JP3683002B2 - DC-DC converter power supply subscriber circuit - Google Patents

Description

[0001]
[Industrial application fields]
The DC-DC converter power supply subscriber circuit according to the present invention relates to a subscriber circuit in which a DC-DC converter is added to the power supply unit of the subscriber circuit, and is particularly regulated by the value of the common-mode voltage as represented by PBX. The present invention relates to a DC-DC converter power supply subscriber circuit having a function of limiting a current value in power supply to a terminal.
[0002]
[Prior art]
A subscriber circuit that accommodates a subscriber terminal in a telephone switchboard employs two types of methods, constant resistance power supply and constant voltage power supply, as a method of supplying a call DC current to the accommodation terminal.
[0003]
The constant resistance power supply is a method used when power is supplied to a terminal such as a normal telephone that flows 15 mA or more as a call current, and power is supplied to the A line and the B line via the power supply resistor R in the power supply unit of the subscriber circuit. In this case, if the voltage between the A line and the B line of the subscriber circuit is VL, and the loop current flowing through the subscriber line is IL, the power supply characteristic is a straight line with a downward slope to which IL decreases as VL increases. On the other hand, the constant voltage power supply is a method in which power is supplied to the A line and the B line via a constant voltage source V in the power supply unit of the subscriber circuit, and is used when power is supplied to a terminal having high impedance such as FAX. It is. When constant resistance power is supplied to a terminal having high impedance, the loop current IL is small and the voltage at the power supply resistor R is reduced. Therefore, the dynamic range of the circuit in this part of the power feeding unit cannot be ensured and cannot operate. Therefore, a constant voltage power supply is provided with a constant voltage source V in order to ensure the dynamic range of the circuit in this part in the power supply unit. The voltage between the A line and the B line of the subscriber circuit is VL, the subscriber Assuming that the loop current flowing in the line is IL, VL is always a constant value regardless of IL.
[0004]
Constant resistance power feeding is a method of feeding power to the A line and the B line via a constant feeding resistance R in the power feeding part of the subscriber circuit, so when the distance to the terminal is long and the connected subscriber line is long Since the line resistance value becomes large, the loop current IL flowing through the subscriber line becomes small. Conversely, when the subscriber line to the terminal is short, the loop current IL becomes large. This has the disadvantage that the constant resistance power supply has a large power consumption (power loss) due to the power supply resistance R when the distance to the accommodated terminal is short.
[0005]
In order to solve this drawback of the constant resistance power supply, there is a DC-DC converter power supply that performs power supply using a DC-DC converter. Similarly to the constant voltage power supply, the DC-DC converter power supply uses a voltage source in a portion corresponding to the power supply resistance in the constant resistance power supply of the power supply unit, and the voltage of the voltage source is changed by using the DC-DC converter. A power supply characteristic similar to that of the resistance power supply is obtained.
[0006]
The power loss PD of the power supply unit due to this DC-DC converter power supply becomes PD = 2VIL when the voltage of the voltage source applied to the A line and the B line is V and the loop current is IL. On the other hand, the power loss PR of the power supply unit in the constant resistance power supply is PR = 2RIL2, where R is the power supply resistance through the A line and B line, and IL is the loop current. Therefore, when the condition of PD <PR is obtained, the power loss is smaller when the DC-DC converter power supply is performed than when the constant resistance power supply is performed when V <RIL. Therefore, the power supply is performed with V = RIL as a boundary point. It can be seen that it is efficient to switch the method from constant resistance feed to DC-DC converter feed.
[0007]
Such a conventional DC-DC converter power supply subscriber circuit will be described with reference to the drawings.
[0008]
5 is a functional block diagram showing the configuration of a conventional DC-DC converter power supply subscriber circuit, FIG. 6 is a power supply characteristic of a conventional DC-DC converter power supply subscriber circuit, and FIG. 7 is a conventional DC-DC converter power supply subscriber. FIG. 8 is a diagram showing characteristics related to the loop resistance value including the terminal resistance of the midpoint potential of the A line, B line and AB line in the circuit, and FIG. .
