Systems and techniques for performing power conversion operations in a portable device are used to convert an input voltage to a voltage at an output. The conversion operations use a two-stage conversion to convert the input voltage to a first voltage and to convert the first voltage to a second voltage. A switching frequency is altered with changes in the input voltage. The switching frequency is selected based on the input voltage level and/or to maintain a substantially consistent ripple at the output, which can correspond to the first voltage and/or the second voltage.