A Single-Stage PFM-APWM Hybrid Modulated Soft-Switched Converter With Low Bus Voltage for High-Power LED Lighting Applications

In order to design a high-efficiency cost-effective high-power LED driver, a single-stage integrated boost- LLC-type soft-switched ac-dc converter is usually employed. The minimized number of semiconductors and the reduced power loss are its main advantages. However, the high bus voltage is its well-known disadvantage, which is caused by the employment of a conventional pulse frequency modulation (PFM) control strategy with the duty cycle of 0.5. The range of the input ac voltage is severely limited. In order to overcome this problem, a hybrid PFM-asymmetric pulse width modulation strategy is proposed in this paper. The proposed strategy can significantly reduce the bus voltage while maintaining the soft-switching operation for both primary MOSFETs and secondary diodes. Furthermore, the electrolytic capacitors are removed by increasing the bus voltage ripple. Hence, high efficiency, long lifetime, low cost, and universal operation are achieved on the proposed LED driver, which is well matched to the virtues of LED lighting source. The detailed operation principles and design consideration for the proposed modulation approach are analyzed and discussed. The feature of the proposed solution was demonstrated using a universal-input 100-W hardware prototype. The experimental results verified the full-range zero-voltage-switching (ZVS) operation for primary switches and the efficiency achieved 91.6% under the 130-V input voltage.