JPH06141355A - Subscriber circuit - Google Patents

Abstract

PURPOSE:To obtain a circuit not requiring connection to a common device such as a 16Hz generator or a test equipment or the like with a small circuit scale and used for an intra-station termination circuit used for the ISDN service by realizing a programmable feeding circuit having a microprocessor controlling the polarity and a level of a voltage generated by a power supply circuit. CONSTITUTION:A current measurement circuit MI of a subscriber circuit 10 is a circuit to measure a current flowing through subscriber lines A, B, a voltage measurement circuit MV measures a voltage between terminals Ta and Tb to measure the voltage between the subscriber lines A, B. A power supply circuit POW sets an output of itself to be positive or negative based on a positive/negative control input and a level control input to control its voltage level. A microprocessor muP controls the polarity and the output voltage level of the power supply circuit POW to obtain an object voltage current characteristic by a program logic based on the measured current and voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber circuit in a digital exchange.

[0002]

2. Description of the Related Art In a digital exchange, a subscriber circuit or an intra-station termination circuit is used for each subscriber line, and these circuits function as a digital line termination circuit (DSU) for a telephone or ISDN and a power supply function to a terminal. Have.

The conventional subscriber circuit is described in the document "D70 Subscriber Circuit Configuration of Digital Switch", Research Report, No. 33.
Volume 7 (1984), and the conventional intra-station termination circuit for ISDN is described in the document "Ping-Pong Transmission System Housing Design" Research Practical Report, Vol. 33, No. 9 (198).
4).

In addition, as a power supply method in the conventional subscriber circuit, modes such as constant voltage constant resistance power supply of normal polarity and reverse polarity, constant voltage power supply, and pure resistance power supply are adopted. Further, in addition to the power feeding circuit, the subscriber circuit is
It has a function of sending a 6 Hz ringing signal and a howler signal to the telephone and also has a function of detecting on-hook and off-hook of the telephone.

FIG. 4 is a diagram showing a conventional subscriber circuit 12.

In FIG. 4, the power supply circuit BS2 individually has a constant voltage constant resistance power supply circuit, a constant voltage power supply circuit, a pure resistance power supply circuit, and a monitoring circuit, and these circuits are mainly composed of analog amplifiers. ing. The power supply circuit BS2 supplies power to the subscriber lines A and B by controlling the power transistors TR1 and TR2, and also monitors the current flowing through the subscriber lines A and B. The power supply modes are realized by the control circuit CONT controlling the power supply circuit BS2.

The relays n1, n2, r1, r2 are relays for controlling the power supply current flowing through the subscriber lines A, B. When the relays n1, n2 are on and the relays r1, r2 are off, the B line → A current is passed through the subscriber lines A and B in the direction of line A (normal power feeding is performed). On the contrary, when the relays n1 and n2 are off and the relays r1 and r2 are on, a current is passed through the subscriber lines A and B in the direction of the A line → B line (reverse power feeding is performed).

The ringer switch RSW rings the bell of the telephone. When the relays n1, n2, r1 and r2 are turned off and the ringer switch RSW is turned on, the output of the 16 Hz generator existing in common in the exchanges is switched to the ringer switch. R
It is output to the subscriber line A via SW, and the DC power supply -48V is output to the subscriber line B via the ringer switch RSW and sent to the telephone.

The ring trip circuit RTC is a circuit for detecting off-hook when an incoming call arrives, and when the transmitter side lifts (off-hook) the handset of the telephone, the subscriber lines A and B are connected.
Since a short circuit occurs between them, a direct current of -48V flows, the ring trip circuit RTC detects this current, and the control circuit CONT is informed that it is in the off-hook state. The switch LTSW is a switch for testing the subscriber lines A and B, and is placed in common in the exchange via the LT terminal by turning off the relays n1, n2, r1 and r2 and turning on the line test switch LTSW. Subscriber lines A and B are connected to the tester, and the resistance value and capacitance value of the subscriber line to the terminal are measured.

