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A bidirectional interleaved forward-flyback DC-DC converter with leakage energy recycled is proposed in this paper. The proposed converter uses two transformers to reduce the current stress on the power components to reduce the conduction loss and improve the efficiency. When the proposed converter is operated in the step-up mode, the voltage across switches is clamped at the input voltage, and the leakage energy is recycled to the voltage source. When the proposed converter is operated in the step-down mode, the voltage of switches is clamped at the input voltage, and the leakage energy is recycled to the clamping capacitor or the voltage source. As the proposed converter is based on flyback converter, it is characterized with simple structure. Since the leakage inductance energy is recycled, the conversion efficiency is improved compared to conventional flyback converter. Finally, a laboratory prototype circuit with 200 V/24 V and output power 500 W is implemented to verify the feasibility of the proposed converter. The highest efficiency in the step-up and step-down stage is 92.3% and 95.5% respectively.

In this paper, the design and implementation of a non-electrolytic capacitor LED driver is proposed. The proposed driver includes a Boost PFC converter as first-stage and a LLC Resonant Converter as second-stage. With feedforward control, the output current ripple can be reduced without electrolytic capacitor, the lifetime of the driver will be increased. In this paper, the operating principles of the LLC resonant Converter with feed-forward control will be discussed. Besides, the optimized design of the proposed control scheme will be discussed, too. Finally, a two-stage non electrolytic capacitor LED driver is implemented to drive 150 W LED load. Experimental results show that the proposed circuit can be operated at 90∼264V rms AC input voltage range and the highest efficiency is 90.4 %. The output current ripple and LED efficacy will be also verified.

A primary-side quasi-resonant (QR) controller IC for single-stage flyback LED driver with high power factor (PF) and low total current harmonic distortion (THDi) is proposed in this paper. Conventionally, the flyback PFC converter with critical conduction mode QR control will suffer from higher switching loss and occur higher THDi at high line condition. To solve this problem, a frequency limit QR control is proposed and analyzed. By using the proposed control, the main switch of flyback converter is turned on with valley voltage switching and the maximum frequency is limited. So that the system efficiency is increased and the input current will follow the input voltage waveform better than that with the conventional control. Finally, this controller is fabricated with TSMC 0.25 μm CMOS high voltage mixed signal general purpose process and applied to an input voltage of 90∼264 Vrms, output voltage of nominal 40 V, and constant output current of 600 mA/24W hardware prototype to verified the feasibility of the proposed control. The experimental result shows that the measured THDi is reduced from 10.5% to 3.3% at low line and 24% to 6.2% at high line compare to the critical conduction mode (CRM) QR flyback power factor correction (PFC) converter. The highest overall power efficiency is 91.4 %.

A novel interleaved flyback converter with leakage energy recycled is proposed. The proposed converter is combined with dual-switch dual-transformer flyback topology. Two clamping diodes are used to reduce the voltage stress on power switches to the input voltage level and also to recycle leakage inductance energy to the input voltage and capacitor. Besides, the interleaved control is implemented to reduce the output current ripple. In addition, the voltage on the primary windings is reduced to the half of the input voltage and thus reducing the turns ratio of transformers to improve efficiency. The operating principle and the steady state analysis of the proposed converter are discussed in detail. Finally, an experimental prototype is implemented with 400V input voltage, 24V/300W output to verify the feasibility of the proposed converter. The experimental results reveals that the highest efficiency of the proposed converter is 94.42%, the full load efficiency is 92.7%, and the 10% load efficiency is 92.61%.