Using a power-dependent small-signal model for stability analysis in resonant dimming ballasts for fluorescent lamps

One important aspect for the design of dimming ballasts for fluorescent lamps is the output power range that can be obtained. Some applications require that the output power can be reduced below 10%. However, in some ballast designs, there is no easy way to reduce the output power to the required minimum level without finding instabilities that could lead to light flicker, audible noise or arc extinction. In this paper, a new power-dependent small-signal model for fluorescent lamps is presented. This model is based in a double-pole double-zero approximation. The generalized multifrequency averaging technique is then used to analyze the lamp-ballast interaction in resonant inverters. This method was used to calculate the actual dimming range in two of the most widely used resonant configurations for a 26W compact fluorescent lamp.