A 6.8-W purely-resistive AC light-emitting diode driver circuit with 95% power factor

A light-emitting diode (LED) driver circuit that can operate off of an AC power supply without any reactive elements is described. The proposed circuit consists of resistive components and switches only, making it suitable for a single-chip integrated-circuit (IC) driver solution to realize a low-cost LED replacement for incandescent light bulbs. The driver circuit employs multiple strings of LEDs and sequences their conduction to shape the off-line current in proportion to the offline voltage, improving the power factors compared to the existing resistive drivers. A prototype circuit made with discrete components demonstrates the peak power factor of 95% and efficacy of 78-lm/V, when delivering 6.8-W to the load at a 220-V AC supply. An equivalent IC chip that integrates all components but the rectifying diodes would occupy only 2.76 mm² when fabricated in a 1.0 μm BCDMOS process.