Design considerations for optimum dimming in single-stage electronic ballasts

Strategies for optimum dimming in single-stage electronic ballasts are presented in this paper. When the lamps are dimmed out to a lower level, the density of electrons will drop significantly, resulting in striation effect. Moreover, power imbalance exists between the power factor correction semi-stage and the ballast semi-stage, which usually results in a high DC-link voltage and might damage the switching devices. Control strategies for suppressing the high DC-link voltage and removing striations occurring in a fluorescent lamp are therefore proposed. In addition, an improvement on the jump phenomenon of lamp luminous output when it is controlled by varying the switching frequency are also proposed. Hardware measurements have been presented to verify the theoretical discussions.