A 52% Peak Efficiency > 1-W Isolated Power Transfer System Using Fully Integrated Transformer With Magnetic Core

This article presents a fully integrated isolated power transfer system using an on-chip transformer with a magnetic core. The integrated magnetic core achieves a transformer quality factor of >12 at 20 MHz. The transformer is switched resonantly at 20 MHz using full-bridge LLC circuits to realize efficient power transfer while eliminating the excess radiated emissions with a fully symmetric topology. A multi-mode approach combining pulse width modulation (PWM) control and frequency control enables >1 W output power at an optimal power efficiency. A 5-kV galvanic isolation is achieved through thick polyimide layers between the transformer windings as well as between the windings and the core. The isolated power transfer system is packaged in a small-outline integrated circuit (SOIC) and delivers 1.1-W isolated power and achieves a peak efficiency of 52%, while passing CISPR 22 Class B radiated emissions limits with 5.8-dB margin.