JP3076233B2 - Drive circuit of alarm sound device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for an alarm sound device such as a district sound device used in a fire alarm system, and more particularly to an alarm sound for sounding by supplying a driving pulse voltage to a piezoelectric element for a buzzer. The present invention relates to a driving circuit of a device.

[0002]

2. Description of the Related Art Conventionally, a bell has been generally used as an area sound device for a fire alarm system. However, in recent years, a piezoelectric buzzer has been used because current consumption can be greatly reduced. Are being considered. FIG. 11 shows a conventional driving circuit for a piezoelectric element, in which the input pulse voltage Vin shown in FIG. 12A is applied to the base of a transistor Q via a resistor R1 to turn on and off. The collector of the transistor Q is connected to the power supply Vcc via the resistor R2, and the piezoelectric element is connected as a driving load. As shown in FIG. 12B, the driving pulse voltage Vo obtained by inverting the input pulse voltage Vin is applied to the piezoelectric element. Supply and ring.

The piezoelectric element 6 has a structure in which a dielectric is sandwiched between electrodes, and emits sound using the effect of mechanical distortion of the dielectric when a driving voltage is applied between the electrodes. A piezoelectric element generally has a higher impedance than a speaker, and is therefore a voltage-driven element.

[0004]

However, in such a conventional piezoelectric element drive circuit, FIG.
As shown in (B), only a drive voltage lower than the power supply voltage Vcc can be applied to the piezoelectric element, and the utilization rate of the power supply voltage is low. That is, in the case of a voltage-driven piezoelectric element,
The intensity of the generated sound depends on the magnitude of the drive voltage, and if only a drive voltage lower than the power supply voltage Vcc can be applied, the volume will be reduced accordingly.

[0005] In particular, in a local sound device of a fire alarm system, a sound volume of 90 dB or more is required, and the power supply voltage supplied from the receiver side is determined to be, for example, 24 V. If it is low, there is a problem that it is not possible to obtain the volume required for the district sound device. FIG.
In order to increase the utilization rate of the power supply voltage in the conventional circuit, the resistance value of the resistor R2 must be made sufficiently smaller than the resistance r of the piezoelectric element 6. However, when the resistance R2 is reduced, the collector current Ic flowing when the transistor Q is turned on increases, and the advantage of the low consumption current characteristic of the piezoelectric element 6 cannot be utilized.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an alarm which can drive a piezoelectric element by applying a drive pulse voltage substantially equal to a power supply voltage without increasing current consumption. An object of the present invention is to provide a driving circuit of an audio device.

[0007]

In order to achieve this object, the present invention is configured as follows. Note that reference numerals in the drawings of the embodiments are also shown. First, the present invention is directed to a drive circuit of an alarm sound device that supplies a drive pulse voltage corresponding to an input pulse signal to a piezoelectric element to make a sound. According to the present invention, as a driving circuit of such an alarm sound device, an input transistor Q1 which is turned on / off by an input pulse signal, a base is connected to a collector of the input transistor Q1, a collector is connected to a power supply line, and an emitter is further connected. An output transistor Q2 connected to a piezoelectric element 6 serving as a driving load, turned off when the input transistor Q1 is turned on, and turned on when the input transistor Q1 is turned off to drive the piezoelectric element 6, and between a power supply line and the emitter of the output transistor Q2. It comprises a series circuit in which a diode D1 and a capacitor C1 are directly connected, and a resistor R connected between a connection point between the diode D1 and the capacitor C1 of the series circuit and a collector of the input transistor Q1.

When the input transistor Q1 is turned on and the output transistor Q2 is turned off by the input pulse signal, the driving circuit of the alarm sound device charges the capacitor C1 to the power supply voltage Vcc via the diode D1, and supplies the input pulse signal. When the input transistor Q1 is turned off and the output transistor Q2 is turned on, a base current is supplied to the output transistor Q2 via the resistor R by the charging power supply voltage Vcc of the capacitor C1 to maintain the on state of the output transistor Q2. A driving voltage substantially equal to the power supply voltage Vcc is supplied to the piezoelectric buser 6 from the emitter of the second transistor Q2.

Further, by setting the resistance value of the resistor R to be equal to or smaller than the value (r × hfe) obtained by multiplying the resistance r of the piezoelectric element 6 by the current amplification factor hfe of the output transistor Q2, the piezoelectric element 6 can be stably provided. A drive voltage substantially equal to the power supply voltage Vcc can be supplied, and the resistance value of the resistor R can be made relatively large, so that current consumption when the input transistor Q1 is turned on can be reduced.

