JP2000224252A - Digital line terminator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain effective heat dissipation and to make a terminator small. SOLUTION: A received signal via subscriber lines L1, L2 is separated into a transmission signal and DC feed power, the transmission signal is fed to a terminal side and a station supply termination circuit 8 consumes the DC feed power. Two transistor(TRs) 21, 22 of Darlington connection of the station supply termination circuit 8 configure a pseudo load circuit, which consumes the DC feed power. Resistors 23, 24 specifying the base potential of the 1st stage TR 21 and a capacitor 26 bypassing an AC component configure a power separation filter that separates the transmission signal and the DC feed power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ISDN (Inte
The present invention relates to a digital circuit terminating device (DSU) connected to a grated services digital network (Grated Services Digital Network) line, and particularly to a digital circuit terminating device that does not use station power.

[0002]

2. Description of the Related Art In recent years, ISDN has become widespread, and many inexpensive terminal devices incorporating a DSU have come to market. When the service of ISDN was started, the service provider provided the DSU exclusively, so the DSU was based on the premise that the station power supply was used. However, the DSU has been built into the terminal device. In general, the DSU is generally supplied with power from the power supply unit of the terminal itself without using station power supply. This form is called local power supply.

FIG. 2 is a circuit diagram showing a configuration of a conventional local power supply type DSU. The received signal received via the subscriber lines L1 and L2 is supplied to the power separation filter 2 via the overvoltage protection circuit 1 for absorbing surge voltage. The power separation filter 2 includes coils 11,
12 for separating a transmission signal and a DC supply current from a reception signal. The separated transmission signal is transferred to the terminal via the capacitor 3 and the transformer 4. On the other hand, the DC power supply current is supplied to the station power supply termination circuit 5. The station feed termination circuit 5 includes a resistor 13 and a diode 14,
1 W of power supplied from the central office is converted into heat and consumed. The switching circuit 6 includes a varistor 15 for voltage detection and a diode 16, and disconnects the loop switch 7 when the voltage applied by the exchange is equal to or less than a certain value for a test on the office side. The loop switch 7 closes the DC loop in response to a call request from the terminal, and at the end of the call,
It comprises a switch 17 for opening and a loop resistor 18.

[0004]

However, in such a conventional digital line terminating apparatus, there is a problem that heat is generated when 1 W of power is consumed by the resistance of the station feed terminating circuit. In addition, a large resistor is required for this heat dissipation, which hinders miniaturization of the device. Similarly, the power separation filter also requires a large coil, which is a factor that hinders miniaturization.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a digital line termination device capable of effectively dissipating heat and reducing the size of the device.

[0006]

A digital line terminal according to the present invention separates a transmission signal and a DC power supply from a reception signal received via a subscriber line, and transmits the transmission signal to a terminal. In the digital line termination device configured to supply and consume the DC power supply in the station power supply termination circuit, the station power supply termination circuit includes a plurality of Darlington-connected transistors, and converts the DC power supply to heat. A pseudo load circuit, and a power separation filter having a resistor for defining a base potential of a transistor at a first stage of the pseudo load circuit and a capacitor for bypassing an AC component and separating the transmission signal and the DC power supply. It is characterized by becoming.

According to the present invention, the station power supply termination circuit has a configuration in which the DC power is mainly consumed by the Darlington-connected last-stage transistor as a surface mount component, so that the heat radiation efficiency is good and the size of the component is small. Can be achieved. In addition, the elements that determine the impedance of the station feed termination circuit are composed of a resistor that defines the base potential of the first-stage transistor and a capacitor that bypasses the AC component, and these constitute a power separation filter. This eliminates the need for a large coil, which can also reduce the size of the device.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a digital line terminal (DS) according to an embodiment of the present invention.
FIG. 3 is a circuit diagram showing the configuration of U). This circuit differs from the conventional circuit shown in FIG. 2 in that the power separation filter 2 is not provided and the configuration of the station power supply termination circuit 8. In this circuit, a power separation filter function and a pseudo load function for power consumption are included in the station power supply termination circuit 8.

The received signal received via the subscriber lines L1 and L2 is input to the overvoltage protection circuit 1. The overvoltage protection circuit 1 is connected to the exchange, but protects the DSU from surge voltages including lightning from the subscriber lines L1 and L2. The switching circuit 6 turns off the varistor 15 at a certain value or less and disconnects the loop switch 7 by a voltage applied by the exchange for a test on the station side. The loop switch 7 closes a DC loop formed by a low-resistance loop resistor 18 capable of flowing a sufficient current in response to a call request from a terminal, and opens the loop at the end of a call.

