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In this paper, a study on LED retrofit solutions for low-voltage halogen cycle lamps is conducted. In the first part of this paper, a lamp based on a LED array is designed to operate in substitution of a 12-V/50-W halogen lamp, for lighting fixtures in which these lamps are supplied using a line transformer. The design includes the selection of an adequate LED array in terms of lumen output and color temperature and the calculation of the necessary heatsink to assure the correct operation of the LED lamp within the selected temperature range. In the second part of this paper, a passive converter based on a bridge rectifier and a limiting resistance is studied and tested in the laboratory. Next, an active solution based on a buck-boost converter operating in discontinuous conduction mode is designed and experimentally evaluated. Finally, a comparison in terms of input power factor, input current harmonic content, LED current ripple, LED current regulation, efficiency, and photometric characteristics is carried out.
Date of Publication: Sept.-Oct. 2012