JPH0367387B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a silent polarity reversing circuit that operates so as not to generate noise such as clicking noise when transmitting a polarity reversal signal from a telephone exchange to a subscriber telephone. .

[Conventional technology]

Conventionally, a polarity reversal signal is used for billing purposes in the power supply circuit from the telephone exchange to the subscriber's telephone, but when sending the polarity reversal signal to the subscriber's telephone, it is necessary to avoid noise such as clicking noises as much as possible. Various circuits have been proposed. Unexamined Japanese Patent Publication 1987-
For example, the technology described in Publication No. 165456 is
In the configuration shown in the figure, 1 and 2 are telephone circuit terminals;
26 is a photocoupler, 27 is a ground potential terminal, 28 is a negative potential circuit, 29 and 30 are control signal A application terminals, 17 and 18 are operational amplifiers, 11 and 12 are capacitors, and 13 and 14 are resistance elements. 11/1
A time constant circuit is constructed by a combination of 3, 12/14. There is a polarity reversing circuit 3 that uses a relay or a thyristor to actually reverse the polarity. terminals 1, 2
A terminal such as a telephone is connected between them, and when the subscriber telephone 4 on the called side that supplies communication current goes off-hook, the photocoupler 26 is turned on by a control signal A via terminals 29 and 30. At that time, the operational amplifiers 17 and 18 operate as comparators, and when the polarity reversing circuit 3 is operated by the control signal B, the potential between terminals 1 and 2 changes more rapidly than when a simple relay or the like is turned on/off. Instead, a power supply current I _L as shown in FIG. 4 is supplied to the subscriber's telephone 4, and a conversation with the calling party's telephone is then made.

[Problem that the invention seeks to solve]

However, the above-mentioned time constant circuit 11/13,
12/14, when the capacitor starts charging and discharging, an exponentially rapid change in potential occurs as shown in Figure 4, so avoid generating noise to the subscriber's telephone at the point of change. I can't do it.

An object of the present invention is to improve the above-mentioned drawbacks, and to provide a polarity reversal circuit used for reversing the communication current on the subscriber side, in which charging and charging of the capacitor constituting the time constant circuit
An object of the present invention is to provide a silent polarity reversing circuit that does not generate noise during polarity reversal operation by performing discharge with a constant current.

[Means for solving problems]

The means adopted by the present invention to achieve the above object are as follows. That is, in order to reverse the path for supplying the call current to the subscriber's telephone when transmitting the billing pulse for a telephone call, a polarity reversal pulse control signal is received by a photocoupler, and a changeover switch and a time constant circuit operated by the output are connected. In a telephone exchange talking current polarity reversal circuit configured to control an operational amplifier through
There are four photocouplers, and the changeover switch includes a first switch that connects in series the transistor elements to which the outputs of two of the photocouplers are applied, and a first switch that connects in series the transistor elements to which the outputs of the remaining two of the photocouplers are respectively applied. A transistor element to be applied is formed with a second switch connected in series, and a capacitor constituting a time constant circuit is connected to each connection midpoint of the first switch and the second switch.
One end of the switch/second switch is connected to ground, and the other end is connected to a negative power supply, and one element of the transistor element forming the first switch is connected to the resistor element connected to the transistor element. The other element of the transistor element forms one constant current circuit together with the resistance element connected to the same element, and one element of the transistor element forming the second switch forms one constant current circuit together with the resistance element connected to the same element. The other element of the transistor element forms the other constant current circuit together with the resistor element connected to the same element, and conduction/non-conduction of each element constituting the first and second switches is determined by the output of the photocoupler. When switched, the constant current circuit operates,
It is constructed by linearly charging and discharging a capacitor that constitutes the time constant circuit.

[Effect]

Since the present invention operates so that the charging current to the capacitor is constant, the potential change is constant and rises linearly. Therefore, there are fewer harmonic components included in the waveform at the moment when charging the capacitor starts, and less noise is generated. Also, since the voltage falls in a straight line at the start of discharge, less noise is generated.

