A Single-Switch AC-DC LED DriverBased on a Boost-Flyback PFC Converter with Lossless Snubber

 

Abstract

A single-switch AC-DC light-emitting-diode (LED) driver based on boost-flyback power factor correction (PFC) converter with a lossless snubber is proposed. In the proposed LED driver, the boost PFC module is designed to be operated in the discontinuous-conduction mode (DCM) to achieve a high power factor. The DC-DC flyback module is designed to provide input-output electrical isolation to improve safety. The lossless snubber circuit clamps the peak voltage spike of switch to a low voltage and the leakage inductor energy is recycled via the DC-DC flyback module. Additionally, a low-voltage-rating capacitor can be used as the DC-buscapacitor because some of the input power is directly conducted to the output; the remaining power is stored in the DC-bus capacitor. Therefore, the proposed LED driver can provide a high power factor and a high power conversion efficiency. These results are verified for an output of 48[V] and 2[A] for the experimental prototype.

EXISTING  SYSTEM:

Two-stage-type LED drivers are suitable for tightly controlled output voltages because they utilize a DC-bus capacitor, which reduces the difference between the input power and the output power. However, these LED drivers have two switches and two control circuits in each stage; therefore, they are usually large size, have a large components, are more expensive and are less energy efficient. To overcome these problems, the two-stage LED driver is modified to become a single-stage LED driver by sharing a switch with both stages. A boost or buck-boost converter for PFC and a flyback converter are integrated in a single stage. Boost and a buck-boost PFC circuits are widely used because they can provide a high power factors using a simple structure and a simple control circuit. Several single-stage LED drivers, which use half-bridge LLC converters at the DC-DC stage, are presented. In the half-bridge LLC converter, soft-switching operation of the power switches reduces switching loss and increases efficiency.

PROPOSED SYSTEM:

In this paper, a single-stage AC-DC LED driver based on a boost-flyback PFC converter with a lossless snubber is proposed. Because the proposed LED driver is based on the boost-flyback structure, it achieves a high power factor based on the boost PFC, which is operated in the discontinuous-conduction mode (DCM). Additionally, the proposed LED driver provides electrical isolation due to the DC-DC flyback module. And, because the lossless snubber circuit is used, the leakage inductor energy is recycled into the DC-DC flyback circuit and the peak voltage spike in the main switch is clamped to a low voltage. Moreover, the DC-bus capacitor is divided into two capacitors, i.e., the snubber capacitor and another DC-bus capacitor.Additionally, some of the input power is directly delivered to the output; the remaining power is stored through the snubber diode. Hence, the energy conversion efficiency is improved and a voltage of DC-bus capacitor is also reduced. In conclusion, the proposed LED driver can provide a high power factor and achieve high power conversion efficiency. A theoretical analysis and an experimental prototype of the proposed LED driver are presented to verify the PFC and efficiency improvement.

CONCLUSIONS

A single-switch AC-DC LED driver based on a boost-flyback PFC converter with a lossless snubber has been proposed. Using the boost PFC circuit in DCM operation, a high power factor is achieved. In the DC-DC flyback circuit, Because of the lossless snubber circuit, the peak voltage stress of the switch is clamped and the leakage inductor energy is recycled. The DC-bus capacitor is split into two capacitors (because the snubber capacitor is used). Additionally, a low-voltage-rating capacitor can be used because some of the input power at the boost inductor is directly conducted to the output. Therefore, the total efficiency is improved. The performance of an LED driver prototype has been experimentally evaluated at an output current of 2[A] and an output voltage of 48[V].

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