A power supply holding capacitor 2 is connected to the power supply line via a diode D3, and a surplus of the charge of the capacitor C1 that is not used when the output transistor Q2 is turned on is returned to the power supply holding capacitor C2. , Reduce current consumption. Further, a constant voltage element such as a Zener diode ZD for suppressing the drive voltage applied to the piezoelectric element 6 to a specified value Vz in response to a change in the power supply voltage Vcc may be connected to the base of the output transistor Q2.

Further, a waveform shaping circuit may be provided between the emitter of the output transistor Q2 and the collector of the input transistor Q1 to suppress the falling waveform distortion of the drive voltage when the output transistor Q2 is turned off when the input transistor Q1 is turned on. . According to such a drive circuit of the alarm sound device of the present invention, it is possible to apply a drive pulse voltage substantially coincident with the power supply voltage to the piezoelectric element to make the piezoelectric element ring, and to make the utilization rate of the power supply voltage approximately 100%. A sufficient volume can be ensured without increasing current consumption.

[0012]

FIG. 1 is a block diagram of a district sound apparatus to which the present invention is applied. The district acoustic device 1 is connected to a control line 3 drawn from a receiver by terminals 3a and 3b. Lines from the terminals 3a and 3b are connected to the power supply circuit 2. As the power supply circuit 2, terminals 3a,
It includes a diode bridge for depolarizing the connection polarity to 3b, a capacitor for holding a power supply, and a voltage conversion circuit for adjusting a supply voltage to each circuit unit.

The power is supplied from the power supply circuit 2 to the piezoelectric element drive circuit 5 and the piezoelectric element drive circuit 5 which are the objects of the present invention.
Is supplied to a sweep oscillation circuit 4 that supplies a pulse signal for outputting sound to the sweep oscillator 4. In this embodiment, 24 V DC is supplied by the control line 3 when a fire is judged by the receiver, and at this time, the power supply circuit 2 applies 24 V DC to the piezoelectric element drive circuit 5 as the power supply voltage Vcc. Further, since the sweep oscillation circuit 4 operates with, for example, a 5V power supply,
The power supply circuit 2 is driven from 24 V to 5
A power supply voltage reduced to V is supplied.

The sweep oscillation circuit 4 outputs to the piezoelectric element drive circuit 5 a sweep signal whose oscillation frequency changes linearly at a constant sweep cycle, for example. In this embodiment, the sweep oscillation circuit 4 is used as an example.
An oscillation circuit that outputs an oscillation pulse of a constant frequency may be used. In the regional sounding apparatus 1, in the steady monitoring state, each circuit is in a stopped state because the driving voltage DC24V is not supplied from the receiver to the control line 3. When the drive voltage DC24V is supplied from the receiver to the control line 3, the drive voltage is received by the power supply circuit 2, and the piezoelectric element drive circuit 5 and the sweep oscillation circuit 4 are put into operation. Receiving a pulse signal from the piezoelectric element 6
A pulse voltage is applied to the device to make it sound.

FIG. 2 is a circuit diagram of an embodiment of the piezoelectric element drive circuit 5 of FIG. First, the input pulse voltage Vin from the sweep oscillation circuit 4 is given to the base of the input transistor Q1. The collector of the input transistor Q1 is connected to the base of the output transistor Q2, and the emitter is grounded. The output transistor Q2 has a collector connected to a power supply line from the power supply circuit 2. In addition,
The power supply line is provided with a diode D3 and a power supply voltage holding capacitor C2.

The emitter of the output transistor Q2 is connected to one terminal of the piezoelectric element 6. A diode D1 is connected between a power supply line from the power supply circuit 2, that is, between the collector of the output transistor Q2 and the emitter to which the piezoelectric element 6 is connected.
And a series circuit of a capacitor C1. The connection point between the diode D1 and the capacitor C1 in this series circuit is connected via a resistor R to the base of the output transistor Q2, that is, the collector of the input transistor Q1.

Further, a Zener diode ZD is connected between the base of the output transistor Q2 and the ground, and a diode D2 is connected from the emitter of the output transistor Q2 to the collector of the input transistor Q1. FIG.
2 shows a part of the basic circuit of the piezoelectric element drive circuit 5 shown in FIG. 2, and shows a zener diode ZD provided between the diode D3 of the power supply line and the power holding capacitor C2 and the input transistor Q1 and the output transistor Q2.
The circuit excluding the diode D2 constitutes the basic circuit 5a of the piezoelectric element drive circuit 5 of the present invention.

