Low Profile, Laminated Nife Transformers for Flyback Converters

We introduce a flyback transformer with a laminated NiFe magnetic core, fabricated using a CMOS-compatible microfabrication technique involving sequential multilayer electrodeposition, and demonstrate its application in a flyback AC/DC converter with constant output voltage control operating at 500 kHz. The core adopts a 'UT' shape to facilitate winding, as opposed to the traditional EI shape. The transformer includes a 45-turn primary winding and a 3-turn secondary winding, featuring a magnetizing inductance of 317 µH and a coupling coefficient of 0.98. The total transformer core thickness was 4.2mm. Electrical performance was evaluated using a customized flyback circuit on a printed circuit board (PCB), which provided a stable isolated 5 V, 1 A DC output from a 60 Hz sinusoidal AC input ranging from 80 Vrms to 220 Vrms. The system achieved an end-to-end efficiency of 80% with a 120 Vrms input and maintained over 68% efficiency across the entire input range.