Magnetising inductance of multiple‐output flyback dc–dc convertor for discontinuous‐conduction mode

Abstract

This study presents the following: (i) detailed derivation of the expressions for the maximum value of the magnetising inductance of the ideal and lossy two‐output flyback dc–dc convertor operating in discontinuous‐conduction mode, (ii) a method to appropriately select the duty cycle for the metal–oxide–semiconductor field‐effect transistor based on the rated output dc voltages of the two stages, and (iii) a design approach for a three‐winding transformer with a gapped core used in the two‐output flyback convertor. The expressions derived and the proposed design technique can be extended to flyback convertors with more than two output stages with equal or unequal load voltages. A universal power supply (ac line adapter) employing a flyback dc–dc convertor with output voltages 15 and 32 V, supplying a rated output current of 0.563 and 0.533 A, and operating at a switching frequency of 85 kHz is designed using the proposed methodology. Simulation and experimental results are presented to validate the theoretical predictions.