Modified TCM Soft-Switching for Efficiency Improvement in Electrolytic-Free, High Power Factor LED Driver

This article presents an light-emitting diode (LED) driver that actively reduces low-frequency output current ripple through a duty-cycle modulation scheme, enabling the use of compact film capacitors and eliminating electrolytic capacitors. The control architecture combines feedforward action with a proportional–integral controller, while the power stage integrates an interleaved boost maintain standard terminology converter with a synchronous buck DC–DC stage. The proposed topology complies with IEC 61000-3-2 Class C input-current harmonic limits and meets IEEE Std. 1789 recommendations for low-frequency LED current ripple, even under dimming conditions. To achieve zero-voltage switching of the power switches, a modified triangular current mode (TCM) technique is employed without requiring additional components. The modified TCM enables soft-switching operation with reduced conduction losses, resulting in a 1.84% efficiency improvement over conventional TCM at nominal output power under the worst-case operating condition. This efficiency improvement remains consistent across the entire dimming range, maintaining efficiency above 94% from nominal to 40% of the output power. Experimental results under nominal conditions (127 VAC input, 78 W output) demonstrate a total harmonic distortion of 9.42%, a power factor of 0.990, and an efficiency of 94.85%.