Patent ID: 7977849

Claim:
An electronic drive system for a droplet spray generation device, the drive system comprising a droplet generator having a perforate membrane driven by a piezoelectric transducer; an electronic circuit controlling a power supply to control the charging of a capacitor to a supply voltage providing power to a power amplifier connected to receive electric power from the capacitor and supply a drive signal to the piezoelectric transducer in use; and wherein the electronic circuit is also arranged to control the operation of the power amplifier including the drive signal operating frequency at substantially its resonant frequency, where the resonant frequency is calculated by measuring and/or timing changes to the voltage across the capacitor when the droplet generator is operated in a plurality of bursts at different frequencies, by charging the capacitor to a given voltage, and either actuating the droplet generator for a given time and either measuring the voltage drop across the capacitor at the end of the given time or the time taken to recharge the capacitor to the set value thereafter, or actuating the droplet generator and measuring the time taken for the voltage to fall to a known value, and determining as the resonant frequency of the droplet generator, the frequency at which respectively the time to recharge is the greatest, or the voltage drop is the greatest, or the time taken for the voltage to fall to the known value is shortest, and to set the drive signal operating frequency at the resonant frequency thus determined.