| •Main Power Supply Besides supplying the lamp with stable DC power, the main power supply gives the cathode an optimal operating temperature at a specified current. The cathode temperature is very important for lamp operation. A cathode temperature that is too high speeds up the evaporation of cathode materials. Too low of a temperature will increase the load on the cathode, causing unstable electron emission and greatly reducing the lamp service life. The lamp current must be set within the specified range to operate the lamp stably over long periods of time. For this reason, the operating current value and its range are specified for each lamp type. •Trigger Power Supply The trigger power supply is for starting lamp discharge. It applies a high-frequency pulse to the lamp load by inductive coupling. (See Figure 14.) In the initial stage of lamp operation, the discharge starts at approximately 10 kV. However, this characteristic varies according to the drop in electron emission capability of the cathode or variations in the fill gas pressure. In actual equipment operation, a trigger voltage of 20 kV to 30 kV should be applied to the lamp, while taking an ample safety margin into account. |