JPH0320958B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a power supply circuit for a communication line device that supplies communication current in a loop to a two-wire subscriber telephone set, etc.
In particular, the present invention relates to a so-called silent reverse control circuit for reducing noise generated in line audio signals when reversing the polarity of a call current during a call to generate billing pulses.

(b) Background of the Technology In digital exchanges and the like, the loop-shaped communication current of the subscriber telephone set accommodated therein is supplied from a communication path device such as a subscriber circuit. However, in a communication path device that accommodates a public telephone, etc., a charging pulse generated by reversing the polarity of the communication current for a short period of time (for example, about 300 milliseconds) is sent to the public telephone to charge the inserted coins. It needs to be stored. In order to reduce the influence of noise generated by the generation of such billing pulses on voice band calls as much as possible,
The polarity of the communication current must be reversed slowly with sufficient transition time. As such a means, it is considered to insert a low-pass filter into the output of the power supply circuit for the communication current, but this is not practical because the wires and capacitors that make up the low-pass filter are large and expensive. poor. As a solution to this problem, two sets of feeder circuits are provided that supply communication currents with opposite polarities, and normally one of the feeder circuits supplies communication current to the line in a loop, and when the polarity of the communication current is reversed, Attempts have been made to provide a silent reverse control circuit that is externally controlled so that one power feeding circuit gradually decreases the current being supplied, and at the same time gradually increases the current flowing through the other power feeding circuit.

(c) Problems with the Prior Art FIG. 1 shows an example of a conventional silent reverse control circuit for a subscriber circuit. In Figure 1,
The subscriber circuit consists of two sets of power supply circuits FD1 and FD2.
and a control circuit CTL. Power supply circuit FD
1 supplies a loop current i 1 that flows from the earth to line L2 of the communication line and flows from line L1 to the negative supply voltage _V1 (for example -48 volts), and
The power supply voltage V1 is supplied from FD2 via lines L1 and L2.
Provides a loop current i ₂ flowing into. power supply circuit
Both FD1 and FD2 have the configuration illustrated in FIG. 2, and have symmetrical configurations with respect to lines L1 and L2, except for the polarities of transistors Q1 and Q2. The operation of the power supply circuit shown in FIG. 2 will be explained below.
First, the basic operation of the circuit will be described assuming that there are no diodes D2 and D3. A certain loop current I _L
Suppose that the signal is flowing through D4, R12, Q2, L2, a telephone (not shown), L1, Q1, R8, and D1. (Strictly speaking, resistors R9, R10, R5, R
There is also a current passing through the resistor 6, but it can be ignored by setting the resistor to a sufficiently high value. )Resistance R12
A voltage of R12×I _L is generated across the terminal. This voltage is applied to the negative input terminal - of the operational amplifier OA2. When an operational amplifier is in normal operation, the negative input terminal - and the positive input terminal + have the same voltage, so the positive input terminal + of OA2 is equal to the voltage at the connection point between the resistor R12 and the transistor Q2. Resistance R
Since no DC current flows through 11, resistors R10 and R
It also becomes equal to the voltage at the connection point 9. A current of R12×I _L /R10 flows through the resistor R10, and all of this current flows through the resistor R9, so the resistor (R9+
The voltage across R10) is I _L × R12 × (R9 + R10)/
It will be R10.

Therefore, the connection point between resistor R12 and diode D4 and the collector of transistor Q2 is equivalently
The resistance is determined by R12×(R9+R10)/R10. Normally, it is set to about 200 ohms to 400 ohms, and the constant is set in the circuit on the transistor Q1 side as well as the circuit on the transistor Q2 side. A subscriber line including a telephone is connected between ends A and B of the two lines L1 and L2.
Its resistance value varies from 0 ohm to about 1800 ohm depending on the length of the subscriber line, so the loop current I _L
The current also varies from about 20mA to about 100mA.
When diodes D2 and D3 are not connected, the power supply circuit is equivalently a resistor, and the voltage v ₄ at the connection point between resistors R9 and R10 and the voltage v ₃ at the connection point between resistors R5 and R6 are the loop currents. It changes in proportion to the size of I _L.