In the basic circuit 5a of FIG. 3, the voltage at the connection point of the series circuit of the diode D1 and the capacitor C1 is V
a, the voltage at the base of the output transistor Q2 is Vb,
The input pulse voltage to the input transistor Q1 is Vin,
Assuming that the drive output voltage of the output transistor Q2 with respect to the piezoelectric element 6 is Vo, each voltage is as shown in FIGS. FIG. 4E shows the power supply voltage Vcc supplied from the receiver via the control line 3.

As shown in FIG. 4E, when the power supply voltage Vcc is supplied with the driving voltage from the receiver via the control line 3, the power supply voltage Vcc becomes 2
When the voltage rises to 4 V, the power supply circuit 2, the sweep oscillation circuit 4, and the piezoelectric element driving circuit 5 shown in FIG. 1 are respectively activated, and the input transistor Q1 in the basic circuit 5a in FIG. Enter. The input transistor Q1 turns on when the input pulse voltage Vin is at the H level, and turns off when the input pulse voltage Vin is at the L level. When the input pulse voltage Vin becomes H level and the input transistor Q1 turns on, the base of the output transistor Q2 is pulled down to 0 volt, and the output transistor Q2 is placed in a cutoff state.

When the output transistor Q2 is off, the capacitor C1 is connected to the power supply + V via the diode D1.
The capacitor Va is quickly charged, and the voltage Va on the capacitor C1 rises to the power supply voltage Vcc as shown in FIG. With the charging of the capacitor C1, the output voltage Vo applied to the piezoelectric element 6 changes so as to decrease in accordance with the charging of the capacitor C1.

Next, when the input pulse voltage Vin goes low, the input transistor Q1 turns off and the output transistor Q2 turns on. At this time, the base current Ib flows to the output transistor Q2 via the resistor R using the charging voltage Vcc of the capacitor C1 charged when the input transistor Q1 is turned on as a power supply, whereby the on state of the transistor Q2 is maintained.

At the same time, the power supply voltage + Vcc from the power supply line is
The output voltage Vo is applied to the piezoelectric element 6 via the transistor Q2 in the ON state. Therefore, the capacitor C
The terminal voltage Va of 1 rises to 2 Vcc, which is the sum of the charging voltage of the capacitor C and the power supply voltage. At this time, the voltage Vb applied to the base of the transistor Q2 becomes a base voltage slightly higher than the power supply voltage Vcc as shown in FIG.
Further, a voltage lower than the voltage Vb by about 0.6 V corresponding to a voltage drop between the base and the emitter of the output transistor Q2 becomes the output voltage Vo substantially matching the power supply voltage Vcc applied to the piezoelectric element 6.

FIG. 5 shows the input pulse voltage Vin in FIG.
3 is an equivalent circuit of FIG. 3 when the transistor Q1 is turned on and the transistor Q2 is turned off when the transistor Q2 is turned off. Since the transistor Q2 is off, the circuit section operates in a state excluded from the circuit of FIG. Only shows. That is, when the input pulse voltage Vin becomes H level and the input transistor Q1 is turned on, the output transistor Q2 is placed in the cutoff state and is not electrically present. Therefore, the output transistor Q2 is provided on the transistor Q2 side. The capacitor C1 is rapidly charged via the diode D1 and the output voltage Vo applied to the piezoelectric element 6 at this timing becomes zero volt after the second pulse, as is apparent from FIG. When the input transistor Q1 is turned on, the diode D1, the resistor R1, and the input transistor Q1 are turned on.
The current flows through. This current value is determined by the value of the resistor R.

FIG. 6 shows an equivalent circuit when the input pulse voltage Vin becomes L level in FIG. 4 and the transistor Q1 in FIG. 3 is turned off and the transistor Q2 is turned on. Only valid circuit parts are shown. As described above, when the transistor Q2 is on, the voltage across the diode D1 is the same, so that the diode D1 does not seem to exist, and the charged voltage of the capacitor C1 becomes a power source and is applied to the transistor Q2 via the resistor R. The base current Ib flows.

