In autonomous sensor nodes, switching dc/dc converters are usually employed to power the sensor electronics and also to maintain the operating voltage of an energy transducer around its maximum power point. In such a context, this paper optimizes the power efficiency of buck dc/dc converters when operating in burst mode, which is preferable than the conventional pulse-width modulation technique in lowpower sensor applications. The optimization is carried out by selecting an optimal inductor current to efficiently transfer the energy from the input to the output during the burst. Such optimization is applied when regulating the converter's output voltage, which corresponds to the supply voltage of the sensor electronics, and also the input voltage, which corresponds to the operating voltage of the energy transducer that is here a photovoltaic module. The theoretical analysis and the experimental results reported herein prove the existence of such an optimal inductor current in both scenarios. Experimental tests with a commercial buck dc/dc converter (TPS62750) show that the use of this optimal inductor current provides up to 9% increase in efficiency, thus prolonging the operating lifetime of the sensor node.