JPH02143672A - Power feeding circuit - Google Patents

Abstract

PURPOSE:To supply an AC signal to a talking line in compliance with the electric communication installation rules for enterprises without forming a DC loop at the line idle state by detecting whether or not a telephone talking line forms a DC loop and switching respectively high and low voltage power supplies of the talking line. CONSTITUTION:A group detection circuit 7 receiving a voltage across resistors 3,4 connecting to talking lines A,B detects whether or not the talking lines A,B form a DC loop. When the telephone set is hooked on and the talking lines A,B do not form a DC loop representing the idle state, a circuit 2 controls power changeover circuits 8,10 to switch the high and low voltage power supplies, the power supply higher than 0V and the power supply lower than -48V of the speech current power supplies are connected, it is in compliance with the electric communication installation rules for enterprises and the subscriber supplies an AC signal to the talking lines A and B without making a DC loop at terminal equipments and a feeding circuit able to make automatic metering or the like is attained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a power supply circuit, and in particular to a pair of resistors having a resistance value lower than the resistance value of a power supply resistor necessary for the circuit determined from the maximum value of communication current. and the high-potential side and low-potential side drive circuits connected in series with them, respectively, to have a resistance value during DC power supply that is the same as the resistance value of the power supply resistor determined from the maximum allowable current value of the telephone and communication circuit. Regarding the power supply circuit obtained.

[Conventional technology]

Conventionally, a power supply circuit that realizes the resistance value of the power supply resistor required for the circuit by using a resistor with a resistance value smaller than the resistance value of the power supply resistor, as shown in the block diagram of Fig. 2, has A resistor with one end connected to the differential amplifier 1 to be detected and each of the communication lines A and B and having a resistance value lower than the resistance value of the power supply resistor determined from the maximum allowable current value of the telephone and communication circuit. 3.4, and a low potential side drive circuit 5 and a high potential side drive circuit 6 that supply communication current to the telephone T connected in series to the other end of the resistor 3.4 and connected to the communication lines A and B, respectively. and resistors 3 and 4 receiving the output of the differential amplifier 1.
The low potential side drive is performed so that the combined resistance value of the low potential side drive circuit 5 and the high potential side drive circuit 6 connected in series with them is the same as the resistance value of the power supply resistor necessary for the circuit. It is comprised of a circuit 5 and a feed resistance composite transfer function feedback circuit 2 that sends a feedback signal to a high potential side drive circuit 6, and supplies a communication current to the telephone T via communication lines A and B.

[Problem that the invention seeks to solve]

When a subscriber makes a call, the conventional power supply circuit described above is
A DC loop is created in the telephone, and when the DC current flows, a DC bias voltage corresponding to the power supply resistor and the DC current is generated, and only then can an AC signal be passed.

However, one of the recent uses of subscriber lines is the telemeter function, which uses the idle state of the line to remotely read meters such as gas meters.In this case, the subscriber does not have to create a DC loop at the terminal It will be required to pass AC signals.

However, in conventional power supply circuits, a power supply for communication current (positive potential side OV, negative potential side 48■) is used as the power supply, and in the case of a high DC resistance load such as when on-footer, communication lines A and B are The potential is approximately OV or -48V, and AC signals cannot be passed through without distortion. To avoid this,
It is possible to set the circuit constants for each of the communication lines A and B at the time of on-footer so that the output of the drive circuit is held within 4V from the terminal voltage of the power supply, but this is currently set for telecommunications equipment in Japan. In addition, it cannot be adopted because it does not satisfy the stipulation in Article 27, Section 1 of the Commercial Telecommunications Equipment Regulations that the line voltage is 42 V or more and 53 V or less when terminal equipment is disconnected. In addition, when expecting the same effect and using a power source with a higher potential than the earth's potential and a power source with a potential lower than -48V to generate a DC bias voltage, it is necessary to also flow a communication current from the power source. However, compared to conventional equipment, there is a problem in that the power supply capacity must be further increased.

