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Cheap Switch Mode DC DC Converter

This circuit is based on mobile phone chargers. These chargers are based on the Motorola MC34063 switchmode IC. By changing the values of the feedback resistors (R1 & R2), the output voltage can be varied over a wide range. Just modify R1 and R2 according to the formula: Vout = 1.25 (1+R2/R1). The values shown give an output of 3V.

Circuit diagram:Author: Timo Mahoney - Copyright: Silicon Chip Electronics Magazine