LLC Resonant Converter Controller with Burst Mode Control and Soft-Start Function

The LLC resonant converter features high efficiency, low electromagnetic interference (EMI), and an isolated architecture. On the primary side, it achieves soft switching, reducing losses and EMI while its isolated design enhances safety in high-power applications. However, it has some control-related drawbacks that need to be addressed. Under light-load conditions, this results in a high switching frequency, which leads to reduced conversion efficiency, and during startup, the low initial output voltage can cause the controller to misjudge and lower the frequency, resulting in excessive converter gain, which in turn leads to excessive voltage and current stress in the resonant network. To address these issues, this paper proposes a control IC implemented using the TSMC 0.18-μm HV BCD process, providing PFM and Burst Mode control under light-load conditions to improve efficiency and incorporating a Flash ADC to enable soft-start functionality. This design achieves a measured peak efficiency of 96.33% at output power of 200 W.