Series-Input-Connected Flyback-Forward Converter with Enlarged Duty Cycle Sunil Kumar Department of Electronics and Communication Engineering, J B Institute of Technology, Shankerpur, Chakrata Road, Dehradun, Uttarakhand, India, PIN-248197 Email: sunilkumar5593@gmail.com Abstract—In this paper, a structure consisting of combination of a flyback and a forward converter capable of making the power switch conduct at wide duty cycle, is presented. The configuration suggested employs sub-converters having their inputs combined in series with each other. In a forward converter, the maximum duty cycle by conventional manner becomes insufficient to utilize the isolation transformer, optimally. Under such condition, it becomes more important to extend the duty cycle, further. Bearing its importance and need in mind, present scheme is employed. By combining a forward with a flyback sub-converter in such a way that the inputs to both the sub- converters are in series, very wide switch duty cycle is obtained. The sub-converters are named as modules, and these are combined with their inputs connected in series with each other. A forward sub-converter is essentially a main module while flyback module is treated as auxiliary module. The configuration consisting of two modules is proposed and examined for the establishment of the results. The duty cycle for the switch has been extended to the expected level. For the validation of the performance, a 24 W, 24 V converter is presented. Index Terms— series-input, parallel-output, main module, auxiliary module, enlarged duty cycle, magnetization and demagnetization. I. INTRODUCTION The need of extended duty cycle in a forward converter is essential for optimum utilization of the transformer core. Converters based on non-cascading structures, reported in [1-8], can be employed for widening of duty cycle. In [9], how the switch duty cycle in a forward converter, by way of demagnetization through secondary side, is presented. In [10], extended switch duty cycle has been realized through a non-cascading structure based operation of the converter. But the stress on the main power switch is more which needs to be reduced to minimum value. A novel scheme based on so called flyboost cell is presented in [11] which when modified becomes suitable for the widening of the duty cycle in any converter. The converters based on non-cascading structures are reported [12-14] but their sole purpose is not widening duty cycle. However, under some circumstances, these are found suitable for use in widening of duty cycle also. But it is observed in these cases that the voltage stress on main switch becomes high. As an alternative to the mentioned methodologies if the configuration is modified to have the inputs connected in series, the problem of excessive voltage stress on the switch can be overcome. A list of different series input based converters given in [15-21] has proved that this class is no less important than non-cascading structure Grenze ID: 01.GIJET.9.1.513 © Grenze Scientific Society, 2023 Grenze International Journal of Engineering and Technology, Jan Issue