A circuit provides a high-voltage low-drop diode-like conductive path between a DC voltage supply terminal and a bootstrap terminal in charging a supply capacitor for driving a power switch with the capacitor set between the bootstrap terminal and an output terminal alternatively switchable between a low voltage and a high voltage DC voltage. In an embodiment, the circuit includes first and second transistors such as LDMOS depletion transistors with the first transistor set in a cascode arrangement between the bootstrap terminal and the DC voltage supply terminal and the second transistor coupled with a sense comparator for comparing the voltage at the bootstrap terminal with the voltage at said DC voltage supply terminal. The first and second transistors have common control terminals coupled with the DC voltage supply terminal and common coupling terminals to the bootstrap terminal.