Design of new piezoelectric ceramic speaker driver

This article compares traditional moving coil speakers, analyzing the characteristics of new piezoelectric ceramic speakers and the requirements for the required audio power amplifier, comparing and analyzing various commonly used boost structures and audio power amplifiers,which tests a variety of boost .The structure and audio power amplifier cooperate with the relevant data and use effect of the pzt ceramic piezoelectric speaker, from the aspects of sound pressure, efficiency, total harmonic distortion and so on. It is concluded that using the boost structure and driving a new type of piezoelectric ceramic speaker with a Class D audio power amplifier is the most compromised solution.

With the development of portable consumer electronics, people are increasingly demanding small and thin portable electronic devices. piezoelectric ceramic speakers are gradually being used by many portable consumer electronic products due to their ultra-light, ultra-thin, efficient, and without requiring a large sound cavity. The development of portable consumer products in the direction of ultra-thin, light and small, how to achieve a slim profile, and to extend the use of a single rechargeable battery has become a major design consideration for various consumer products. Such system requirements place thinner, smaller, and more power-saving requirements on individual electronic piezo ceramic plate components.

Basic characteristics of piezoelectric ceramic speakers

Compared with a moving coil speaker, the diaphragm of the piezoelectric speaker of piezoelectric ceramics plates is driven by the piezoelectric material bonded to it to produce bending, so the shape of the diaphragm is almost unlimited, and the diaphragm or paper cone of the moving coil speaker .They are usually round or oval, which often limits the product's design. All moving coil speakers must have a magnet to drive the voice coil, which increases the overall height and weight of the speaker, but the piezo ceramic speaker does not require a magnet to drive, so that a thin shape can be achieved to reduce the terminal height of the product.

Faced with compact mobile phones and thinner and thinner computers, moving-coil speakers have become a limiting factor for manufacturers to produce ultra-thin products. Piezoelectric ceramic speakers can provide highly competitive sound pressure levels (SPL) in ultra-thin, compact packages, and have great potential to replace traditional moving coil speakers.

Amplifier circuits for driving piezoelectric ceramic speakers have different output drive requirements than conventional moving coil speakers. The structure of the piezoelectric ceramic speaker requires the amplifier to drive a large capacitive load and output more current at a higher frequency while maintaining a high output voltage. The efficiency of traditional moving coil speakers is easy to calculate. The audio coil winding can be approximated as a fixed resistance in series with a large inductance. If the speaker resistance is known, Ohm's law can be used to calculate the load power: P = I2R, or P = VI. Most of the power of the speaker is converted into the heat of the coil. Since piezoelectric ceramic speakers have capacitive characteristics, the heat generated when consuming power is not high.

A piezo ceramic sensor at 1 kHz, 90 dB (measuring distance 10 cm) sound pressure waveform, the voltage is 8 V, the current is 15.6 mA, the phase difference between the voltage and current is 79.2 °, so the power consumption is 8 & TImes; 15.6 & TImes; cos79.2 ° = 23mW. It is equivalent to 18% of the power consumption of a dynamic coil speaker with a diameter of 20 mm at a sound pressure of 90 dB (measured distance of 10 cm).