Study Of Analytical Model And Control Method To Improve Cross-regulation In Multiple-output Flyback Converters

Flyback converters are widely used in the applications that load is less than 150W, because they are simple composed, low cost and less devices are needed. A multiple-output flyback converter can be achieved when auxiliary output windings and rectifier circuits are added to a common flyback converter, so it enhances fatherly cost advantage of the converter. However, the voltage of auxiliary output may varies largely when main output's load or auxiliary output's load changes, for only main output is sampled to keep its voltage stable but auxiliary output is in the open-loop situation. That's multiple-output flyback converters'cross-regulation problem. In practice, the output whose load needs stable voltage critically and the largest power is selected as main output. And the outputs, whose load allow voltage to vary in an acceptable range, are selected as auxiliary outputs. So, appropriate method should be adopted or auxiliary devices should be added to the converter to constrain auxiliary output's voltage within adoptable range. Meanwhile, the cost advantage should be kept. That's the purpose and significance to improve cross-regulation in multiple-output flyback converters.This article includes the following works:Firstly, the cross-regulation problem in multiple-output flyback converters is introduced. Current methods to improve cross-regulation in multiple-output flyback converters are given, as well as their merits and disadvantages.Secondly, analytical model is achieved on the base of magnetic coupling relationship between windings of a multiple-winding transformer. Switch modes of multiple-output flyback converters under different working modes are presented. Duration and current of inductance in different switch modes are calculated out.Thirdly, forcibly coupled rectification is presented to improve cross-regulation in multiple-output flyback converters. Switch modes of converter using forcibly coupled rectification are given on the base of precedent analytical model. It is drawn from simulations and experiments that voltage of auxiliary output varies less in multiple-output flyback converters using the new rectification method. Also, characters and applications of this new method are discussed.In the end, this paper is summarized and further research direction is proposed.