A wide supply range flyback converter consists of a Schmitt trigger driving a switching device such as MOSFET. The method includes providing a substantially horizontal wellbore having at least one productive interval within a hydrocarbon reservoir and forming at least one non-conductive transverse fracture in the reservoir along the substantially horizontal wellbore. An elongated probe has a distal end arranged to extend at least to the measurement region, and a heat-disseminating end in thermal contact with a thermally-conductive outer housing surface of the bimetal disc thermostat.