The design guide "Trilogy of Magnetics" Würth Elektronik now launches the 4th edition of the design guide in the German language. The English edition will be published in April 2009. The design guide for EMI filter design and SMPS & RF design circuits is completely revised, newly structured, and covers a multitude of new components and applications. The design guide is divided into the following chapters: Basics Principles, Components, and Applications. A keyword index, as well as a formulary, closes the book. The objective of the design guide, "Trilogy of Magnetics," is to practically familiarize customers and users with the characteristics and applications of inductive components. The design guide was published 8 years ago for the first time and is now a standard work for many development departments and universities. The book has sold over 15,000 copies in the last 8 years. In the 4th edition, the explanation of old techniques and components was extracted to have more room for new components and applications. Notably, a multitude of external authors from our customer base and our well-known manufacturers passed on their experiences and solutions in the Basic Principles and Applications section. The following articles are exemplary highlights: - Calculation, dimensioning, and construction of customer-specific transformers (Do-it-yourself transformer design) - A transformer's effect on return loss - Class-D amplifier - An introduction to frequency compensation - Basic principles of Ethernet & Power-over-Ethernet. Furthermore, the Trilogy includes over 200 practical examples on the following topics: - Filter circuits - Audio circuits - Video circuits - Interfaces - HF circuits - Motor control units - SMPS - Line filter - Power supply.