Case 1: Transistor Circuit

Example of a drive circuit for a piezoelectric sounder and a piezoelectric diaphragm (external drive type)
in the case where a transistor circuit is used

The higher the value of the voltage applied to V, the higher becomes the sound pressure of the piezoelectric sound component. Consequently, this drive method is widely used in cases where a power supply voltage that is higher than the drive voltage for the microcomputer can be obtained.
Please refer to the following supplementary notes regarding the components shown in the circuit diagram.

• Rp in the diagram is necessary for discharging the charge accumulated in the piezoelectric sound component, so be sure to use it.
  Also, if necessary, use Rs for volume adjustment.
• The transistor functions as a buffer for protecting the IC from back electromotive force generated by the piezoelectric sound component. Also, in order to protect the transistor itself, consider connecting a Zener diode in parallel with the piezoelectric sound component and Rp if necessary.
• In the diagram, the piezoelectric sound component and the resistors are connected between the collector of the transistor and V. However, these components can be installed between the emitter of the transistor and GND instead.
• A FET can be used instead of the transistor.

Case 2: Driven directly from a microcomputer.

Example of a drive circuit for a piezoelectric sounder or a piezoelectric diaphragm in the case
where the sounder or diaphragm is driven directly from a microcomputer

A piezoelectric sound component has high impedance and is a voltage-driven device, so it can be driven directly from an IC.
Please refer to the following supplementary notes regarding the components shown in the circuit diagram.

• In order to protect the IC from back electromotive force generated by a piezoelectric sound component, consider connecting a Zener diode in parallel with the piezoelectric sound component and Rp if necessary.
• Design the circuit in such a way that a DC voltage is not applied to the piezoelectric sound component for a long period.

Regarding the drive circuit for a piezoelectric sounder (self drive type), we set a standard circuit for each product. For details, please refer to our catalog.
Our catalog is on our website. Please refer to the link to it (PDF: 872 KB).

When you add a series resistor between the DC voltage V and the piezoelectric buzzer in order to adjust the sound pressure of the buzzer, insert a capacitor (of about 1 mF) in parallel with the piezoelectric buzzer. This is effective for preventing irregular oscillation.

The current consumption (excluding that of the peripheral circuit) by a piezoelectric sounder (external drive type) can be calculated simply from the theoretical equation below.

Average value of current (theoretical value)

When the charging and discharging times of a piezoelectric sounder (external drive type) are significantly smaller than the length of one period of the input signal, the average value of the current which flows into the piezoelectric sounder (external drive type) during a half period can be calculated from the following equation.

Q: Charge accumulated in the piezoelectric sounder, T: Length of one period of the drive signal (=1/f),
C: Electrostatic capacitance of the piezoelectric sounder, V: Drive voltage, f: Frequency of the drive signal

Calculated value of the consumption current

The average value of the current flowing through the piezoelectric sounder (external excited type), calculated using the above equation for each part No., is shown in the table below.

Calculated value of current consumption for each part No.

[mA]

(*) The electrostatic capacitance is the center value, the tolerance is ±30%, and PKLCS is a reference value.

(Example) Piezoelectric Sounder: PKM17EPP-2002-B0

However, there are cases in which the sound pressure level becomes very small depending upon the drive frequency, although this will also depend upon the frequency characteristics of sound pressure level of each product, so check and evaluate the product before using it.

Fig.1 Duty ratio

When a piezoelectric sounder intended to be driven at 4 kHz in order to obtain the specified sound pressure is to be driven at 2 kHz, change the duty ratio of the input signal from 50% to 25%. Taking our piezoelectric sounder PKM13EPYH4002-B0 as an example, this will cause the sound pressure to rise by approximately 10 dB. (Refer to Fig.2 and Fig.3.)

Fig.2 Difference between the frequency characteristics of sound
pressure level for duty ratios of 25% and 50%

Fig.3 Relationship between the sound pressure and the duty
ratio for input signals of 2 kHz and 4 kHz

Because the 4 kHz sound, which is the second harmonic sound at a duty ratio of 25%, is combined with the 2 kHz sound, the sound pressure rises.
This result depends upon the frequency characteristics of sound pressure level of the piezoelectric sounder, so the value of the increase in sound pressure will differ according to the type of product. Also, if the duty ratio is changed, a frequency component that is different from the input signal will be used, so the tone will change. It is necessary to check this point while listening to the sound.

Fig.1 Example of a drive circuit for an electromagnetic buzzer

You cannot produce a sound from a piezoelectric sounder by simply replacing an electromagnetic buzzer with a piezoelectric sounder in this circuit. It is necessary to replace the diode (used for suppressing spike current) with a resistor. Also, if necessary please study the addition of the series resistor and Zener diodes shown in Fig.2 for protecting the transistor from back electromotive force generated by the piezoelectric sound component.

Fig.2 Example of additional drive circuit

Because a piezoelectric sounder has high impedance and is also voltage-driven, it can be driven directly from an IC. Consequently, the configuration of the drive circuit itself can also be simplified.

Please refer
Q. Please give me an example of the drive circuit for a piezoelectric sounder or a piezoelectric diaphragm (external drive type)

After the change in the drive circuit has been completed, select a piezoelectric sounder that has an appropriate performance. When selecting the piezoelectric sounder, take into account the following points.

• Carry out a comparative study of the drive frequency and the sound pressure level.
• Carry out a study of the product size, pitch, and so on. Mounting conditions
  (Reflow soldering cannot be used on a lead type piezoelectric sounder.)
• Current Consumption
  In contrast to an electromagnetic buzzer which is driven by current flowing through a built-in electromagnetic coil, a piezoelectric sounder is driven by a voltage applied to piezoelectric ceramic, so it consumes much less current than an electromagnetic buzzer.

• Soldering Iron
  • Lead terminals are immersed up to 1.5mm from components body in soldering bath of +260+/-5 degrees C for 10+/-1.0 seconds.
  • Lead terminal is directly contacted with the tip of soldering iron of +350+/-0.5 seconds
• Reflow
  (Lead type piezoelectric sounder cannot withstand reflow soldering.)

When melted solder touches to the base of lead terminal, a part of plastic case shall be melted and it may cause electrical failure. Use a single-sided PCB.

We have a lineup of water proof piezoelectric sound components. The electrode surface of the diaphragm of these components is coated with resin.
Note, however, that depending upon the environment in which they are used, it may not always be possible to guarantee performance. Please contact us for details.