Temperature-Robust LC3 Passive LED Drivers With Low THD, High Efficiency and PF, and Long Life

New passive LED drivers that can reduce the total harmonic distortion (THD) significantly by LC parallel resonance are proposed. Using an inductor and three capacitors, called LC³, novel characteristics, such as high power efficiency and power factor (PF) with extremely long life time are achieved. The proposed LED drivers have a temperature-robust characteristic, because their power is hardly changed by temperature. By selecting the number of LEDs in series n_s appropriately, the LED power variation caused by temperature change in LED can be zero. For the universal use of the proposed LED drivers in various countries with different frequencies, circuit configurations applicable to 50/60 Hz are proposed. To analyze the LED power and PF of the proposed LED driver, the phasor transformation was, for the first time, applied to nonlinear diode rectifier modeling. Although the proposed LED driver is a nonlinear switching circuit, the proposed analyses matched well with simulation and experimental results. A prototype LED driver showed a very high power efficiency of 95.2% at 70 W, meeting PF and THD regulations for source voltage variation of ±6% of 220 V, even when a reasonably small number of filters were used.