LED driver compatible with electronic ballast

Abstract

This work presents a LED driver compatible with electronic ballast to replace the fluorescent lamp to the LED lamp without removing the electronic ballast. Different from the conventional LED drivers of which input is well-defined voltage-source, the input to the LED driver compatible with electronic ballast has non-ideal current source characteristic. Various electronic ballasts with different topologies are installed in fluorescent lamp fixtures and ceilings of buildings and the most important specification for the LED driver is to regulate the LED current with different electronic ballasts. In addition, the LED driver should operate normally with protection functions in programmed-start electronic ballast. To introduce an interface circuit that does not interrupt the existing lamp driver, a brief review of the fluorescent lamp and the electronic ballast is presented. The electronic ballast converts the AC main voltage to the AC current output with carrier frequency of tens of kilohertz and includes several power converters such as power factor correction (PFC) circuit and resonant DC-AC inverter. These sub-converters have a wide variety of choices and electronic ballasts with different combinations are being manufactured. The key requirements for the LED driver can be summarized as follow: First, the LED driver should be able operate with different electronic ballast. Second, a power control scheme with a non-ideal current source input is needed to regulate different output powers from different electronic ballasts. Finally, the LED driver should avoid triggering the protection functions in the electronic ballasts. To regulate the output power of the electronic ballast, a current switching scheme with a parallel switch to return the redundant input current is proposed. The output current of the electronic ballast is transferred to the LED load when the switch is opened and is returned to the electronic ballast when the switch is closed. By changing the cond...