The switch NTSW is a network test switch for testing the power supply circuit BS2 and the codec Codec, connects a circuit equivalent to a telephone to the NT terminal, turns on the switch NTSW, and relays n1, n2, r1,
Turn off r2, feed circuit BS2, codec Code
Perform test c. The relays n1, n2, r1, r
2. In some cases, the relays such as the switch LTSW and the switch NTSW are made of high voltage semiconductor technology and optical MOS switch. Reference characters Ta and Tb indicate terminals.

FIG. 5 is a circuit diagram showing a conventional intra-station termination circuit 13.

In FIG. 5, the power supply circuit BS3 is composed of a constant current power supply circuit and a loop detection and monitoring circuit. The relays n1, n2, r1, and r2 are relays that control the direction of the power supply current, and are used in the intra-station termination circuit 13 for activation to the terminal when a call arrives.

The switch LTSW1 is a line test switch for testing the subscriber lines A and B similarly to the switch LTSW in the subscriber circuit 12, and includes relays n1 and n2.
By turning off r1 and r2 and turning on the switch LTSW1, the subscriber lines A and B are connected to the tester placed in common with the exchange via the LT terminal, and the resistance values and capacitances of the subscriber lines A and B are connected. The value is measured.

Similar to the switch NTSW in the subscriber circuit 12, the switch NTSW1 is a switch for testing the power supply circuit BS3, the equalization circuit EQ, and the buffer circuit Buff on the terminal termination circuit side, and is a digital line termination placed on the terminal side. Connect the circuit (DSU) and the circuit corresponding to the terminal to the NT terminal, turn on the switch NTSW1, and turn on the relay n.
The test is performed by turning off 1, n2, r1 and r2.

The equalizer circuit EQ is for equalizing the line of a digital signal, and the buffer Buff uses a ping-pong transmission system for transmitting up-link and down-link information in a time-sharing manner so that necessary information can be stored. It is composed of a buffer circuit and the like. The power supply circuit BS3, each switch circuit, the equalization circuit EQ, and the like are controlled by the control circuit CONT.

When a call is made from the terminal side (digital line termination circuit (DSU) connected to the terminal), normally,
Since the relays n1 and n2 are on and the relays r1 and r2 are off, the loop closure of the line on the DSU side causes
A current flows, the loop detection circuit in the current supply circuit operates, and a call is detected. After that, the digital training pattern is transmitted and received between the DSU and the intra-station termination circuit 13, the equalization circuit EQ is adjusted, and the communication phase is entered.

On the contrary, when an incoming call is made to the terminal from the exchange side, the relays n1 and n2 are turned on and the relays r1 and r2 are turned off, and then the relays n1 and n2 are turned off and the relays r1 and r2 are turned on. By turning on, the DSU side detects that the current flows in the opposite direction, the incoming call from the exchange side is detected, and the terminal power is turned on. After that, in the same procedure as the transmission, first, the transmission and reception of the digital training pattern are performed between the DSU and the intra-station termination circuit 13, the equalization circuit EQ is adjusted, and the communication phase is entered. Here, as in the case of the subscriber circuit 12, the relays n1, n
2, r1, r2, switch LTSW, switch NTSW
In some cases, etc. are made by high voltage semiconductor technology and optical MOS switch. It should be noted that in the intra-station termination circuit 13, 39 mA
The constant-current power supply method is adopted, which is different from the subscriber circuit 12 in this respect.

As described above, the conventional intra-station termination circuit 13 has a problem that the circuit scale is large because a switch is prepared for each function, and wiring work for connecting to a common device such as a tester is required. There is a problem that it is complicated.

[0019]

In the conventional subscriber circuit described above, it is necessary to provide various kinds of power supply circuits, a ringer sending switch circuit, and a normal power supply / reverse power supply switching switch circuit, so that the circuit scale is large. There is a problem that it is large, and since it is connected to a common device such as a 16 Hz power generator and a tester, the wiring work for connecting to this common device is complicated.

Further, although the power supply circuit of the subscriber circuit and the power supply circuit of the ISDN intra-station termination circuit are manufactured by the same technology, they are realized as separate circuits, which causes a problem of high cost. is there.

