One form of the invention is directed to an apparatus that comprises step-down circuitry to better match impedance between an input and an output that includes a number of stages each electrically coupled to another and each including a charge storage device. The circuitry further includes a number of switching devices operable in a first electrical connectivity state to connect the charge storage device of each of the stages in series to receive electrical charge from the input and in a second electrical connectivity state opposite the first state to connect the charge storage device of each of the stages in parallel to discharge electricity through the output. This circuitry can be used in connection with a radioisotopic conversion cell.