Abstract:
A telephone terminal includes: a main unit; an optional unit that performs an arbitrary additional communication function and detachably attached to the main unit; a distribution unit that distributes a drive power supplied through a communication network into a first channel and a second channel when a power of the telephone terminal is turned on; a first power supplying unit that supplies the first channel of the drive power to the main unit at a first timing; and a second power supplying unit that supplies the second channel of the drive power to the optional unit at a second timing shifted from the first timing.

Description:
RELATED APPLICATIONS 
   The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2004-194950 filed on Jun. 30, 2004, which is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a telephone terminal of a network telephone system for conducting voice communications between telephone terminals through an IP network, such as an IP (Internet Protocol) telephone system, for example, and a power supply method used with the telephone terminal. 
   2. Description of the Related Art 
   In recent years, a network telephone system (IP telephone system) for transmitting and receiving an image and voice as packet data bi-directionally in real time through a packet network has begun to become widespread. 
   In the IP telephone system, inter-extension communications can be conducted and outside line outgoing and incoming calls can be made for each gateway connected to the packet network, of course, and in addition, extension communications can be conducted and outside line outgoing and incoming calls can be made between the gateway via the packet network. In this case, communications can be carried out as power (drive power) is supplied to an IP telephone terminal in accordance with a power supply technique such as POE (Power Over Ethernet), which is described in below. 
   Power supply is received through the packet network from the gateway. 
   Power supply is received from a network component of a router, a switching hub, etc., forming a part of a LAN. 
   Power supply is received from a midspan unit. The midspan unit is a power supply dedicated unit being installed between a “network component with no power supply function” and a “terminal to which power is to be supplied” for allowing a LAN signal to pass through and adding only supply power. 
   In the IP telephone system, to purchase an IP telephone terminal for use, the user generally selects an IP telephone terminal having necessary functions at the point in time. However, after use of the IP telephone terminal is started, it becomes necessary to add a function in response to change in the use situation, etc. In such a case, a technique for the user of the IP telephone terminal to connect an optional unit for executing any desired function to the IP telephone terminal main unit is proposed. (For example, refer to JP-A-4-192698 and JP-A-4-239898.) 
   SUMMARY OF THE INVENTION 
   However, in the POE technique mentioned above, there is a limit on rush current at the power on time. Thus, if the rush current is too large, there is a possibility that power supply from the gateway will not be received. Particularly, if an optional unit is connected to the IP telephone terminal, the rush current at the power on time, of the optional unit as well as the IP telephone terminal main unit is added. Thus, if the total rush current is too large and is placed out of the POE standard, it becomes impossible to receive power supply. 
   The present invention provides a telephone terminal of a network telephone system and a power supply method used with the telephone terminal for making it possible to place rush current at the power on time within a stipulated value and moreover reduce the cost when a plurality of optional units are connected. 
   According to a first aspect of the invention, there is provided a telephone terminal connected via a communication network for transmitting a communication packet to a gateway to which a plurality of the telephone terminals are to be connected and supplies drive power to the telephone terminals required for communication operation through the communication network. The telephone terminal includes: a main unit; an optional unit that performs an arbitrary additional communication function and detachably attached to the main unit; a distribution unit that distributes the drive power supplied through the communication network into a first channel and a second channel when a power of the telephone terminal is turned on; a first power supplying unit that supplies the first channel of the drive power to the main unit at a first timing; and a second power supplying unit that supplies the second channel of the drive power to the optional unit at a second timing shifted from the first timing. 
   According to a second aspect of the invention, there is provided a method for supplying a drive power to a telephone terminal connected via a communication network for transmitting a communication packet to a gateway to which a plurality of the telephone terminals are to be connected and supplies drive power to the telephone terminals required for communication operation through the communication network. The method includes: distributing the drive power supplied through the communication network into a first channel and a second channel when a power of the telephone terminal is turned on; supplying the first channel of the drive power to a main unit of the telephone terminal at a first timing; and supplying the second channel of the drive power to an optional unit of the telephone terminal at a second timing different from the first timing, the optional unit performing an arbitrary additional communication function and detachably attached to the main unit. 
