1 Introduction

The UCC28782 is a transition-mode (TM) active clamp flyback (ACF) controller, equipped with advanced control schemes, to enable significant size reduction of passive components, for higher power density and higher average efficiency. The control law is optimized for Silicon (Si) and Gallium Nitride (GaN) power FETs in a half-bridge configuration and is capable of driving high-frequency AC/DC converters up to 1.5 MHz. The zero voltage switching (ZVS) control of the UCC28782 is capable of auto-tuning the on-time of a high-side clamp switch (QH) by using a unique loss less ZVS sensing network connected between the switch-node voltage (VSW) and SWS pin. The ACF controller is designed to adaptively achieve targeted full-ZVS or partial-ZVS conditions for the low-side main switch (QL) with minimum circulating energy over wide operating conditions. Auto-tuning eliminates the risk of losing ZVS due to component tolerance, input/output voltage changes, and temperature variations, since the QH on-time is corrected cycle-by-cycle.

Figure 1-1 Simplified Type Circuit