High output audible alarm device utilizing a piezoelectric transducer

Abstract

An audible alarm device comprises solid-state amplifier drive circuit cooperating with a piezoelectric transducer to convert electrical energy into sound energy. An acoustical loading means, such as a horn, effectively transmits the sound to the air.

Description

BACKGROUND OF THE INVENTION

Generally speaking, the present invention relates to audible alarm devices and more specifically to audible alarm devices that utilize piezoelectric transducers of the type that convert electrical energy into sound energy. The illustrated embodiment of the present invention includes an acoustical loading means, a piezoelectric transducer in spaced relation to the acoustical loading means, and a solid-state amplifier drive circuit cooperating with the piezoelectric transducer to produce an audible signal wherein the drive circuit includes an activation circuit connected to the piezoelectric transducer, a voltage regulator connected to the activation circuit, and a power supply connecting means connected to the voltage regulator.

Audible alarm devices utilizing piezoelectric transducers are in common use in many different applications. One example of such devices is the SONALERT electronic audible signal produced by P. R. Mallory and Co. Inc. of Indianapolis, Ind., U.S.A. SONALERT is a registered trademark owned by P. R. Mallory and Co. Inc. These audible alarm devices are employed for a variety of applications requiring an audible warning signal including fault alarms, fire and smoke detection signals, and monitors for medical instruments. In many other applications including some intrusion alarms, piezoelectric alarm devices are not used because they are incapable of producing a sufficiently high volume of sound output for the application. An embodiment of the present invention solves this problem of insufficient sound output by producing a volume level of sound higher than can be achieved in alarm devices utilizing piezoelectric transducers of the same size.

Accordingly, a feature of the present invention is to provide an audible alarm device that utilizes a piezoelectric transducer of the type that converts electrical energy into sound energy. Another feature of the present invention is to provide an audible alarm device that includes an acoustical loading means. Another feature of the present invention is to provide an audible alarm device that includes a piezoelectric transducer cooperating with a solid-state amplifier drive circuit to produce an audible signal. Yet another feature of the present invention is to provide an audible alarm device including a solid-state amplifier drive circuit that includes an activation circuit connected to a piezoelectric transducer, a voltage regulator connected to the activation circuit, and a power supply connecting means connected to the voltage regulator. Another feature of the present invention is to provide an audible alarm device capable of producing a high volume of sound output. Still another feature of the present invention is to provide an audible alarm device including a piezoelectric transducer in spaced relation to an acoustical loading means and cooperating with a solid-state amplifier drive circuit, wherein the drive circuit includes an activation circuit, a voltage regulator, and a power supply connecting means.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features will become more apparent from the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a wiring diagram of an amplifier drive circuit including a piezoelectric transducer.

FIG. 2 is a sectional elevation-view of a high volume piezoelectric audible alarm.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a solid-state amplifier drive circuit 10 comprises an activation circuit 12, a voltage regulator circuit 14, and a power supply connection means 16. Circuit 10 is connected to piezoelectric transducer 18.

Activation circuit 12 includes an NPN transistor 20 connected emitter E to voltage regulator 14 and to a first side of a first resistance means 22. Base B of transistor 20 is connected to a first side of a second resistance means 24, to a first side of a third resistance means 26, and also to a first side of a first capacitance means 28. Collector C of transistor 20 is connected to a second side of first capacitance means 28 and also to a primary winding 31 of a transformer coil 30. A second side of third resistance means 26 is connected to voltage regulator 14, to a first side of a second capacitance means 32, and also to a tap T on transformer coil 30 between primary winding 31 and a secondary winding 29. Secondary winding 29 of transformer coil 30 is connected to a second side of second capacitance means 32 and also to a first terminal 34 of piezoelectric transducer 18. A second side of first resistance means 22 is connected to a second side of second resistance means 24 and also to a second terminal 36 of piezoelectric transducer 18.

Voltage regulator circuit 14 includes a second NPN transistor 38 connected emitter E2 to activation circuit 12 and to a first side of a filter capacitor 40. Base B2 of NPN transistor 38 is connected to a first side of a fourth resistance means 42 and to the cathode of a zener diode 44. Collector C2 of transistor 38 is connected to a positive power terminal 46 of power supply connection means 16 and to second side of fourth resistance means 42. A second side of filter capacitor 40 is connected to a negative power terminal 48 of power supply connection means 16, to the anode of zener diode 44, and to activation circuit 12. Power supply connection means 16, comprising power terminals 46 and 48, is capable of being connected to a suitable direct current power supply 50. Power terminals 46 and 48 comprise lead wires 52 and 54. Resistance means 22, 24, 26, and 42 comprise respectively resistors 21, 23, 25, and 41. Capacitance means 28 and 32 comprise capacitors 27 and 33 respectively.

