A single-switch high-voltage lamp tester for cold cathode fluorescent lamps

This paper proposes a novel high-voltage generator served as a lamp tester for cold cathode fluorescent lamps (CCFLs). The proposed circuit consists of a buck-boost converter, an L-C resonant network and a step-up transformer. Only one active switch with simple control for turning on and off the switch at a high frequency is used. The inductance of the transformer serves as the inductor of the L-C resonant. In the L-C resonant network, the inductor stores and then releases energy to the capacitor across which the voltage is build up step by step until a relatively high voltage is achieved. This voltage is then stepped up by a transformer to provide the required high voltage for discharging the CCFLs. The proposed circuit has the advantage of simple configuration, small volume and low cost. Besides, a high power factor at the ac line source can be obtained by operating the buck-boost converter at discontinuous conduction mode (DCM). The proposed circuit is analyzed and the design equations are derived to determine the circuit parameters. A prototype circuit was built for testing 19 inch CCFLs. The discharging tests are made to recognize the malfunctions during the manufacturing process. Moreover, the distributions on the spectral power and chromaticity of lamps can be examined to ensure the product quality.