Two-Switch Electrolytic Capacitor-Less LED Driving Circuit Topology and Control Strategy

As the fourth generation lighting source, the Lighting Emitting Diode (LED) has gradually replaced conventional sources of light in various lighting fields due to its excellent qualities in luminous efficiency, Service life, environmental protection, and production cost. Designing an LED driving power supply with a long service life, low device cost, high efficiency, and high reliability is urgent.This paper proposes a two-switch electrolytic capacitor-less LED driving circuit topology, which integrates the auxiliary energy storage circuit into the flyback Converter to suppress low-frequency ripples of the Output current and remove the electrolytic capacitor in the LED driving power supply. This circuit only contains two Switches and two diodes by sharing power Switches and energy storage components, reducing circuit cost and improving the efficiency of the LED driving power supply. The auxiliary energy storage capacitor for balancing the input and Output ripple power difference is isolated from the LED load. Thus, the energy storage capacitance can be reduced by increasing the energy storage capacitor's average voltage or ripple value. The maximum capacitor value used in the entire LED driving power supply is reduced to 6.8uF, and the electrolytic capacitor is replaced by the film capacitor with smaller capacitance and longer life, which improves the service life and reliability of the LED driving power supply. Moreover, the auxiliary circuit without additional structures absorbs the voltage spike caused by the leakage inductance of its energy storage capacitor, reducing the voltage stress of the switch and enabling a wide AC input voltage ränge.A control strategy for ripple suppression and minimum energy storage capacitor voltage is proposed. According to the relationship among the duty cycle of each switch, the auxiliary energy storage capacitor voltage, the Output current, and the changing rules of the working duty cycle are obtained under the conditions that the two switches turn off at the same time when charging the auxiliary energy storage capacitor and turn on at the same time when discharging. The low-frequency ripple of the Output current is suppressed by Controlling the minimum value of the auxiliary energy storage capacitor voltage, and the efficiency of the LED driving power supply is further improved.Based on the working principle of the circuit, the critical parameter design method is given, the selection principles of the energy storage capacitor value are determined, and the corresponding control strategy is proposed. Finally, a 35 W principle prototype is built. The results show that when the auxiliary energy storage capacitor and Output filter capacitor are both 6.8 uE, the Output current ripple of the prototype is less than 10% in the AC input voltage ränge of 90~264 V, the maximum efficiency reaches 87.8%, and the circuit power factors are higher than 0.95. The proposed circuit topology and control strategy achieve electrolytic capacitor-less, Output current ripple suppression, high power factor, and wide AC input voltage ränge, which eliminates the impact of the electrolytic capacitor on the Service life of the LED driving power supply. © 2024 China Machine Press. All rights reserved.