Design transformers, inductors, and coupled inductors with
- a web containing MathCAD 8 programs via email attachment.
Magnetics Design is a suite of MathCAD programs for designing flyback, Cuk, and other converters, and the magnetics used by them, with explanation of the code used in the programs. The design parameters entered by the user are highlighted in yellow in the programs.
MAGDESN.MCD is a magnetics design program with optimized primary and secondary winding areas, for a single secondary winding. (A "Multiple Secondary Winding Design" section is included in the program description.) The design parameters are given for a 5 W discontinuous flyback converter. This program uses MathCAD 2000 Professional iterative programming for winding-area optimization. For MathCAD Standard (not Professional), use the MAGDESN2.MCD program.
MAGDESN2.MCD is the magnetics design program simplified by removal of the primary-secondary winding area optimization. For flanged bobbins separating primary and secondary windings, the areas are fixed (and in most cases, they are approximately equal anyway). The initial program parameters are set for the design of an inductor for an isolated 800 W Cuk converter.
Inductor Design-150W.mcd is MAGDESN2.MCD with a 150 W Cuk inductor design example.
DCMFLYBK.MCD is a discontinuous flyback converter design program. Its circuit parameters are input to the magnetics design program. The converter parameters are for a 5 W flyback converter, similar (but not identical) to the parameters in 5W-MAGDESN.MCD.
5W-DCMFLYBK.MCD is an example of an off-line 5W flyback converter design.
The following HTML pages explain the MathCAD programs.
MAGDESN explanation starting page
DCMFLYBK explanation of a discontinuous-current flyback converter design
The following HTML pages provide selected converter background theory supportive of the magnetics and converter design programs.
Basic Power-Converter Configurations
The inductive switch cell used in switching power converters is the basis for three converter types. These types are configurations of the basic inductive switch cell, just as transistors have three configurations, with one terminal in common with input and output circuits. This article presents the three basic converter configurations.
Flyback Transformer Leakage Inductance: Part 1: Introduction
Flyback converters are a common design choice for low-power (< 100 W) converters. At low power, it is more difficult to achieve high efficiency because otherwise negligible power losses, such as in the control circuitry, have a significant effect on efficiency. One of the main causes of power loss in flyback converters is due to the leakage inductance of the coupled inductor (transformer). Minimization of leakage-inductance power loss is consequently of major interest in the design of flyback converters.
Flyback Transformer Leakage Inductance: Part 2: Primary to Secondary Current Transfer
When a flyback converter's primary power switch turns off, current is transferred from the primary to the secondary winding. This does not occur instantaneously and the transfer delay depends on the primary-side clamp voltage. This current-transfer phenomenon is examined here.
The Power Switch Model
Power converters and motor current-control loops contain switching elements – nonlinear functions that require linearization for incremental (small-signal) modeling of loop dynamic response. As with transistors, an operating point is chosen and the incremental model is developed using the static (dc) values of currents and voltages at this point. This article develops the incremental switch model.
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