| 摘要 |
In a frequency control for a high pressure discharge lamp ballast, short-term increase and decrease of a lamp voltage are suppressed. The high pressure discharge lamp ballast drives a high pressure discharge lamp with a synthesized-waveform alternating current made of multiple frequency components, the high pressure discharge lamp having a pair of electrodes disposed to face each other. The ballast includes: a control means for controlling a component contained ratio of the multiple frequency components per unit time; an output means for applying a synthesized-waveform current in accordance with the component contained ratio to the high pressure discharge lamp; and detection means for detecting a lamp parameter of the high pressure discharge lamp. The control circuit is configured to shift the component contained ratio to a first component contained ratio when the lamp parameter is in a first state, and shift the component contained ratio to a second component contained ratio when the lamp parameter is in a second state. The control circuit is configured to change the component contained ratio stepwise when the component contained ratio is shifted from the first component contained ratio to the second component contained ratio, or when the component contained ratio is shifted from the second component contained ratio to the first component contained ratio. |
