JPS6239435Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for a piezoelectric buzzer using a piezoelectric vibrator, and more particularly to a circuit for driving a piezoelectric buzzer without using a resonant circuit using a coil.

Conventionally, when using a piezoelectric vibrator as an electronic buzzer, methods have been used to increase the sound pressure, such as forming a resonant circuit with a coil and making the piezoelectric vibrator resonate with the case. However, if a coil is used, the overall size cannot be made small, especially thin, so it has a drawback that it is difficult to use it in electronic desktop calculators.

The present invention solves the above problems and will be explained below with reference to the drawings.

In the figure, reference numeral 1 denotes an LSI of an electronic desktop calculator, which performs calculations based on input from a keyboard 2, and provides its output to a display circuit 3 to display results and the like. 4 is a power supply, for example, a lithium battery provides DC voltage V to LSI 1, transistor Tr, and resistor R.
Supplied to 1st class.

The base of the transistor Tr is connected via the resistor R2.
It is connected to the signal terminal T for driving the buzzer of LSI1, and the transistor Tr is turned off when the signal terminal T is at a high level V _H (V _H ≒V), while the signal terminal T is at a low level V _L (V _L = Turns on when 0). A piezoelectric vibrator 5 has one electrode a connected to a signal terminal T, and the other electrode b connected to a connection point C between the transistor Tr and the resistor R1. R3 is a resistance. Reference numeral 6 is a power switch, but it is not necessary if the watch also functions as a clock.

Next, the operation will be explained. First, when the buzzer is not used, the signal terminal T is maintained at a high level, the transistor Tr is turned off, and the connection point C between the transistor Tr and the resistor R1 is at a low level V _L.
In the piezoelectric vibrator 5, the electrode a side is relatively positive, and the electrode b side is relatively positive.
Although the side is negative and a DC voltage is applied, there is no vibration and no sound is generated. In this state, a DC voltage is always applied to the piezoelectric vibrator 5, so if this is considered to be inconvenient, a capacitor for cutting off the DC voltage may be connected in series.

When the buzzer sounds when a key is input or when the number of digits is exceeded, an AC signal (usually a pulse signal) is applied to the signal terminal T, and the voltage at the signal terminal T changes from high level V _H to low level as shown in Figure 2 A. Repeat level V _L. When the output becomes a low level V _L , the transistor Tr is turned on, and the connection point C becomes a high level V _H. Therefore, the piezoelectric vibrator 5 has a negative electrode a side,
The electrode b side is positive, which is opposite to the case where the output of the signal terminal T is high level. 2B and 2C show the voltage waveforms of electrodes a and b. Therefore, the voltage when the signal terminal T is at a high level and the voltage when it is at a low level are superimposed on the piezoelectric vibrator 5, and as shown in FIG. The relative change is approximately twice the voltage of the power source 4, and each time the transistor Tr is turned on and off by the pulse signal, it is driven with twice the voltage of the power source 4. In other words, the piezoelectric vibrator 5 is considered a type of capacitor, so when it is charged with one voltage and reversely charged with the other voltage, the amount of charge transfer is doubled, and it is driven at approximately twice the voltage of the power source 4. is the same as

As described above, the present invention includes a transistor whose base side is connected to a signal source that generates a pulse signal for driving a buzzer and forms a series circuit with a resistor, a power supply that supplies DC voltage to the signal source and the series circuit, It consists of a piezoelectric vibrator inserted between a connection point between a transistor and a resistor and a signal source, and when the potential of the signal source is at a high level, the transistor is turned off, the potential at the connection point is set to a low level, and the signal source is turned off. It is characterized by turning on the transistor when the potential of the connection point is low level and driving the piezoelectric vibrator by setting the potential of the connection point to high level, eliminating the need for a coil and making it suitable for use in electronic desktop calculators, etc. It has a great practical effect because it can be made thinner, has a large sound output, and can be used in the same way as before.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is an output waveform diagram of the main part of FIG. 1. 1...LSI, 2...keyboard, 3...display circuit, 4...power supply, 5...piezoelectric vibrator, Tr...transistor, R1, R2, R3...resistance.

Claims (1)

[Scope of utility model registration request] a transistor whose base side is connected to a signal source that generates a pulse signal for driving a buzzer and forms a series circuit with a resistor; a power source that supplies DC voltage to the signal source and the series circuit; and a transistor and the resistor. and a piezoelectric vibrator inserted between a connection point and the signal source, and when the potential of the signal source is high level, the transistor is turned off, the potential of the connection point is low level, and the signal source A drive circuit for a piezoelectric buzzer, characterized in that when a potential at a low level, the transistor is turned on, and a potential at the connection point is set at a high level to drive the piezoelectric vibrator.