The present invention provides a subscriber circuit that does not require connection with a common device such as a 16 Hz generator and a tester, has a small circuit scale, and can be used as an intra-station termination circuit used for ISDN service. That is the purpose.

[0022]

SUMMARY OF THE INVENTION According to the present invention, a measuring means for measuring a value of a voltage between terminals connected to a subscriber line and a value of a current flowing in the subscriber line, and a positive and a negative voltage are provided. A power supply circuit that is generated and is capable of controlling this voltage level; and a microprocessor that controls the positive, negative, and level of the voltage that the power supply circuit generates, based on the measured current value and voltage value of the subscriber line. And realizes a desired power supply characteristic by the program logic of the microprocessor.

[0023]

According to the present invention, since various power supply circuits required for telephone service and ISDN service are realized by programmable power supply circuits, connection with a common device such as a 16 Hz generator and a tester is not required, Circuit scale is small and I
It can also be used as an intra-station termination circuit used for SDN service.

[0024]

1 is a diagram showing a subscriber circuit 10 according to a first embodiment of the present invention.

The output terminals Ta and Tb of the subscriber circuit 10 are
Terminals connected to subscriber lines A and B, and subscriber lines A and B
The subscriber circuit 10 is connected to the terminal via B. The current measuring circuit MI is a circuit that measures the value of the current flowing through the subscriber lines A and B, and the voltage measuring circuit MV is the terminals Ta and Tb.
Is a circuit for measuring the voltage between the subscriber lines A and B by measuring the value of the voltage between them.
Depending on the negative control input and the level control input, the power supply circuit PO
It is a circuit in which the output of W has a positive polarity or a negative polarity and the voltage level thereof can be controlled.

The microprocessor μP controls the positive / negative polarity and the output voltage level of the power supply circuit POW so that the target voltage and current characteristics are obtained based on the measured current value and voltage value. , Is controlled by the main processor of the exchange (not shown). The signal processing circuit SP is a circuit that performs A / D conversion, D / A conversion of a voice signal, line equalization and echo canceling for a digital signal, and is connected to a speech path of an exchange.

The control line C is a line connecting the microprocessor μP and the signal processing circuit SP. If high speed is required for the microprocessor μP, a digital signal processor may be used as the microprocessor μP.

Further, the current measuring circuit MI and the voltage measuring circuit M
V is an example of measuring means for measuring the value of the voltage between the terminals connected to the subscriber line and the value of the current flowing in the subscriber line, and the power supply circuit POW generates positive and negative voltages. However, this is an example of a power supply circuit capable of controlling this voltage level. The microprocessor μP is an example of a microprocessor that controls the positive, negative, and level of the voltage generated by the power supply circuit based on the measured current value and voltage value. In the above embodiment, the microprocessor μP is used. The desired logic of power supply is realized by the program logic.

FIG. 2 is a circuit diagram showing the above embodiment more specifically, and is a diagram showing an example in which a DC-DC converter is used as the power supply circuit POW. The same members are designated by the same reference numerals.

The power supply circuit BS is composed of a power supply circuit POW, measuring means having a current measuring circuit MI and a voltage measuring circuit MV, and a filter Fil.

The power supply circuit POW is composed of a DC-DC converter. This DC-DC converter has a transformer T1, which has a first primary winding P1.
It has W1, a second primary winding PW2, and a secondary winding SW connected to the subscriber line and connected to the output terminal of the power supply circuit POW.

The DC-DC converter further includes a power source E, a first switch S1 for controlling the power supply of the power source E to the first primary winding PW1, and a second primary winding PW2. A second switch S2 for controlling the power supply of the power source E of
A first diode D1 connected between one terminal of the secondary winding SW and one output terminal of the power supply circuit POW;
A second diode D2 connected between the other terminal of the next winding SW and the other output terminal of the power supply circuit POW, and having a polarity opposite to that of the first diode D1, and a first diode D.
It has a third switch S3 connected in parallel to 1, a fourth switch S4 connected in parallel to a second diode D2, and a capacitor C1.

