METHOD OF CONTROLLING AN OPERATING FREQUENCY OF AN INVERTER CIRCUIT IN AN ELECTRONIC DIMMING BALLAST

摘要

An electronic ballast having an inverter circuit for driving a gas discharge lamp prevents allows some hard switching to occur in the inverter circuit in order to ensure adequate ballasting impedance to provide stable operation of the lamp, but not enough hard switching to generate excessive power loss in the inverter circuit. The inverter circuit comprises two switching devices that are coupled in series between a DC bus voltage and circuit common and are rendered conductive on a complementary basis, such that a high-frequency output voltage is generated at the junction of the switching devices. When the intensity of the lamp is at or near a low-end intensity, an operating frequency of the high-frequency output voltage is controlled to a low-end frequency that is low enough to ensure stable operation of the lamp and to allow some hard switching to occur in the switching devices, but high enough to prevent excessive power loss due to the hard switching in the switching devices.