In operation of solid-state amplifier drive circuit 10, direct-current power is applied from power supply 50 to activation circuit 12. Resistance means 26 provides direct-current bias to transistor 20 to cause the circuit to start oscillation when power supply 50 is connected. A first capacitance means 28 facilitates starting oscillation of the circuit for a wide range of voltage applied to circuit 10 from power supply 50. Second capacitance means 32 also facilitates starting oscillation of the circuit for a wider range of gain of transistor 20. Voltage induced in secondary winding 29 of transformer 30 by current in primary winding 31 through collector C of transistor 20 is fed to piezoelectric transducer 18 and to negative power terminal 48 through first resistance means 22. The transformer provides positive feedback through transducer 18 and second resistance means 24 to the base of transistor 20 so that oscillation is sustained.

If voltage applied to activation circuit 12 by power supply 50 exceeds the working voltage of transistor 20, the transistor may be damaged or its life may be shortened. In some applications, power supply 50 may not be constant. Voltage spikes may occur. To protect transistor 20, voltage regulator 14 prevents activation circuit 12 from receiving more than the working voltage of the transistor.

Voltage is also applied to voltage regulator 14 from power supply 50. Transistor 38 is turned on by the bias current through a fourth resistance means 42. If the voltage from power supply 50 exceeds a predetermined voltage that is substantially equal to the upper limit of optimum working voltage for transistor 20, the bias current is directed through a zener diode 44. This causes the voltage at emitter E2 of transistor 38 to be nearly constant. Capacitance means 40 stores current for pulse current drawn by activation circuit 12.

Referring now to FIG. 2, an audible alarm device 56 is shown attached to a panel 58. Panel 58 is a typical panel or bracket into which audible alarm device 56 may be mounted. Audible alarm device 56 includes an acoustical loading means 60 which, in the illustrated embodiment, comprises a horn 62. The small end of horn 62 fits into an opening 64 in a housing 66. A threaded section 68 is carried by housing 66 over the outside of opening 64. A threaded member 70 is screwed onto threaded section 68.

In assembly, threaded section 68 of housing 66 is inserted through an aperture 72 in panel 58. Threaded member 70 is screwed onto threaded section 68 thereby securing housing 66 tightly to panel 58. The small end of horn 62 is then pressed into opening 64. The horn may be secured by friction or adhesive or any other suitable attachment means.

Piezoelectric transducer 18 is attached to a ring-shaped projection 74 with a resilient adhesive means 76. Resilient adhesive means 76, in the illustrated embodiment comprises a room-temperature vulcanizing silicon rubber compound (RTV) 78. Piezoelectric transducer 18 is electrically connected to a printed circuit board 80 by lead wires 82. The components of solid-state amplifier drive circuit 10 are carried on printed circuit board 80. A second housing member 88 is suitably attached to housing 66, and a potting material 84 such as epoxy 86 encases components of circuit 10 within housing 66 and second housing member 88. Lead wires 52 and 54 extend through epoxy 86 to the outside of the device where they may be suitably attached to direct current power supply 50.

Claims

What is claimed is:

1. An audible alarm device comprising:

a. an acoustical loading means;

b. a piezoelectric transducer in spaced relation to said acoustical loading means;

c. a solid-state amplifier drive circuit cooperating with said piezoelectric transducer to produce an audible signal including an activation circuit connected to said piezoelectric transducer, a voltage regulator connected to said activation circuit, and a power supply connection means connected to said voltage regulator, said activation circuit comprising:

a transformer coil to increase voltage from a power supply to said piezoelectric transducer, a first NPN transistor, emitter connected to said voltage regulator and to a first side of a first resistance means, base connected to a first side of a second resistance means, to a first side of a third resistance means and also to a first side of a first capacitance means, collector connected to a second side of said first capacitance means and also to a primary winding of said transformer coil; a second side of said third resistance means connected to said voltage regulator, to a first side of a second capacitance means and also to a tap on said transformer coil; a secondary winding of said transformer coil connected to a second side of said second capacitance means and also to a first terminal of a piezoelectric transducer; a second side of said first resistance means connected to a second side of said resistance means and also to a second terminal of said piezoelectric transducer.

2. The audible alarm device according to claim 1 wherein said voltage regulator comprises a second NPN transistor, emitter connected to said activation circuit and to one side of a filter capacitor, base connected to a first side of a fourth resistance means and to the cathode of a zener diode, collector connected to a second side of said fourth resistance means and also to a power terminal of a power supply connection means; a second side of said filter capacitor connected to a second power terminal of said power supply connection means, to the anode of said zener diode and to said activation circuit.

3. The audible alarm device according to claim 1 wherein said power supply connection means comprises two lead wires capable of being connected to said power supply.

4. The audible alarm device according to claim 2 wherein each of said resistance means comprises a resistor.

5. The audible alarm device according to claim 2 wherein each of said capacitance means comprises a capacitor.

6. The audible alarm device according to claim 1 wherein said acoustical loading means comprises a horn.