The diodes D1 and D2 are examples of polarity control diodes connected in series to the secondary winding, and cooperate with the switches S3 and S4 to control the polarity of the output of the power supply circuit POW. . That is, the switch S3 is turned off,
When the switch S4 is turned on, the diode D1 becomes effective and a current flows in the conduction direction of the diode D1. On the contrary, when the switch S3 is turned on and the switch S4 is turned off, the diode D2 becomes effective and a current flows in the conduction direction of the diode D2.

The microprocessor μP has input terminals Ii and Vi for inputting measurement signals from the current measuring circuit MI and the voltage measuring circuit MV, respectively, and switches S1, S2, S3, and
Control terminals S for outputting control signals for controlling S4 respectively
1o, S2o, S3o, S4o. Further, the microprocessor μP periodically turns on and off the first switch S1, turns off the switch S3 and turns on the switch S4, thereby generating a positive voltage across the capacitor C1 and causing the second switch By periodically turning on and off S2, turning on the switch S3 and turning off the switch S4, a negative voltage is generated across the capacitor C1, and the first switch S1 or the second switch S2 is turned on. , OFF cycle is changed to change the output voltage level of the power supply circuit POW. The microprocessor μP is connected to the main processor of the exchange through a control line.

Further, the power supply circuit BS is provided with an AC signal inflow prevention filter Fil.
Is to prevent a voice signal or a digital signal from flowing into the power supply circuit BS.

The signal processing circuit SP has a signal processing section SP1 including an analog signal processing circuit and a digital signal processing circuit, a DC cut capacitor C2, and a signal transformer T2. The signal processing unit SP1 is connected to the call path via the call line.

Next, the operation of the above embodiment will be described.

First, when the microprocessor μP controls the switches S1, S2, S3 and S4 as follows, a positive voltage is generated across the capacitor C1. That is, by turning off the switch S3, the diode D
When the switch S1 is periodically connected with the diode D2 short-circuited by enabling 1 and turning on the switch S4, an AC voltage is generated at both ends of the secondary winding SW. Since only the positive component passes through diode D1, a positive voltage develops across capacitor C1. In this case, switch S1 is turned on /
By changing the off-time ratio, the voltage value across the capacitor C1 can be raised or lowered.

When the microprocessor μP controls the switches S1, S2, S3 and S4 as follows, a negative voltage is generated across the capacitor C1. That is, the diode D is turned on by turning on the switch S3.
When the switch S2 is periodically connected in a state in which the diode D2 is enabled by short-circuiting 1 and turning off the switch S4, an AC voltage is generated across the secondary winding SW. Since only the negative component passes through the diode D2, a negative voltage is generated across the capacitor C1. Also in this case, the voltage value across the capacitor C1 can be raised or lowered by changing the on / off time ratio of the switch S2.

With the above arrangement, a positive or negative voltage can be generated between the subscriber lines A and B.

In the on-hook or off-hook state, the subscriber lines A and B form a loop through the terminals, and at this time, a loop current flows through the subscriber lines A and B. This loop current is measured by the current measuring circuit MI. The voltage between the subscriber lines A and B is measured by the voltage measuring circuit MV, and the measured value is input to the microprocessor μP via the terminals Ii and Vi. The voltage measuring circuit MV may be provided on the subscriber line A, B side of the current measuring circuit MI.

Further, the filter Fil prevents the voice signal or the digital signal from flowing into the power feeding circuit BS,
A voice signal or a digital signal is input to the signal processing unit SP1 through the DC cut capacitor C2, and if it is a voice signal, it is AD converted and converted into a digital signal. If it is a digital signal, the digital signal is converted by an echo canceller or an equalization filter. Regenerated and molded. In addition,
The processing method of the signal processing circuit SP is a microprocessor μP.
Controlled by.

In the above embodiment, various power feeding methods are realized by controlling the microprocessor μP.
A specific example is shown below.

