DIMMABLE BALLAST FOR AN ELECTRODELESS DISCHARGE LAMP

摘要

A ballast for an electrodeless discharge lamp includes a high frequency power supply that supplies a high frequency electric power to an induction coil for operating the lamp. A dimmer controller generates a control signal in response to a dimmer command designating a varying dimming ratio. The control signal defines a first period Ton in which the power supply is controlled to apply a coil voltage of a first level V 1 to the induction coil for operating the lamp. The first period is followed by a second period Toff in which the power supply is controlled to apply the coil voltage of a second level V 2 that is lower than the first level and fails to sustain the lamp. The control signal defines, between the second period and the first period, a starting period Tst in which the coil voltage increases continuously for smooth transition from an off-condition to an on-condition of the lamp.