[0009]
In FIG. 5, a conventional DC-DC converter power supply subscriber circuit includes a current detection circuit 2 that detects a loop current, and a power supply mode switching circuit that compares the output of the current detection circuit 2 with a threshold value and outputs a power supply mode switching signal. 3, a battery feed circuit 4 that operates in a constant voltage power supply mode and a constant resistance power supply mode, and a DC-DC converter 5 that changes the power supply voltage supplied to the battery feed circuit 4 in accordance with the output of the current detection circuit 2. Have.
[0010]
Next, the operation of such a conventional DC-DC converter power supply subscriber circuit will be described.
[0011]
When a subscriber makes a call, a loop circuit is formed in the subscriber terminal 1, and the current supplied from the battery feed circuit 4 of the subscriber circuit is A line 8, the loop circuit of the subscriber terminal 1, B line 9. A loop current IL flows through a path returning to the current detection circuit 2 and the battery feed circuit 4. The value of the loop current IL is detected by the current detection circuit 2, and a detection signal having a level corresponding to the value of the loop current IL is output.
[0012]
The power supply mode switching circuit 3 takes in the detection signal output from the current detection circuit 2 and compares it with a predetermined threshold value. The battery feed circuit 4 is operated in the constant voltage power supply mode circuit configuration in which the voltage source is used for the portion corresponding to the power supply resistance in the constant resistance power supply of the power supply unit if the circuit configuration is in the constant resistance power supply mode. Switch to let Further, when the power supply mode switching circuit 3 detects a threshold value or more, the DC-DC converter 5 is operated, and the subscriber uses the detection signal output from the current detection circuit 2 and the output voltage VBB of the DC-DC converter 5 as control signals. The current value fed to the terminal 1 is controlled so as to have the same feeding characteristics as those of the conventional constant resistance feeding. That is, the DC-DC converter 5 operates to increase the potential of the output voltage VBB and decrease the output voltage of the subscriber circuit when the loop current IL increases. As a result, the common-mode voltage that is the midpoint potential of the A line / B line increases.
[0013]
[Problems to be solved by the invention]
When DC-DC converter power supply is performed, the battery feed circuit operates in a constant voltage power supply mode in which the voltage between the ground and B lines and the output voltage VBB / A line of the DC-DC converter 5 is constant regardless of the loop current. I am letting. For this reason, a terminal that is regulated by the value of the common-mode voltage at the near end (for example, in PBX, if the common-mode voltage exceeds -15V, PBX misrecognizes lever power feeding as normal and releases the primary response loop. When the power is supplied, the loop current I L becomes large and the DC-DC converter operates to increase the output voltage VBB potential. The voltage between the ground and the B line and between the VBB and the A line must be increased so as not to be higher than the specified value, resulting in a problem that the power loss does not decrease. For example, taking a terminal whose voltage value VL at the output of the subscriber circuit is 1V as an example, the midpoint potential is − (V + 0.5). If this terminal has no specified common-mode voltage, the battery feed circuit is fed. If the voltage source value V of the power supply section can be set to about 5 V, but the PBX needs to satisfy the common-mode voltage regulation, the voltage source value V of the power supply section is 14.4. Must be set to 5V.
[0014]
[Means for Solving the Problems]
A DC-DC converter-fed subscriber circuit according to the present invention is a subscriber circuit that accommodates a subscriber terminal in a telephone exchange via a subscriber line, and has the following configuration and characteristics.
[0015]
(1) Constant resistance power supply mode in which the supply current changes according to the loop resistance value of the subscriber line, or a constant voltage that supplies a constant voltage between the two lines of the subscriber line regardless of the loop resistance value of the subscriber line A power supply circuit that operates in any one of the power supply modes.
[0016]
(2) A current detection circuit that detects a loop current of a subscriber line and outputs a detection signal corresponding to the loop current value.
[0017]
(3) The detection signal of the current detection circuit is captured, the value of the detection signal is compared with a predetermined threshold value, and a switching signal that specifies the power supply mode to be operated in the power supply circuit is output based on the comparison result. Power supply mode switching circuit.