An object of the present invention is to connect a power source with a potential higher than OV of the power supply for communication current and a power source with a potential lower than -48V only when the line is idle, thereby complying with the regulations for commercial telecommunications equipment. There is almost no change in capacity compared to conventional ones,
To provide a power supply circuit that allows a subscriber to pass an AC signal to a communication line without creating a DC loop at a terminal.

[Means for solving problems]

The power supply circuit of the present invention includes a differential amplifier that detects the voltage between a pair of communication lines, and a power supply resistor, one end of which is connected to each of the pair of communication lines, and which is determined based on the maximum allowable current value of the telephone and the communication circuit. and a load that is connected in series to the other ends of the first and second resistors and connected to the pair of communication lines. and the low potential side and high potential side drive circuits receiving the output of the differential amplifier and connected in series to the first and second resistors, respectively. a feeding resistance composite transfer function feedback circuit that sends a feedback signal to the low potential side and high potential side drive circuits so that the combined resistance value is the same as the resistance value of the feeding resistor; In the power supply circuit that supplies direct current to the telephone via the first
and a loop detection circuit that detects whether or not a load connected to the pair of communication lines forms a DC loop by receiving a terminal voltage applied to both ends of each of the second resistors, and the low potential side drive. As a power supply for the circuit, either a power source for talking current or a power source with a potential lower than the potential of the power source for talking current is connected, and if the loop detection circuit detects a DC loop, it selects the power source for talking current and does not detect it. In this case, a first power supply switching circuit that selects a potential lower than the potential of the power supply for communication current is connected to either the earth or a positive potential power supply as a power supply for the high potential side drive circuit, and the loop If the detection circuit detects the DC loop, it selects the earth potential, and if the detection circuit does not detect the DC loop, it selects the positive potential.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

Telephone T is connected to telephone lines A and B.

The output of the differential amplifier 1, which is connected to the communication lines A and B and detects the voltage between the communication lines A and B, is connected to the feed resistance composite transfer function feedback circuit 2.
It is connected to the. One end of a resistor 3 is connected to the communication line A, and one end of a resistor 4 is connected to the communication line B.

The other end of the resistor 3 is connected to the output of a low potential drive circuit 5 that drives a load connected to the communication line, and the other end of the resistor 4 is connected to the output of a low potential side drive circuit 5 that drives a load connected to the communication line. The output of the high potential side drive circuit 6 is connected thereto. The feed resistance composite transfer function feedback circuit 2 which receives the output of the differential amplifier 1 calculates the composite resistance value of the resistor 3.4 and the low potential side drive circuit 5 and the high potential side drive circuit 6 connected in series with each of them. A feedback signal is sent to the low-potential side drive circuit 5 and the high-potential side drive circuit 6 so that the resistance value is the same as the resistance value of the power supply resistor determined from the maximum allowable current value of the telephone or communication circuit. The loop detection circuit 7 detects whether or not the loads connected to the communication lines A and B form a DC loop by receiving terminal voltages applied to both ends of the resistors 3.4. The power supply switching circuit 8 is configured to connect either a power supply for communication current, that is, a negative power supply 9 with a potential lower than -48V, as a power supply for the low potential side drive circuit 5, and a loop detection circuit. 7 detects a DC loop, connects -48V by issuing a switching instruction signal,
If not detected, connect the negative power supply 9 with a potential lower than -48V. The power supply switching circuit 10 is configured to connect either the earth, that is, OV, or a positive potential positive power supply 11 as a power supply for the high potential side drive circuit 6, and when the loop detection circuit 7 detects a DC loop. If detected, the OV is connected by issuing a switching instruction signal, and if no detection is detected, the positive power source 11 is connected.

Next, the operation of this embodiment will be explained.

If there is a DC loop between the communication lines A and B, the loop detection circuit 7 detects the DC loop and outputs a switching instruction signal to switch the communication current power supply (positive potential side OV, negative potential side -
48■> is connected, but as with conventional power supply circuits, a DC bias is generated by the loop current, so AC signals pass through without distortion.

