CN2101353U - Constant current supplying device for subscriber's line interface - Google Patents

Abstract

A constant current supplying device for subscriber line interface is connected in series with a direct-current speech power source balanced loop which is connected in parallel with an interface of an external circuit and an internal system of a programmed control simulate automatic exchange. The device is mainly served by a semiconductor triode Q5, and a feeding source of power-V< C > is earthed through R28 R29, and the base of Q5 is connected with the junction points of R28 R29, so as to form a bias circuit of Q5. The collector of Q5 is connected with the R wire of an external circuit by connecting in parallel with a direct current speech power source feeding balanced resistor R3, and the T wire of the external circuit is connected with an equivalent ground wire by connecting in parallel with a direct current speech power source feeding balanced resistor R2. An alternating current by-path large capacitance C is connected in parallel between the collector and the emitter resistance R27 of Q5, the merge end of the negative pole of capacitors C and R27, R28 is communicated to a power source-V< C >.

Description

Constant current supplying device for subscriber's line interface

The utility model relates to the current supply arrangement of telephonic communication system, the constant current power supply installation of particularly program control simulation dial exchange and button dial exchange system and subscriber line interface.

Special-purpose dial exchange provides working power to subscriber's line usually, to realize calling, the conversation of extension by dial exchange and another extension.Common discrete component user interface circuit, employing degree of balance hybrid coil converter preferably realizes the conversion of two or four lines, DC feedback voltage can be brought up to 48 volts even 60 volts, has the advantage that improves the telex network distance, but each converter occupies bigger space increases the whole volume of dial exchange, and reliability is also relatively poor; The recent Canadian MH88500 thick film element subscriber line interface circuit that occurs, adopt resistance-type to mix the networking, cancelled coil transformation device, the incorporate structure of each subscriber line interface circuit has been dwindled the volume of dial exchange greatly, but this subscriber line interface circuit for the zonule use, DC feedback voltage adopts 24 volts of low pressure usually, when the telephone subscriber to the circuit loop resistance of dial exchange be more than 700 ohm the time, loop current will be reduced to below 18 milliamperes, can not satisfy China Ministry of Posts and Telecommunications 2000 ohm of loop currents of regulation circuit loop resistance far away and be not less than 18 milliamperes requirement, thereby limit automatic telephone user's communications distance.If in order to satisfy the requirement of DR telephone telex network, when DC feedback voltage is brought up to 48 volts, because the feed loop does not have constant-current characteristics, when the near telephone subscriber line loop resistance of dial exchange is 200 ohm, loop current will reach 60 milliamperes, singly do not cause power loss in vain, burning of subscriber line circuit also taken place easily.Rich " Subscriber Line Interface Circuit " that logical Co., Ltd. of the open Japan of Chinese patent CN8610105317, adopt three pairs to interconnect to eliminate mirror image circuit vertical and the hot-tempered sound of power supply, by send with two systems between signal code be grounded with width of cloth reverse current and separate, complex structure, element is numerous, so that need semiconductor integrated circuit to go to finish, cause cost to increase.Chinese patent CN85108019 discloses Canadian Mitel Corp " constant current line circuit ", on digital dial exchange, adopt the differential amplifier detection to export the separation that direct current signal is controlled feed current and realized alternating current-direct current, influenced the coverage of DC feedback, the circuit more complicated is not used for analog automatic exchanger yet.

The purpose of this utility model is to adopt thick film element, makes the analog automatic exchanger subscriber line interface constant current power supply installation of a suitable DR telephone telex network.

Circuit theory of the present utility model as shown in Figure 1.

Of the present utility model being characterised in that: on the built-in system and external circuit interface parallel connection direct conversation power feed balanced loop of program control simulation dial exchange, seal in a subscriber line interface constant current power supply installation.This device is mainly by NPN transistor Q ₅Serve as feed power supply-V _CPass through R ₂₈R ₂₉Ground connection, Q ₅Base stage meets R ₂₈R ₂₉Tie point, form Q ₅Biasing circuit, Q ₅Collector electrode is by parallel connection direct conversation power feed balance resistance R ₃Insert the R line of external circuit, the T line of external circuit is by parallel connection direct conversation power feed balance resistance R ₂Connect equivalent ground wire, Q ₅Collector electrode and emitter resistance R ₂₇Between, one in parallel exchanges the big capacitor C of bypass, the negative pole of capacitor C, R ₂₇, R ₂₈And connect end and be communicated with power supply-V _C

The equivalent electric circuit of subscriber line interface constant current power supply installation, the parallel circuits that is actually an equivalent resistance R and big capacitor C is serially connected on the dc communicating power feed balanced loop, as shown in Figure 2.

For the AC signal in the automatic telephone communication, transmit as path through the big capacitor C that is connected in parallel on the equivalent resistance R, big capacitor C can be ignored to the loss of AC signal, makes interchange input and output impedance, the degree of balance, the transmission gain of dial exchange external circuit input and automatic telephone user interface still keep original characteristic.

