Data circuit-terminating equipment with power source device attached thereto

Abstract: A data circuit-terminating equipment with a power source device attached thereto comprising a data circuit-­ terminating equipment such as a modem and a power source device attached thereto for supplying a power extracted from a telephone circuit to the data circuit-terminating equip­ ment.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to the improvement of a data circuit-terminating equipment with a power source device attached thereto. Description of the Related Arts In US 4,415,774, a data circuit-terminating equipment is shown, which is connected to a telephone circuit and a data terminal equipment at least for demodulating a circuit signal which is input from said telephone circuit and supplying the demodulated signal to said data terminal equipment. Further, a power source device for extracting power from an offhook current, which flows on said telephone circuit at the time of offhook and for supplying said power to said data circuit-terminating equipment is provided. Said data circuit-terminating equipment includes a net control unit supplying power from the circuit signals and the offhook current, which flows on the telephone circuit to said power source device. Further, a modem is shown in this document. US 4,395,590 shows a line powered modem for coupling any apparatus to a telephone line and deriving its operating power for transmitting and receiving operations from the telephone line. In JP-A-59-188269, a power source circuit for a control circuit of a public telephone circuit is shown. In this power source circuit, the power is extracted from the telephone line only in an onhook status. A data communication system for connecting the data terminal equipments (hereinunder referred to as "DTE") of personal computers or the like through a telephone circuit and transmitting and receiving data between the DTEs has recently been rapidly spread. Modems (modulator/demodulator) 10 are attached to respective DTEs 12 in the data communication system schematically shown in Fig. 5, and are connected with each other by a telephone circuit 14. The modem 10 is a device for modulating the signal from the DTE 12 to a signal suitable for the telephone circuit 14 and demodulating the signal received from the telephone circuit 14 to a signal suitable for the DTE 12, and plays an important role in a data communication system having the structure such as that shown in Fig. 5. The reference numeral 16 represents an RS232C cable. The structure of the conventional modem 10 will be explained with reference to Fig. 6. As shown in Fig. 6, the modem 10 mainly includes a modulation and demodulation circuit 18 for modulating a digital signal supplied from the DTE 12 to a circuit signal, demodulating the received circuit signal to a digital signal of an RS232C type and supplying it to the DTE 12, and a net control unit 20 (hereinunder referred to as NCU) for controlling the connection between the modulation and demodulation circuit 18 and a telephone circuit 14. The modem 10 is further provided with a two-wire four-wire circuit 22, namely, a circuit for dividing the telephone circuit 14 connected to the terminals 11 and 12 of the NCU 20 into a transmitting circuit and a receiving circuit. A conventional data circuit-terminating equipment such as a modem has the above-described structure. This equipment is disadvantageous in that since a power source 24 exclusively for driving the equipment is necessary, the miniaturization of a data communication system is difficult. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to eliminate the above-described problems in the prior art and to provide a simple and small-sized equipment for constituting a data communication system. To achieve this aim, an equipment according to the present invention is provided with a power source device for extracting the power from the offhook current supplied from a telephone circuit and supplying the power from the power source device to a data circuit-terminating equipment such as a modem. According to the equipment of the present invention, since the power source device can obtain a power for driving a modem or the like by utilizing the power of an offhook current which is conventionally wasted by an NCU or the like, it is possible to reduce the size of the equipment and improve the efficiency thereof. It is preferable to provide a power converter circuit within the power source device so as to extract the power. The power converter circuit includes, for example, a DC-DC converter. As the DC-DC converter, either a self-excited converter or a separately-excited converter may be used. The power source device may also include a battery which outputs a power only at the time of onhook. In the case of using a modem as the data circuit-terminating equipment, the modem generally includes a modulation and demodulation circuit, a two-wire four-wire circuit and an NCU. The two-wire four-wire circuit receives and supplies a signal from and to the modulation and demodulation circuit by using a light receiving element and a light emitting element such as a photodiode. It is also preferable to provide the NCU with a light receiving element for detecting offhook. The NCU preferably includes a constant-current circuit, a shunt regulator, a smoothing circuit, etc. In the case of adopting a modem as the data circuit-terminating