When the transistor Q2 is turned on, the power supply voltage + Vcc of the power supply line is applied to the emitter, so that the voltage Va rises to 2Vcc. The resistance R for applying the same output voltage Vo as the power supply voltage Vcc to the piezoelectric element 6 when the output transistor Q2 in FIG. 6 is on is determined as follows. Assuming that the resistance of the piezoelectric element 6 is r and the DC current gain of the transistor Q2 is hfe, the power supply voltage V
The following relationship exists between the collector current Ic flowing through cc and the collector current Ic.

Ic = Vcc / r = Ib × hfe = (Vcc / R) × hfe (1) Here, the relationship between the resistance r of the piezoelectric element 6 and the resistance R on the base side of the transistor Q2 is obtained by the following equation. Become like Vcc / r = (Vcc / R) × hfe (2) Therefore, the relationship of r × hfe = R (3) is established between the resistance r of the piezoelectric element 5 and the resistance R. Therefore, in order to set the output voltage Vo applied to the piezoelectric element 6 when the transistor Q2 is turned on to the power supply voltage Vcc, the value of the resistor R is determined so as to satisfy the condition of r × hfe> R (4) Good.

By determining the value of the resistance R with respect to the resistance r of the piezoelectric element 6 based on the relationship of the above equation (4),
As shown in the figure, the output transistor Q corresponding to the ON / OFF of the input transistor Q1 by the input pulse voltage Vin
When the output transistor Q2 is turned on when the output transistor Q2 is turned on, the output voltage Vo which is the same as the power supply voltage + Vcc is applied to the piezoelectric element 6 and the sound is generated.

For this reason, in the piezoelectric element drive circuit of the present invention, the drive voltage supplied from the receiver via the control line 3, for example, D
C24V can be directly applied as a drive voltage of the piezoelectric element 6 without loss, and the drive of the piezoelectric element 6 using almost 100% of the power supply voltage Vcc can be realized. Further, since the value of the resistor R can be set to a large value within a range that satisfies the condition of the expression (4), the current consumption when the input transistor Q1 is turned on can be reduced. For example, the value of the resistance R can be set to several tens kΩ or more.

FIG. 7 shows the operation of the power supply line diode D3 and power supply holding capacitor C2 provided in the piezoelectric element drive circuit 5 shown in the embodiment of FIG. That is, when the input transistor Q1 is turned off and the output transistor Q2 is turned on, a base current due to the charging voltage of the capacitor C1 flows to hold the transistor Q2 in an on state. By providing the diode D3 in the power supply line, the power can be returned to the capacitor C2 for holding the power. This can save as much power consumption as possible.

FIG. 8 is a diagram showing the function of the Zener diode ZD provided in the piezoelectric element driving circuit 5 of FIG. By connecting the Zener diode ZD to the base of the output transistor Q2, for example, as shown in FIG.
When the cc changes, the Zener voltage Vz as shown in FIG.
In the portion exceeding the value, the increase of the output voltage Vo can be suppressed, and the amplitude of the pulse voltage applied to the piezoelectric element 6 can be suppressed to a constant voltage determined by the Zener voltage Vz of the Zener diode ZD.

FIG. 9 shows the operation of the diode D2 provided in the piezoelectric element drive circuit 5 of FIG. The output voltage Vo when the diode D2 is not provided is as shown in FIG.
When the transistor Q2 is turned off by turning on the transistor Q1, a distortion is generated that does not drop sharply to zero volts. If the falling edge is distorted in this way, the change in the drive voltage applied to the piezoelectric element 6 is suppressed, and the volume is reduced.

When the diode D2 is connected, the output voltage V
o falls sharply as shown in FIG. 9B, and distortion can be eliminated. That is, when the transistor Q1 is turned on, the emitter of the transistor Q2 is also pulled in through the diode D2, so that the transistor Q2 can fall sharply without causing distortion. The circuit using the diode D2 functions as a waveform shaping circuit for the output voltage Vo.

FIG. 10 shows another embodiment of the piezoelectric element driving circuit 5 according to the present invention.
Is characterized in that a transistor Q3 is provided instead of. That is, the output transistor Q2 is turned off when the transistor Q1 is turned on, and at the same time, the transistor Q3 is turned on at the same time by flowing a base current to the transistor Q3. it can.

Although the above embodiment has been described with reference to a district sound device as an example, the present invention is not limited to this, and may be applied to a main sound device provided in a receiver or any other appropriate alarm sound device. Can be used as is.