For example, if the combined power supply resistance of the resistor 3 and the low potential drive circuit 5 and the combined power supply resistance of the resistor 4 and the high potential drive circuit 6 are both 200Ω and the loop current is 20mA, then the communication line A, The potential of B is 4■ from each power supply.
The potential that entered the inside becomes the resistance value of resistor 3.4.
Ω, the potential at the point where the low potential drive circuit 5 and the high potential drive circuit 6 are connected to the resistor 3.4 is a potential within 3.0 V from the respective power supplies.

Furthermore, the non-operating region of the low potential drive circuit 5 and the high potential drive circuit 6 is two stages of diodes (1.4 V) from the power supply potential.
), there is still room for a 1.6V fluctuation, and 3
Even dBm signals can pass through without distortion.

If there is no DC loop between communication lines A and B, the loop detection circuit 7 will not detect a DC loop and will issue a switching instruction signal.The power supply switching circuit 8 will switch the negative power supply 9, which is 5V lower than 48V, to the low potential side drive circuit. 5, and the power supply switching circuit 10 connects the positive power supply 11 which is 5V higher than Ov to the high potential side drive circuit 6. On the other hand, the feed resistance composite transfer function feedback circuit 2, which receives the output of the differential amplifier 1 that detects the voltage between the communication lines A and B, controls the low potential drive circuit 5 and the high potential drive circuit 6 to The detection voltage difference of amplifier 1 is set to 48V. As a result, the provisions of the Business Telecommunications Equipment Regulations can be satisfied.

In addition, the potentials of communication lines A and B are within 5V of their respective power supplies, and the non-operating regions of low potential drive circuit 5 and high potential drive circuit 6 are two diode stages (1 step) from the power supply potential. , 4V), there is a margin for fluctuation of 3.6V, which is sufficient to pass an AC signal.

〔Effect of the invention〕

As explained above, the present invention connects a power source with a potential higher than 0■ of the power supply for communication current to -48V only when the line is idle.
By connecting a power supply with a lower potential, it complies with commercial telecommunications equipment regulations, and the power supply capacity does not need to be changed much compared to conventional ones, allowing AC signals to be sent to the telephone line without the need for subscribers to create a DC loop at their terminals. This has the effect of allowing the passage of

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional power supply circuit. 1...Differential amplifier, 2...Feeding resistance composite transfer function feedback circuit, 3.4...Resistor, 5...
. . . Low potential side drive circuit, 6 . . . High potential side drive circuit, 7 . . . Loop detection circuit, 8, 10.
...Power supply switching circuit, 9...Negative power supply, 1
1...Positive power supply, A, B...Talking line, T
・・・・・・Telephone. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] A differential amplifier that detects the voltage between a pair of communication lines, and a resistance value lower than the resistance value of a power supply resistor whose one end is connected to each of the pair of communication lines and which is determined from the maximum allowable current value of the telephone and communication circuit. and a low potential side and a high potential side that drive a load connected in series to the other ends of the first and second resistors and connected to the pair of communication lines. The combined resistance value of the side drive circuit, the first and second resistors receiving the output of the differential amplifier, and the low-potential side and high-potential side drive circuits connected in series thereto, respectively, is determined as the power supply resistance. and a feed resistance composite transfer function feedback circuit that sends a feedback signal to the low potential side and high potential side drive circuits so that the resistance value is the same as the resistance value of the telephone. In a power feeding circuit that supplies terminal voltage applied to both ends of each of the first and second resistors, it is detected whether or not a load connected to the pair of communication lines forms a DC loop. The loop detection circuit is connected to either a power supply for talk current or a power supply having a potential lower than the potential of the power supply for talk current as a power supply for the low potential side drive circuit, and the loop detection circuit detects a DC loop. For example, a first power supply switching circuit that selects a power supply for communication current and selects a potential lower than the potential of the power supply for communication current if it is not detected; and a power source of earth or positive potential as a power supply for the high potential side drive circuit; A power supply circuit characterized in that it has a second power supply switching circuit that connects any one of the power supplies and selects earth potential if the loop detection circuit detects a DC loop, and selects a positive potential if the loop detection circuit does not detect a DC loop.