JPH09147268A - Drive circuit for alarm sounding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive a piezoelectric element with application of the drive pulse voltage almost equal to the power source voltage and without increasing the current consumption. SOLUTION: When an input transistor TR Q1 and an output TR Q2 are turned on and off respectively by an input pulse signal, a capacitor C1 is charged up to the power voltage Vcc via a diode D1. When the TR Q1 and Q2 are turned off and on respectively by the input pulse signal, a base current is supplied to the TR Q2 by the charging power voltage Vcc of the capacitor C1 via a resistor R. So that the TR Q2 is kept in its ON state and the drive voltage equal to the voltage Vcc is supplied to a piezoelectric element 6 from the emitter of the TR Q2. Then the drive voltage almost equal to the voltage Vcc is stably supplied to the element 6 as long as the resistance value of the resistor R is set at a level (r×hfe) or less (r: resistance value of element 6, hfe: current amplification factor of TR Q2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive 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 supplying a drive pulse voltage to a piezoelectric element for a buzzer to sound. The present invention relates to a drive circuit of a device.

[0002]

2. Description of the Related Art Conventionally, a bell is generally used as a district sound device of a fire alarm system, but in recent years, a piezoelectric buzzer has been used because the current consumption can be greatly reduced. Is being considered. FIG. 11 shows a conventional piezoelectric element drive circuit, in which the input pulse voltage Vin of FIG. 12A is applied to the base of a transistor Q via a resistor R1 to turn it 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 drive load. As shown in FIG. 12B, the drive pulse voltage Vo, which is the inverted 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 produces a sound by utilizing the effect of mechanical distortion of the dielectric when a drive voltage is applied between the electrodes. Piezoelectric elements generally have higher impedance than speakers, and are therefore voltage-driven elements.

[0004]

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

In particular, in the area sound device of the fire alarm system, the 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. Therefore, the utilization rate of the power supply voltage is high. If it is low, there is a problem that the volume required for the district audio system cannot be obtained. FIG.
In order to increase the utilization factor of the power supply voltage in the conventional circuit of No. 1, the resistance value of the resistor R2 must be made sufficiently smaller than the resistance component r of the piezoelectric element 6. However, if the resistance R2 is reduced, the collector current Ic that flows when the transistor Q is turned on increases, and it is not possible to take advantage of the low current consumption that is a feature of the piezoelectric element 6.

The present invention has been made in view of the above-mentioned conventional problems, and an alarm which enables the piezoelectric element to be driven by applying a drive pulse voltage substantially the same as the power supply voltage without increasing the current consumption. An object is to provide a driving circuit for an audio device.

[0007]

In order to achieve this object, the present invention is configured as follows. The 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 according to an input pulse signal to a piezoelectric element to cause the piezoelectric element to ring. As a drive circuit of such an alarm sound device, the present invention has an input transistor Q1 which is turned on and off by an input pulse signal, a base connected to the collector of the input transistor Q1, a collector connected to a power supply line, and an emitter connected. An output transistor Q2 that is connected to the piezoelectric element 6 serving as a driving load, is turned off by turning on the input transistor Q1, and is turned on by turning off the input transistor Q1 to drive the piezoelectric element 6, and between the power supply line and the emitter of the output transistor Q2. It is composed of a series circuit in which the diode D1 and the capacitor C1 are directly connected, and a resistor R connected between the connection point of the diode D1 and the capacitor C1 of the series circuit and the collector of the input transistor Q1.

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

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

Further, a power source holding capacitor 2 is connected to the power source line via a diode D3, and a surplus portion of the charge charged in the capacitor C1 which is not used when the output transistor Q2 is turned on is returned to the power source holding capacitor C2. , Reduce current consumption. Further, a constant voltage element such as a Zener diode ZD that suppresses 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 by turning on the input transistor Q1. . According to the drive circuit of the alarm sound device of the present invention as described above, it is possible to apply a drive pulse voltage that is substantially equal to the power supply voltage to the piezoelectric element to cause the piezoelectric element to ring, and set the utilization rate of the power supply voltage to approximately 100%. Sufficient volume can be secured without increasing current consumption.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a district audio system to which the present invention is applied. The district audio device 1 is connected to the control line 3 led out from the receiver by the terminals 3a and 3b. The lines from the terminals 3a and 3b are connected to the power supply circuit 2. The power supply circuit 2 includes terminals 3a,
It includes a diode bridge for making the connection polarity to 3b non-polarized, a capacitor for holding the power supply, and a voltage conversion circuit for adjusting the supply voltage to each circuit portion.

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 objects of the present invention.
Is supplied to the sweep oscillation circuit 4 which supplies a pulse signal for acoustic output. In this embodiment, DC24V 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 DC24V to the piezoelectric element drive circuit 5 as the power supply voltage Vcc. Further, since the sweep oscillation circuit 4 operates with a 5V power source, for example,
The power supply circuit 2 uses a Zener diode or the like from 24V to 5
The power supply voltage stepped down to V is supplied.

