Self-oscillating dimmable electronic ballast to supply two independent lamps

This paper presents a self-oscillating dimmable electronic ballast to supply two independent lamps. A simple modification in the driver circuit allows dimming of the lamps; this modification consists of only two additional low power passive components. The describing function method and the extended Nyquist criterion are used in the analysis and design. An improved arrangement of the lamps in the half-bridge topology is done, putting one lamp in each switch of the converter. The advantages of this new arrangement are: if one lamp is damaged, the other keeps working; it has an efficiency improvement when compared to ballasts that supply only one lamp; and the voltage supported by the switches is smaller when compared to the conventional ballasts which supply two lamps in series. Dim feature allows correcting the switching frequency when one of the lamps is out of the circuit.