Computer Aided Analysis of a Multi-Winging Flyback Converter Including the EMI Line Filter

Abstract

A two-transistor flyback-converter, originally built to be used as a measure object for measuring electromagnetic interference is thoroughly analyzed by using the circuit analysis programme KREAN. the flyback converter is operated in current-mode using the switchmode control-IC UC3842. Input voltage is 230 V mains. The output is on multiple windings with a total power of 260 W. The analysis is split into 3 major sections: 1. Regulator parameters. One of two secondary windings is regulated in a PI voltage regulator loop, with an inner current loop controling the (primary) transistor-current. The secondary windings are simulated with different leakage inductances. The unregulated output voltage is studied with low and high load, with fixed load at the regulated voltage. 2. Switchinq behaviour. The converter is simulated with leakage inductance in both primary and secondary windings of the transformer, and in the paths of the freewheeling diodes. Parasitic capacitances are included across the primary and secondary windings of the transformer and across drain-source of the transistors. 3. EMI-line-filter. Two major sources of EMI are simulated and Fourier transformed to find the expected conducted noise levels from the converter with and without the EMI line filter. The results are compared to measurements on the actual converter, and show acceptable accuracy.