Analysis and Design of a Single-Stage Isolated AC-DC LED Driver with a Voltage Doubler Rectifier
Abstract
In order to reduce the cost and volume of small-medium power AC-DC LED lighting systems,single-stage LED drivers are often used to drive LEDs withconstant current. In this paper, a single-stage isolated highpower factor AC-DC LED driver is proposed and analyzedin detail, which is composed of a Buck-Boost power factorcorrection (PFC) unit operating in discontinuous conduction mode (DCM) and an isolated DC/DC unit with avoltage doubler rectifier, and the two units are integratedtogether by sharing the same power switch. Very highinput power factor is achieved since the power factorcorrection unit operates with almost fixed duty ratio duringhalf period of the utility line voltage. Since a voltagedoubler rectifier is included in the isolated DC/DC unit,magnetic core size of the transformer and voltage stress ofthe secondary side diodes are reduced remarkably. First,the operating principle and performance of the LED driverare analyzed. Then, the main parameters are quantitativelycalculated out in detail. Finally, a comparative analysis ispresented and a 120W experimental prototype with 1Aoutput current is built according to the calculatedparameters and the experimental results are presented toverify the correctness of the theoretical analysis andparameter design.
EXISTING SYSTEM:
Boost converter, Sepic converter and Buck-Boost converterare most frequently used as the PFC unit of the single-stagedrivers. They operate in DCM to achieve high power factorinternally on the condition that the duty ratio D of the powerswitch keeps constant in half line cycle. The Boost-typePFC unit is quite simple and features high efficiency; however,the output voltage of it must be higher than the peak value ofthe input voltage at least, which leads to high voltage stress ofthe switch; Moreover, higher PF means higher output voltageand higher voltage stress. The Sepic-type PFC unitcan reduce the voltage stress imposed on both theenergy-storage capacitor and the switch due to its step up/downcapability. However, it contains two inductors and many othercomponents, which may lead to higher cost and lower reliability than the Boost-type PFC unit.Comparatively, the Buck-Boost-type PFC unit has manyadvantages such as simple structure, low voltage stress, andvery high power factor, thus, it is a proper choice and widelyused. Flyback converter, LLC resonant converter and class-Eresonant converter are commonly used as the DC-DC unitswhich realize electrical isolation and constant output current.LLC resonant converter features high conversion efficiencydue to its soft switching properties, thus has gained manyattentions. However, it contains two switches, a resonant inductor and a resonant capacitor at least, which leadto higher cost than its competitive ones, and it is suitable forthese applications where the efficiency but not the cost is themain concern.
PROPOSED SYSTEM:
A single-stage isolated high power factor LED driverwith leakage inductor energy recycling is proposed as shown inFig. 1, which integrates a Buck-Boost converter with a Flybackconverter by sharing the power switch Sw. The Buck-Boostconverter operating in DCM can achieve high power factorinternally. The voltage spike and ringing on the switch isalleviated due to the leakage inductor energy is recycled via a unidirectional diode, so the switching loss can be reduced andconversion efficiency can be improved. However, the Flybackconverter transfers energy from the primary side to thesecondary side only when the switch is turned off. Lowmagnetic core utilization results in large volume of thetransformer and limits its use to low power applications. In thispaper, a voltage doubler rectifier is included in the secondaryside of the transformer, thus, the energy is transferred from theprimary side to the secondary side whenever the switch is turned on or turned off. The magnetic core utilization oftransformer is improved and may be adopted in higher powerapplications. Furthermore, the voltage stress of the secondarydiodes can be reduced remarkably to lower the conducing loss.
CONCLUSION
0278-0046 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.=60W. This paper analyzes the performance of a single-stageisolated AC-DC LED driver with a voltage doubler rectifier indetail and the parameter design of it has been carried out.According to the predetermined variation range of maximumduty ratio and the voltage stress limit value of the power switch,the value of LB, n, Lm1.0000.9950.9900.9850.980 and Cdc have been calculated outquantitatively. The Buck-Boost PFC unit is always operated inDCM to realize the function of power factor correctioninternally and a high power factor can be achieved. The resultsof comparative analysis between the proposed driver and thatone in [23] indicate that the voltage doubler rectifier circuit inthe secondary side greatly reduces the volume of the isolatedtransformer as well as the voltage stress of the secondary sidediodes which are forced on or off with zero current. A 120Wexperimental prototype of the proposed LED driver has beenimplemented to demonstrate the validity of the theoretical analysis and parameter design. The experimental results showthat the power factor is always higher than 0.990 and themaximum efficiency can reach 89.3%.
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