High efficiency electronic ballast for high intensity discharge lamps

摘要

An electronic ballast is powered by power source (102) and (104). The ballast controls the electrical power supplied to a gas discharge lamp (116), providing the voltages and currents required to start, warm-up and operate the lamp (116). Line power conditioner (100) reduces interference and harmonic generation, and provides a source of DC power (103), which may be regulated. DC power (103) is applied to inverter (105), which generates a square-wave voltage at a variable frequency determined by control circuit (200). Inverter (105) output is connected to resonant circuit (600) consisting of series inductor (110), series capacitors (112) and (118), and parallel inductor (114), across which gas discharge lamp (116) is connected. Operation begins with inverter (105) running at a frequency initially near but above the unloaded series resonance frequency of resonant circuit (600). Controller (200) reduces the frequency until resonant circuit (600) gives sufficient voltage to start lamp (116). After lamp (116) starts, controller (200) increases inverter (105) frequency to an intermediate frequency near but above one-third of the resonance of the series inductor (110) and the capacitors ( 112) and (118 causing a high current to flow in lamp (116), for warm-up. After a warm-up interval, controller (200) further increases inverter (105) frequency to a final value which is also above the frequency of acoustic arc resonance and above the loaded resonance frequency of resonant circuit (600).