[0018]
(4) When the power supply circuit operates in the constant resistance power supply mode, the power supply circuit is supplied to the power supply circuit as it is. When the power supply circuit operates in the constant voltage power supply mode, the detection signal output from the current detection circuit is captured. A DC-DC converter that changes the voltage supplied to the power supply circuit in accordance with the value of the detection signal.
[0019]
(5) The power feeding circuit further includes a current limiting circuit that switches a value of a maximum loop current to be supplied based on a current limit switching signal given from the outside.
[0020]
Further, the DC-DC converter power supply subscriber circuit according to the present invention stops the operation of the DC-DC converter in the power supply circuit based on the current limit switching signal given from the outside, and the subscriber terminal It is characterized in that it operates in a constant voltage power supply mode for a near-end subscriber with a short subscriber line, and in a constant resistance power supply mode for a far-end subscriber with a long subscriber line to a subscriber terminal.
[0021]
[Action]
When power is supplied to a terminal having a specified common-mode voltage, an external current limit switching signal is received and operated by a current limit circuit to limit the maximum loop current. As a result, the DC-DC converter also does not raise the output potential beyond the voltage corresponding to the maximum loop current.
[0022]
【Example】
Next, the present invention will be described with reference to the drawings.
[0023]
FIG. 1 is a functional block diagram showing the configuration of an embodiment of a DC-DC converter power supply subscriber circuit according to the present invention. In the figure, a DC-DC converter power supply subscriber circuit includes a current detection circuit 2 that detects a loop current, and a power supply mode switching circuit 3 that compares the output of the current detection circuit 2 with a threshold value and outputs a power supply mode switching signal. The battery feed circuit 4 that operates in the constant voltage power supply mode and the constant resistance power supply mode, the DC-DC converter 5 that changes the power supply voltage supplied to the battery feed circuit 4 according to the output of the current detection circuit 2, and the loop current Accordingly, a loop current clamp circuit 7 for limiting the maximum loop current by an external control signal is provided.
[0024]
When a subscriber makes a call, a loop circuit is formed in the subscriber terminal 1, and the current supplied from the battery feed circuit 4 of the subscriber circuit is A line 8, the loop circuit of the subscriber terminal 1, B line 9. A loop current IL flows through a path returning to the current detection circuit 2 and the battery feed circuit 4. The value of the loop current IL is detected by the current detection circuit 2, and a detection signal having a level corresponding to the value of the loop current IL is output.
[0025]
The power supply mode switching circuit 3 takes in the detection signal output from the current detection circuit 2 and compares it with a predetermined threshold value. The battery feed circuit 4 is operated in the constant voltage power supply mode circuit configuration in which the voltage source is used for the portion corresponding to the power supply resistance in the constant resistance power supply of the power supply unit if the circuit configuration is in the constant resistance power supply mode. Switch to let At this time, the value of the voltage source of the circuit configuration in the constant voltage power supply mode is set to the lowest voltage that can ensure the dynamic range of the internal circuit of the power supply unit. Further, when the power supply mode switching circuit 3 detects a threshold value or more, the DC-DC converter 5 is operated, and the subscriber uses the detection signal output from the current detection circuit 2 and the output voltage VBB of the DC-DC converter 5 as control signals. The current value fed to the terminal 1 is controlled so as to have the same feeding characteristics as those of the conventional constant resistance feeding.
[0026]
Here, when power is supplied to a terminal having a specified common-mode voltage, an external current limit switching signal is received by the loop current clamp circuit 7, the loop current clamp circuit 7 is operated, and the maximum loop current is limited. As a result, the DC-DC converter 5 also does not raise the VBB potential beyond the voltage corresponding to the maximum loop current. For terminals that attempt to flow more than the maximum loop current, the current is clamped by increasing the voltage between the ground and B lines and the voltage between VBB and A lines.
[0027]
FIG. 2 is a graph showing the feeding characteristics of the DC-DC converter feeding subscriber circuit of the present invention. In the figure, a characteristic curve 10 is a case where the common-mode voltage is not defined, and a characteristic curve 11 is a case where the common-mode voltage is defined. However, this clamp current value shows one embodiment and is not limited to this value.
