1. First, let’s talk about the buzzer. The buzzer is made of silver metal, as shown in the figure below. Some of them do not have welding cables. They mainly rely on two vibrating plates to convert electrical energy into mechanical energy when powered on

Generation principle and driving circuit of buzzer

The occurrence principle of buzzer film is as follows, with the help of the great God amber_ Mon’s explanation:

The sound source of the sound element of the piezoelectric buzzer mainly comes from the piezoelectric vibrating plate. The piezoelectric vibrating plate is composed of a piezoelectric ceramic plate with electrodes printed on both sides and a metal plate (brass or stainless steel, etc.). The piezoelectric vibrating plate and metal sheet are bonded together with adhesive, which is commonly known as buzzer.

Generation principle and driving circuit of buzzer

Figure 2 shows the oscillation system of piezoelectric vibrating plate. When a DC voltage is applied between the two electrodes of the piezoelectric vibrating plate, mechanical deformation is caused due to the piezoelectric effect. For the piezoelectric element with distorted shape, its deformation extends in the radiation direction.

The piezoelectric vibrating plate is bent in the direction shown in Fig. 2 (a), and the metal sheet bonded to the piezoelectric vibrating plate will not extend. On the contrary, when the piezoelectric element shrinks, the piezoelectric vibrating plate will bend in the direction shown in Fig. 2 (b). Therefore, when the AC voltage passes through the electrode, as shown in Fig. 2 (c), the bending shown in Fig. 2 (a) and Fig. 2 (b) will occur alternately and repeatedly, thereby generating sound waves in the air.

Generally speaking, the human audio frequency range is about 20Hz to 20kHz. The most audible audio frequency is 2KHz to 4kHz. Therefore, most piezoelectric sound elements are used in this audio range.

Generally speaking, the human audio frequency range is about 20Hz to 20kHz. The most audible audio frequency is 2KHz to 4kHz. Therefore, most piezoelectric sound elements are used in this audio range. At the same time, the resonant frequency (F0) of the buzzer is generally selected in the same range. As shown in Figure 3, the resonant frequency depends on the method used to support the piezoelectric vibrating plate. If the shape of the piezoelectric vibrating plate is the same, its value will be reduced in the order of (a), (b) and (c).

Generation principle and driving circuit of buzzer

However, the sound effect of the exposed piezoelectric ceramic sheet is relatively poor, so a sound chamber, that is, a resonance chamber, is required. The piezoelectric vibrating plate is installed in the resonance chamber to produce high sound pressure (as shown in Fig. 4). Using formula (1) (Helmholtz formula), the resonant frequency (fcav) of the resonant chamber in Fig. 4 can be calculated. Since the piezoelectric vibrating plate and the resonant chamber have appropriate resonant frequencies (F0) and (fcav), respectively, the sound pressure at a specific frequency and the specific bandwidth can be increased by controlling their positions.

The direct effect of the resonant cavity is to amplify the volume of the sound, which is also to concentrate the sound together. This is the same as the effect of installing the horn cavity. If you are interested, you take a horn without a sound cavity, put a music first, and find that the sound is very small. Take a cardboard and surround the horn, and find that the effect increases a lot. That’s the principle.

Driving circuit of buzzer

2. Then, the buzzer, which is the generator that encapsulates the buzzer chip in a cavity, is divided into active and passive,

Generation principle and driving circuit of buzzer

The difference between active and passive is that the driver does not need the pulse generation of output frequency, the active can make sound directly at high and low levels, and the passive needs to output a certain frequency waveform to drive the sound. The two circuits can be compatible and universal

3. Difference of driving circuit

In fact, the buzzer and buzzer chip are the same type of devices from the above analysis, so the driving circuits are the same. They are amplified and driven by triodes. The circuit diagram is like this:

Generation principle and driving circuit of buzzer

However,….. If you drive the buzzer in this way, you can only hear the chirping Lori sound. Hahaha, so the buzzer is generally driven by boost, and the boost inductor will be used,

With this boost inductor and the following circuit, the buzzer + sound cavity can be achieved to produce the same alarm sound as the roaring sound, provided that the frequency design is correct.

Generation principle and driving circuit of buzzer

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