[0035]

As described above, according to the present invention, the piezoelectric element can be driven by applying a drive pulse voltage having substantially the same voltage as the power supply voltage. When the power supply voltage that can be supplied from the receiver is determined, such as in a district acoustic device, the power supply voltage is used to the maximum, and the required sound volume of, for example, 90 dB or more is efficiently used. I can put it out well.

Further, it is possible to suppress unnecessary current consumption flowing at the timing when the driving voltage of the piezoelectric element is turned off to the minimum necessary.

[Brief description of the drawings]

FIG. 1 is a block diagram of a district acoustic device using the present invention.

FIG. 2 is a circuit diagram of a piezoelectric element drive circuit according to the present invention.

FIG. 3 is an equivalent circuit diagram of FIG. 2;

FIG. 4 is a time chart of signal waveforms at various parts in FIG. 2;

FIG. 5 is an equivalent circuit diagram when the input transistor Q1 is turned on and the output transistor Q2 is turned off in FIG.

FIG. 6 is an equivalent circuit diagram when the input transistor Q1 is turned off and the output transistor Q2 is turned on in FIG.

FIG. 7 is an explanatory diagram of a charging function for a power line diode and a power holding capacitor.

FIG. 8 is an explanatory diagram of a drive pulse voltage limiter function by the Zener diode ZD of FIG. 2;

FIG. 9 is an explanatory diagram of distortion suppression at the falling edge of the waveform by the diode D2 of FIG. 1;

FIG. 10 is a circuit diagram of another embodiment for suppressing distortion at the falling edge of a waveform.

FIG. 11 is a circuit diagram of a conventional circuit.

FIG. 12 is a time chart of input / output signals of the circuit of FIG. 11;

[Explanation of symbols]

 1: district acoustic device 2: power supply circuit 3a, 3b: control terminal 4: sweep oscillation circuit 5: piezoelectric element drive circuit 6: piezoelectric element Q1: input transistor Q2: output transistor Q3: waveform shaping transistor D1, D2, D3: Diode R: Resistance ZD: Zener diode

Claims (5)

(57) [Claims] In a driving circuit of an alarm sound device which supplies a driving pulse voltage corresponding to an input pulse signal to a piezoelectric element to sound, an input transistor which is turned on / off by an input pulse signal and a base are connected to the input circuit. The collector is connected to the transistor, the collector is connected to the power supply line, the emitter is connected to the piezoelectric element as a driving load, and the piezoelectric element is driven by turning off the input transistor and turning on by turning off the input transistor. An output transistor, a series circuit in which a diode and a capacitor are connected in series between a power supply line and an emitter of the second transistor, and a resistor connected between a connection point of the diode and the capacitor in the series circuit and a collector of the first transistor. The input transistor is turned on by the input pulse signal, and the output transistor is turned on. When the transistor is turned off, the capacitor is charged to a power supply voltage via the diode, and when the input transistor is turned off and the output transistor is turned on by an input pulse signal, the charged voltage of the capacitor is used to charge the resistor through the resistor. A base current is supplied to the output transistor to maintain an ON state of the output transistor, and a driving voltage substantially equal to a power supply voltage is supplied to the piezoelectric element from an emitter of the second transistor. The driving circuit of the alarm sound device. 2. The driving circuit for an alarm sound device according to claim 1, wherein a resistance value R of said resistor is multiplied by a resistance r of said piezoelectric element by a DC current amplification factor hfe of said output transistor. r × hfe) A driving circuit for an alarm sound device, wherein the driving circuit is set as follows. 3. A driving circuit for an alarm sound device according to claim 1, wherein a power holding capacitor is connected to said power line via a diode, and said output transistor is turned on among charges charged in said capacitor. A drive circuit for the alarm sound device, wherein a surplus not used at the time of the return is returned to the power holding capacitor. 4. A driving circuit for an alarm sound device according to claim 1, wherein a constant voltage element for suppressing a driving voltage applied to said piezoelectric element to a specified value with respect to a change in power supply voltage is provided at a base of said output transistor. A driving circuit for an alarm sound device, wherein the driving circuit is connected. 5. A drive circuit for an alarm sound device according to claim 1, wherein a drive voltage between an emitter of said output transistor and a collector of said input transistor when the output transistor is turned off by turning on the input transistor. A driving circuit for an alarm sound device, further comprising a waveform shaping circuit for suppressing downstream waveform distortion.