The sweep oscillation circuit 4 outputs to the piezoelectric element drive circuit 5, for example, a sweep signal whose oscillation frequency changes linearly at a constant sweep cycle. Although the sweep oscillation circuit 4 is taken as an example in this embodiment,
It may be an oscillation circuit that outputs an oscillation pulse having a constant frequency. In the district sound device 1, each circuit is in a stopped state because the drive voltage DC24V is not supplied from the receiver to the control line 3 in the steady monitoring state. When the drive voltage DC24V is supplied from the receiver to the control line 3, the power supply circuit 2 receives the drive voltage DC24V to activate the piezoelectric element drive circuit 5 and the sweep oscillation circuit 4, and the piezoelectric element drive circuit 5 causes the sweep oscillation circuit 4 to operate. Receiving the pulse signal from the piezoelectric element 6
A pulse voltage is applied to the device to make it ring.

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

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 the basic circuit portion of the piezoelectric element driving circuit 5 of FIG. 2 by extracting it, and shows the diode D3 of the power source line and the power source holding capacitor C2, and the Zener diode ZD provided between 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 of the base portion of the output transistor Q2 is Vb,
The input pulse voltage for the input transistor Q1 is Vin,
When the drive output voltage of the output transistor Q2 for the piezoelectric element 6 is Vo, each voltage becomes as shown in FIGS. 4 (A) to 4 (D). Note that FIG. 4E shows the power supply voltage Vcc supplied from the receiver through the control line 3.

As shown in FIG. 4E, the power supply voltage Vcc is Vcc = 2 when the drive voltage is supplied from the receiver through the control line 3.
When the voltage rises to 4V, the power supply circuit 2, the sweep oscillation circuit 4 and the piezoelectric element drive circuit 5 shown in FIG. 1 are in the operating state, and the pulse voltage Vin of FIG. 4A is applied to the input transistor Q1 in the basic circuit 5a of FIG. To 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 is turned on, the base of the output transistor Q2 is pulled to 0 volt, and the output transistor Q2 is placed in the cutoff state.

When the output transistor Q2 is off, the capacitor C1 is connected to the power source + V via the diode D1.
It is quickly charged by cc, and the voltage Va on the capacitor C1 side rises to the power supply voltage Vcc as shown in FIG. 4 (B). As the capacitor C1 is charged, the output voltage Vo applied to the piezoelectric element 6 changes in accordance with the charging of the capacitor C1.

Next, when the input pulse voltage Vin becomes L level, the input transistor Q1 turns off and the output transistor Q2 turns on. At this time, in the output transistor Q2, the base current Ib flows through the resistor R by using the charging voltage Vcc of the capacitor C1 charged when the input transistor Q1 is turned on as a power source, whereby the on state of the transistor Q2 is maintained.

At the same time, the power supply voltage + Vcc from the power supply line
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 this voltage Vb by a voltage drop of about 0.6V between the base and the emitter of the output transistor Q2 becomes the output voltage Vo which substantially matches the power supply voltage Vcc applied to the piezoelectric element 6.

FIG. 5 shows the input pulse voltage Vin in FIG.
Is an H level and the transistor Q1 is on and the transistor Q2 is off, it is an equivalent circuit of FIG. 3, and since the transistor Q2 is off, the circuit portion that operates in the state excluding the circuit of FIG. Shows only. That is, since the input pulse voltage Vin is at the H level and the input transistor Q1 is turned on, the output transistor Q2 is placed in a cutoff state and does not electrically exist. Therefore, the output transistor Q2 is provided on the transistor Q2 side. The capacitor C1 is rapidly charged through the diode D1 existing therein, and as is apparent from FIG. 4, the output voltage Vo applied to the piezoelectric element 6 at this timing becomes zero volts after the second pulse. Further, when the input transistor Q1 is turned on, the diode D1, the resistor R1, the input transistor Q1
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 is at L level in FIG. 4, the transistor Q1 in FIG. 3 is off and the transistor Q2 is on, except for the transistor Q1 in the off state. Only the effective circuit part is shown. Since the voltage across the diode D1 is the same when the transistor Q2 is on, the diode D1 apparently does not exist, and the charging voltage of the capacitor C1 serves as a power source to the transistor Q2 via the resistor R. A base current Ib is passed.

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 resistor 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 turned on is determined as follows. Now, assuming that the resistance of the piezoelectric element 6 is r and the direct current amplification factor of the transistor Q2 is hfe, the power supply voltage V
There is the following relationship with the collector current Ic flowing by cc.

