Compact Hardware Implementation of Power Factor Control for LLC converter with Event-Driven-Timer Based Digital Controller

LLC converter is well known as an attractive topology however, it suffers from system stability degradation depending on load conditions, which has limited use for many applications. The previous study addressed this problem by proposing a novel control, called the “power factor (cosθ) control”, which adjusts the phase difference θ between the inverter voltage and primary current of the LLC half-bridge instead of adjusting the operating frequency. However, the previous prototype required a complicated analog circuit for the control, which appeared difficult for practical application. This paper aims at achieving a compact implementation of the control circuit. A special "Event-Driven-Timer Based" digital control is adopted which can automatically track the timing and frequency by detecting the resonant trigger point and turning on the main switch. The prototype board exhibited great size reduction of the control circuit as well as excellent controllability, supporting promising features for practical application.