Series strings of photovoltaic modules with integrated dc-dc microconverters can harvest more energy compared to conventional string-inverter architectures if the arrays are partially shaded or the modules mismatched. This work presents a multi-mode dc-dc converter as a candidate microconverter topology for photovoltaic modules. The topology constitutes a single inductor and four switching devices and can function in either buck, boost or an intermediate bridge mode based on the load. The proposed maximum power point tracking scheme is capable of tracking the true maximum even in partially-shaded PV modules. An experimental prototype demonstrates efficiency above 95 % at 215 W over a load range of 3 A to 7 A.