| Summary: | 碩士 === 國立臺北科技大學 === 電能轉換與控制產業碩士專班 === 101 === A novel bridgeless isolated AC LED dimmable driver is developed, which improves LED utilization and application flexibility due to a coupled inductor inserted between the power switch and the AC LED module. By reducing the turns ratio of the coupled inductor, the voltage across the secondary side will be decreased so as to lessen the voltage across the LED string and hence to reduce the number of LEDs, thereby making the load design of the AC LED driver more flexible. It is noted that the coupled inductor plays the role of not only galvanic isolation but also inductor behavior as well as transformer behavior. Therefore, during the turn-on period of the power switch, the coupled inductor can transfer the energy to one LED string and store the energy simultaneously, whereas during the turn-off period of the power switch, the coupled inductor can release the stored energy to the other LED string. That is, two LED strings are conducted for any half cycle, implying that LED utilization is upgraded. As for PWM dimming, it is realized by directly tuning the control signal for the power switch without any dimming circuit. Finally, the basic operating principles and theoretical deductions are given along with some simulated and experimental results provided to verify the feasibility and effectiveness of the proposed topology.
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