Improving SRC with capacitor bypassing method for universal AC-DC adapter

Abstract

Technologies associated with power adapters for laptops and cellphones are fast advancing with new protocols and devices unveiled. A universal adapter operating from 100 VAC to 240 VAC has long been a prized feature among consumers, yet a challenge for the designers. This paper proposed a series resonant converter with capacitor bypassing method to accommodate the wide AC voltage range, and achieve high performance. Two resonant capacitors are used for the 120 VAC and 220 VAC lines, respectively. Thus, the resonant inductor size and loss can be significantly reduced as compared to the conventional series resonant converter. This technology is easy to implement in terms of both circuitry and control. The added MOSFET and capacitor are of low voltage rating, and consumes minimum board area. A 30 W prototype was built to verify the feasibility and demonstrate the advantages. A 93.3% efficiency is achieved with silicon operating at 1-MHz level.