A Study Of The Stability Of High-frequency Resonance Transforming System Of HID Lamps

The reason, phenomena and model for the acoustic resonance of metal halide (MH) lamps when working in high frequency are investigated. A ballast circuit which makes use of the power amplifier to output the square-wave current are built to drive the 70-W metal halide lamps on the open-loop condition. It is operated over a high-frequency range from 1kHz to 30kHz. For the ballast circuit, the operating frequency and the magnitude of the lamp current can be controlled independently. And a measuring system is set up to examine the effects of the acoustic resonance to the shape of the lamp arc, the color temperature, the light output as well as electrical characteristics. The discussion on stable state and the acoustic resonance model employ empirical and curve-fitting methods. In addition, the unstable state phenomena caused by MH lamp are researched, which puts forward some theoretical guidance and reference on the inhibition of acoustic resonance and the design of electronic ballast circuit.The experiments are conducted on the 70-W metal halide lamps. The experimental results show that the acoustic resonance of MH lamp is caused by itself at high frequency, which exclude the effects of electronic ballast circuit and resonance circuit to the acoustic resonance. Based on the experiments, the stable operating frequency range is under 10 kHz when the lamps are driven by the square-wave current. And it would be very difficult to operate the lamp in frequency range of 10 kHz without serious arc instabilities or arc extinction. At the same time, when the dead-time of the high frequency square-wave current is below 2.4μs, the drivingmethod would suppress the acoustic resonance. With operating frequency raising, the scope of dimming of MH lamp would reduce. Finally, the high frequency stable state model is initially established with piecewise linearization, and we discover it is a dynamic resistance in frequency range of 1 kHz to 30 kHz and is verified by simulations. Model of the acoustic resonance is discussed and bring some explanation about phenomena of the acoustic resonance.