On the other hand, in such a power supply circuit, if the voltage v ₄ at the connection point between resistors R9 and R10 is fixed to a constant voltage, the current flowing through resistor R12 will not exceed the current value specified by v ₄ /R12. . Therefore, if the voltage across the resistor R10 is set below OV, the loop current I _L can be set to 0. Diode D
2, D3, resistors R13, R14, transistor Q
3 is a circuit that controls ON/OFF of the loop current I _L between the lines L1 and L2. The values of resistors R13 and R14 are equal and the resistor R
9, R10, R5, and R6. There is a loop through which a subscriber line passes between the lines L1 and L2, and a loop current I _L flows therethrough. The voltage across resistor R14 is
If the voltage at the base terminal _T1 of the transistor Q3 is set so as to be larger than the voltage across the terminal of 0 (setting voltage is set to _v1 ), the diode D3 becomes reverse biased, which affects the above-mentioned power supply operation. Normal power supply status is established. From this state, transistor Q
When base terminal _T1 of 3 is set to ground level,
The transistor Q3 is turned off, the voltage across the resistor R14 becomes OV, the voltage _v4 at the connection point between the resistors R9 and R10 becomes approximately OV through the diode D3, and the loop current I _L no longer flows. By gradually changing the voltage at the base terminal T ₁ of the transistor Q3 from OV to voltage v ₁ or from voltage v ₁ to OV, the loop current I _L can also be gradually turned ON/OFF. The voltage required for this, v ₁ , is the loop current
Since it depends on _IL , the voltage v ₁ is determined from the maximum value of the loop current _IL . (And the value of this voltage v ₁ is
As V2, it is assumed that the control power supply voltage V2 of the conventional silent reverse control circuit CTL described below is used. ) The conventional silent reverse control circuit shown in FIG. 1, which is constituted by the power supply circuits FD1 and FD2 and the control circuit CTL, will be explained below. The control circuit CTL in Figure 1 is the power supply circuit FD
The control voltages v ₁ and v ₂ to be applied to the terminal T ₁ of the power supply circuit 1 and the terminal T ₂ of the power supply circuit FD2 are generated. control circuit
When the switch S in the CTL is in the recovery state as shown in the figure, the capacitor C1 is charged by the control power supply voltage V2, and the capacitor C2 is in a discharged state. As a result, the control voltage v ₁ applied to the terminal T ₁ of the feed circuit FD1 becomes equal to the control power supply voltage V2, the control voltage v ₂ applied to the terminal T ₂ of the feed circuit FD2 becomes 0, and the Line L from circuit FD1
1, a loop current is supplied to L2, but at this time,
The power supply circuit FD2 is in an OFF state. In this state, when the switch S of the control circuit CTL is operated to reverse the polarity of the loop current _i1 , the capacitor C1 is discharged through the resistors R1 and R2, and the capacitor C2 is connected to the control power supply through the resistor R3. It is charged by the voltage V2, and the control voltage _v1 gradually decreases from the control power supply voltage V2. As a result, the voltages v ₃ and v ₄ in the feeder circuit FD1 also gradually decrease,
The loop current i ₁ also gradually decreases. on the other hand,
The voltages v ₃ and v ₄ in the feed circuit FD2 gradually rise, and the lube current i ₂ gradually increases accordingly. Eventually, the control voltage v ₁ becomes 0, and the control voltage v ₂ becomes the control power supply voltage.
When V2 is reached, the loop current flows from the feed circuit FD1.
i ₁ is no longer supplied, and loop current i ₂ is supplied from the power supply circuit FD2, and the wires L1 and L2
This results in a reversal of the polarity of the loop current i ₁ delivered to . Further, reversing the polarity of the loop current i ₂ is achieved by restoring the switch S of the control circuit CTL, in a process reverse to that described above. A in FIG. 3 shows an example of a change in loop current in the conventional example shown in FIG. In the case of Ia in A of FIG. 3 where the subscriber line is short and the loop current is large, the voltage v ₃ in the feeder circuit FD1 or FD2 is
and v ₄ are higher voltages than the control power supply voltage V2, so from the beginning of the operation time t1 of the switch S in the control circuit CTL, the voltage v ₃ or v ₄ becomes the control voltage v ₁
or decreases with v ₂ and the loop current i ₁ or i ₂ is
It starts to decrease from time t1, reaches 0 after a sufficient transition time, and reaches the time t2 when switch S is restored.
After a sufficient transition time has elapsed, the saturation value Ia is restored again at time t3. However, in the case of Ib in A of Fig. 3 where the subscriber line is sufficiently long and the loop current is small, the voltages v ₃ and v ₄ in the feeder circuit FD1 or FD2 will be lower voltages than the control power supply voltage V2. Therefore, the operating time t of switch S in the control circuit CTL
1, the voltage v ₃ or v ₄ begins to decrease only at time t1' when the control voltage v ₁ or v ₂ has decreased for a while, and the transient time of the loop current i ₁ or i ₂ is also shortened. Further, after a short transient time has elapsed from the restoration time t2 of the switch S, the loop current is restored to the loop current Ib again at the time t3'. As is clear from the above explanation, in the conventional silent reverse control circuit shown in FIG.
The control voltages v ₁ and v ₂ applied to the control terminals T ₁ and T ₂ of FD1 and FD2 are a constant control power supply voltage V2, regardless of the value of the loop current i ₁ or i ₂ ,
Capacitor C1 or C2 and resistor R1, R
2 or the time constant determined by R3 and R4. Therefore, in the case of Ib in A of FIG. 3 where the value of the loop current is small, the power supply circuit FD1,
The controllable range of the voltage v ₃ or v ₄ in the FD 2 is reduced, the transient time of the loop current i ₁ or i ₂ is shortened, and the effect of the resulting noise on the speech is also increased. This situation will be explained using B in FIG. If the subscriber line is short and a subscriber at a short distance is connected, the loop current will also be large, and the voltage between lines A and B between the lines L1 and L2 will be small as shown in (a). As mentioned above, the current change time varies depending on the time constant set in the control circuit CTL, so it is sufficiently long from time t ₁ to t ₂ , and therefore A
- There are fewer components in the audio band due to changes in the voltage between the B lines, making it less likely to become noise. On the other hand, when the subscriber line is long and long-distance subscribers are connected, the loop current becomes small and the voltage between lines A and B between lines L1 and L2 becomes large as shown in (b). As mentioned above, the current change time changes in a short time, and the voltage change between the A and B lines becomes steep from time t ₁ ' to t ₂ , and the generated noise becomes noise in the voice band of the call. easy.

