PIEZOELEOTRIC ELEMENT DRIVE CIRCUIT

PURPOSE:To increase the degree of freedom of circuit characteristics setting by installing a transformer with a primary-side coil connected to a dc and a secondary-side coil connected to a piezoelectric element and switching devices each placed between the primary-side coil and a dc and between the secondary- side coil and the piezoelectric element respectively. CONSTITUTION:The maximum current I1p induced in a primary-side coil 31 is proportioned to the time t1 during which a switching transistor TR1 is held 'on'. The moment a TR2 is turned 'off' and the current >=1 of the coil 31 turns from I1p to zero, an induced current 12 is induced in a secondary-side coil 32. The induced current 12 is the maximum value I2p first but it turns to zero after the passage of the time t2 and so a piezoelectric element 2 is charged. When the TR2 is held 'on' for the time 't' until a difference in potential Vc between both ends of the piezoelectric element 2 becomes zero, the current 12 flows in the coil 32 and the moment the TR2 turns 'off', the induced current 11 is induced in the coil 31 and is regenerated to a dc supply 1 through a diode 33. Consequently, the power consumption can be kept low.