Two-stage electronic ballast for metal halide lamps with embedded buck-conversion and ignition circuit

A novel electronic ballast with a repeatedly resonating ignition circuit is proposed for metal halide lamp (MHL). The proposed electronic ballast features a two-stage structure that comprises a power factor corrector and a full-bridge inverter used for current control, filtering and ignition. The full-bridge inverter consists of a low-frequency leg with unilateral switches and a high-frequency leg with bidirectional switches. During starting, the low-frequency side performs repetitive resonance on a resonant energy tank to accumulate a high ignition voltage. At the steady state, the resonant energy tank serves as a filter to drive the lamp with a low-frequency square-wave current. A prototype is designed for 150-W metal halide lamps. Experimental results demonstrate that the proposed electronic ballast is capable of tackling the demanding staring transient and steady state operation.