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.