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The two-stage 48V-12V-1.8V Voltage Regulator Module (VRM) structure is gaining more and more attention in high-end server applications. The LLC converter is the preferred choice for the first conversion stage because it provides the isolated 12V output efficiently, which is then converted to 1.8V by the multi-phase Buck converter. Since the CPU works in sleep-mode most of the time, the light load...
In this paper, an adaptive synchronous rectifier (SR) driving scheme for the LLC resonant converters using the ripple counter concept is proposed, along with two methods of implementation. With the proposed scheme, the SR drain to source voltage is sensed to detect the body diode conduction, based on which the SR on-time can be well tuned to eliminate the body diode conduction. One proposed implementation...
This paper investigates how to integrate state-trajectory control functions of LLC resonant converter within a commercial low-cost microcontroller, including Simplified Optimal Trajectory Control (SOTC) for load transient, burst mode and soft start up. Simplified calculation process is proposed for SOTC to minimize digital delay. Guideline to select a proper microcontroller is presented to limit calculation...
The LLC resonant converter has drawn much attention for high efficiency. However, its light-load efficiency still cannot meet the ever increasing requirements. This paper proposes a novel burst-mode control for the LLC resonant converter to improve the light-load efficiency. Based on the state-plane trajectory analysis, during the burst-on time, a three-pulse switching pattern is implemented. By optimizing...
In this paper, a novel burst mode control solution for LLC resonant converters is proposed for the highest efficiency and small output voltage ripple. The burst time is set to be constant, the off time is modulated by load conditions. During the burst time, three pulse switching pattern is implemented to keep output voltage low frequency ripple minimal. The switch first turned on is controlled to...
A digital implementation of synchronous rectification (SR) driving scheme for LLC resonant converter is proposed in this paper. Compared with analog ones, digital implementation enables more intelligent and precise SR control, improving converter efficiency. In the proposed SR driving scheme, the drain to source voltage of synchronous rectifier on the secondary side is sensed, so that the paralleled...
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