   According to a third aspect of the invention, there is provided a telephone terminal connected via a communication network for transmitting a communication packet to a gateway to which a plurality of the telephone terminals are to be connected and supplies drive power to the telephone terminals required for communication operation through the communication network. The telephone terminal includes: a main unit; an optional unit that performs an arbitrary additional communication function and detachably attached to the main unit; a distribution means for distributing the drive power supplied through the communication network into a first channel and a second channel when a power of the telephone terminal is turned on; a first power supplying means for supplying the first channel of the drive power to the main unit at a first timing; and a second power supplying means for supplying the second channel of the drive power to the optional unit at a second timing shifted from the first timing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, 
       FIG. 1  is a drawing to show the schematic configuration of a network telephone system according to a first embodiment of the invention; 
       FIG. 2  is a block diagram to show the connection relationship between an IP telephone terminal and optional units in the first embodiment; 
       FIG. 3  is a circuit diagram of a switch and a timing generation circuit in the optional unit in the first embodiment; 
       FIG. 4  is a drawing to describe how rush current exceeds a stipulated value; 
       FIG. 5  is a drawing to describe how rush current is placed within a stipulated value in the first embodiment; 
       FIG. 6  is a block diagram to show the connection relationship between an IP telephone terminal and optional units according to a second embodiment of the invention; 
       FIG. 7  is a circuit diagram of an IP telephone terminal main unit according to a third embodiment of the invention; and 
       FIG. 8  is a circuit diagram of an optional unit according to the third embodiment. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Hereinafter, embodiments of the invention will be described by reference to the drawings in detail. 
   First Embodiment 
     FIG. 1  is a drawing to show the schematic configuration of a network telephone system according to a first embodiment of the invention. 
   The network telephone system includes a LAN  1 . A plurality of IP telephone terminals  2 - 1  to  2 - n  (where n is a natural number) are connected to the LAN  1 . A gateway (telephone switching equipment) BT is also connected to the LAN  1 . The gateway BT connects the IP telephone terminals  2 - 1  to  2 - n  connected to the LAN  1  and connects the LAN  1  and a public switched telephone network NW and has a conversion function of communication protocol and signal format between the LAN  1  and the public switched telephone network NW. Further, the gateway BT supplies drive power to the IP telephone terminals  2 - 1  to  2 - n  at the starting time. Drive power may be supplied to the IP telephone terminals  2 - 1  to  2 - n  from a switching hub  6  and a router  7  installed in the LAN  1 . 
   Optional units  3  to  5  to execute any desired additional function are connected to the IP telephone terminal  2 - 1 . 
     FIG. 2  is a block diagram to show the connection relationship between the IP telephone terminal  2 - 1  and the optional units  3  to  5 . In the figure, numeral  21  denotes an intra-unit load circuit for controlling the sections of the IP telephone terminal  2 - 1  and performing communication processing with the gateway BT through the LAN  1 . 
   In the figure, numerals  31 ,  41 , and  51  denote intra-unit load circuits of the optional units  3 ,  4 , and  5  for controlling the sections of the optional units  3 ,  4 , and  5  and performing communication processing with the gateway BT through the LAN  1  as drive power is fed from the gateway BT. 
   At the power on time (the time when the IP telephone terminal  2 - n  is turned on), the drive power fed from the gateway BT through the LAN  1  is distributed to an IP telephone terminal main unit  2  and the optional units  3  to  5  through a power distributor  22 . In the IP telephone terminal main unit  2 , the distributed drive power is selectively supplied to the intra-unit load circuit  21  by a switch  23 . On/off control of the switch  23  is performed by a timing generation circuit  24 . 
   On the other hand, in the optional unit  3 , the distributed drive power is selectively supplied to the intra-unit load circuit  31  by a switch  32 . On/off control of the switch  32  is performed at a switch timing different from the timing generation circuit  24  by a timing generation circuit  33 . 
   In the optional unit  4 , the distributed drive power is selectively supplied to the intra-unit load circuit  41  by a switch  42 . On/off control of the switch  42  is performed at a switch timing different from the timing generation circuit  24  by a timing generation circuit  43 . 
   Further, in the optional unit  5 , the distributed drive power is selectively supplied to the intra-unit load circuit  51  by a switch  52 . On/off control of the switch  52  is performed at a switch timing different from the timing generation circuit  24  by a timing generation circuit  53 . 
   The switch  32  and the timing generation circuit  33  in the optional unit  3  make up a circuit as shown in  FIG. 3 . 
   The switch  32  and the timing generation circuit  33  are made up of resistance elements R 1  and R 2 , a capacitor C 1 , and a transistor TR 1 . Output current of the power distributor  22  is supplied through the resistance element R 2  to the capacitor C 1  and is accumulated in the capacitor C 1 . The capacitor C 1  supplies the accumulated current to the transistor TR 1 . Then, the transistor TR 1  connects the path between the resistance element R 1  and the intra-unit load circuit  31 , whereby the output current of the power distributor  22  is supplied to the intra-unit load circuit  31 . After this, the intra-unit load circuit  31  is started. 
