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 with constant current. In this paper, a single-stage isolated high power factor AC-DC LED driver is proposed and analyzed in detail, which is composed of a Buck-Boost power factor correction (PFC) unit operating in discontinuous conduction mode (DCM) and an isolated DC/DC unit with a voltage doubler rectifier, and the two units are integrated together by sharing the same power switch. Very high input power factor is achieved since the power factor correction unit operates with almost fixed duty ratio during half period of the utility line voltage. Since a voltage doubler rectifier is included in the isolated DC/DC unit, magnetic core size of the transformer and voltage stress of the secondary side diodes are reduced remarkably. First, the operating principle and performance of the LED driver are analyzed. Then, the main parameters are quantitatively calculated out in detail.

Existing System

Soft-Switching Asymmetrical Half-Bridge Converter.

Proposed System

This paper analyzes the performance of a single-stage isolated AC-DC LED driver with a voltage doubler rectifier in detail and the parameter design of it has been carried out. According to the predetermined variation range of maximum duty ratio and the voltage stress limit value of the power switch, the value of LB, n, Lm and Cdc have been calculated out quantitatively. The Buck-Boost PFC unit is always operated in DCM to realize the function of power factor correction internally and a high power factor can be achieved. The results of comparative analysis between the proposed driver and that one indicates that the voltage doubler rectifier circuit in the secondary side greatly reduces the volume of the isolated transformer as well as the voltage stress of the secondary side diodes which are forced on or off with zero current.

Architecture

The proposed single-stage isolated AC-DC LED driver with a voltage doubler rectifier. (a) Circuit diagram. (b) Simplified circuit diagram.