Research Of A Novel Quasi-resonant Forward-flyback Hybird DC/DC Converter

Power electronics technology is used in almost every application area of national economy in today’s society,the development of household and consumer electronic products is rapid and the market is wide.Power adapter is an irreplaceable part of electronic products,and the the inevitable trend of development are miniaturization,high efficiency and low cost.So inventing new topologies is one of the key to updating converters and promoting the development of converters.In this paper,a novel quasi-resonant forward-flyback hybird DC/DC converter is proposed,which is very suitable for small power supply situations as the latter DC/DC converter of two-stage power supply.Specifically,the primary side of the converter is the same as the flyback and the forward,and the secondary side of the flyback is connected to the primary side of the converter.In order to push the converter to high frequency,using resonant capacitor to replace the freewheel diode in the secondary side so that the capacitor can resonant with transformer leakage inductance,introducing a resonant tank without adding devices.It is benefit to achieve zero-current-switching of the primary switch and the secondary diode,reducing the switching loss and facilitating the high frequency and miniaturization of the converter.The convertor adopts the constant-on-time frequency conversion control strategy,keeping the ontime of the switch constant,so as to ensure that the converter work in a fully resonant mode.This paper firstly introduces the topology derivation and operating principle of the proposed converter,giving the relationship of the input and output voltage as well as the external characteristic of the converter.Secondly,appropriate control strategy is selected according to the working conditions of the converter and feasibility is verified through simulation.Lastly,according to the technical indicators of 400 V input and 20V/65 W output,the parameters of the proposed converter are designed and the losses are analyzed.A prototype was established for experimental results to verify the theoretical analysis.