A low cost low power Flyback converter with a simple transformer

Flyback converter is widely adopted in low power application. In order to get a high efficiency, the Flyback transformer should be well coupled with interleaved structure, which makes the transformer construction labor intensive. Usually the triple insulation wire is used to meet the safety regulation, which further increases the cost of the transformer. The simple transformer structure by separating the primary winding and secondary side winding with a chamber bobbin can greatly decrease the effort of the transformer construction, increase the productivity and achieve good isolation using cheap magnet wire. However, the high leakage inductance due to simple structure will deteriorate the efficiency. In this paper, the Flyback topology with a lossless snubber for the simple transformer structure is analyzed. The optimal parameters design considerations with off-time control are also presented. Finally, a 6V/900mA prototype with simple transformer and bipolar transistor are built, and the experimental results verify the theoretical analysis and the design methodology.