High-precision LED driving system based on LLC resonant converter

A novel high-precision LED driving system based on LLC resonant converter is presented in this paper. Dual control loops are embedded in this system. One is used as the main loop of the whole system, which can regulate the output signal, and realize analog dimming. The other loop is an assistant loop, which is used to achieve high-precision PWM dimming. Analog dimming loop achieves constant current through the error amplifier (EA) and the voltage-controlled oscillator (VCO). Intelligent duty-cycle builder (IDCB) is realized with the external PWM signal and the difference between the actual output current and the pre-set current. The actual PWM control signal in the system can be dynamically adjusted by the IDCB, which can greatly improve the accuracy of PWM dimming. Besides, the transformer-isolated driver is adopted in this system to reduce the operating voltage of the control chip. The proposed LED driving system has been validated with 0.35μm BCD technology. The accuracy of PWM dimming can be improved by 17% with the assistant loop and reaches up to 95%. The current consumption of the LLC resonant controller IC is 5mA for a 100 kHz operation frequency using a 400V supply voltage. In addition, the power switching MOSFETs can achieve zero-voltage switching (ZVS) and the rectifier diodes can achieve zero-current switching (ZCS).