Research On LED Power Supply With Current Adaptive Driving Technology

Light Emitting Diode(LED)has the advantages of no pollution,high efficiency,high reliability,long life and etc.,which makes it widely used in various fields as the new generation of electric light source.The application of LED lighting depends on the advancement of LED power supply technology.To let LED operate properly,it is important to design LED power supply with high performance.This paper studies a novel topology of AC/DC LED power supply without electrolytic capacitor,as well as the optimization method of the drive circuit for the switching device in the main circuit.The topology is a modified forward circuit,which operates in the discontinous mode to realize the power factor correction(PFC).A film capacitor is added on the high voltage side to balance the double-frequency pulsed power,instead of using a bulky electrolytic capacitor.This circuit also has a low ripple on the output current to satisfy the constant current output for LED.This paper analyzes the opearting principle of the circuit,elaborates the relationship of the characteristic and the parameters and then optimizes the parameter design,establishes the small signal model and designs the current closed loop based on the model.This paper also discusses the relationship between the voltage stress of the switching device and the current through the load,and the intermittent full bridge current source drive circuit with adaptive turn-off strategy with voltage spike limitationis applied to solve the high voltage stress problem.This improves the efficiency under different load.A 100 W prototype is set up to verify the theoretical analysis.The experiment result shows that the electrolytic capacitor is not necessary while the PFC is realized and the low-ripple output current is guaranteed.Compared to full load,the voltage stress on the switching device is higher under half load,so the maximum peak voltage of main circuit MOSFET switches in the LED power supply under half load can be chosen to be the limitation.When the load increases,the switch driving current adaptively increases to speed up the shutdown speed and reduce the turn off loss.By contrast,the load current adaptive drive control method can effectively improve the full load efficiency of LED power supply.