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This paper presents a full ballast for driving an assembly of high brightness LEDs, based on a new dc to dc converter. The converter provides a constant current waveform to the load parting from a DC bus voltage. The converter, operating with a peak current control, keeps the current through the LEDs constant independently of the bus voltage. This is carried out internally by self-adjusting the switching frequency of the converter. Thus, the requirements of the capacitance of the bus capacitor are greatly diminished, allowing the avoidance of electrolytic technology. Also, low frequency PWM dimming can be carried out easily. The present work shows the design procedure and the experimental results obtained after building a prototype of a full ballast for HB LEDs.