Most piezos have two contacts, but this type possesses three. They are referred to as self drive types, and they're meant to be used in the oscillator.

The piezo influence works both ways: if you ever apply a voltage the actual piezo stretches, but furthermore if it stretches this creates a voltage. This principle must be used to create a opinions signal which drives this oscillator.

The advantage on the self drive is it will automagically work from its resonance frequency, wherever it produces the loudest sound.
Murata is active inside R&D of new electronic components, seeking infinite options with ceramic materials.
Particularly, as a pioneer in the development of piezoelectric ceramics, Murata has met the needs in the
 technical revolution in technology with original products. Each of our ceramic resonators (CERALOCK®), ceramic filters
 (CERAFIL®), piezo sound components and various ultrasonic transducers have contributed towards
 development of electronics. The "Piezoelectric sound components" introduced herein operate on an innovative principle working with natural oscillation of piezoelectric ceramics. Today, piezoelectric sound components are employed in many ways like home appliances, OA machines, audio equipment telephones, and so forth. And they are used widely, for example, within alarms, speakers, telephone rings, receivers, transmitters,
beep seems, etc. This manual is made for customers to use piezoelectric sound components efficiently and with no trouble. It is recommended the manual be read while looking at the catalog
 MAS6240 can be a piezo driver IC which will create a multi-tone sound depending on a charge pump know-how. It is a large efficiency, easy to use and low priced IC perfect for power supply driven equipment or alternative low voltage applications where a superior sound pressure is needed.

MAS6240 can drive outputs up to 18 VP-P from single 3 V supply voltage. An input voltage amplification factor could be selected as 1, Two or three. The output can end up being single mode or differential style.

The inductorless design brings about significantly less disturbance for the surrounding circuits, making it a perfect choice Heart rate Monitors along with other sensitive designs. Only four small benefit capacitors are needed in addition to a sound element. The usage of small capacitors also tends to make this solution more reliable when compared with an inductive solution having a heavy coil that can brake loose if your equipment is dropped.

MAS6240 will also be used in other applications. For example as some sort of white LED driver. Together it can be attached to a piezo sounder in a differential output configuration.
 https://www.kailitech.net/Self-Drive-Piezo-Buzzer-pl3604953.html 
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