JPH0436621B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a subscriber line off-current appropriate circuit in a subscriber circuit capable of reversing the polarity of the current supplied to the subscriber line.

In a digital exchange, the function of supplying current to accommodated subscribers is provided in the subscriber circuit. Furthermore, in a subscriber circuit accommodating a public telephone, the polarity of the supplied current must be reversed at a predetermined time as a charging pulse for storing coins inserted into the public telephone. Since this polarity reversal is performed during a call, it is necessary to suppress the noise generated by the polarity reversal, so a low-pass filter consisting of a large-capacity capacitor and a wire ring is used to reverse the power supply current. A method of relaxing the poles was also used, but this was not suitable for high-density mounting due to the number of parts and shape. In order to achieve miniaturization and high-density packaging of such subscriber circuits, two sets of power supply circuits are provided in which the rise and fall of the power supply current are moderated by external control, and each supply current of opposite polarity is connected to the subscriber line. Normally, current is supplied from one power supply circuit, and when transmitting charging pulses, the current supply from one power supply circuit is stopped, and a current of opposite polarity is supplied from the other power supply circuit. [For example, IEICE technical research report (IEICE Technical Report Vol. 84 No. 147) "Study of all-electronization of public subscriber circuits in digital exchanges" September 21, 1984 (cited below) ).

[Conventional technology]

FIG. 2 is a diagram showing an example of a conventional current supply system in this type of subscriber circuit, and FIG. 3 is a diagram showing an example of the charging pulse generation process.
1 shows the normal current supplied from the power supply circuit 1, b in the figure shows the reverse current supplied from the power supply circuit 2, and c in the figure shows the subscriber current. In FIG. 2, the power supply circuit 1 connects the positive polarity terminal (+) of the built-in amplifier circuit 11 to the B line of the subscriber line 3, and the negative polarity terminal (-) to the A line of the subscriber line 3. and supplies normal current i1. In addition, the power supply circuit 2 is connected to the positive polarity terminal (+) of the built-in amplifier circuit 21.
is connected to the A line of the subscriber line 3, and the negative polarity terminal (-) is connected to the B line of the subscriber line 3, respectively, to supply a reverse current i2 having a polarity opposite to the normal current i1. Each of the power supply circuits 1 and 2 supplies or stops the normal current i1 or the reverse current i2 in response to a control signal from an external device (not shown).

In Figure 3, normal current from power supply circuit 1
When transmitting a charging pulse from a call state where i1 is being supplied, the normal current i1 currently being supplied from the power supply circuit 1 is stopped from time t1 to t2, and after a predetermined period from time t3 to t4, the normal current i1 is stopped from the power supply circuit 1. A reverse current i2 is supplied from the reverse current i2. Furthermore, after a predetermined period, the reverse current i2 currently being supplied from the power supply circuit 2 is stopped from time t5 to t6, and the normal current i1 is again supplied from the power supply circuit 1 from time t7 to t8 after a predetermined period. As described above, the polarity of the subscriber current i3 supplied to the subscriber line 3 is reversed from time t1 to t8, and a billing pulse is sent out.

In addition to the function of supplying current to the subscriber line 3, the power supply circuit 1 is equipped with a two-wire/four-wire conversion function, etc., and in order to maintain this function, the power supply circuit 1 is also equipped with a predetermined current supply function during the power supply suspension period from time t2 to t7. current value (e.g. 14
It is necessary to output an off-state current io1 of (milliampere) between the positive polarity terminal (+) and the negative polarity terminal (-) of the amplifier circuit 11 (see the above cited example). For this purpose, a constant current source 12 is provided in the power supply circuit 1, and supplies a source current ic1, which is a source of off-current io1, to a terminal C of the amplifier circuit 11. Note that the capacitor 13 is provided for the purpose of removing high frequency noise superimposed on the normal current i1. on the other hand,
In public telephones connected to subscriber lines, paid calls and free calls can be distinguished by the length of the no-current period (time t2 to t3) when subscriber current i3 transitions from normal current i1 to reverse current i2. Therefore, if the subscriber current i3 at time t2 to t3 falls outside of a predetermined current range (e.g. -10 to +1.7 milliamperes), it will be mistaken to distinguish between paid calls and free calls. Also, there are inconveniences such as not being able to store coins. Therefore, even within the power supply circuit 2, the constant current source 22
is connected to terminal C of the amplifier circuit 21, and the amplifier circuit 21
The off-state current io1 is offset by outputting the same off-state current io2 from the off-state current io2. As a result, the subscriber current i3 changes from time t2 to t, as shown in FIG.
3 and is maintained within a predetermined current value from time t6 to time t7.

[Problem that the invention seeks to solve]

Although circuits of the same standard are used for power supply circuits 1 and 2, individual circuits always have built-in deviations in characteristics, and are output from power supply circuits 1 and 2, respectively, used for the same subscriber circuit. off current io
1 and io2 do not cancel out reliably, and the subscriber current i
3 may not be maintained within a predetermined current value.
If the subscriber current i3 exceeds the predetermined current value,
As mentioned above, public telephones misidentify paid calls and free calls, causing inconveniences such as not storing coins even for paid calls, so such subscriber circuits should be discarded or used for the same subscriber circuit. There is no other way than to change the combination of the feeder circuits 1 and 2, which reduces the yield of the feeder circuit and impairs the economic efficiency of the subscriber circuit.

