Abstract—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.
(Index
Terms—Frequency control, interleaved flyback, lightemitting diode (LED), power
factor correction (PFC), single-stage, total harmonic distortion (THD).)
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