Compared with the fluorescent lamp electronic ballast, the special requirements of HID lamp electronic ballasts have two mainly aspects:
1. To avoid acoustic resonance, HID lamp electronic ballast is suitable for working under low frequency，fluorescent lamp electronic ballast work under 40 KHz high frequency, when the working frequency of HID lamp electronic ballasts over than 10 KHz(some HID lights for more than 1 KHz), high intensity gas discharge will become unstable, this unstable phenomenon is called “resonance”. Once HID lamp occurs “Resonance”, lamp power instantaneous change will cause the plasma temperature fluctuation. Due to the direct relationship between the gas temperature and pressure, temperature fluctuation can cause the pressure change, at a result, the pressure occurs fluctuation, the electric arc shape become deformed. Because of the arc discharge is bound between two electrodes, so can produce a standing wave (similar to organ). The effect of the acoustic resonance is very strong and unpredictable. On a certain frequency, one or two cycles is enough to make the arc extinguishing. In addition, the arc shape changes will change the discharge chemical balance, can cause the light color changed, light intensity measurement inaccuracy and the change of electrical properties.
Most HID lamp work under 50Hz ~ 10 KHz frequency can avoid the acoustic resonance. In the design of HID lamp electronic ballasts, most of its output frequency set in the range of 100 ~ 400 Hz. If the frequency is lower than 100 Hz, sometimes easy cause lights flashing. Therefore, usually HID lamp electronic ballast is not a high-frequency electronic ballasts, but a low frequency electronic ballasts.
2.HID lamp trigger voltage is commonly 3 ~ 5 kv. HID lamp from trigger (ignition) to the normal work often need to pass sustain stage and voltage rise stage. For the sustain stage, the lamp voltage is only about 25% of their normal working voltage (usually about 20v), the duration is about 1 ms. Continuous current depends on the light resistance. It will put out if the current is too small or the lamp voltage is too low , it needs to trigger again. In voltage rising stage, the lamp voltage gradually rise to its rating value (85v), the duration about 2 min. In order to prevent lights putting out, need a relatively larger rising current, but should not be too large, in order to prevent the lamp electrode melt.
In addition, because of HID lamp application environment is poor, such as the HPS lamp used for outdoor lighting such as road, airport and wharf and metal halide lamp used in automobile headlights, etc.), so the require HID lamp electronic ballasts should have very high reliability, high/low temperature, resistance to vibration, to prevent the rain and protect themselves from blowing sand. So, in order to design a good electronic ballast, Lisun developed WT5000 Electronic Ballast Tester to test it.