For the output of the direct current in the automatic telephone communication, subscriber line interface constant current power supply installation can equivalence be a variable resistor R, and as automatic telephone user when the circuit loop resistance is big between dial exchange, Q flows through ₅The electric current of pipe is less, Q ₅Emitter current negative feedback resistor R ₂₇Negative feedback voltage also little, equivalent resistance R is also less, for example when Vc be 48 volts, when the circuit loop resistance is 2000 ohm, its electric current can reach 18 milliamperes of China Ministry of Posts and Telecommunications regulation, at this moment the equivalent resistance R of constant current line interface circuit is close to 0; When the automatic telephone user to circuit loop resistance between dial exchange hour, Q flows through ₅The electric current of pipe will be bigger, Q ₅Emitter current negative feedback resistor R ₂₇Negative feedback voltage also big, equivalent resistance R is also bigger, direct current is roughly maintained about 25 milliamperes, being the automatic telephone user changes in 0 to 2000 ohm of scope to circuit resistance between dial exchange, loop current is supplied with and is roughly kept identical, guaranteed automatic telephone user proper communication, also guaranteed to use from the near automatic telephone user security of dial exchange distance from the dial exchange distance.

The square frame principle that the utility model uses in program control simulation dial exchange device interior system as shown in Figure 3, circulation and ringing-current feed circuit 1 provide the working power of ringing-current and conversation for the automatic telephone user, relay drive circuit 2 is finished the control of ringing-current break-make between the automatic telephone user, speech circuit 3 guarantees that the two way audio signal transmits necessary signal level between the automatic telephone user, loop detection circuit 4 is in order to measure the DC and AC characteristics of automatic telephone system, and its practical circuit as shown in Figure 4.

Shown in Figure 1 is the balance resistance R that this device seals in external circuit interface parallel connection direct conversation power feed balanced loop ₃One side, at this moment Q ₅Adopt the NPN pipe; When this device seals in the balance resistance opposite side R2 in external circuit interface parallel connection direct conversation power feed balance resistance loop, Q ₅Use the PNP pipe instead, circuit as shown in Figure 5.

This device also can adopt field effect transistor to seal in balance resistance R ₂Or R ₃Loop one side is finished, and as shown in Figure 6, drain electrode d connects positive source, and source electrode s is by source resistance R _sThe energized negative pole also is communicated with grid g, drain electrode d, source electrode s, source resistance R _sBetween one in parallel exchange the big capacitor C of bypass.Source electrode s serial connection source resistance R _sMake field effect transistor be operated in the autobias state, continuous current output size depends primarily on source resistance R _s, less when automatic telephone user circuit loop resistance between dial exchange, make drain source voltage V _DsSurpass pinch-off voltage V _pThe time, drain current i _dThe value of reaching capacity is high-impedance state between the field effect transistor drain-source, and promptly equivalent resistance R increases, and loop current roughly maintains about 25 milliamperes; As automatic telephone user when the circuit loop resistance is big between dial exchange, drain source voltage is less, and field effect transistor keeps the following leakage current characteristic of pinch-off voltage, at this moment is low resistive state between drain-source, be that equivalent resistance R reduces, loop current roughly maintains about 18 milliamperes.

The utility model adds the constant current power supply circuits on the original MH88500 thick film circuit basis that produces.The big capacitor C of the interchange bypass of this device weldering and on 4,7 terminals of circuit board, as shown in Figure 7, than being easier to reach the purpose that increases automatic telephone telex network distance, compact conformation, volume is little, and large-scale production is made simple and easy, and scrap build is convenient.

Claims (4)

1, a kind of subscriber line interface constant current power supply installation, form by DC source, balance resistance, subscriber's line, it is characterized in that: on the built-in system and external circuit interface parallel connection direct conversation power feed balanced loop of program control analog automatic exchanger, seal in a subscriber line interface constant current power supply installation, this installs mainly by NPN transistor Q ₅Serve as feed power supply-V _cPass through R ₂₈R ₂₉Ground connection, Q ₅Base stage meets R ₂₈R ₂₉Tie point, form Q ₅Biasing circuit, Q ₅Collector electrode is by parallel connection direct conversation power feed balance electricity group R ₃Insert the R line of external circuit, the T line of external circuit is by parallel connection direct conversation power feed balance resistance R ₂Connect equivalent ground wire, Q ₅Collector electrode and emitter resistance R ₂₇Between, one in parallel exchanges the big capacitor C of bypass, the negative pole of capacitor C, R ₂₇, R ₂₈And connect end and be communicated with power supply-V _c

2, subscriber line interface constant current power supply installation according to claim 1 is characterized in that: the balance resistance opposite side R that seals in external circuit interface parallel connection direct conversation power feed balance resistance loop when this device ₂The time, Q ₅Use the PNP pipe instead.

3, subscriber line interface constant current power supply installation according to claim 1 is characterized in that: this device also can adopt field effect transistor to seal in balance resistance R ₂Or R ₃Loop one side is finished, and drain electrode d connects positive source, and source electrode s is by source resistance R _sThe energized negative pole also is communicated with grid g, drain electrode d, source electrode s, source resistance R _sBetween one in parallel exchange the big capacitor C of bypass.

4, subscriber line interface constant current power supply installation according to claim 1 is characterized in that: exchange the big capacitor C weldering of bypass and on 4,7 terminals of circuit board.

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