1 Overview of Half-Bridge (HB) LLC Topology

LLC resonant converters continue to be a popular topology for server and data-center applications due to their high efficiency and low EMI noise. With the ever-increasing power demands, interleaving LLC converters is becoming essential. Multiphase systems can be further interleaved to provide higher power capacity and reduce ripple current even further. This application note focuses on one configuration: a dual 3-phase interleaved half-bridge, utilizing a center-tapped transformer and a ‘Y’ output structure. The primary side is comprised of a half-bridge driver and an LLC resonant tank. The secondary side rectifier is implemented with power switches with active control. The secondary winding is center-tapped and becomes the DC output. A high-level schematic of a half-bridge LLC is shown in Figure 1-1. Figure 1-2 combines three phases into one half of the dual interleaved application. In total, there are six phases, each driven with a pair of PWM outputs for a total of 24 switches. The main PWM peripheral includes eight high-speed PWM generators (PG), but this dual 3-phase interleaved system requires 12 individual PWM pairs. Certain dsPIC33AK device families include an additional PWM peripheral named the Auxiliary PWM (APWM). The PWM and APWM share the same system resources and have interconnectivity of events and signals.