Usually the first step in any power supply designer's checklist is to choose an appropriate power transfer circuitry, commonly referred to topology, based on the customer's requirements, and whether they need to design an isolated or non isolated unit. The different topologies or the way the power is transferred from input to output are Buck, Boost, Flyback, Forward ( Push-pull, Half Bridge, full bridge), and resonate to name a few.
After choosing the topology, transformer design is the most critical step. This requires choosing the other elements like primary main power switches (MOSFETs), output rectifiers (Schottkies, Fast and Ultra fast), and snubbers.
In the majority of power supply applications, with wattage levels in between few watts and a few hundred watts, the market demands attention to a few key issues:
As in the majority of the power supply designs, transformers and inductors are the major contributors to the size. Increasing the operating frequency can reduce the size of these magnetic. This desire for smaller size forces the power supply designers to increase the switching frequency. For example in a PoE discontinuous flyback with Duty of.275 and 46Vin to 3.3Vout at 3Amp output load for a given core, the needed primary inductance can be lowered to 19uH from 39uH when the frequency increase from 200Khz to 400Khz respectively.