A circuit for charging a capacitance using an LDMOS integrated transistor functioning as a source follower and controlled, in a manner to emulate a high voltage charging diode of the capacitance. The LDMOS transistor is controlled via a bootstrap capacitor charged by a diode at the supply voltage of the circuit, and by an inverter driven by a logic control circuit as a function of a Low Gate Drive Signal and of a second logic signal which is active during a phase wherein the supply voltage is lower than the minimum switch-on voltage of the integrated circuit. The circuit uses a first zener diode to charge the bootstrap capacitor and the source of the transistor is connected to the supply node through a second zener diode.