| 摘要 |
A dimmer for a lighting fixture, which has a fluorescent lamp operated with a saturable magnetic ballast, has an inductor in series with silicon controlled rectifiers used for phase control of the AC voltage applied to the fixture. The inductor attenuates flickering that tends to occur between power settings of 70 and 85% of full power operation, and also induces the lamp to drop-out, rather than graying gradually, in response to very low power settings. Controls performs a diagnostic procedure upon start-up to identify and record the flicker zone, if any, and drop-out setting, which are characteristic of the fixture, and then adjust user-specified power settings to avoid flicker and drop-out. The controls also monitor fixture current to detect flicker and drop-out, adjusting recorded data and adjusting actual phase angles and power settings to ensure proper operation. After a power failure, the controls respond to restoration of the AC voltage by implementing a cold start procedure before implementing any user specified phase control. During phase control, the fixture may be shunted when current drops substantially to zero to discharge capacitive voltages.
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