a predetermined frequency and adjustable level excitation circuit for a capacitive load having a first terminal connected to a reference voltage . the circuit includes two switches connected in series between a supply voltage and the reference voltage . the junction of the two switches is coupled to the second terminal of the load . the two switches are not simultaneously closed . a circuit periodically controls the closing of the switch connected to the supply voltage . a regulation circuit acts on the control circuit to trigger opening of one of the switches when the voltage across the load reaches a predetermined value .