Audio Buzzers Expansion

In the ever-evolving world of acoustic signaling devices, PUI Audio stands at the forefront, introducing 11 new buzzers, including lead-free options. These new products combine high sound pressure levels (SPL) and temperature resilience to address a diverse range of application needs, particularly where sustainability is critical. Buzzers are essential for providing immediate auditory feedback or alerts across various industries and everyday situations. Key application scenarios include alerts for household appliances, security systems, user-input confirmation, automotive safety warnings, healthcare equipment, industrial machine diagnostics, and consumer electronic devices.

Buzzers Introduction

An Audio Indicator : If your application requires a simple beep, ring or tone, an indicator is a perfect choice which has a built-in oscillator to produce specific tones and sound and just needs a supply voltage.

An Audio Transducer is simply an Electro-Acoustic Transducer which transforms AC voltages to sound pressure waves. It contain no electronics to generate its own audible tone. An external circuit is required to drive transducers to their maximum potential, offering flexibility and customization for various applications.

Consequently, its frequency and sound output levels are completely dependent on the frequency, voltage level and other characteristics of the signal applied to its terminals.
The piezo transducer consists of a brass and ceramic disc in a tuned enclosure (Helmholtz Chamber) which not only provides mechanical support and electrical connection but also acoustically amplifies the sound being generated by the disc.
The brass and ceramic disc assembly has piezoelectric characteristics. That is, the application of a DC voltage causes this assembly to flex in one particular direction. Reversing the polarity of the voltage forces the assembly to flex in the opposite direction. An AC voltage applied thus causes the assembly to flex back and forth with the frequency of the applied voltage, much like the cone on the loudspeaker, generating an audible sound.
In applications where high efficiency, low current drain, light weight, resistance to cleaning solvents and long life are required; the audio transducer may directly replace a small loudspeaker.

Drive Circuit for Buzzers

A well-designed drive circuit ensures the buzzer operates at peak efficiency and produces the desired acoustic output. PUI Audio offers comprehensive documentation and support to assist engineers in designing optimal drive circuits tailored to their specific requirements. There are various ways to drive buzzers, as explained below.

Indicators

Audio Indicators do not require external drive circuitry; a supply voltage at the rated voltage of the indicator is sufficient to power the device. Audio Indicators may be controlled by modulating the voltage supply. A current limiting resistor may be placed in series with the Audio Indicator to prevent damage to the indicator or the rest of the system. Typical values are below 100 Ω but may depend on the application.

Drive Circuit for Buzzers

A well-designed drive circuit ensures the buzzer operates at peak efficiency and produces the desired acoustic output. To achieve the highest sound pressure level (SPL) from the transducer, it is recommended to drive the transducer with a 50% duty cycle, 0V-VPK square wave, where VPK is equal to the rated voltage of the transducer. Half-rectified sine waves may also be used to create softer, less harsh tones, but the SPL will decrease. The drive circuit for an Audio Transducer depends on the driving signal’s available current and voltage levels. Suppose the signal has sufficient current and voltage to drive the transducer. In that case, it can be connected directly to a DC voltage supply to control the sound output by modulating the positive voltage supply on/off rate. However, designing a separate drive circuit is recommended if the available current output is limited.

Drive circuit for Electromagnetic Transducers

A typical design includes a NPN transistor in a low-side drive configuration. In this configuration, the transistor is connected between the ground and the transducer, and the signal is applied to the transistor’s base. The transistor switches the current flow to the transducer, allowing the transducer to produce sound at the switching frequency. R1 is used to limit any current spikes, preventing damage to the microcontroller GPIO pin. When designing a drive circuit for an electromechanical audio transducer, it is important to consider the power dissipation of the drive transistor, particularly if it is a small-signal BJT in a TO-92 package.

Using a MOSFET instead of a BJT in circuits prioritizing efficiency can provide positive results. MOSFETs have a significantly lower on-resistance than BJTs, resulting in lower power dissipation and higher efficiency. Additionally, MOSFETs typically have a higher input impedance than BJTs, making them easier to drive from current-restricted sources such as microcontrollers.

Drive circuit for Piezoelectric Transducers

If the transducer is driven below its resonant frequency, then the piezoelectric material may be considered a purely capacitive load; to begin the audio output, the drive circuit must supply a charge to the piezoelectric element in the transducer, then remove the charge to cause movement in the opposite direction. The resulting sound will be at the frequency at which charge is applied and removed from the transducer by the drive circuit.

When operating at or near the transducer’s resonant frequency, the piezoelectric transducer has a small resistive element that appears electrically in parallel with the capacitance of the transducer (generally no more than 100 Ω). The drive circuit must have an adequate current supply to ensure the rated voltage of the transducer is dropped across its resistive element under regular operation.

R2 provides an additional resistive element in series with the transducer to ensure sufficient current dissipation for the transducer when operating outside of resonance and not appearing as having a resistive element. An additional resistance may be placed in parallel across the piezoelectric buzzer to allow for any stored charges to dissipate when the transistor switch is open. This may improve performance and reliability in designs.

Specific values for resistors will depend on the application and circuit design, though a typical value is between 100-1k ohms.

A diode is typically used in place of the parallel resistor for magnetic circuits; since the buzzer has an internal resistive element, any stored energy will dissipate immediately when the switch is open, and the diode protects the voltage rail from any feedback.

Due to its high impedance and piezoelectric property, a piezoelectric buzzer can also be directly driven from an integrated circuit (IC) (shown in Figure 4). However, for stable sound production and IC protection, it is advisable to insert a resistor in series between the IC output and the piezoelectric buzzer. Resistor value should be
such that it does not exceed the maximum current rating of IC.

Predicting SPL

Regardless of the driving circuit, any design starts with an output requirement that generates the appropriate circuitry. Estimating the SPL output of an audio transducer is a challenging task, as the characteristics of the transducer and the way sound pressure waves propagate from the source are heavily influenced by the acoustic environment and the waveform utilized.

All PUI Audio transducers have been specified based on a specific voltage level, waveform input, mounting surface, and testing environment. This allows for a reasonable approximation of the SPL output. When the drive levels are within the device’s specified limits, and a square wave input is used, the transducer’s output at a specific input level can be estimated using Equation 1:

Equation 1
Approximating SPL for Specific Voltage
𝑺𝑷𝑳𝒙 = 𝑺𝑷𝑳𝟎 + 𝟐𝟎 ∗ 𝐥𝐨𝐠𝟏𝟎 (𝑽𝑿 / 𝑽𝟎)
Where: SPLX = SPL at desired voltage (Vx)
SPL0 = SPL at rated voltage (V0)

CONCLUSION

Many different drive circuits can be used to provide various SPL outputs and overall efficiencies. The applied waveform can be shaped, frequency-shifted, or amplitude-modulated to achieve the desired tone quality, and an estimation of SPL output can be made for certain strictly defined measuring conditions. However, one should always keep in mind that SPL measurement and prediction are complicated by the fact that the environment in which the device is measured greatly influences the measurement.

With these innovative offerings, PUI Audio continues to be a leading player in the field of acoustic solutions, providing engineers with the tools they need to create reliable and attention-grabbing auditory notifications in their designs.