A 2.4-to-240W, 95.04% Peak Efficiency LLC Isolate Converter Controller with Symmetric Pulse-Width Balancing and Fixed-Period Hysteresis Burst Control

In recent years, DC-DC converters with high voltage conversion ratio have attracted ever-increasing attention in the field of power management. Conventional buck converters often exhibit limited duty cycle and hard switching, making them struggle to realize high conversion ratio and large output power [1]. Alternatively, LLC converters are favored for medium-to-high power applications due to their high gain, high power density, and soft switching capability. Conventional LLC controllers based on direct frequency control (DFC) are hard to compensate. Hybrid hysteresis control (HHC) [2] simplifies the power stage compensation by directly controlling the input charge of the resonant tank (Fig. 1 top left). However, two slope compensation current sources in the HHC (Fig. 1 bottom left) have to be sized large to mitigate noise and precisely matched [3]. Another concern is that according to the frequency response (Fig. 1 bottom right), the switching frequency increases as the load decreases, resulting in more switching losses and reduced efficiency. Burst-mode [4] is used to reduce the switching frequency equivalently by inserting idle periods. While this improves light load efficiency, load-depended burst frequency can generate audible noise that is generally not acceptable in practice. Finally, despite the merits of LLC converters, less work, however, has focused on integrated LLC controllers. Previous LLC controllers relied heavily on general-purpose processors and FPGAs [4]–[6], resulting in very low integration and unnecessary power overhead.