Abstract:
A protection device includes a substrate capable of suppressing electromagnetic fields, with a channel formed therein, a current dependent circuit interrupter disposed inside the channel, and voltage management circuitry coupled to the substrate. The voltage management circuitry is electrically coupled to the current dependent circuit interrupter so as to form a crowbar circuit in the presence of overvoltage or undervoltage conditions as determined according to a reference voltage.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to telephony, and more particularly to telephony protection devices. 
     BACKGROUND 
     Telephones are an integral part of global communication. As such, a vast number of telephone lines are connected to private residences and commercial buildings. These lines, made of copper, are extremely conductive, requiring that special consideration be given to hazardous overvoltage and overcurrent conditions and to radiated electromagnetic noise which can interfere with, among others, television and radio. The overvoltage and overcurrent conditions are particularly troublesome since they can cause injury to people and damage to equipment. 
     These are legitimate concerns due to the hostile environment in which the lines operate. For example, a large number of lines are hung from telephone poles which may be struck by lightning, which can produce hazardous overvoltage and overcurrent in a line connected to a residence or business. Alternatively, the telephone lines are sometimes hung on the same poles as high tension wires. If, for instance, a violent storm or a car crashing into the pole should cause one of the high tension wires to fall onto a phone line, a power cross results, possibly causing overvoltage and overcurrent conditions. Similarly, if someone accidentally cross-wires a phone line to an electrical main, a power cross results. Thus, protection is needed to deal with overvoltage, overcurrent, and radiated electromagnetic interference. 
     In any telephone subscriber line interface, there are usually two levels of protection. First, the primary protectors deal with the initial overvoltage and overcurrent conditions on the line. These suppression devices are usually either gas tubes or heat coils, and although they take the brunt of the overvoltage and overcurrent, up to 25 kilowatts can still pass through. Thus, secondary protectors are needed to deal with the residual overvoltage and overcurrent conditions, as well as electromagnetic interference. The various embodiments disclosed in the Detailed Description are directed to secondary protection. 
     Typically, secondary protector circuits are unbounded, having many discrete components and requiring between ¼ square inch and 1 square inch per channel for every interface termination. This can amount to the protection circuit occupying up to half of the area needed for the interface. 
     SUMMARY 
     In one embodiment, an apparatus is disclosed which comprises a substrate capable of suppressing electromagnetic fields, with a channel formed therein, a current dependent circuit interrupter disposed inside the channel, and voltage management circuitry coupled to the substrate and electrically coupled to the current dependent circuit interrupter so as to form a crowbar circuit in the presence of overvoltage or undervoltage conditions as determined according to a reference voltage. 
     In various embodiments, the voltage management circuitry can be directly coupled to the substrate, or the voltage management circuitry can be coupled to a printed circuit board which is coupled to the substrate. 
     In various embodiments, the substrate is a ferrite material. Among others, the current dependent circuit interrupter can be at least one of a physical link fuse and a self-resettable positive temperature coefficient thermistor. In addition, the voltage management circuitry can be at least one of a symmetrical thyristor arrangement and a zener diode. 
     The various embodiments described herein advantageously provide for suppression of electromagnetic radiation and protection against overcurrent and overvoltage while reducing the amount of space required for such protection. For example, the various embodiments only require between one sixth to one tenth of the space currently needed by existing secondary protection circuitry. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Various embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an,” “one,” or “various” embodiments in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     FIG. 1 is a top view of an embodiment with thyristors directly mounted to the substrate. 
     FIG. 2 is a side view of an embodiment with the thyristors mounted on a board, which is mounted to the substrate. 
     FIG. 3 is a cross-sectional view of the embodiment shown in FIG.  2 . 
     FIG. 4 is a schematic of a protection circuit for a single line. 
    
    
     DETAILED DESCRIPTION 
     Various embodiments described herein overcome the problems in the existing art described above by providing a single device which incorporates overcurrent protection, overvoltage protection and suppression of electromagnetic radiation. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. It will be apparent, however, to one skilled in the art that the various embodiments may be practiced without some of the specific details. The following description and accompanying drawings provide various examples for the purposes of illustration. However, these examples should not be construed in a limiting sense as they are merely intended to provide examples of the various embodiments, rather than to provide an exhaustive list of all possible implementations. 