(d) Object of the Invention The object of the present invention is to eliminate the drawbacks of the conventional silent reverse control circuits mentioned above, and to eliminate the noise generated when the polarity of the loop current is reversed, regardless of the value of the loop current. The aim is to provide a means to minimize the impact on

(e) Structure of the Invention The purpose is to connect loop currents (i _{1 or i 2 ) of opposite polarity to the line, which are proportional to the control voltages (v 1 , v 2 ) applied} to the control terminals T ₁ and T ₂ , respectively. L1,
Two sets of power supply circuits FD1 and FD2 that supply to L2,
and a silent reverse control circuit CTL that applies the control voltages (v ₁ , v ₂ ) which are gradually increased and decreased in an exclusive manner to the control terminals T ₁ and T ₂ of both the power supply circuits, respectively. means D5, D6, R15, R16 for extracting and holding a voltage (V _4-1 , V _4-2 ) proportional to the loop current from the power supply circuit;
C5 and OA3 are provided, and the silent reverse control circuit CTL generates a control voltage that gradually increases and decreases with the voltage (V3) held by the means as a saturation value, and applies it to the control terminals T ₁ and T ₂ of the two sets of power supply circuits. This is achieved by configuring the device to apply the voltage.

(f) Examples of the invention Examples of the invention will be described below with reference to the drawings.
FIG. 4 is a diagram showing the configuration of a silent reverse control circuit according to an embodiment of the present invention, A in FIG. An example of voltage change between lines A and B of L1 and L2 is shown. Note that the same reference numerals indicate the same objects throughout the figures.

The silent reverse control circuit CTL in the embodiment _shown in FIG _.
As the power supply voltages for v ₁ and v ₂ , instead of using the constant control power supply voltage V2 of the conventional example shown in Fig. 1, the power supply circuits FD1,
The voltages V _4-1 and V _4-2 proportional to the loop current i ₁ or i ₂ taken out from FD2 are applied to the diodes D5, D6,
A voltage V3 is used which is held in a capacitor C5 via resistors R15 and R16 and further supplied via a voltage follower using an operational amplifier OA3.
In the conventional example shown in Figure 1, the voltage required for the control power supply voltage V2 is a high voltage when the loop current is large, and a low voltage when the loop current is small, but if it is fixed at a lower voltage, the power supply current is limited. Therefore, the voltage when the loop current is at its maximum was set as the control voltage, but in the embodiment of the present invention shown in FIG.
By generating the held control voltage V3 through a time constant circuit that extracts V _4-1 and V _4-2 and keeping the change time of the loop current constant, noise generation during silent reverse can be reduced. There is. Silent reverse control circuit in the embodiment of the present invention shown in FIG.
The operation of the CTL will be explained with reference to the power supply circuit shown in FIG.