Constant Voltage Constant Resistance Power Supply In order to perform constant voltage constant resistance power supply with normal polarity, power supply may be performed so as to satisfy the following expression (1). I _L = 48 (V) / {R _L +440 (Ω)} (1) In addition, I _L is a target loop current value, and R _L is composed of a terminal and subscriber lines A and B. It is the sum of the resistance of the loop.

In order to realize this constant voltage / constant resistance power supply, the current flowing through the subscriber lines A and B and the voltage between the subscriber lines A and B are measured and input to the microprocessor μP.
Assuming that the measured current value is I _m and the measured voltage value is V _m , in the microprocessor μP, based on the current value I _m and the voltage value V _m , the sum _{RL of the} loop resistance is calculated by _RL = V _m / I _m .
Is calculated, and the target loop current value I _L is calculated by the equation (1).

If the loop current value I _L is the measured current value I _m
If more greater, the measured current value I _m is, since it does not reach the loop current value I _L to be the target, by controlling the on / off time ratio of the switch S1, the voltage across the capacitor C1 Increase by + ΔE1. At this time, the diode D1 is enabled (switch S3 is turned off), and the diode D2 is short-circuited (switch S4 is turned on).
Conversely, when the loop current I _L is smaller than the measured current value I _m, since the loop current to be a target I _L value measured current I _m in comparison with a large, the on / off time ratio of the switch S1 The voltage across the capacitor C1 is controlled to decrease by ΔE1.

By such control, the measured current value I _m is brought closer to the target loop current value I _L. Finally, a normal polarity power supply circuit having a power supply characteristic satisfying the equation (1) can be realized.

In the same manner as described above, in order to perform constant voltage constant resistance power supply with reverse polarity, power supply may be performed so as to satisfy the following expression (2). I _L = -48 (V) / { _RL +440 (Ω)} (2) In this case, the diode D2 is enabled (switch S4 is turned off) and the diode D1 is short-circuited (switch S3 is turned on). , Controlling the on / off time ratio of switch S2,
When the loop current value I _L is larger than the measured current value I _m , the voltage across the capacitor C1 is increased by ΔE1, and when the loop current value I _L is smaller than the measured current value I _m , the voltage across the capacitor C1 is ΔE1. Just lower it.

[0049] When performing a constant current power supply of 39mA required in the case of the constant current power supply for ISDN station terminating circuit in normal polarity, as _{I L = 39 (mA) ......} (3), to enable the diode D1 (switch S3 is turned off), the diode D2 is short-circuited (the switch S4 is turned on), and when the loop current value I _L is larger than the measured current value I _m , the voltage across the capacitor C1 is increased by ΔE1 and the loop current value I _{When L} is smaller than the measured current value I _m , the on / off time ratio of the switch S1 is controlled so that the voltage across the capacitor C1 is lowered by ΔE1.

On the other hand, if you run a constant current power supply 39mA in reverse polarity, as _{I L = -39 (mA) ......} (4), to enable the diode D2 (turning off the switch S4), short-circuits the diode D1 and (turns on the switch S3), when the loop current I _L is greater than the measured current value I _m is the voltage across the capacitor C1 △ E1 only raised, smaller than the loop current I _L is the measured current value I _m At times, the on / off time ratio of the switch S2 is controlled so that the voltage across the capacitor C1 is lowered by ΔE1.

Constant-voltage power supply When the constant-voltage value is 48 V and constant-voltage power is supplied with normal polarity, V _L = 48 V (5), the diode D1 is enabled (switch S3 is turned off), and the diode D2 is short-circuited. and (turns on the switch S4), when the voltage value V _L of the target is greater than the measured voltage value V _m is the voltage across the capacitor C1 △ E2 only raised, the voltage value and the target V _L is the measured voltage value V When it is smaller than _m , the on / off time ratio of the switch S1 is controlled so that the voltage across the capacitor C1 is lowered by ΔE2.

