ABSTRACT
A step-up isolated dc–dc converter is proposed in this study, named the flyback converter. The topology consists of rectifier converting ac voltage to dc voltage and it is subjected to current following control for flyback converters to improve the power factor. The proposed converter has the potential to be used in low voltage and low power applications. The performance of the converter is noted for different loading conditions. The simulation is carried out using MATLAB/Simulink.

INTRODUCTION
Due to high efficiency and high power density as well as reduced costs, switched mode power supplies (SMPS) are now becoming more popular compared to the linear power supplies. This topology perfectly suits off-line low-cost power supply applications due to the facts that it provides input-output isolation and the number of its semiconductor and magnetic components is less than other SMPS. Flyback converter has been employed operating both in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) as well as critical conduction mode, i.e., at the boundary between CCM and DCM. Compared with CCM, critical conduction mode enjoys benefits such as zero current turn-on of the switch and zero current turn-off of the freewheeling diode. These soft switching transitions reduce the switching losses as well at the electromagnetic interference (EMI) noise. Critical conduction mode has less current stress than DCM and higher current stress than CCM. Furthermore, the transfer function of the flyback converter operating in critical conduction mode is of order one; thus, the feedback compensation is less complicated than CCM. However, despite the advantageous benefits of critical conduction mode, its major drawback is the variations of the switching frequency of the converter as the output load changes.

Block Diagram