equipment, the DC-DC converter preferably supplies a power to both of the modulation and demodulation circuit and the two-wire four-wire circuit. The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows the structure of a data communication system adopting a first embodiment of the present invention, wherein a power source device 124 is connected to a telephone circuit 114 and a modem 110; Fig. 2 is a block diagram of the details of the modem 110 and the power source device 124 shown in Fig. 1; Fig. 3 is a circuit diagram of an NCU 120, a two-wire four-wire circuit 122 and a DC-DC converter 126; Fig. 4 is a circuit diagram of a power converter circuit 226, which is a separately-excited DC-DC converter, used in a second embodiment of the present invention; Fig. 5 shows the structure of a conventional data communication system; and Fig. 6 is a block diagram of the structure of the modem 10 in the conventional data communication system shown in Fig. 5. DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the equipment according to the present invention will be explained hereinunder with reference to the accompanying drawings. In Fig. 1, the power source device 124 is connected to a telephone circuit 114 to take in the power of the circuit, thereby stabilizing the voltage, and outputs a predetermined voltage which is electrically separated from that of the input side so as to supply a power to, for example, the modem 110. The modem 110 is connected to a DTE 112 through an RS232C cable 116 and is also connected to the telephone circuit 114 through the modem 110. In Fig. 2, the modem 110 is connected to the telephone circuit 114 (not shown) through the terminals 11 and 12. To the modem 110, a power converter circuit 126 including a DC-DC converter for converting the power of an offhook current is connected. An offhook current input from the terminals 11 and 12 is input to the power converter circuit 126 through an NCU 120. The NCU 120 supplies a signal current overlapping with the offhook current input from the terminals 11 and 12 to a two-wire four-wire circuit 122 and also supplies the residual current of the offhook current to the power converter circuit 126. The power converter circuit 126 converts the offhook current to a predetermined voltage level and supplies the thus-converted power to the two-wire four-wire circuit 122 and the modulation and demodulation circuit 118 as a driving power. A battery 128 supplies a power to the modulation and demodulation circuit 118 only when the circuit 114 is in the onhook state. It is therefore unnecessary to provide a self-excited power source exclusively for the modem 110 and it is possible to use the offhook current, which is the telephone circuit current, as a driving power source by converting the power thereof by the power converter circuit 126. As shown in Fig. 3, when the modem 110 is in the communication state, in other words, in the offhook state, a photocoupler PH₁ in the NCU 120 is turned on, and transistors Tr₁ and Tr₂ are turned on, whereby a constant current flows from the telephone circuit 114. The current output from the telephone circuit 114 at this time is the offhook current and the offhook current is output to the two-wire four-wire circuit 122. The offhook current is further converted to four-wire signals by operational amplifiers I c1-1 and I C1-2 . Since the operational amplifiers I c1-1 and I c1-2 are connected to the modulation and demodulation circuit 118 (not shown) through the photocouplers PH₂ and PH₃, respectively, in the state of being insulated therefrom, the signals are transmitted and received between the operational amplifiers I c1-1 and I c1-2 and the modulation and demodulation circuit 118 (not shown). The NCU 120 is provided with a constant-current circuit 130, a shunt regulator 132 and a smoothing circuit 134. The constant-current circuit 130 is composed of a transistor Tr₃, a resistance R₃ and a capacitor C₁. In the offhook state, since the impedance on the collector side of the transistor Tr₃ becomes high, it is possible to transmit and receive a signal to the modulation and demodulation circuit 118 (not shown) through the two-wire four-wire circuit 122 which is connected to the collector side in the same way as in the prior art. The shunt regulator 132, which is composed of a Zener diode ZD₁ and resistances R₄ and R₅, is provided in order to normally operate the power converter circuit 126 when the offhook current is slightly excessive. The smoothing circuit 134 is a circuit for smoothing the input current of the power converter circuit 126 and is composed of a coil L₁ and a capacitor C₂. Therefore, the NCU 120 in this embodiment of an equipment of the present invention in the offhook state supplies a signal current input from the telephone circuit 114 to the two-wire four-wire circuit 122 and also supplies the residual current of the offhook current to the power converter circuit 126. The power converter circuit 126 is composed of what is called a self-excited converter. As the output terminals of the power converter circuit 126, a GND terminal, a positive terminal V cc1 and a negative terminal VEE₁ for the two-wire four-wire circuit 122, and a terminal V cc2 for the modulation and demodulation circuit 118 are provided. Signals having the same voltage level when the GND is a zero point are output to the positive terminal V cc1 and the negative terminal VEE₁ for the two-wire