Abstract:
A telephone line connection and disconnection circuit has a diode bridge coupled to the telephone line which converts different voltages of the telephone line into a voltage referenced to ground. A switching circuit is coupled to the diode bridge which opens and closes a conductive pathway for connecting and disconnecting a telephony product from the telephone line. A resistive element is coupled to the diode bridge and the switching circuit which allows for the conductive pathway to be normally closed. An optical isolator is coupled to the switching circuit and the resistive element for sending a control signal to the circuit when required.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to telephony products and, more specifically, to a telephone line connection and disconnection circuit which does not require the use of a relay. By eliminating the need for a relay, the telephone line connection and disconnection circuit will consume less power and be less expensive to produce.  
           [0003]    2. Description of the Prior Art  
           [0004]    Many telephone adjunct boxes are required to disconnect the associate telephone from the telephone line. The reason for requiring the disconnection of the telephone from the telephone line is to suppress the telephone ringing and to mute the telephone conversation during a call. It is also the best way to check if another extension is in the off-hook condition. Presently, all devices which connect or disconnect the associate telephone from the telephone adjunct box use some type of relay for switching.  
           [0005]    While relays do work, there are several problems associated with there use. First, mechanical relays are very large and bulky. Thus, the circuits that are used to connect and disconnect the associate telephone from the telephone adjunct box tend to be large and bulky. Furthermore, mechanical relays consume more power than other types of switches. While there are other types of relays which are smaller in size, such as solid state relays, solid state relays are more expensive to build and implement thus driving up the cost of the circuit used to connect and/or disconnect the associate telephone from the telephone adjunct box. Another problem with using relays is the noise that these types of devices create. Generally, when switching a relay from one position to another, there is noise that is generated. The noise will generally be a clicking sound when the relay changes position. While the noise generally will not interfere with the operation of the circuitry, it&#39;s very annoying to the end user.  
           [0006]    Therefore, a need existed to provide an improved circuit for connecting and disconnecting an associate telephone from a telephone adjunct box. The improved circuit must reduce the size of present circuits which use mechanical relays. The improved circuit must also reduce the amount of power consumed by present circuits which use mechanical relays. The improved circuit must further eliminate the noise involved when connecting and disconnecting the associate telephone from a telephone adjunct box. Finally, the improved circuit must be fairly inexpensive to build and operate.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with one embodiment of the present invention, it is an object of the present invention to provide an improved circuit for connecting and/or disconnecting an associate telephone from a telephone adjunct box.  
           [0008]    It is another object of the present invention to provide an improved circuit for connecting and/or disconnecting an associate telephone from a telephone adjunct box that reduces the size of present circuits which use mechanical relays.  
           [0009]    It is still another object of the present invention to provide an improved circuit for connecting and/or disconnecting an associate telephone from a telephone adjunct box that reduces the amount of power consumed by present circuits which use mechanical relays.  
           [0010]    It is yet another object of the present invention to provide an improved circuit for connecting and/or disconnecting an associate telephone from a telephone adjunct box that eliminates the noise involved when connecting and/or disconnecting the associate telephone from a telephone adjunct box.  
           [0011]    It is still a further object of the present invention to provide an improved circuit for connecting and/or disconnecting an associate telephone from a telephone adjunct box that is inexpensive to build and operate.  
         BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS  
         [0012]    In accordance with one embodiment of the present invention a telephone line connection and disconnection circuit is disclosed. The circuit has a diode bridge coupled to the telephone line which converts different voltages of the telephone line into a voltage referenced to ground. A switching circuit is coupled to the diode bridge which opens and closes a conductive pathway for connecting and disconnecting a telephony product from the telephone line. A resistive element is coupled to the diode bridge and the switching circuit which allows for the conductive pathway to be normally closed. An optical isolator is coupled to the switching circuit and the resistive element for sending a control signal to the circuit when required.  
           [0013]    The foregoing and other objects, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiments of the invention, as illustrated in the accompanying drawing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a prior art diagram of a circuit used for connecting and disconnecting an associate telephone from a telephone adjunct box.  
