Piezoelectric element driving circuit and pump device

A pump device comprising:

• a pump having a pump chamber one side of which is sealed by one of a piezoelectric material of a piezoelectric element and a vibrating member vibrating together with said piezoelectric material, the pump discharging, from a discharge opening, a fluid sucked in from a fluid suction opening of said pump chamber;
• and
• a driving circuit for vibrating and driving said piezoelectric element of said pump;
• wherein said driving circuit includes
• a transformer having a turns ratio at which a rate of a number of turns of a secondary winding on a load side is high with respect to a number of turns of a primary winding on a power supply side, exceeding a ratio of a power supply side voltage value to a specification voltage value on the load side,
• a switch circuit for performing switching operation on power supply voltage at a driving frequency on a primary side of said transformer to apply a driving voltage to a piezoelectric element connected to a secondary side of said transformer,
• a reactance element connected in parallel with said piezoelectric element on one of the primary side and the secondary side of said transformer, the reactance element forming a resonant circuit that performs parallel resonance at said driving frequency with a capacitance component in an equivalent circuit of said piezoelectric element and an inductance component of said transformer,
• a pulse generating circuit for generating a driving pulse for said switch circuit, and
• a duty ratio controlling circuit for being supplied with said driving pulse, limiting a duty ratio of said driving pulse such that a value of said driving voltage falls within a range equal to or lower than the specification voltage value on said load side, and outputting the driving pulse whose duty ratio is limited to said switch circuit.