ABSTRACT
Voltage regulation, a fixed frequency control technique, is introduced and applied to flyback converter operating in discontinuous conduction mode (DCM). The control parameters are designed in a way that the converter operates as close as possible to the critical conduction mode. The design procedure of the flyback converter is provided in this. The proposed technique is applicable to any converter operating in DCM. However, this work mainly focuses on flyback topology. The Multi output Flyback converter is examined as a low voltage, low current with low ripple power supply. The converter operates at 100kHz. Low Dropout Regulators are used for post regulation at the secondary side to improve line, load, and cross regulation.
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.