〔Example〕

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention. In Fig. 1, 1 and 2 are telephone circuit terminals;
4 is a subscriber telephone, R _B is a resistive element, and the line from the operational amplifier 31 to the telephone 4 is commonly called the B line.
R _A is a resistive element, and the line from the operational amplifier 81 to the telephone set 4 is commonly referred to as the A line. 11, 12, 13, 6
1, 62, 63 are transistors, 21, 91 are capacitors, 26-1 to 26-4 are photocouplers, 2
9, 30 are photocoupler control signal terminals, 31, 81
is an operational amplifier, and 42 is a connection point between transistors 12 and 13, which is a point A. 83 is a transistor 62,
The connection point of 63 is designated as point B. When subscriber telephone 4 is on-hook, all photocouplers 26-
1 to 26-4 are off, point A is at ground potential,
Point B has approximately the same potential as the negative power supply potential. Transistors 11, 12, 61, and 63 are in an on state. The operational amplifier 31 outputs a ground potential, and the operational amplifier 81 outputs a negative power supply potential, and is connected to the subscriber telephone 4. Next, when the subscriber telephone 4 goes off-hook, all of the photocouplers 26-1 to 26-4 light up due to the control signals via the terminals 29 and 30. Therefore, transistors 11, 12, 61, 6
3 is turned off, and transistor 1 is turned off instead.
3 and 62 are turned on. That is, the transistors 12, 13, 62, and 63 function as changeover switches for polarity reversal operation. Charge is accumulated in the capacitor 21 along the path of ground potential (earth) -> capacitor 21 -> transistor 13 -> resistance element 52 -> negative power supply (-48V). Similarly, charge is accumulated in the capacitor 91 along the path of ground potential (earth) -> resistance element 75 -> transistor 62 -> capacitor 91 -> negative potential (-48V). The accumulated states of the charges are shown as v ₁ and v ₂ in the center of FIG. 2. That is, according to the present invention, the change is shown by the solid line. It is resistance elements 51, 52, 53
and 73, 74, 75 are transistors 13, 62
This is because it keeps the output current constant and suppresses sudden changes in potential at the start of charging. As a result, as shown in the lower part of FIG. 2, the feed current I _L does not change exponentially at the time of polarity change, but changes linearly. Note that the curve shown in the upper part of Fig. 2 indicates that when the polarity reversing circuit using transistors operates,
It shows potential changes occurring at each point A and B.

〔Effect of the invention〕

In this manner, according to the present invention, the current in the pole reversal circuit changes linearly, rather than exponentially, immediately after the subscriber's telephone goes off-hook, so that almost no clicking noise accompanies the pole reversal signal occurs. . Therefore, the loud click sound does not reach the subscriber's telephone as in the conventional case. Furthermore, since a transistor element is used as the polarity reversing circuit instead of using mechanical parts such as a relay, the circuit is miniaturized and is less susceptible to the effects of noise generated when a relay or the like operates.

[Brief explanation of drawings]

FIG. 1 is a main diagram showing the configuration of an embodiment of the present invention;
2 is an explanatory diagram of the operation of FIG. 1, FIG. 3 is a diagram showing a conventional circuit configuration, and FIG. 4 is an explanatory diagram of the operation of FIG. 3. 1, 2...Telephone circuit terminal, 11, 12, 13,
62, 63...Semiconductor element, 21...Capacitor, 26-1 to 26-4...Photocoupler, 29,
30...Photocoupler control signal terminal, 31...Operation amplifier, 41...Ground potential point, 42...-48V power supply terminal, 43...Semiconductor element connection terminal, 51,
52, 53, 54, 55...Resistance element, 71, 7
2, 73, 74, 75...resistance element.

Claims (1)

[Claims] 1. In order to reverse the path for supplying call current to a subscriber's telephone when transmitting a billing pulse for a telephone call, a polarity reversal pulse control signal is received by a photocoupler, and a changeover switch is operated by the output. In the telephone exchange call current polarity reversal circuit configured to control an operational amplifier via a time constant circuit, the photocouplers include four, and the changeover switch is configured to control two of the photocouplers.
a first switch that connects in series transistor elements 12 and 13 to which the remaining two outputs of the photocoupler are applied, and a second switch that connects in series transistor elements 62 and 63 to which the remaining two outputs of the photocoupler are applied, respectively. A capacitor forming a time constant circuit is connected to each connection midpoint of the first switch and the second switch, and one end of each of the first switch and the second switch is connected to the ground, and the other end of each is connected to the negative terminal. One element 13 of the transistor elements connected to the power supply and forming the first switch is connected to the resistor elements 51, 52, 53 connected to the same element 13, and the other element 12 of the transistor elements is connected to the same element 12. Together with the connected resistance elements 54 and 55, one constant current circuit is formed, and one element 62 of the transistor element forming the second switch, together with the resistance elements 73, 74, 75 connected to the same element 62, Further, the other element 63 of the transistor element forms the other constant current circuit together with the resistor elements 71 and 72 connected to the same element 63, and the output of the photocoupler allows each element constituting the first and second switches to be connected to each other. A silent polarity reversal circuit characterized in that when conduction and non-conduction are respectively switched, the constant current circuit operates to linearly charge and discharge a capacitor constituting the time constant circuit.