High Step-Up Flyback with Low-Overshoot Voltage Stress on Secondary GaN Rectifier

Abstract

This paper presents a new technique to mitigate the high voltage stress on the secondary gallium nitride (GaN) transistor in a high step-up flyback application. GaN devices provide a means of achieving high efficiency at hundreds (and thousands) of kHz of switching frequency. Presently however, commercially available GaN is limited to only a 650 V absolute voltage rating. Such a limitation is challenging in high step-up flyback applications due to the secondary leakage. The leakage imposes high voltage stress on the secondary GaN rectifier during its turn-off transient. Such stress may cause irreversible damage to the GaN device. A new method of leakage bypass is presented to mitigate the high voltage stress issue. The experimental results suggest that when compared to conventional secondary active clamp, a 2.3-fold reduction in overshoot voltage stress percentage is achievable with the technique. As a result, it is possible to utilize GaN as the rectifier while keeping the peak voltage stress within the 650 V limitation with the technique.