| Metal Halide Lamps (MHL) have not only the characteristics of high luminous efficacy, high luminance, and long life as other High Intensity Discharge (HID) lamps, but also the characteristic of good color rendering. Therefore, MHL is widely used in venue lightings. Because of characteristics of ignition and negative-resistance, suitable ballast should be applied with MHL. However, traditional electromagnetic ballasts for MHL cannot satisfy the demands of modern lighting system, due to their drawbacks including large size, lower power factor, flicker, and poor power regulation. But digital electronic ballasts based on microcontroller can overcome most of the above drawbacks, and have advantages of simplifying the circuit and providing plentiful functions.For low wattage MHL, low frequency square waveform (LFSW) operation has been confirmed to be best choice to avoid acoustic resonance. Based on researching two-stage ballast, analysis on a novel two-stage dual Buck inverter is performed in this paper. First, Zero Voltage Switching (ZVS) sampling signals processing circuit is designed to keep switching device operate under adaptive ZVS condition. Second, because of excessive inductor current during low frequency transient reversal, single cycle current control circuit is used to limit peak current of inductor. Third, a method through adjusting turn-on time to realize constant power control is proposed. Because ignition method using adaptive frequency-sliding could result in inductor saturation, it is necessary to design additional high voltage(HV) pulse generation circuit. And analysis on influence of key parameters is performed at last.Through system test, efficiency is 92%, it will take 50~60 seconds to get rated power, has protect function including open circuit and short circuit. |
PDF Full Text Request