Engineer's Notebook on Inductor and Transformer Circuits: problems, solutions and simulations

This notebook should interest anyone who needs to design circuits using inductors and transformers. It covers the basics of using these components in a circuit. The more complex modeling that sometimes needs to be done at higher frequencies is not covered.

This is not so much a pedagogical work as it is a collection of example circuits collected from our notes. It is a real engineer's notebook in the sense that you do need to know at least the basics of electric circuit analysis for it to be useful. Familiarity with differential equations and Laplace transforms is also helpful. A table of Laplace transforms and their properties is included.

It starts with a simple explanation of the basic physics behind magnetic circuit theory. Magnetic circuits are almost essential for analyzing some of the more complex transformer circuits. The effect of core saturation is explained.

This is followed by a series of inductor and transformer circuits with accompanying problems and solutions. Some of these solutions show how to model the circuit using ngspice. Ngspice is an open source circuit simulator (runs on Windows, macOS, Linux and BSD) that can model magnetic circuits. It can model saturation and hysteresis effects in inductors and transformers. The most complex circuit covered is the Royer oscillator which finds many uses in power supply circuits and high voltage generation.

We think that a circuit designer should be able to use the examples covered in this notebook as a starting point for most circuit design problems involving inductors and transformers.