four-wire circuit 122. Since the self-excited converter is a known circuit, detailed explanation thereof will be omitted but the structure and the operation thereof will be briefly explained in the following. To the base terminal of a transistor Tr 4, the positive terminal of the smoothing circuit 134 is connected through a resistor R 6, and the emitter terminal of the transistor Tr₄ is connected to the GND terminal. The collector terminal of the transistor Tr₄ is connected to the positive terminal of the smoothing circuit 134 through a coiled winding n₂ of a transformer T₁. The transformer T₁ further has a primary winding n₁, which is wound so as to have the same polarity as the primary winding n₂ and to be in series therewith. One end of the primary winding n₁ is connected to the cathode of a diode D₂ and the anode of the diode D₂ is connected to the GND terminal. The other end of the primary winding n₁ is connected to the base terminal of the transistor Tr₄ through a capacitor C 3˙ The primary circuit of the transformer T₁ constitutes the self-excited oscillator, as described above. The oscillating operation will now be explained briefly. When a predetermined voltage is applied from the positive terminal of the smoothing circuit 134, a base current is supplied to the transistor Tr₄ through the resistance R₆, whereby the transistor Tr₄ is turned on and is supplied a collector current from the positive terminal of the smoothing circuit 134 through the primary winding n₂. At the same time, a charging current is supplied from the positive terminal of the smoothing circuit 134 to the capacitor C₃ through the primary winding n₁. The charging current acts in the direction of increasing the conductivity of the transistor Tr₄, and the transistor Tr₄ increases the collector current. However, the current flowing through the winding n₁ becomes extinct in a comparatively short time because the capacity of the capacitor C₃ is small and, as a result, the base current cannot catch up with the increase in the collector current of the transistor Tr₄, and when the collector current exceeds the necessary amplified collector current based on the base current, as represented by the following formula (1), the transistor Tr₄ is rapidly inverted to the off state. I c > I B · hf e When the transistor Tr₄ is in the off state, the energy stored while the transistor Tr₄ is in the on state flows from the winding n₁ toward the capacitor C₂, thereby retaining the off period of the transistor Tr₄. When the stored energy has been released, the base current of the transistor Tr₄ is again supplied through the resistance R₁ and the circuit continues self-excited oscillation. Therefore, the self-excited oscillation frequency is determined by the circuit constant and the load. By the self-excited oscillation, a current flows in the reverse direction on secondary windings n₃ and n₄ and charges capacitors C₄, C₅ and C₆ by diodes D₃, D₄ and D₅, respectively. Consequently, it is possible to output positive and negative voltages of the same level to the positive and the negative terminals V CC1 and VEE₁, as compared with the GND level respectively, thereby supplying a power to the two-wire four-wire circuit 122. A predetermined voltage level is output to the terminal V CC2 and supply of a power to the modulation and demodulation circuit 118 is also enabled. In this way, it is possible to output positive and negative voltages of 5 to 10 V from the power converter circuit 126, which is a DC-DC converter, in accordance with the offhook current signal of 48 V, for example, which is output from the telephone circuit 114 in the offhook state. In this embodiment, the shunt regulator 132 can be dispensed with, and the smoothing circuit 134 may use a transformer. Fig. 4 shows the structure of a second embodiment of an equipment according to the present invention, in particular, the structure of a power converter circuit 226. The power converter circuit 226 shown in Fig. 4 is a separately-excited DC-DC converter including a self-excited oscillator 228. The operation of the power converter circuit 226 is as follows. A transistor Tr₁₄ is first switched by a synchronous signal output from the self-excited oscillator 228. When the transistor Tr₁₄ is on, a current is supplied from the smoothing circuit 134 to the collector of the transistor Tr₁₄ through a primary winding n₁₂ of a transformer T₁₁. On the other hand, when the transistor Tr₁₄ is off, a capacitor C₁₉ is charged by the counter electromotive force produced on a primary winding n₁₁. As a result of these operations, a voltage is induced on a secondary winding n₁₃, and the voltage is rectified by a diode D₁₃ to be output to the outside, e.g., a two-wire four wire circuit and a modulation demodulation circuit (not shown). In Fig. 4, the winding of the transformer T₁₁ is a forward type coil directed toward the converter, but it may be a flyback type coil. As described above, according to the present invention, since the offhook current input from the telephone circuit through the NCU is supplied to the data circuit-terminating equipment after the power of the current is converted, no device for self power supply is necessary, thereby enabling the realization a small-sized data communication system. While there has been described what are at present considered to be preferred embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the scope of the invention.

