A constant-on-time based buck controller with active PFC for universal input LED system

A constant-on-time (COT) based buck controller for driving LED lamp is presented in this paper. The chip integrates active power factor correction (PFC) and is suitable for universal input application. The buck converter is working in critical conduction mode (CRM). With COT control strategy, the input current of the buck converter could well follow the input voltage, thus high power factor (PF) can be attained. Also, the implementation of floating ground architecture helps to simplify the design of the control circuits. Furthermore, since the buck converter operates under CRM, the dynamic loss is also reduced. The chip is designed in CSMC 1.0 μm 40V process. Simulation results show that a power factor of 0.98 is achieved; the deviation of output average driving current is within ±3%, and the power efficiency at full load with 220Vrms input is 96%.