[Means for solving problems]

The present invention provides two sets of power supply circuits having the same configuration, each having a function of supplying current to a subscriber line, and a two-wire/four-wire conversion function capable of performing two-wire/four-wire conversion when a current exceeding a certain current is supplied. The subscriber lines are connected so as to supply subscriber currents of opposite polarity to each other, and the supply of subscriber current from one power supply circuit to the subscriber line is temporarily stopped, while the other power supply circuit is connected to the subscriber line from the other power supply circuit. By supplying the subscriber current, the polarity of the subscriber current supplied to the subscriber line is temporarily reversed, and the two-wire/four-wire conversion function is enabled even while the supply of the subscriber current is stopped. In a subscriber circuit that has a built-in constant current source that generates the source current necessary to supply the off-state current necessary for The above-mentioned problem is solved by adding a current increasing means for increasing the generated source current and making the difference between the off-currents supplied by the two power supply circuits below a specified value.

[Effect]

That is, according to the present invention, if there is a difference in the off-state currents of two sets of power supply circuits used for the same subscriber circuit that exceeds an allowable value, a current increasing means is added to one of the power supply circuits. This makes it possible to adjust the difference in off-state current to below the allowable level, and eliminates the need to discard subscriber circuits or select combinations of power supply circuits.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a subscriber line off-current appropriate circuit according to an embodiment of the present invention. Note that the same reference numerals indicate the same objects throughout the figures. In FIG. 1, a high resistance 4 is added to one of the power supply circuits 1 and 2 as current increasing means.

In FIG. 1, when the subscriber current i3 exceeds the predetermined current value because the off-state current io1 output from the power supply circuit 1 is smaller than the off-state current io2 output from the power supply circuit 2, the amplifier circuit 11 A high resistance 4 is connected to the terminal C of the constant current source 12, and a current is applied from the outside by adding the high resistance 4 between the voltages generated by flowing a constant current.
As a result, the source current ic input to the amplifier circuit 11
1' increases, and the off-state current io1 also increases. In addition, since the off-state current io2 output from the power supply circuit 2 is smaller than the off-state current io1 output from the power supply circuit 1, if the subscriber current i3 exceeds the predetermined current value, the terminal C of the amplifier circuit 21 Connect high resistance 4. As a result, the source current ic2' input to the amplifier circuit 21 increases, and the off-state current io2 also increases.
If the resistance value of the high resistor 4 is properly determined, the subscriber current i3 can be adjusted to within a predetermined current value by connecting the high resistor 4 as described above.

As is clear from the above description, according to this embodiment, when the subscriber current i3 exceeds a predetermined current value, it can be adjusted by adding a high resistance 4 to either of the power supply circuits 1 and 2. There is no need to discard subscriber circuits or select combinations of power supply circuits 1 and 2.

〔Effect of the invention〕

As described above, according to the present invention, in the subscriber circuit, by adding a constant current source to either of the two sets of power supply circuits, the off-state current can be adjusted, thereby improving the yield of the power supply circuit and the economic efficiency of the subscriber circuit. improves.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a subscriber line off-current appropriate circuit according to an embodiment of the present invention, FIG. 2 is a diagram illustrating an example of a conventional current supply system, and FIG. 3 is an example of a billing pulse generation process. It is a diagram. In the figure, 1 and 2 are power supply circuits, 3 is a subscriber line, 4 is a high resistance, 11 and 21 are amplifier circuits,
12 and 22 are constant current sources, 13 and 23 are capacitors, i1 is a normal current, i2 is a reverse current, i3 is a subscriber current, ic1, ic1', ic2 and ic2' are source currents, io1 and io2 are off-state currents, t1 to t8 indicate time points.

Claims (1)

[Claims] 1 The function of supplying current to each subscriber line,
Two sets of power feeding circuits having the same configuration each having a two-wire/four-wire conversion function capable of performing two-wire/four-wire conversion when supplying a current of a constant current or more supply subscriber currents of opposite polarities to the subscriber line. and temporarily stop the supply of subscriber current from one power supply circuit to the subscriber line, and during that time, supply the subscriber current to the subscriber line from the other power supply circuit, thereby supplying the subscriber current to the subscriber line. Even when the polarity of the subscriber current is temporarily reversed and the supply of the subscriber current is stopped, the source current necessary to supply the off-state current necessary to enable the two-wire/four-wire conversion function is maintained. In a subscriber circuit that has a built-in constant current source that generates, either one of the constant current sources that is built in the both power supply circuits,
A subscriber line off-current appropriate circuit characterized in that a current increasing means for increasing the source current generated by the constant current source is added, and the current difference between the off-state currents supplied by the two power supply circuits is set to be equal to or less than a specified value.