Group-Asymmetrical PWM Control for Dimmable Fluorescent Lamp Ballast Without Striation and Thermostat Effect

In this paper a group-asymmetrical pulsewidth modulation (GAPWM) by signal process is explored to modulate the lamp current comprising even and odd harmonics, which can then eliminate striation and thermostat effects in a fluorescent lamp. Using GAPWM control, a hiding dc, like an electron cloud inside the lamp, disappears and good rejection to the thermostat effect is achieved since the average lamp current is null in the whole group period. The proposed ballast can actually operate in continuous-conduction mode to keep zero-voltage switching achieving a high power efficiency up to 90%. High lighting efficiency 20% more than that of the traditional ballast is also achieved. The fluorescent lamp is capable of obtaining wide dimmer range between 100% and 0% of the full luminance.