JPH04275594A - Driving device for piezoelectric buzzer - Google Patents

Abstract

PURPOSE:To prevent the power generation by the reverberation of the amplitude of a piezoelectric body at the time of stopping and to suppress the voltage to be impressed to a switching element to a lower level by operating a switching element to turn on several times the on time at the time of driving at the time of stopping then operating to turn off. CONSTITUTION:An FET 12 is operated to turn on and off at a high speed of 125mus interval by a control circuit 16, by which a piezoelectric buzzer 13 is driven. The piezoelectric buzzer 13 is stopped when this operation is repeated 400 times and the FET 12 is maintained in the on state for 10ms at this time and is then turned off. The vibration of the piezoelectric body 13 is stopped in a certain deformed state when the FET 12 is held in the on state. The piezoelectric body 13 starts operating again when the FET 12 is turned off after lapse of 10ms. The amplitude of this time is smaller than the amplitude at the time of the driving but attains the stop state in a short period of time. The voltage impressed to the drain is decreased to the voltage lower than heretofore at the moment when the FET 12 is turned off at the time of this stopping.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for a separately excited piezoelectric buzzer.

0002

2. Description of the Related Art As shown in FIG. 6, a drive device for a separately excited piezoelectric buzzer connects a separately excited piezoelectric buzzer 3 to a DC power supply VDD through a charging resistor 1 and a field effect transistor (FET) 2 in series. A discharge resistor 4 is connected to the buzzer 3 in parallel. The piezoelectric buzzer 3 is then driven by controlling the transistor 2 to turn on and off at a desired frequency.

In this device, when the transistor 2 is turned on, a current +IB flows through the piezoelectric buser 3 and the charging resistor 1 as shown in FIG. 7(a), and when the transistor 2 is turned off, a current +IB flows as shown in FIG. 7(b). ) As shown in the piezoelectric buser 3
A current -IB flows in the opposite direction through the closed loop of the discharge resistor 4, and this causes the piezoelectric body of the piezoelectric buzzer 3 to vibrate and generate sound. Further, when stopping, it was necessary to turn off the transistor 2 due to the characteristics of the piezoelectric electrode using a silver material.

0004

[Problem to be Solved by the Invention] When the piezoelectric buzzer 3 is stopped from an oscillating state by turning off the transistor 2 in such a drive device, as shown in FIG. There was a problem in that a large voltage of VDD+V1, which is higher than the power supply voltage VDD, is applied to the transistor 2, and the transistor 2 may be destroyed in some cases. When we investigated the cause of this, we found that the power generation caused by the lingering amplitude of the piezoelectric body especially when stopped was a major influence.

Therefore, the present invention aims to provide a piezoelectric buzzer drive device that can prevent as much as possible the generation of electricity due to the lingering amplitude of the piezoelectric body when it is stopped, and thereby suppress the voltage applied to the switching element when it is stopped. It is something to do.

[0006]

[Means for Solving the Problems] The present invention provides a separately excited piezoelectric buzzer connected to a DC power source via a switching element, and controls the switching element to be turned on and off at relatively high speed to drive the piezoelectric buzzer. A control means is provided for turning the switching element on for at least several times the on time during driving and then turning it off when driving is stopped.

[0007]

[Operation] In the present invention having such a structure, the switching element is turned on for at least several times the on time during driving when the driving is stopped. As a result, the piezoelectric body of the piezoelectric buzzer is held in a certain state while being deformed. After that, when the switching element is turned off, the aftereffect of the amplitude of the piezoelectric body becomes smaller.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, a separately excited piezoelectric buzzer 13 is connected to a DC power supply VDD through a charging resistor 11 and a field effect transistor (hereinafter referred to as FET) 12 in series. A discharge resistor 14 is connected in parallel to the piezoelectric buzzer 13.

The FET 12 is connected to the microcomputer 1.
This is a MOS type transistor incorporated in 5, and a driving ON/OFF signal is supplied to its gate from a control circuit 16.

As shown in FIG. 2, the piezoelectric buzzer 13 has a diaphragm 13 in a cylindrical case 13a with an open center at the top.
b is provided, and a piezoelectric body 13c is provided on one surface of this diaphragm 13b.
is installed. And from the piezoelectric electrode to the terminal 13d
, 13e extend outside the case 13a. The control circuit 16 uses a timer 17 to perform buzzer control based on the flowchart shown in FIG.

First, FET 12 is turned off. In this state, timer 17 is made to count time, and the count time is 125.
When the time reaches μs, the FET 12 is turned on. In this state, timer 17 is made to count time, and the count time is 125.
When it reaches μs, the number of times is incremented and FET1
Turn 2 off again. In this state, the timer 17 counts the time, and when the count time reaches 125 μs, the FE
Turn on T12 again.

The above control is repeated until the number of times reaches 400, and when the number reaches 400, the timer 17 is caused to count 10 ms while keeping the FET 12 on. When the timer 17 counts 10 ms, the FET 12 is turned off to stop driving.

In the embodiment having such a configuration, the FET 12 is turned on and off at high speeds of 125 μs by the control circuit 16, and the piezoelectric buzzer 13 is driven. When this on and off operation is repeated 400 times,
The driving of the piezoelectric buzzer 13 is stopped. At this time, FET1
2 remains on for 10ms and then turns off.

When the FET 12 is kept on, the piezoelectric body 13c of the piezoelectric buzzer 13 stops vibrating in a certain deformed state as shown in FIG. 5(a). When the FET 12 is turned off after 10 ms has elapsed, the piezoelectric body 13c starts to vibrate again, but the amplitude at that time is smaller than the amplitude during driving, as shown in FIG. Before long, the engine will be in a stopped state as shown in FIG. 5(c).

The voltage applied to the drain of the FET 12 during this series of operations is as shown in FIG.
It can be made smaller than D+V1.

In this way, the voltage applied to the drain of the FET 12 can be kept low at the moment the FET 12 is turned off, so the FET 12 will not be destroyed. Further, as the FET 12, one having low withstand voltage characteristics can be used, and costs can be reduced.

In the above embodiment, the time for keeping the FET 12 in the on state during stoppage was set at 10 ms, but it is not necessarily limited to this; in short, the on state should be kept on for at least several times the on time during driving. Just let it happen.

[0019]

[Effects of the Invention] As detailed above, according to the present invention, it is possible to prevent as much as possible the generation of electricity due to the lingering amplitude of the piezoelectric body when it is stopped, and thereby to suppress the voltage applied to the switching element when it is stopped. A piezoelectric buzzer driving device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a piezoelectric buzzer according to the same embodiment.

FIG. 3 is a flowchart showing piezoelectric buzzer drive control in the same embodiment.

FIG. 4 is a graph showing drain voltage characteristics of the FET in the same example.

FIG. 5 is a diagram showing the deformation of the piezoelectric body when driving is stopped in the same embodiment.

FIG. 6 is a circuit diagram showing a conventional example.

FIG. 7 is a diagram for explaining the operating principle of a piezoelectric buzzer.

FIG. 8 is a graph showing drain voltage characteristics of a conventional FET.

[Explanation of symbols]

12...FET (field effect transistor), 13...piezoelectric buzzer, 16...control circuit, 17...timer.

Claims (1)

[Claims] 1. A separately excited piezoelectric buzzer connected to a DC power source via a switching element, the switching element being controlled on and off at relatively high speed to drive the piezoelectric buzzer, and the switching element being connected to the switching element when driving is stopped. 1. A piezoelectric buzzer drive device, comprising: control means for turning off the buzzer after turning it on for at least several times the on time during driving.