   The operation in the described configuration is as follows: 
   Assume that the IP telephone terminal main unit  2  and the optional units  3  to  5  are started at the same time, as shown in  FIG. 4 . Then, rush current becomes the total rush current of the IP telephone terminal main unit  2  and the optional units  3  to  5  and exceeds the limit of the stipulated peak value. 
   Then, in the embodiment, the power on/off timings are shifted in the timing generation circuits  24 ,  33 ,  43 , and  53  of the IP telephone terminal main unit  2  and the optional units  3  to  5 , thereby shifting the rush current occurrence timing. 
   In this case, in the IP telephone terminal main unit  2 , the time constant (R×C) of the timing generation circuit  24  is made small for early starting and in the optional units  3  to  5 , the time constants (R×C) of the timing generation circuits  33 ,  43 , and  53  are made large for late starting. 
   Then, the rush current occurs at different timings in the IP telephone terminal main unit  2  and the optional units  3  to  5  and does not exceed the stipulated peak value, as shown in  FIG. 5 . 
   As described above, in the first embodiment, the IP telephone terminal main unit  2  and the optional units  3  to  5  are provided with the switches  23 ,  32 ,  42 , and  52  and the timing generation circuits  24 ,  33 ,  43 , and  53  different in time constant and at the power on time, the supply timings of drive power to the intra-unit load circuits  21 ,  31 ,  41 , and  51  are shifted (or made different) among the IP telephone terminal main unit  2  and the optional units  3  to  5 , so that the total rush current does not exceed the value stipulated in POE. 
   Therefore, it is not necessary to provide a new signal line of a control signal required for controlling start of each of the optional units  3  to  5 , so that the number of pins for connecting the optional units  3  to  5  can be decreased, resulting in a decrease in the cost. 
   In the first embodiment described above, the switch  23 ,  32 ,  42 ,  52  and the timing generation circuit  24 ,  33 ,  43 ,  53  can be formed simply by using a transistor and an RC circuit, so that the configurations of the IP telephone terminal main unit  2  and the optional units  3  to  5  can be simplified and miniaturized. 
   Second Embodiment 
     FIG. 6  is a block diagram to show the connection relationship between an IP telephone terminal  2 - 1  and optional units  3  to  5  according to a second embodiment of the invention. Parts identical with those previously described with reference to  FIG. 2  are denoted by the same reference numerals in  FIG. 6  and will not be discussed again in detail. 
   That is, an IP telephone terminal main unit  2  is provided with a timing generation circuit  25  shared with the optional units  3  to  5 . The timing generation circuit  25  outputs output current supplied to intra-unit load circuits  21 ,  31 ,  41 , and  51  at different timings. 
   The optional unit  3  is provided with a transistor  34  and a resistance element  35 . When the output current is supplied from the timing generation circuit  25 , the transistor  34  supplies drive power to the intra-unit load circuit  31  through the resistance element  35 . 
   The optional unit  4  is provided with a transistor  44  and a resistance element  45 . When the output current is supplied from the timing generation circuit  25 , the transistor  44  supplies drive power to the intra-unit load circuit  41  through the resistance element  45 . 
   The optional unit  5  is provided with a transistor  54  and a resistance element  55 . When the output current is supplied from the timing generation circuit  25 , the transistor  54  supplies drive power to the intra-unit load circuit  51  through the resistance element  55 . 
   As described above, in the second embodiment, the timing generation circuit  25  installed in the IP telephone terminal main unit  2  is shared by the IP telephone terminal main unit  2  and the optional units  3  to  5  for supplying the drive power to the optional units  3  to  5  collectively. 
   Since the optional units  3  to  5  are provided with no timing generation circuit, the configuration is simplified and further it is made possible to decrease the number of parts for miniaturizing the unit and reducing the cost. 
   In the second embodiment, for example, when the optional unit  4  fails, it needs only to be replaced with a new optional unit. Further, in the second embodiment, if a connection connector of the timing generation circuit  25  has an unassigned pin, a new additional optional unit can be easily connected. 
   Third Embodiment 
     FIG. 7  is a circuit diagram of an IP telephone terminal main unit  2  according to a third embodiment of the invention. Parts identical with those previously described with reference to  FIG. 2  are denoted by the same reference numerals in  FIG. 7  and will not be discussed again in detail. 
   A voltage correction circuit  26  is provided at the preceding stage of a timing generation circuit  24 . The voltage correction circuit  26  includes a Zener diode  261  and a transistor  262 . When power is turned on, the Zener diode  261  turns on the transistor  262 . Accordingly, if power supply voltage fluctuates, the power supply start voltage to the timing generation circuit  24  can be stabilized. 
