inductor, we showed that there is just one equation that must be obeyed for proper design. Beyond this one equation, engineers are encouraged to use design iteration to explore the possibilities of a design task. For the inductor, the equation is:  

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Figure 2: The Single Inductor Design Equation

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