     Referring now to FIG. 1, device  10  is shown according to an embodiment. Device  10  has three connections or interfaces for telephone lines which may enter device  10  on the Line side (e.g., the portion of the line located after the primary protector but before the secondary protector) and exit device  10  on the Protected side (e.g., the portion of the line located after the secondary protector, here device  10 ). 
     Each telephone line interface has a Tip connection  11  and a Ring connection  13 . The physical subscriber connects to device  10  on the Protected side. 
     Substrate  12  is capable of suppressing electromagnetic fields. Thus, substrate  12  acts as a choke to block radiated emissions, such as noise from device  10  by way of an impedance to high radio frequency emissions. 
     Although not shown in FIG. 1, channels are formed within substrate  12 , and Tip and Ring connections  11  and  13  run through these channels. Each of these channels has a current dependent circuit interrupter disposed therein which acts to protect against overcurrent. For example, the current dependent circuit interrupter could be a physical link fuse or a self-resettable positive temperature coefficient thermistor. One advantage of using self-resettable thermistors is that they allow short term energy hits to pass (e.g., induced lightning rather than direct lightning or a power cross). 
     In addition, voltage management circuitry  14  is coupled directly to substrate  12 . It is worth noting that the space needed for device  10  could be further reduced by not using pre-packaged physical thyristors. Rather, the die could be directly coupled to substrate  12  or printed circuit board  16  (See FIG.  2  and accompanying text). 
     In various embodiments, voltage management circuitry  14  includes a symmetrical thyristor arrangement or a zener diode. As can be seen from FIG. 1, voltage management circuitry  14  is electrically coupled to reference voltage sources, positive Vprotect and negative Vprotect. These reference voltage sources are adapted to meet the requirements of the environment in which device  10  is used. 
     Moreover, a crowbar circuit effect is formed by voltage management circuitry  14  and the current dependent circuit interrupter once the voltage goes above or below a certain point. For instance, the circuit will shunt to chassis ground through a low impedance path if the voltage level become too high or too low. The crowbar effect is seen when the current dependent circuit interrupter fails due to overcurrent. 
     In embodiments which utilize thyristors as part of voltage management circuitry  14 , small transient events will cause the thyristors to fire (e.g., to shunt), but the current dependent circuit interrupters will not fail. It is more desirable to use a thyristor-based voltage management circuit than a zener diode-based voltage management circuit since zener diodes are not programmable and do not have a low impedance shunt path. As such, circuits with zener diode-based voltage management circuitry would tend not to deal efficiently with repeated events. 
     It is worth noting that substrate  12  may be made of a channelized piece of a ceramic material, such as alumina or ferrite. One advantage of using ferrite is that ferrite acts as a choke to suppress electromagnetic radiation which may be emitted by or carried through the telephone lines. The ferrite can be any of type  43 ,  60 ,  62 , or  80 . However, the type of ferrite chosen will depend on the desired electromagnetic characteristics of device  10 . For instance, different impedances will be required at different operating frequencies. 
     FIG. 2 shows an embodiment in which voltage management circuitry  14  is mounted on printed circuit board  16 , which is further coupled to substrate  12 . In addition, channels  18  are each configured to have a current dependent circuit interrupter (not shown in FIG. 2) disposed therein. 
     FIG. 3 is a cross-sectional view of the embodiment shown in FIG.  2 . As can be seen, current dependent circuit interrupters  20  are shown disposed within channels  18 . In this particular embodiment, current dependent circuit interrupters  20  are physical link fuses. 
     FIG. 4 shows an electrical schematic for a single line of device  10  of FIG.  1 . Specifically, choke  22  acts to suppress electromagnetic radiation from device  10  and is physically embodied as substrate  12 , discussed above. Fuses  24  are the current dependent circuit interrupters of the embodiment shown and are disposed within channels formed in substrate  12 . As previously discussed, the current dependent circuit interrupters (fuses or self-resettable positive temperature coefficient thermistors) protect against overcurrent conditions. Overvoltage assembly  26  comprises thyristors  28  coupled to reference voltages, positive Vprotect and negative Vprotect, and ground  30  to provide protection against overvoltage conditions. Thyristors  28  are physically embodied as voltage management circuitry  14  of FIG.  1 . 
     It is to be understood that even though numerous characteristics and advantages of the various embodiments have been set forth in the foregoing description, together with details of the structure and function of the various embodiments, this disclosure is illustrative only. Changes may be made in detail, especially matters of structure and management of parts, without departing from the scope of the various embodiments as expressed by the broad general meaning of the terms of the appended claims.