Low-Cost Drive Circuit for AC-Direct LED Lamps

This paper proposes a drive circuit for ac-direct LED lamps. The proposed circuit consists only of a line filter, an LED bridge, a load inductor, a bidirectional switch, and a switch-control circuit. The switch connects the LED bridge to the power line directly. Each leg of the LED bridge consists of LEDs and a protection diode, all connected in series. The load inductor limits the bridge current. The switch operates at a zero current switching condition, so the circuit has high power efficiency. The circuit can operate at a free-volt input condition (
$85 < V_{{\rm in,rms}} < 265\; {\bf V}$
). For all input voltage conditions the circuit had PE > 89%, luminous efficiency ∼90 lm/W, power factor >0.9, and 120-Hz flicker index ∼0.3. The circuit satisfies the IEC 61000-3-2 Class C and the EN 55015 regulations. The proposed LED driver is well suited for use in household LED lamps.