The station power supply termination circuit 8 is composed mainly of two transistors 21 and 22 connected in Darlington. The base voltage of the first transistor 21 is determined by the resistors 23 and 24. A resistor 25 is connected to the emitter side of the second-stage transistor 22. The transistors 21 and 22 and the resistor 25 constitute a pseudo load circuit having a loop circuit of 812Ω or less that consumes a DC supply current. The resistance 2
3 and 24 are capacitors 2 connected in parallel with the resistor 24.
6 and the impedance of the station feed termination circuit 8 is determined,
A power separation filter that allows an AC component to pass to the terminal side and consumes only a DC supply current by a pseudo load circuit. The photocoupler 27 is provided to detect and display that a current is flowing through the station power supply termination circuit 8, and the diode 28 operates when a reverse polarity voltage is applied to the subscriber lines L1 and L2. This is provided in order to prevent the current from flowing backward.

Next, the operation of the thus configured digital line terminal will be described. Normally, when the terminal is not communicating, the subscriber lines L1 and L2 are in a state of being DC-separated. When there is a call request from the terminal side, the loop switch 7 closes the DC loop,
A start request is made to the exchange connected through the subscriber lines L1 and L2. In response to this start request, the exchange returns a response with the power supply polarity set to the reverse polarity. After this, the switch sends an equalizer training signal containing the framing information,
Thereafter, data transmission is performed with the terminal.

Here, regarding the relationship between the transmission signal and the station power supply, the ISDN adopts a two-wire direct current superposition type station power supply system, in which the transmission signal and the DC power are supplied on a two-wire metallic cable as a subscriber line. The feed current is superimposed. In the prior art, the transmission signal and the DC power are separated by the power separation filter 2, but in this embodiment, the station power supply termination circuit 8 is provided with a power separation filter function. The station power supply terminating circuit 8 has a configuration in which a circuit that has a high impedance with respect to AC is added to a circuit that consumes DC transmission power from the station, which is an original function, so that a transmission signal is not consumed by the station power supply terminating circuit 8. .

Looking at the power transmitted from the station, for example, a power supply of 39 mA is mostly composed of the transistor 22 and the resistor 25.
Flows through. Here, the base current of the transistor 21 is i
b, assuming that the current amplification factor is hfe1 and the current amplification factor of the transistor 22 is hfe2,

[0014]

## EQU1 ## ib × (hfe1 × hfe2) = 39 mA

## EQU1 ## That is, the transistors 21 and 22
Are connected in Darlington, the base current ib may be extremely small to flow a current of 39 mA. Further, assuming that the resistance values of the resistors 23 and 24 are R1 and R2, respectively, by increasing the voltage applied to the transistor 22 by adjusting the ratio of R1 and R2 and increasing the amount of heat generated on the transistor 22 side, The heat generated from the power consumed by the power supply termination circuit 8 can be mainly consumed by the transistor 22. The important point here is that the transistor 22
Since the component is a surface mount component, heat can be effectively dissipated through the pattern. For this reason, in this circuit, components do not increase in size due to heat radiation.

The DC resistance of the station power supply termination circuit 8 increases according to the resistance value of the sum of R1 and R2 if the parameters of the transistors 21, 22 and the resistance 25 are fixed. Resistance 2
By adding the capacitor 26 in parallel to the terminal 4, the impedance of the station power supply termination circuit 8 increases, and the transmission signal from the station is 320 Kbit / s AMI (it can be seen as a 160 KHz pseudo AC signal). Is the station feed termination circuit 8
Is not consumed and is sent to the terminal via the transformer 4. Therefore, the input / output impedance of the DSU is not affected. As for the AC signal, C is connected in parallel to R2, so that the AC component flows as ic. Therefore, the AC component acts as if R2 has become smaller, and ib also decreases, so that the impedance of the station feed termination circuit 8 increases. In this manner, the same circuit consumes DC power and does not allow an AC signal as a transmission signal to flow.
One operation can be realized.

[0017]

As described above, according to the present invention, the local power supply terminating circuit has a configuration in which the DC power is mainly consumed by the Darlington-connected last-stage transistor as a surface-mounted component. Efficient,
Parts can be reduced in size. In addition, the elements that determine the impedance of the station feed termination circuit are composed of a resistor that defines the base potential of the first-stage transistor and a capacitor that bypasses the AC component, and these constitute a power separation filter. Eliminates the need for large coils
This also has the effect that the size of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a digital line terminal according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional digital line termination device.

[Explanation of symbols]

1: overvoltage protection circuit, 2: power separation filter, 5, 8 ...
Station power supply termination circuit, 6 switching circuit, 7 loop filter.

Claims (1)

[Claims] 1. A transmission signal and a DC power supply are separated from a reception signal received via a subscriber line, and the transmission signal is supplied to a terminal side, and the DC power supply is consumed by a station power supply termination circuit. In the digital line terminating device, the station power supply terminating circuit is composed of a plurality of Darlington-connected transistors and converts the DC power supply into heat, and a first transistor of the pseudo load circuit. A digital line termination device comprising a resistor for defining a base potential and a capacitor for bypassing an AC component, and a power separation filter for separating the transmission signal and the DC power supply.