   The timing generation circuit  24  is provided with a timing generation control circuit  27 . The timing generation control circuit  27  includes a diode  271  and a resistance element  272 . The diode  271  releases charges of a capacitor  241  installed in the timing generation circuit  24  when an instantaneous power interruption occurs. Accordingly, when the power supply voltage is recovered to the normal voltage, the same start time as the usual start can be provided. 
   An electrolytic capacitor  28  is connected to an intra-unit load circuit  21 , thereby stabilizing the power supply. 
     FIG. 8  is a circuit diagram of an optional unit  3  to  5  according to the third embodiment of the invention. Parts identical with those previously described with reference to  FIG. 2  are denoted by the same reference numerals in  FIG. 8  and will not be discussed again in detail. Here, the optional unit  3  will be discussed as a representative. 
   A voltage correction circuit  66  is provided at the preceding stage of a timing generation circuit  33 . The voltage correction circuit  36  includes a Zener diode  361  and a transistor  362 . When power is turned on, the Zener diode  361  turns on the transistor  362 . Accordingly, if power supply voltage fluctuates, the power supply start voltage to the timing generation circuit  33  can be stabilized. 
   The timing generation circuit  33  is provided with a timing generation control circuit  37 . The timing generation control circuit  37  includes a diode  371  and a capacitative element  372 . The diode  371  releases charges of a capacitor  331  installed in the timing generation circuit  33  when an instantaneous power interruption occurs. Accordingly, when the power supply voltage is recovered to the normal voltage, the same start time as the usual start can be provided. 
   Further, an electrolytic capacitor  38  is connected to an intra-unit load circuit  31 , thereby stabilizing the power supply. 
   As described above, in the third embodiment, the IP telephone terminal main unit  2  and the optional unit  3  are provided with the voltage correction circuits  26  and  36  respectively for automatically correcting fluctuation of the voltage supplied to the timing generation circuits  24  and  33 , so that if power supply voltage fluctuates, the start time can be stabilized. 
   In the third embodiment, the IP telephone terminal main unit  2  and the optional unit  3  are provided with the timing generation control circuits  27  and  37  respectively, so that if the power to be supplied to the IP telephone terminal main unit  2  and the optional unit  3  drops instantaneously, drive power can be rapidly supplied when the power supply is recovered. 
   Miscellaneous Embodiments 
   The invention is not limited to the specific embodiments described above. 
   In the description of the embodiments, the drive power supply timing is shifted for each of the IP telephone terminal main unit and the optional units by way of example, but the invention is not limited to the mode. For example, the IP telephone terminal main unit may be divided into a plurality of units and drive power may be supplied to the plurality of units at different supply timings. In doing so, if the rush current fed into the IP telephone terminal main unit exceeds the stipulated value, the rush current can be decreased because the drive power is supplied to the plurality of units at different supply timings. A similar description also applies to the optional unit. 
   In the description of the embodiments, the IP telephone terminal is taken as an example, but a base station of a radio LAN or a personal computer or a server having a telephone function, for example, may be adopted. 
   It is to be understood that various modifications and changes of the system configuration and type, the configuration of the IP telephone terminal, the optional unit configuration and type, the circuit configuration of the timing generation circuit, etc., may be made without departing from the spirit and the scope of the invention. 
   As described above in detail, according to the embodiments, at the power on time, the drive power supply timing is shifted between the telephone terminal main unit and the optional unit, so that the total rush current does not exceed the value stipulated in POE. Therefore, it is not necessary to provide a new signal line of a control signal required for controlling start of the optional unit, so that the number of pins for connecting the optional unit can be decreased, resulting in a decrease in the cost. 
   According to the embodiments, the first and second delay circuits can be formed simply by using a transistor and an RC circuit, so that the configuration of the delay circuit can be simplified and miniaturized 
   According to the embodiments, fluctuation of the voltage supplied to the first and second delay circuits is automatically corrected, so that if power supply voltage fluctuates, the start time can be stabilized. 
   According to the embodiments, when the drive power to be supplied to the telephone terminal main unit and the optional unit drops instantaneously, drive power can be rapidly supplied when the power supply is recovered. 
   According to the embodiments, when the rush current fed into the telephone terminal main unit exceeds the stipulated value, the telephone terminal main unit is divided into a plurality of units and drive power is supplied to the plurality of units at different supply timings, so that the rush current can be decreased. 
   According to the embodiments, there is provided the telephone terminal of the network telephone system and the power supply method used with the telephone terminal for making it possible to place the rush current at the power on time within the stipulated value and moreover reduce the cost when a plurality of optional units are connected.