On the other hand, when the constant voltage value is 48V and the constant voltage is fed in the reverse polarity, _VL = -48V (6), and similarly the diode D1 is short-circuited (switch S
3 is turned on) and the diode D2 is enabled (switch S
4 is turned off), and the target voltage value V _L is the measured voltage value V _m
If it is larger than, the voltage across the capacitor C1 is
The target voltage value V _L is increased by E2 and the target voltage value V _L is measured voltage value I _m.
Is smaller than, the voltage across the capacitor C1 is
The on / off time ratio of the switch S2 is controlled so that it is lowered by E2.

Sending Ringing Signal The ringing signal sent to the telephone is 16 V of 75 Vrms.
It is obtained by superimposing a direct current of -48V on z. In this case, V _L = 75 × 2 ^1/2 × Sin (2π16t) −48 (V) (7), and when the target voltage value V _L is larger than the measured voltage value V _m , the capacitor C1 When the voltage between both ends is increased by ΔE2 and the target voltage value V _L is smaller than the measured voltage value V _m , the on / off time ratio of the switch S1 is controlled so as to decrease the voltage between both ends of the capacitor C1 by ΔE2. . When _VL is positive, diode D1 is enabled (switch S3 is off), diode D2 is shorted (switch S4 is on), and the on / off time ratio of switch S1 is controlled. When V _L is negative, diode D2 is enabled (switch S4 is off), diode D1 is short-circuited (switch S3 is on), and the on / off time ratio of switch S2 is controlled. by this,
A ringing signal according to the equation (7) is generated on the subscriber lines A and B, and this is sent to the terminal side.

In all of the above four examples, equation (1)
When the current is set to the target value based on the equation (7), if the loop current value I _L is larger than the measured current value I _{m, the} voltage across the capacitor C1 is increased by ΔE1 to set the loop current value I _L. Is smaller than the measured current value I _{m, the} voltage across the capacitor C1 is reduced by ΔE1. On the other hand, when the voltage is set to the target value, if the target voltage value V _L is larger than the measured voltage value V _m , the voltage across the capacitor C1 is Δ.
E2 is raised and the target voltage value V _L is the measured voltage value V _m
If it is smaller than, the voltage across the capacitor C1 is ΔE2.
Just lower it.

When the polarity is normal, the diode D1 is enabled (switch S3 is turned off), the diode D2 is short-circuited (switch S4 is turned on), and the switch S is turned on.
Control the on / off time ratio of 1. When the polarity is reverse, the diode D2 is enabled (switch S4 is turned off), the diode D1 is short-circuited (switch S3 is turned on), and the on / off time ratio of the switch S2 may be controlled.

The values of ΔE1 and ΔE2 may be constant values, but ΔE1 = (I _L −I _m ) × α or ΔE2 = (V _L −V _m ) × α. You may use it. As a result, the loop current value I _L and the measured current value I
When the difference from _m is large, ΔE1 also becomes large, and as the difference becomes smaller, ΔE1 becomes smaller, so that adaptive control becomes possible. Note that α is a constant and adjusts the convergence speed. Even in the case of pure resistance feeding, the convergence speed can be adjusted by changing the constant α.

The power supply circuit BS detects off-hook at the time of calling from the telephone, on-hook at the time of ending the call, and off-hook at the time of calling. Further, although the ISDN terminal needs to detect a call, the power supply circuit BS in the above embodiment
The measured current value I _m and the measured voltage value V _m are constantly sampled, and a rapid change in the current value can be detected by the microprocessor μP. Therefore, the above embodiment can detect on-hook and off-hook.

Further, the current value synchronized with the ringing signal,
Since the voltage value can be monitored, it is possible to easily detect the response (off-hook) at the time of calling.

In the above embodiment, various power feeding characteristics can be realized by one circuit, and the normal polarity can be changed to the reverse polarity smoothly. Further, conventionally, a ringing signal is generated in a common device of a telephone station, is sent to each circuit, and is connected by a ringer switch. However, in the above embodiment, a ringing signal is generated in the power feeding circuit BS. However, since it can be sent to the subscriber, the line for sending the ringing signal and the ringer switch RSW are not required, which can contribute to the economy of the subscriber circuit and the simplification of the wiring work.

