Design considerations of highly-efficient active clamp flyback converter using GaN power ICs

High switching frequency and high efficiency are critical in reducing power adapter size. The active clamp flyback (ACF) allows soft switching under all line and load conditions, eliminating all leakage inductance and snubber losses. This paper discusses key design considerations for high density ACF converters by looking into ZVS condition, RMS current reduction, and EMI optimization. Current-dip effect and secondary resonant scheme are found to significantly improve efficiency. GaN power ICs, with low output charge & integrated drive with reduced parasitics, are ideal for high frequency ACF. A 65 W USB-PD adapter was built to 24 W/in³ cased power density and 93.4% worst case efficiency. The design met European CoC Tier 2 and US DoE Level VI efficiency requirement and the EN55022 Class B conducted EMI standard.