Buzzer drive circuit

Details Buzzer drive circuit Buzzer drive circuit

2001-02-08

2002-06-25

Tran, Toan (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Current driver

C327S427000, C327S434000

Reexamination Certificate

active

06411138

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a buzzer drive circuit, and more particularly to a buzzer drive circuit implementing a reduction in a size of the circuit and stabilization of a buzzer output.
FIG. 2
shows a conventional buzzer drive circuit. The buzzer drive circuit comprises an IC section
13
including a logic section
14
, AND gates
15
to
18
, FETs
19
to
22
and terminals
23
to
28
. The terminal
28
is used for controlling a buzzer output waveform. The terminal
24
is grounded. Resistors
29
to
32
for determining weighting of a current flowing in a path between the terminals
25
to
28
and the buzzer
12
are connected to the respective terminals. Each of the AND gates
15
to
18
calculates AND of an output of the logic section
14
and a control input sent from the terminal
23
, and supplies the AND to gates of the FETs
19
to
22
. Sources of the FETs
19
to
22
are connected to the terminal
24
in common. Drains of the FETs
19
to
22
are connected to the terminals
25
to
28
.
In the buzzer drive circuit having such a structure, the FETs
19
to
22
are ON/OFF controlled according to control data transferred from the logic section
14
so that the output of the buzzer is controlled. Moreover, the buzzer output waveform is controlled in response to a signal sent to the terminal
23
. More specifically, when the terminal
23
is set in an OFF state, the AND gates
15
to
18
are always set in an OFF state and the buzzer does not sound. When the terminal
23
is set in an ON state, the AND gates
15
to
18
are selected to be turned ON/OFF according to the control data. For this reason, the buzzer sounds in a cycle of the signal input to the terminal
23
. These AND gates are connected to the terminals
25
to
28
through the FETs, respectively. Therefore, the FETs are ON/OFF controlled depending on the ON/OFF of the AND gates, thereby opening or closing the paths reaching the terminals
25
to
28
. Furthermore, the resistors
29
to
32
for determining the weighting of the current flowing to the respective paths are connected to the terminals
25
to
28
, and the buzzer output is controlled by opening or closing the paths reaching the same terminals.
In
FIG. 2
, the number of data bits for buzzer output control is four, and the parts provided in the IC section
13
include four AND gates and four FETs in the same manner as the control data bits. Thus, the total number of the parts is eight. Moreover, the number of the terminals is six, that is, the terminal
23
for the ON/OFF control of the buzzer section, the terminal
24
, and the terminals
25
to
28
connected to the drains of the FETs
19
to
22
respectively. Furthermore, it is necessary to provide four parts outside the IC other than the buzzer, that is, the resistors
29
to
32
for determining the weighting of the current flowing to the respective paths are required for the terminals
25
to
28
.
In the conventional circuit structure, however, a path including an AND gate and an FET is provided corresponding to the number of bits of the control data transferred from the logic section. For this reason, when the number of bits of the control data is increased to enhance precision in buzzer control, the number of paths reaching the buzzer and the numbers of parts and terminals in the IC section are increased. Furthermore, a resistor to be externally provided is required for each terminal so that the number of parts to be externally provided is also increased. Moreover, paths are provided from the logic section to the terminals
25
to
28
in the IC section. Therefore, the buzzer output is influenced by the paths due to a variation in a value of the resistor connected to each terminal. Furthermore, the buzzer output is controlled under the control of an operation for opening/closing the paths to the terminals
25
to
28
. Therefore, the output is affected by a change in an operating environment such as a temperature or a noise.
SUMMARY OF THE INVENTION
The invention has been made to solve the conventional problems and has an object to provide a buzzer drive circuit which can reduce a size of the circuit, can relieve the influence of a path on a buzzer output and can enhance stability of the buzzer output, and does not depend on the number of bits of control data.
A buzzer drive circuit according to the invention comprises: a buzzer output control voltage generator which generates a voltage corresponding to buzzer output control data; a transistor for buzzer output waveform control, in which a control signal of a buzzer output waveform is applied to a gate; and a transistor for buzzer output control in which an output of the buzzer output control voltage generator and an output of the transistor for buzzer output waveform control are applied to a gate. By such a structure, the voltage corresponding to the buzzer output control data which is generated by the buzzer output control voltage generator can be applied to the gate of the transistor for buzzer output control to control the buzzer output, and the output of the transistor for buzzer output waveform control can be applied to the gate of the transistor for buzzer output control, thereby controlling the buzzer output waveform. Therefore, it is possible to implement a circuit structure which can reduce the size of the buzzer drive circuit, can relieve the influence of the path on the buzzer output and does not depend on the number of bits of the control data.
Moreover, the buzzer output control voltage generator includes: a variable power supply for changing an output voltage in accordance with buzzer output control data transferred from a logic section; and an operational amplifier in which an output of the variable power supply is applied to a non-inverted input terminal and a negative feedback output of the transistor for buzzer output control is applied to an inverted input terminal. By such a structure, the stability of the buzzer output can be enhanced.


REFERENCES:
patent: 4491744 (1985-01-01), Corey
patent: 5514989 (1996-05-01), Sato et al.
patent: 5798662 (1998-08-01), Marosek et al.
patent: 2 019 696 (1979-04-01), None

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