Further, in the above embodiment, the constant current power supply required for the ISDN in-station termination circuit can be realized by only changing the program in the microprocessor μP. IS circuit 10
It can be used as an intra-station terminating circuit for DN, that is, it is possible to integrate a telephone subscriber circuit and an ISDN intra-station terminating circuit, and even if the terminal is changed on the subscriber side, the station side device is not changed. Only the software of the microprocessor μP and the signal processing circuit SP need be changed, and efficient investment can be made in the communication network.

FIG. 3 is a circuit diagram showing a subscriber circuit 11 which is a second embodiment of the present invention.

The subscriber circuit 11 is basically the same as the subscriber circuit 10, and differs from the subscriber circuit 10 only in that an isolation amplifier is used for the current measuring circuit MI1 and the voltage measuring circuit MV1. As a result, the high-voltage circuit (subscriber lines A, B), the microprocessor μP, and the signal processing circuit SP can be electrically separated completely, and the ground unbalance attenuation amount can be increased. Although the switches S1 and S2 are shown by the symbols of switches, they can be realized by MOSFETs, transistors and the like.

The method of measuring the voltage and current in the subscriber circuit 11 and controlling the DC-DC converter by the microprocessor μP is the same as that in the subscriber circuit 10.

[0064]

According to the present invention, telephone service, ISD
Since various power supply circuits required for N service are realized by programmable power supply circuits, it is not necessary to connect to a common device such as a 16 Hz generator and tester, the circuit scale is small, and it is used for ISDN service. There is an effect that it can be used also as an intra-station termination circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing a subscriber circuit 10 according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing the above embodiment more specifically, showing an example in which a DC-DC converter is used as a power supply circuit POW.

FIG. 3 is a circuit diagram showing a subscriber circuit 11 according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a conventional subscriber circuit 12.

FIG. 5 is a circuit diagram showing a conventional intra-station termination circuit 13.

[Explanation of symbols]

 A, B ... Subscriber line, BS, BS1 ... Feeding circuit, MI, MI1 ... Current measuring circuit, MV, MV1 ... Voltage measuring circuit, POW ... Power supply circuit, μP ... Microprocessor, SP ... Signal processing circuit, S1, S2 , S3, S4 ... Switch, D1, D2 ... Diode, T1 ... Transformer, PW1 ... First primary winding, PW2 ... Second primary winding, SW ... Secondary winding, C1 ... Capacitor, Fil ... AC signal inflow prevention filter, n1, n2 ... Normal power supply relay, r1, r2 ... Reverse power supply relay, RSW ... Ringer switch, 10, 11 ... Subscriber circuit.

Claims (3)

[Claims] 1. In a subscriber circuit for a digital exchange, measuring means for measuring a value of a voltage between terminals connected to the subscriber line and a value of a current flowing through the subscriber line; positive and negative. A power supply circuit that generates a voltage and is capable of controlling the voltage level; a micro that controls the positive, negative and level of the voltage generated by the power supply circuit based on the measured current value and voltage value A subscriber circuit having a processor; and realizing a desired power supply characteristic by the program logic of the microprocessor. 2. The power supply circuit according to claim 1, wherein the power supply circuit includes a DC-DC converter, and the DC-DC converter includes a first primary winding and a first primary winding.
A first switch connected in series to the primary winding, a second primary winding, a second switch connected in series to the second primary winding, and the subscriber line A secondary winding connected to the output terminal of the power supply circuit, and a polarity control diode connected in series to the secondary winding. The first switch is periodically turned on and off to control the polarity control diode to generate a positive voltage in the second winding, and the microprocessor periodically turns on the second switch. , OFF to control the polarity control diode to generate a negative voltage in the second winding, and change the ON / OFF time ratio to change the output voltage level of the power supply circuit. Characterized by being Subscriber circuit. 3. The subscriber circuit according to claim 1, wherein an isolation amplifier is used for the measuring means, and the measuring means and the power supply circuit are insulated from the microprocessor.