         [0015]    [0015]FIG. 2 is a circuit diagram of the present invention which is used for connecting and/or disconnecting an associate telephone from a telephone adjunct box and which uses no relays.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Referring to FIG. 1, a prior art circuit  10  is shown which is used to connect and disconnect an associate telephone from a telephone adjunct box. The telephone adjunct box is any box between a telephone jack and a corresponding telephone. For example, a caller identification box, a telephone answering machine, and similar apparatus are typical examples of a telephone adjunct box. The telephone adjunct box is used to suppress telephone ringing and/or to mute telephone conversation during a call. It is also used to check if another extension is in the off-hook condition.  
         [0017]    The circuit  10  is generally held within the adjunct box  12 . The circuit  10  generally uses a relay  14 . There are numerous problem with using a relay  14 . For example, if the relay  14  is a mechanical relay, the relay  14  will tend to be rather bulky. This will increase the size of the circuit  10  and the adjunct box  12  used to hold the circuit  10 . The relay  14  could be a solid state relay which is smaller in size, but solid state relays are more expensive to build and implement thus driving up the cost of the circuit  10 . A further problem if the relay  14  is a mechanical relay is that the circuit  10  will consume more power than is desirable. Another problem with using a relay  14  is the noise that the relay  14  generates. If one is on the telephone  22  and the relay  14  switches to disconnect the telephone  22  from the telephone line  16 , a loud click noise is heard. While the noise generally will not interfere with the operation of the circuit  10 , it&#39;s very annoying to the user.  
         [0018]    The circuit  10  is coupled to one end of the telephone line  16  via a connector  18 . The other end of the telephone line  16  will generally be coupled to a telephone jack (not shown). From the connector  18 , the telephone line  16  is coupled to a telephone  22  via a second connector  20 . Presently, a relay  14  is used to connect and disconnect the telephone  22  from the adjunct box  12 . The relay  14  is controlled by a control signal  24 . The control signal  24  is generally generated by a microcontroller (not shown). The control signal  24  is sent to a transistor  26  via a resistor  28 . The transistor  26  is used to turn on and turn off the relay  14 . By turning on and turning off the relay  14 , the relay will connect and disconnect the telephone  22  from the telephone adjunct box  12 .  
         [0019]    In the embodiment depicted in FIG. 1, if the control signal  24  is high, the transistor  26  is conducting so the relay  14  is active. Conversely, if the control signal  24  is low, the transistor  26  is turned off. Thus, the relay  14  is not active. Generally, the relay  14  is a normally closed relay. Thus, if there is no power to the adjunct box  12 , the telephone  22  will still function.  
         [0020]    Referring now to FIG. 2, a circuit diagram of the present invention is shown. Like the prior art, the circuit  50  is also used to connect and/or disconnect an associate telephone  54  from the telephone adjunct box  51 . The circuit  50  removes the relay  14  (FIG. 1) and the problems associated with the use of the relay  14 . The circuit  50  uses a diode bridge  56  and a plurality of transistors to connect and/or disconnect the associate telephone  54  from the telephone adjunct box  51 .  
         [0021]    It should be noted that while the circuit  50  is shown in FIG. 2 to be in the adjunct box  51 , the circuit  50  may be installed in other areas and the adjunct box  51  should not be seen as to limit the scope of the present invention. The circuit  50 , for example, may be installed inside a telephony product for high voltage line switching.  
         [0022]    The circuit  50  is coupled to a telephone line  52  via a connector  56 . One section of the telephone line  52  (i.e., the ring)is coupled to the telephone  54  via a connector  58 . A second section from the telephone line  52  (i.e., tip) is coupled to a diode bridge  60 . The diode bridge  60  is comprised of a plurality of diodes coupled together. In the embodiment depicted in FIG. 2, the diode bridge  60  has a first diode  62  which has a first terminal coupled to the telephone line  52  and a second terminal coupled to ground potential. A second diode  64  has a first terminal coupled to a transistor  66  and a second terminal coupled to the first terminal of the diode  62 . A third diode  68  has a first terminal coupled to the telephone line  52  and a second terminal coupled to both the second terminal of the first diode  62  and ground potential. A fourth diode  70  has a first terminal coupled to both the first terminal of the second diode  64  and the transistor  66  and a second terminal coupled to both the first terminal of the third diode  68  and the telephone line  52 . The diode bridge  60  converts the different voltage of the telephone line  52  (i.e., on-hook and off-hook conditions) into a voltage at node V 1  which is referenced to ground.  
