Electronic dimming ballast for compact fluorescent lamps

Abstract

The operating frequency of a ballast is sufficiently far from resonance that, when a compact fluorescent lamp is dimmed to about one percent light output level, the ballast is operating with an open loop gain below a predetermined level, such as, for example, 15, and is operating with an output impedance greater than a predetermined level, such as, for example, the absolute value of the maximum negative incremental impedance of the lamp, and more preferably, greater than twice the absolute value of the maximum negative incremental impedance of the lamp. By changing the frequency to 85 kHz from 80 kHz, for example, the gain is maintained about the same whether the light output is at five percent or one percent, for example. This provides a stable control loop. In this manner, compact fluorescent lamps can be dimmed below about one percent light output, without dropping out and without observable flicker.

Dependencies are inferred from the claim text.