JPS58132288A - Sound volume adjustment circuit for piezo- electric buzzer - 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 an improvement in a volume adjustment circuit for a piezoelectric buzzer.

Generally, a drive circuit using a self-oscillating piezoelectric buzzer has a first
As shown in the figure, the piezoelectric buzzer has a feedback electrode on its main body, and forms a modified circuit of a grounded emitter and tray oscillator. In this case, the voltage v applied to the return electrode
f deviates from vo by 1800 Hiel the input resistance of the register
, the current amplification rate is hfe1), the DC bias point of the transistor Tr1 is % of the power supply voltage, and the resistor R2 is adjusted to prevent spurious oscillation. There are conditions.

Next, a conventional example of a volume adjustment circuit for a piezoelectric buzzer will be described with reference to FIG.

In FIG. 2, A is a microcomputer, OUT is its output, and P is a piezoelectric buzzer drive circuit.

As explained in FIG. 1, in FIG. 2, the voltage applied to the piezoelectric buzzer drive circuit 2 is adjusted by the semi-fixed resistor VR/. In this case, the power supply impedance seen from the piezoelectric buzzer drive circuit 2 is at least higher than the impedance of the semi-fixed resistor VR'. Since the current waveform flowing through the piezoelectric buzzer drive circuit 2 roughly approximates the oscillation waveform, the voltage applied to the piezoelectric buzzer drive circuit 2 will have large fluctuations. As a result, the oscillation conditions explained in FIG. 1 are disrupted, the distortion of the oscillation sound increases, and in extreme cases, the oscillation may stop.

In order to eliminate such problems, the present invention focuses on the power source impedance leaking from the piezoelectric buzzer, and aims to provide a circuit that provides a minimum power source impedance even at any setting point for adjusting the volume.

An embodiment of the present invention will be described below with reference to the piezoelectric buzzer volume adjustment circuit shown in FIG. 1 is a P-channel microcomputer, which serves as a controller, and is connected to the open drain output terminal OUT, which outputs an intermittent waveform, through a semi-fixed resistor VR, a fixed resistor R4, and grounded, and an NPN type transistor connected to the midpoint between the two. Connect the base of TR2.

This constitutes a kind of emitter follower circuit. That is, the output terminal O of the microcomputer 1
By outputting a pulse waveform to the UT, the oscillation circuit of the piezoelectric buzzer is controlled and an intermittent sound is generated. Since the power consumption of the piezoelectric buzzer is extremely small, the semi-fixed resistor VR
, if the value of the fixed resistor R4 is set to a certain small value, the base potential VB of the transistor TR2 can be made variable by changing the semi-fixed resistor VR. Furthermore, the base-emitter potential vB of the transistor TR2
The value obtained by subtracting E appears as the emitter voltage vE. The emitter voltage vE serves as a kind of stabilized power source. In this way, the voltage vE applied to the piezoelectric buzzer drive circuit 2 is adjusted. On the other hand, if the voltage +V has a low impedance, the power supply impedance R seen from the piezoelectric buzzer drive circuit 2 is the current amplification rate of the transistor TR2.

Since this current amplification factor hfe2 can normally be set to 100 or more, the power source impedance is dramatically lowered than in the conventional example.

As is clear from the description of the embodiments above, the piezoelectric buzzer volume adjustment circuit of the present invention includes a controller that outputs an intermittent waveform, an NPN transistor whose collector terminal is connected to a power supply, and a midpoint connected to the NPN transistor. A cascade circuit of a variable resistor and a fixed resistor is connected to the base terminal of the controller, and both ends are connected to the output terminal and the ground terminal of the controller, and a piezoelectric voltage is connected between the emitter terminal of the NPN transistor and the ground terminal. Piezoelectric buzzer oscillation N including buzzer
Since the piezoelectric buzzer drive circuit has a simple circuit configuration, the volume can be varied and the piezoelectric buzzer drive circuit has sound quality without distortion.

If a microcomputer is used as the controller, it is possible to effectively combine other functions and the piezoelectric buzzer to easily configure various controls.

[Brief explanation of the drawing]

Fig. 1 is a drive circuit diagram of a conventional self-oscillating piezoelectric buzzer, and Fig. 2 is a conventional piezoelectric buzzer volume adjustment circuit 4.1.
...Microcomputer (controller), 2
...Piezoelectric buzzer drive circuit, TR2...
NPN type transistor, VR...semi-fixed resistor, R4... fixed resistor.

Claims (2)

[Claims] (1) A controller that outputs an intermittent waveform, an NPN transistor whose collector terminal is connected to a power supply, a midpoint connected to the base terminal of the NPN transistor, and both ends connected to the output terminal and ground terminal of the controller. A piezoelectric buzzer volume adjustment circuit comprising a cascade connection circuit of a variable resistor and a fixed resistor, and a piezoelectric buzzer drive circuit including a piezoelectric buzzer connected between the emitter terminal of the NPN transistor and the ground terminal. (2) A volume adjustment circuit for a piezoelectric buzzer according to claim 1, wherein the controller is a microcomputer.