Claims: A data circuit-terminating equipment with a power source device attached thereto comprising a) a data circuit-terminating equipment (110) which is connected to a telephone circuit (11, 12, 114) and a data terminal equipment (112) at least for demodulating a circuit signal which is input from said telephone circuit (11, 12, 114) and supplying the demodulated signal to said data terminal equipment (112), b) a power source device (124) for extracting power from an offhook current which flows on said telephone circuit (11, 12, 114) at the time of offhook and supplying said power to said data circuit-terminating equipment (110), said data circuit-terminating equipment (110) including c) a net control unit (120) for supplying power from the circuit signals in the offhook current which flows on the telephone circuit (11, 12, 114) to said power source device (124), and d) a modulation and demodulation circuit (118) for modulating a signal supplied from said data terminal equipment (112) and demodulating a circuit signal supplied from said telephone circuit (11, 12, 114), said data circuit-terminating equipment (110) being characterized by e) a two-wire four-wire circuit (122) connected to said modulation and demodulation circuit (118) which is divided into a transmitting circuit and a receiving circuit, and wherein said net control unit (120) includes f1) a detecting element for detecting the offhook state, f2) a constant current circuit (130) for keeping an offhook current in the form of a constant current; and f3) a smoothing circuit (134) for smoothing said offhook current output from said constant current circuit (130), which is composed of a coil (L₁) and capacitor (C₂); and wherein said power source device (124) includes g) a power converter circuit (126) for converting said offhook current output from said smoothing circuit (134) to said power. A data circuit-terminating equipment with a power source device attached thereto according to claim 1, wherein said power source device includes a battery for supplying a battery power to said data circuit-terminating equipment only at the time of onhook. A data circuit-terminating equipment with a power source device attached thereto according to claim 1, wherein said power converter circuit includes a DC-DC converter for converting said offhook current to a DC current having a different value. A data circuit-terminating equipment with a power source device attached thereto according to claim 3, wherein said DC-DC converter is a self-excited converter. A data circuit-terminating equipment with a power source device attached thereto according to claim 1, wherein said data circuit-terminating equipment is a modem and said net control circuit includes a means for controlling the connection between said modulation and demodulation circuit and said telephone circuit. A data circuit-terminating equipment with a power source device attached thereto according to claim 5, wherein said two-wire four-wire circuit includes: a light receiving element for receiving a signal in the form of light transmitted from said modulation and demodulation circuit; and a light emitting element for emitting a signal in the form of light to said modulation and demodulation circuit. A data circuit-terminating equipment with a power source device attached thereto according to claim 5, wherein said net control unit includes a shunt regulator for suppressing the excess of said offhook current output from said constant-current circuit in the form of a constant current. A data circuit-terminating equipment with a power source device attached thereto according to claim 7, wherein said net control unit includes a smoothing circuit for smoothing said offhook current output from said shunt requlator in the form of a constant current. A data circuit-terminating equipment with a power source device attached thereto, according to claim 1, wherein said net control unit includes a transistor circuit which is turned on when said detecting element detects the offhook state, and wherein said two-wire four-wire circuit includes a light receiving element for receiving a signal in the form of light transmitted from said modulation and demodulation circuit, and a light emitting element for emitting a signal in the form of light to said modulation and demodulation circuit; and wherein said data circuit-terminating equipment is a modem which is connected to said telephone circuit and said data terminal equipment so as to demodulate said circuit signal input from said telephone circuit and output said signal to said data terminal equipment, and modulate a signal input from said data terminal equipment and supply said signal to said telephone circuit; and wherein said power source device extracts a power from an offhook current which flows on said telephone circuit at the time of offhook when said circuit signals overlap each other and supplies said power to said data circuit-terminating equipment. A data circuit-terminating equipment with a power source device attached thereto according to claim 9, wherein said power source device includes a battery for supplying a power to said circuit-terminating equipment only at the time of onhook. A data circuit-terminating equipment with a power source device attached thereto according to claim 9, wherein said power source device includes a DC-DC converter for converting said offhook current to a DC current having a different value. A data circuit-terminating equipment with a power source device attached thereto according to claim 11, wherein said DC-DC converter is a self-excited converter. A data circuit-terminating equipment with a power source device attached thereto according to claim 11, wherein said DC-DC converter outputs two kinds of currents which are to be supplied to said modulation and demodulation circuit and said two-wire four-wire circuit, respectively. A data circuit-terminating equipment with a power source device attached thereto according to claim 12, wherein said power source device further includes a battery for supplying a power to said data circuit-terminating equipment only at the time of onhook, and said DC-DC converter outputs two kinds of currents which are to be supplied to said modulation and demodulation circuit and said two-wire four-wire circuit, respectively.

Inventors: IKEDA TAKESHI, KURODA TAKASHI, SAKURAGI SATOSHI, IKEDA, TAKESHI, KURODA, TAKASHI, SAKURAGI, SATOSHI
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1989
Main classification: H04M19
IPC codes: H04M11, H04M19