With the rapid advancement of technology and the evolution of modern society, Light Emitting Diodes (LEDs) have become a fundamental part of daily life, finding extensive applications in areas such as general illumination, healthcare, and transportation. As current-driven devices, LEDs rely heavily on the stability and consistency of the current flowing through them. Therefore, the performance of LED lighting systems is largely dependent on the design and innovation of their power drivers [1-2].
In recent years, LED driver technology has matured significantly, with two main topologies: single-stage and two-stage. Single-stage drivers, such as Buck, Buck-Boost, and Flyback circuits, are known for their simplicity, ease of control, and low cost. However, they suffer from poor power factor and high output current ripple, which can negatively impact the quality of light emitted by LEDs. On the other hand, two-stage drivers consist of a Power Factor Correction (PFC) stage followed by a DC-DC conversion stage. While more complex and expensive, they offer better power factor and reduced current ripple, making them suitable for meeting stringent IEC 61000-3-2 harmonic standards [3-8].
A notable approach proposed in literature [9] is a quadratic Buck-free stroboscopic transformerless LED driver that improves power factor and reduces output ripple. However, it still suffers from a zero-crossing dead zone in the input current, leading to increased Total Harmonic Distortion (THD).
To address these limitations, this paper introduces a novel LED driver based on a Buck-Boost cascade quadratic Buck topology. By integrating a Buck-Boost converter into the existing quadratic Buck structure, the zero-crossing dead zone in the input current is eliminated, resulting in improved THD and higher power factor. Additionally, the two-stage configuration reduces the voltage stress on the diodes and allows the switch to operate within a more favorable duty cycle range.
The main circuit topology of the proposed driver combines a Buck-Boost stage with a quadratic Buck stage, sharing a common switch Q. The Buck-Boost stage includes components such as an inductor L1, capacitor C1, and diodes D2 and D3, while the quadratic Buck stage incorporates additional inductors L2 and L3, capacitors C2 and Co, and multiple diodes. When inductors L1 and L2 operate in Discontinuous Conduction Mode (DCM), the circuit inherently performs PFC. To enhance efficiency, inductor L3 operates in Critical Conduction Mode (CRM).
Assuming ideal components and a switching frequency much higher than the grid frequency, the converter operates in two primary modes: when the switch is on and when it is off. During the on-time, energy is stored in the inductors, while during the off-time, the stored energy is transferred to the capacitors and the load.
Through detailed analysis, it was found that the proposed topology offers a more favorable duty cycle compared to conventional quadratic Buck configurations, thereby improving power supply stability and efficiency. Capacitors C1 and C2 play a crucial role in filtering and stabilizing the voltage, while the inductors L1, L2, and L3 are carefully designed to meet CRM and DCM operating conditions.
Experimental results confirm the effectiveness of the proposed driver. A 32 W prototype was built with an input voltage of 220 V, 50 Hz, and an output of 1.6 A at 20 V. The measured power factor reached an impressive 97.7%, and the input current waveform showed minimal distortion, with a significant reduction in THD. The output current was stable, with very low ripple, ensuring consistent LED illumination.
In conclusion, the proposed LED driver based on the Buck-Boost cascade quadratic Buck topology offers a robust and efficient solution for modern lighting applications. It addresses key issues such as power factor, THD, and current ripple, while maintaining a simple control strategy and cost-effective design. This makes it a promising candidate for future LED driver development.
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