JPS5917591A - Piezo-electric enuntiation element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for piezoelectric sounding elements, ie, piezoelectric buzzers, piezoelectric speakers, and the like.

An example of a conventional separately excitation type drive circuit is shown in FIG.

In the figure, 1 is an IC drive circuit, 2 is a protective resistor, and 3 is a piezoelectric buzzer. A protective resistor 2 and a piezoelectric buzzer 3 are connected in series between the output end of the drive circuit 1 and ground.

The protective resistor 2 is an IC generated by the back electromotive force from the piezoelectric buzzer 3.
This is to prevent destruction.

With such a circuit configuration, the maximum amplitude of the drive voltage of the piezoelectric buzzer 3 cannot exceed the value of the power supply voltage VCC to the maximum extent possible.

Piezoelectric buzzers and piezoelectric speakers have high impedance, so they require high driving voltage to obtain high sound pressure. In order to obtain a high drive voltage, measures have been taken such as: ■ Increasing the power supply voltage VCIC, ■ Using a step-up transformer, ■ Creating resonance between the piezoelectric buzzer's capacitance and external inductance, but ■ Batteries. A large power supply voltage VCC cannot be obtained with the model used. ■ Using a step-up 1 to lance will increase the cost and increase the size of the parts. ■ If resonance is achieved with an external inductance, the frequency characteristics will change. It has the disadvantage that only one specific frequency can be used.

The purpose of this invention is to obtain a drive voltage approximately twice the power supply voltage without using a transformer or external inductance.
Another object of the present invention is to provide a drive circuit with flat frequency characteristics.

That is, the gist of the present invention is that one end of the two-terminal piezoelectric sound element is connected to the output end of the drive circuit, and the other end is connected to the power supply line and to one end of the switching element. This is a drive circuit for a piezoelectric sound element, in which the other end is grounded, and the switching element is repeatedly turned on and off every half cycle of the drive voltage.

An embodiment of the present invention will be described below.

4 is an NPN type switching transistor, the base of which is connected via a bias resistor 5 to a connecting line between the resistor 2 and one end 3a of the piezoelectric buzzer 3, and the collector thereof is connected to a power supply line via a load resistor 6; The emitter is grounded. The other end 3b of the piezoelectric buzzer 3 is connected to a connection line between the resistor 6 and the collector of the transistor 4.

With this circuit configuration, when a drive voltage of maximum amplitude VCC is applied to one end 3a of the piezoelectric buzzer 3 with respect to ground,
The transistor 4 is on during periods 0 to T/2, and is off during periods T/2 to T/2. Therefore, the drive voltage is applied to the other end 3b of the piezoelectric preamplifier 3. A voltage that is in an antiphase relationship with that will be applied. Therefore, the maximum amplitude of 2VC is applied to both ends of the piezoelectric buzzer 30.
A driving voltage of C is applied.

As is clear from the above embodiments, according to the present invention, a phase inversion circuit using a switching element is provided on the side of the piezoelectric sounding element that was conventionally connected to ground.
Approximately twice as much drive voltage as before is applied to the piezoelectric sound element, eliminating the need for a transformer or external inductance as in the past, making the entire set smaller and lower in cost, especially for portable type sets. suitable for use. Further, since the booster circuit has no frequency characteristics, it is suitable for piezoelectric sounding devices driven at various frequencies.

When driving with a sine wave or a composite wave that does not clip, adjust the amplification degree of the phase inversion circuit including the bias resistor 5 and transistor load resistance 6 to make the output level of the drive circuit 1 and the output level of the phase inversion circuit 4 equal. If so, twice the driving voltage can be obtained without clipping. Note that the protective resistor 2 may be omitted. Furthermore, if the frequency is limited and a large drive voltage is required, an external inductance may be used instead of the load resistor 6.

[Brief explanation of the drawing]

FIG. 1 is a conventional circuit diagram, and FIG. 2 is an embodiment of the present invention. Patent applicant Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] One end of the two-terminal piezoelectric sound element is connected to the output end of the drive circuit, the other end is connected to the power line and one end of the switching element, and the other end of the switching element is grounded. , a drive circuit for a piezoelectric sounding element, characterized in that the switching element is repeatedly turned on and off every half cycle of the drive voltage.