Modeling and analysis of variable frequency control method for switched-capacitor based LED driver

This paper proposes a constant on time variable frequency controlled resonant switched-capacitor (RSC) converter for driving high power light-emitting diodes (LEDs). The on time of a transistor is set constant which is less than the time constant τ of capacitor charge loop, as a result, the RSC converter has a wide operation range. In contrast to the conventional constant current DC drivers (the output current regulation is achieved by using the digital control circuit), the simple analog circuit is adopted to acquire the regulation issue. The output current value of the RSC converter could be kept constant by varying the switching frequency. On the other hand, the output current could be rearranged by setting the related reference value. In the RSC converter presented in this paper, a small value inductor is injected into the charge loop of RSC converter to improve the switching behavior of the converter. A 10W RSC converter was built to verify the modeling method and the proposed control method. The experiments and simulation were conducted to demonstrate the feasibility of the proposed control method. The experimental and simulated results show that, with the proposed control method, the RSC converter provides fast dynamical response speed with good regulation. What's more, the RSC converter presents robust performance. This control method is a general control method and it could be expanded to other topologies of RSC converters.