With the rapid advancement of technology and the evolving demands of modern life, Light Emitting Diodes (LEDs) have found widespread applications in various fields such as general illumination, healthcare, and transportation. As current-driven devices, LEDs rely heavily on the stability and consistency of the current passing through them to ensure high-quality light output. Therefore, the development of efficient LED driver circuits has become a critical area of research [1-2].
Currently, LED driver technologies are continuously improving, with two main topologies: single-stage and two-stage. Single-stage drivers, such as Buck, Buck-Boost, and Flyback configurations, offer simplicity, ease of control, and lower costs. However, they typically suffer from low power factor and significant output current ripple, which can degrade the quality of the LED lighting. 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 costly, they provide better power factor and reduced current ripple, making them suitable for meeting stringent standards like IEC 61000-3-2 [3-8].
In literature [9], a quadratic Buck-free stroboscopic transformerless LED driver was introduced, featuring a high power factor and reduced output ripple. However, it still faced challenges related to the zero-crossing dead zone in the input current, leading to higher Total Harmonic Distortion (THD).
To address these issues, this paper proposes a novel LED driver based on a Buck-Boost cascade quadratic Buck topology. By integrating a Buck-Boost converter with the quadratic Buck configuration, the design eliminates the zero-crossing dead zone in the input current, significantly improves THD, and enhances the overall power factor. Additionally, the two-stage cascaded structure reduces the voltage stress on diodes and allows the switch to operate within a more optimal duty cycle range.
The main circuit topology of the proposed driver is shown in Figure 1. It combines a Buck-Boost stage with a quadratic Buck stage, sharing a common switch Q. The Buck-Boost section includes a switching transistor Q, an inductor L1, a capacitor C1, and diodes D2 and D3. The quadratic Buck section comprises another set of components, including inductors L2 and L3, capacitors C2 and Co, and diodes D4–D7. When inductors L1 and L2 operate in Discontinuous Conduction Mode (DCM), the circuit automatically achieves PFC. Inductor L3 operates in Critical Conduction Mode (CRM) to enhance efficiency.
For analysis, we assume ideal components, a switching frequency much higher than the grid frequency, and constant capacitor voltages during the switching period. The converter operates in two primary modes: when the switch is on and when it is off. The equivalent circuits for these modes are illustrated in Figure 2, along with the main driving waveforms in Figure 3.
When the switch is turned off, diodes D3, D5, and D7 conduct, allowing the inductor currents to continue flowing and discharge into the respective capacitors. The peak inductor current and freewheeling time relationship is given by:
$$
I_{L1\_peak} = \frac{V_{in} \cdot t_{off}}{L_1}
$$
Since inductor L3 operates in CRM mode, its current waveform is continuous and well-controlled, ensuring stable operation.
In terms of operating characteristics, the duty cycle plays a crucial role in determining the voltage transfer ratio. Compared to conventional quadratic Buck topologies, the proposed design offers improved performance under the same voltage ratio, enhancing both stability and efficiency. Capacitors C1 and C2 are analyzed for their roles in filtering and energy storage, while inductors L1, L2, and L3 are studied for their conduction modes and impact on overall performance.
Experimental results confirm the theoretical analysis. A 32 W LED driver was built with an input of 220 V, 50 Hz, and an output of 1.6 A at 20 V, operating at a switching frequency of 30 kHz. The measured power factor reached 97.7%, and the input current showed minimal distortion, with no zero-crossing dead zones. The output current was smooth, with low ripple and no stroboscopic effects.
The experimental data aligns with the theoretical predictions, confirming that inductors L1 and L2 operate in DCM, while L3 works in CRM, as expected.
In conclusion, the proposed LED driver based on the Buck-Boost cascade quadratic Buck topology offers significant improvements over traditional designs. It effectively eliminates the zero-crossing dead zone, enhances the power factor, and reduces THD. Experimental results validate the design’s ability to deliver stable, low-ripple current, making it a promising solution for modern LED lighting systems.
Screw Terminal Connector,Pcb Screw Terminal,Screw Terminal Block Connector,Screw Type Terminal Blocks
Cixi Xinke Electronic Technology Co., Ltd. , https://www.cxxinke.com