LED Drive Circuit with Series Input Connected Converter Cells Operating in Continuous Conduction Mode

This paper introduces an LED drive circuit implemented by series input connected converter cells with a common duty cycle control approach operating from a dc voltage bus. With this structure, low voltage high frequency ICs and low profile components can be applied in high voltage applications. Flexibility is provided for the cells to work under different voltage supply conditions by simply changing the number of series converters. With the converters operating in continuous conduction mode (CCM), the common duty cycle control approach enables automatic line voltage sharing and output current copying. The approach results in a control-to-output transfer function of the system that is close to that of a single converter for ease of feedback loop design. The modular approach also allows continued operation in the presence of open circuit LED failures. Design considerations and experimental results are presented for a 25 W 3-cell system with 9 Luxeon K2 high brightness LEDs, demonstrating line voltage sharing, output current copying and LED failure response.