Group-asymmetrical PWM controller for dimmable fluorescent lamp ballast without striation and thermostat effect

A signal process for eliminating striation and thermostat effect in a fluorescent lamp by group-asymmetrical pulse-width-modulation (GAPWM) control strategy is explored. The proposed GAPWM can make the odd harmonic energies of the lamp sharing on all the harmonics in low-level dimmer so as to eliminate striation and thermostat effect. Dimmer by signal process instead of hardware approach can make the control strategy easy to implement. A prototype of 80 W GAPWM fluorescent lamp ballast is examined for assessing the theoretical investigation and practicality. The GAPWM ballast can operate at ZVS and increase lighting efficiency up to 20% compared with the traditional one. Besides, it can make the fluorescent lamp without striation and thermostat effect during a wide dimming range from 100% to 1% of the full luminance.