A flyback converter is used for getting DC output and for isolating input mains and output voltage. A flyback converter is like a buck-boost converter with input and output isolated. There are two modes in flyback converter one is continuous mode and second is discontinuous mode. The discontinuous mode flyback converter is used for those applications which require constant current. And continuous mode flyback converter is use for those applications which requires constant voltage.
Flyback converter consists of one controllable switch like MOSFET. And power transformer, diode, and capacitor. The efficiency of flyback converter is low due to the power transformer. The output inductor is absent in flyback converter which is advantageous for cost and size. During the on time of controllable switch the transformer stores the energy and during the off time transformer transfer the energy to load.