When the dotted line subscriber telephone connected to ends A and B of two subscriber lines L1 and L2 makes a call, line L
1, the loop of L2 is closed and the power supply circuit FD1 or
Loop current i ₁ or i ₂ flows due to FD2. In the feeder circuit FD1 or FD2, as already explained in the prior art section, a voltage proportional to the loop current _i1 is generated across the resistor R12 of FD1 in FIG. A voltage equal to this voltage appears across the resistor R10. This voltage is defined as voltage _v4 at the connection point with resistors R9 and R10, and in FD2, the voltage across resistor R8 is
The voltage at the connection point between the resistors R5 and R6 is taken out as v ₃ (voltages V _4-1 and V _4-2 in FIG. 4) and input to the silent reverse control circuit CTL in FIG. 4.
In the silent reverse control circuit CTL, in order to make these voltages V _4-1 and V _4-2 the necessary control voltages v ₁ and v ₂ to the control terminals T ₁ and T ₂ of the power supply circuits FD1 and FD2, Diode D5, resistor R15, capacitor C
5 or a holding circuit consisting of a diode D6, a resistor R16, and a capacitor C5, and further generates a control power supply voltage V3 through a voltage follower using an operational amplifier OA3. This holding circuit is a type of peak hold circuit, and when a subscriber telephone makes a call and a loop current flows, it holds a voltage proportional to the current value, and the current temporarily decreases as in the case of silent reverse. Even if the diode D5, D
6 and capacitor C5, the voltage
V3 is retained.

In the conventional example shown in Fig. 1, the control power supply voltage V2 is fixedly determined by the maximum value Ia of the loop current I _L , so when the loop current I _L is a small value Ib,
Even if the output v ₁ of the control circuit CTL changes from the voltage V 2 to 0, the time until it reaches the control voltage determined by the current value Ib, that is, from time t ₁ to t ₁ ' at A in FIG. There was no change in the current, and the current changed for the first time from time t ₁ '. However, in the embodiment of the present invention shown in FIG. 4, since the control voltage V3 in the control circuit CTV is a voltage proportional to the loop current I _L of the lines L1 and L2, the loop current increases as shown in A in FIG. Regardless of the magnitude of I _L , the current change always starts from time t ₁ , so a sufficient transition time can be provided, and the generation of noise can be reduced. the result,
When the switch S in the control circuit CTL is operated or restored in order to reverse the polarity of the current i ₁ or i ₂ of the loop current I _L , the subscriber lines L 1 and L 2 are short and the value of the loop current is large ( Ia in Figure 5)
In the case where the subscriber lines L1 and L2 are long and the value of the loop current is small (Ib in Fig. 5), the loop currents Ia and Ib are equal to the initial value at the operating time _t1 of the switch S in the control circuit CTL. After a sufficient transition time, the current value Ia starts to decrease and becomes 0 at time t ₂ , and again at the same time t ₃ after a sufficient transition time from the time t ₂ when the switch S is restored, the current value Ia,
Restore to Ib.

As is clear from the above explanation, according to the silent reverse control circuit of this embodiment shown in FIG. 4, regardless of the values of the loop currents of the lines L1 and L2,
Since a sufficiently long transition time elapses when the polarity is reversed, the noise generated due to the polarity reversal is reduced, and the influence on the telephone conversation of the subscriber telephone is also reduced, so there is no problem. Note that FIGS. 4 and 5 are only one embodiment of the present invention, and the power supply circuits FD1,
Voltage proportional to loop current extracted from FD2
V _4-1 and V _4-2 are not limited to the voltages v ₃ and v ₄ across the resistors R6 and R10 in FIG. The effect of the invention remains the same. Furthermore, the configurations of the power supply circuits FD1 and FD2 are not limited to those shown in FIG. 2, and it goes without saying that the communication path device to which the present invention is applied is not limited to a subscriber circuit accommodating a telephone or the like. do not have.

(g) Effects of the invention As described above, according to the present invention, in the communication path device,
An effect can be obtained in which the influence of noise generated when the loop currents of the two lines are reversed on communication is kept to a minimum regardless of the value of the loop currents.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional silent reverse control circuit, FIG. 2 is a diagram showing an example of a power supply circuit for the silent reverse control circuit in FIG. A diagram showing an example of a change in loop current and a change in voltage between lines A and B. FIG. 4 is a diagram showing a silent reverse control circuit according to an embodiment of the present invention. FIG. It is a figure which shows an example of the change of a loop current, and the change of the voltage between AB lines.

Claims (1)

[Claims] 1. Loop currents (i ₁ or i ₂ ) with opposite polarities, which are proportional to the control voltages (v ₁ , v ₂ ) applied to the control terminals T ₁ , T ₂ respectively, are connected to the lines L1, L2. The two sets of feeder circuits _FD1 and _FD2 that supply the
In a communication path device having a silent reverse control circuit CTL that applies gradually decreasing control voltages (v ₁ , v ₂ ), voltages (v _4-1 , v _{4 )} proportional to the loop current are supplied from the power supply circuits FD1, FD2. _-2 ) means for extracting and retaining D5, D6, R15, R16, C5, OA3
is provided, and the silent reverse control circuit gradually increases the voltage (V3) held by the means as a saturation value.
A silent reverse control circuit that generates a control voltage that gradually decreases in accordance with the magnitude of the loop current (i ₁ or i ₂ ) and applies it to control terminals T ₁ and T ₂ of two sets of power supply circuits. .