A circuit for a volatile material emitting device, comprising: a piezoelectric pump (58, 166) including an impedance connected in series with a piezoelectric element, wherein the impedance and the piezoelectric element form a tank circuit (168, 62) having a resonant frequency; a driver connected to the piezoelectric pump, wherein the driver comprises four transistors (180, 182, 184, 186) coupled in a full bridge configuration, having first and second p-channels transistors (180, 184) with their respective source electrodes coupled to a high voltage supply and first and second n-channel transistors (182, 186) with their respective source electrodes coupled to ground, the drain electrode of the first p-channel transistor being connected to the drain electrode of the first n-channel transistor to form a first output pin and the drain electrode of the second p-channel transistor being connected to the drain electrode of the second n-channel transistor to form a second output pin, wherein the tank circuit (168, 62) is connected between the first output pin and the second output pin; wherein the driver is adapted to generate a drive waveform to drive the transistors (180, 182, 184, 186) in one of a first and second states comprising a first state in which the first p-channel transistor and the second n-channel transistor are turned "ON" and the second p-channel transistor and the first n-channel transistor are turned "OFF", and a second state in which the first p-channel transistor and the second n-channel transistor are turned "OFF" and the second p-channel transistor and the first n-channel transistor are turned "ON"; characterized in that the circuit further comprises: first and second comparators (192, 194) coupled between the driver and the tank circuit (168, 62), wherein the comparators (192, 194) are adapted to detect a parameter of power applied to the piezoelectric pump (58, 166) by the driver to operate the piezoelectric pump (58, 166) at a mechanical resonant frequency thereof; said first comparator having its inputs connected between the first output pin and ground; said second comparator having its inputs connected between the second output pin and ground; the driver being configured to switch to the first state when the first comparator detects a zero crossing of voltage across its inputs representing a zero crossing of current in the first n-channel transistor, and to switch to the second state when the second comparator detects a zero crossing of voltage across its inputs representing a zero crossing of current in the second n-channel transistor. a piezoelectric pump (58, 166) including an impedance connected in series with a piezoelectric element, wherein the impedance and the piezoelectric element form a tank circuit (168, 62) having a resonant frequency; a driver connected to the piezoelectric pump, wherein the driver comprises four transistors (180, 182, 184, 186) coupled in a full bridge configuration, having first and second p-channels transistors (180, 184) with their respective source electrodes coupled to a high voltage supply and first and second n-channel transistors (182, 186) with their respective source electrodes coupled to ground, the drain electrode of the first p-channel transistor being connected to the drain electrode of the first n-channel transistor to form a first output pin and the drain electrode of the second p-channel transistor being connected to the drain electrode of the second n-channel transistor to form a second output pin, wherein the tank circuit (168, 62) is connected between the first output pin and the second output pin; wherein the driver is adapted to generate a drive waveform to drive the transistors (180, 182, 184, 186) in one of a first and second states comprising a first state in which the first p-channel transistor and the second n-channel transistor are turned "ON" and the second p-channel transistor and the first n-channel transistor are turned "OFF", and a second state in which the first p-channel transistor and the second n-channel transistor are turned "OFF" and the second p-channel transistor and the first n-channel transistor are turned "ON"; first and second comparators (192, 194) coupled between the driver and the tank circuit (168, 62), wherein the comparators (192, 194) are adapted to detect a parameter of power applied to the piezoelectric pump (58, 166) by the driver to operate the piezoelectric pump (58, 166) at a mechanical resonant frequency thereof; said first comparator having its inputs connected between the first output pin and ground; said second comparator having its inputs connected between the second output pin and ground; the driver being configured to switch to the first state when the first comparator detects a zero crossing of voltage across its inputs representing a zero crossing of current in the first n-channel transistor, and to switch to the second state when the second comparator detects a zero crossing of voltage across its inputs representing a zero crossing of current in the second n-channel transistor.