An inexpensive ac-direct LED drive circuit is proposed. It
consists of only a line filter, an LED bridge, a load inductor, a
bi-directional switch, and a switch control circuit. This circuit
requires few components and can operate at a free-volt input
condition. The power efficiency was > 89%, the luminous
efficiency was ~ 90 lm/W, the power factor was > 0.9, and the
120 Hz flicker index was ~ 0.3 for all input voltage conditions
(85 < Vin,rms < 265 V). The circuit satisfies the IEC 61000-3-2
Class C and the EN 55015 regulations. The circuit can be
implemented at lower cost than the multiple-string LED driver.
The proposed LED driver is well suited for use in household
LED lamps.