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In outdoor light-emitting diode (LED) lighting systems, there are a lot of applications. Depending on the output power rating, the power stage to drive an LED can be classified into single-stage and two-stage structures. The single-stage structure is for low-power LED lighting applications. However, it is difficult to apply at over 60-70 W of output power because of its low efficiency and huge transformer at high power. On the other hand, the two-stage structure is usually used for high power applications. However, it is undesirable to cover wide output power range because of its poor power factor (PF) under the light load condition. To solve these problems, this paper proposes a new pulse duty cycle control method with pulse frequency modulation for an interleaved single-stage flyback ac-dc converter. The proposed converter provides high efficiency under heavy loads with low ac line condition and under light loads with high ac line condition. In addition, the proposed converter shows high PF and low total harmonic distortion even when the output power is very low. As a result, a single LED ac-dc converter can cover wide power range for outdoor LED lighting applications. To verify the validity of the proposed converter, an 81-W prototype converter has been implemented and experimented on.
Date of Publication: Aug. 2013