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 taken out as follows. Like Vcc / r = (Vcc / R) × hfe (2) Therefore, the relationship of r × hfe = R (3) is established between the resistance r and the resistance R of the piezoelectric element 5. 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 equation (4),
As shown in, 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, the output voltage Vo which is the same as the power supply voltage + Vcc can be applied to the piezoelectric element 6 when the output transistor Q2 is turned on.

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

FIG. 7 shows the operation of the diode D3 of the power supply line and the 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 the on state. At this time, the excess charge of the capacitor C1 is removed. By providing the diode D3 on the power supply line, the capacitor can be returned to the power supply holding capacitor C2. This allows the power consumption to be saved as much as possible.

FIG. 8 is a diagram showing the function of the Zener diode ZD provided in the piezoelectric element drive 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 cc changes, the Zener voltage Vz is changed as shown in FIG.
With respect to the portion exceeding, it is possible to suppress further increase in the output voltage Vo and suppress the amplitude of the pulse voltage applied to the piezoelectric element 6 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 Q1 is turned on, a distortion occurs which is not abruptly lowered to zero volt when the transistor Q2 is turned off. When the trailing edge is distorted in this manner, the change in the drive voltage applied to the piezoelectric element 6 is suppressed, which causes a decrease in volume.

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

FIG. 10 shows another embodiment of the piezoelectric element drive circuit 5 of the present invention, which is the waveform shaping diode D2 of FIG.
Is provided with a transistor Q3 instead of. That is, when the transistor Q1 is turned on, the output transistor Q2 is turned off, and at the same time, the base current is passed through the transistor Q3, so that the transistor Q3 is turned on at the same time, whereby the distortion caused by turning off the transistor Q2 can be eliminated and the transistor Q3 can be steeply dropped. it can.

Although the above embodiment has been described by taking the district audio device as an example, the present invention is not limited to this, and may be applied to the main audio device provided in the receiver and other appropriate alarm audio devices. It can be used as it is.

[0035]

As described above, according to the present invention, it is possible to drive a piezoelectric element by applying a drive pulse voltage having a voltage substantially the same as the power supply voltage. If the power supply voltage that can be supplied from the receiver is set to 100%, as in district audio equipment, the power supply voltage can be used to the maximum, and the required volume of 90 dB or more can be efficiently used. I can put it out well.

Further, it is possible to suppress the useless consumption current 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 sound device using the present invention.

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

3 is an equivalent circuit diagram of FIG.

FIG. 4 is a time chart of the signal waveform of each part in 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 the diode of the power supply line and the capacitor for holding the power supply.

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

9 is an explanatory view of suppressing distortion of a waveform falling edge by a diode D2 of FIG.

FIG. 10 is a circuit diagram of another embodiment for suppressing the waveform trailing distortion.

FIG. 11 is a circuit portion of a conventional circuit

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

[Explanation of symbols]

 1: District audio 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)

[Claims] 1. In a drive circuit of an alarm sound device for supplying a drive pulse voltage according to an input pulse signal to a piezoelectric element to ring the piezoelectric element, an input transistor which is turned on / off by an input pulse signal, and a base are input. The piezoelectric element is driven by connecting it to the collector of the transistor, connecting the collector to the power supply line, connecting the emitter to the piezoelectric element serving as a driving load, turning it off by turning on the input transistor and turning it 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 the power supply voltage through the diode, and when the input transistor is turned off by the input pulse signal and the output transistor is turned on, the charging voltage of the capacitor is passed through the resistor. Is configured to supply a base current to the output transistor to maintain an ON state of the output transistor, and to supply a drive voltage to the piezoelectric element from the emitter of the second transistor, the drive voltage being substantially equal to the power supply voltage. Drive circuit for alarm sound device. 2. A drive circuit for an alarm sound device according to claim 1, wherein a resistance value R of the resistor is multiplied by a resistance r of the piezoelectric element and a direct current amplification factor hfe of the output transistor ( r × hfe) A drive circuit for an alarm sound device characterized by being set as follows. 3. The drive circuit for an alarm sound device according to claim 1, wherein a power source holding capacitor is connected to the power source line via a diode, and the output transistor is turned on among charges charged in the capacitor. A drive circuit for an alarm sound device, wherein a surplus not used at the time of returning is returned to the power source holding capacitor. 4. The drive circuit for an alarm sound device according to claim 1, wherein a constant voltage element for suppressing a drive voltage applied to the piezoelectric element to a specified value in response to a change in power supply voltage is provided at the base of the output transistor. A drive circuit for an alarm sound device characterized by being connected. 5. The drive circuit for an alarm sound device according to claim 1, wherein a drive voltage rises between the emitter of the output transistor and the collector of the input transistor when the output transistor is turned off by turning on the input transistor. A drive circuit for an alarm sound device, which is provided with a waveform shaping circuit for suppressing downstream waveform distortion.