This paper proposes a novel line frequency multistage conduction LED driver with current-limiting mechanism. By operating the LED driver in multistage conduction, the number of LEDs can be automatically adjusted to be driven with low ac voltage, which increases the LED utilization rate. The current-limiting mechanism offers overcurrent protection to the LEDs. With the aim of shaping the input current into a sinusoidal waveform, the number of LEDs and the current-limit values are determined by the proposed analysis methods; these steps improve the power factor (PF) and the total harmonic distortion of input current (THDi). Finally, two prototype circuits - two-stage conduction and three-stage conduction LED drivers - are built to verify the performances, such as LED utilization rate, THDi, PF, and system efficiency.
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