         [0023]    The diode bridge  60  is coupled to a resistive element  72  and the transistor  66 . The first terminals of the second and fourth diodes  64  and  70  respectively of the diode bridge  60 , are coupled to the resistive element  72  and the transistor  66 . The transistor  66  has three terminals. The first terminal is coupled to ground potential which is also the same ground potential as the diode bridge  60 . The second terminal of the transistor  66  is coupled to a second transistor  74 . The third terminal is coupled to the diode bridge  60  and the resistive element  72 . In the embodiment depicted in FIG. 2, the transistor  66  is a PNP transistor. The resistor  72  has a first terminal coupled to the second transistor  74  and a second terminal coupled to both the third terminal of the first transistor  66  and the diode bridge  60 . The resistor  72  is used to allow the circuit  50  to function as normally closed. This will be explained below in the Operation section.  
         [0024]    The second transistor  74  also has three terminals. The first terminal is coupled to the second terminal of the first transistor  66 . The third terminal of the second transistor  74  is coupled to ground. The second terminal of the second transistor  74  is coupled to the first terminal of the resistive element  72 . The second terminal of the second transistor  74  is also coupled to an optical isolator  76 . The transistor  74  is used for control. It allows the control signal  78  to pull more current through. In the embodiment depicted in FIG. 2, the transistor  74  is an NPN transistor.  
         [0025]    The optical isolator  76  is used for isolating a control signal  78  from a microcontroller (not shown) from the circuit  50 . The optical isolator  76  is comprised of a light emitting diode  80  and a transistor  82 . The light emitting diode  80  has a first terminal coupled to a resistor  84  and a second terminal coupled to the control signal  78 . The control signal  78  will activate and deactivate the light emitting diode. The transistor  82  has three terminals. The first terminal is coupled to the second terminal of the transistor  74  and to the first terminal of the resistor  72 . The second terminal of the transistor  82  is receives a signal from the light emitting diode  80 . The third terminal of the transistor  82  is coupled to ground. The ground in which the resistor  84  and the transistor  82  are coupled to are different grounds. The transistor  82  functions like a switch and will activate when the control signal  78  activates the light emitting diode  80 .  
       OPERATION  
       [0026]    The circuit  50  operates in the following manner. Generally there is a voltage between the tip and ring of the telephone line  52 . For an on-hook state, the voltage between the tip and ring and thus the voltage at node V 1  is approximately  48  volts. For an off-hook state, the voltage between the tip and ring and thus the voltage at node V 1  is approximately  6  volts.  
         [0027]    In the absence of any control signal  78 , the transistor  82  will not be active. The impedance between the emitter and collector of the transistor  66  is high. This is because there will be a voltage applied at the node V 1  caused by the voltage between the tip and ring of the telephone line  52  which the diode bridge  60  converts into a voltage at node V 1  which is referenced to ground. The voltage at node V 1  allows the resistor  72  to provide a current to the base of the transistor  74 . The current will activate the transistor  74  pulling the voltage at node V 2  low to ground. This turns the transistor  66  on thus pulling the voltage at node V 1  to ground. Since the transistor  66  and the diode bridge  60  are connected to the same ground potential, a conducting path is formed when the transistor  66  is active. The conducting path allows a signal to flow from the tip of the telephone line  52  through the diode  64  and through the transistor  66  to ground. Since the ground of transistor  66  and the ground of the diode bridge  60  are coupled together, the signal can flow back from ground through the diode  68  of the diode bridge  60  to the associated telephone  54  to the ring of the telephone line  52 .  
         [0028]    When the control signal  78  is active, the light emitting diode  80  will generate a light signal which will activate the transistor  82 . This will cause the voltage at node V 3  to be pulled towards ground, thus turning off the transistor  74 . If the transistor  74  is turned off, the transistor  66  is also turned off. The associated telephone set  54  is thus disconnected from the telephone line  52 .  
         [0029]    While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.