[0028]
FIG. 3 is a graph showing the characteristics of the midpoint potential of the A-line, B-line, and AB-line with respect to the loop resistance RL of the DC-DC converter power supply subscriber circuit of the present invention. In the figure, characteristic curves 12, 13, and 14 show characteristics when power is supplied to a terminal that is not regulated by the common-mode voltage, and characteristic curves 15, 16, and 17 show characteristics when power is fed to a terminal that is regulated by the common-mode voltage. Show. It can be seen that the common-mode voltage specification is satisfied by clamping the maximum loop current.
[0029]
FIG. 4 is a graph showing power loss characteristics in the DC-DC converter power supply circuit of the present invention. In the figure, a characteristic curve 18 indicates the characteristics of a terminal that is not defined for the common-mode voltage, and a characteristic curve 19 indicates the characteristics of the terminal that is defined for the common-mode voltage.
[0030]
【The invention's effect】
As described above, the DC-DC converter power supply circuit according to the present invention is controlled from the outside so as to reduce the maximum loop current when power is supplied to a terminal having a common-mode voltage at the near end, and the DC-DC converter Since the VBB voltage to be controlled is fixed, the set voltage between the ground / B line and the VBB / A line can be reduced, and the power loss in the power feeding circuit can be reduced. In addition, when power is supplied to a terminal whose common-mode voltage is not specified, there is no need for current clamping, so that power loss in the power supply circuit of the near-end subscriber can be further reduced.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration of an embodiment of a DC-DC converter power supply subscriber circuit according to the present invention.
FIG. 2 is a graph showing power supply characteristics of the DC-DC converter power supply subscriber circuit of the present invention.
FIG. 3 is a graph showing the characteristics of the midpoint potential of the A-line, B-line, and AB-line with respect to the loop resistance RL of the DC-DC converter-fed subscriber circuit of the present invention.
FIG. 4 is a graph showing power loss characteristics in the DC-DC converter power supply circuit of the present invention.
FIG. 5 is a functional block diagram showing a configuration of a conventional DC-DC converter power supply subscriber circuit.
FIG. 6 is a diagram showing power supply characteristics of a conventional DC-DC converter power supply subscriber circuit.
FIG. 7 is a diagram showing a related characteristic with a loop resistance value including a terminal resistance of a midpoint potential of the A line, the B line, and the AB line in a conventional DC-DC converter power supply subscriber circuit.
FIG. 8 is a diagram illustrating a related characteristic between a loop resistance value of a power feeding circuit and power loss in a conventional DC-DC converter power feeding subscriber circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Subscriber terminal 2 Current detection circuit 3 Feeding mode switching circuit 4 Battery feed circuit 5 DC-DC converter 6 Power supply 7 Current clamp circuit 8 A line 9 B line

Claims (2)

In a subscriber circuit that accommodates a subscriber terminal via a subscriber line in a telephone exchange,
The constant resistance power supply mode in which the supply current changes according to the loop resistance value of the subscriber line, or the constant voltage power supply mode in which a constant voltage is supplied between the two lines of the subscriber line regardless of the loop resistance value of the subscriber line. A power supply circuit that operates in any power supply mode;
A current detection circuit that detects a loop current of a subscriber line and outputs a detection signal corresponding to the loop current value;
Power supply that takes in a detection signal of the current detection circuit, compares the value of the detection signal with a predetermined threshold value, and outputs a switching signal that specifies a power supply mode to be operated in the power supply circuit based on the comparison result A mode switching circuit;
When the power supply circuit operates in the constant resistance power supply mode, the power supply circuit is supplied to the power supply circuit as it is. When the power supply circuit operates in the constant voltage power supply mode, the detection signal output by the current detection circuit is captured. And a DC-DC converter that changes the voltage supplied to the power supply circuit in accordance with the value of the detection signal,
The power supply circuit further includes a current limit circuit that switches a value of a maximum loop current to be supplied based on a current limit switching signal given from the outside when power is supplied to a terminal having a common mode voltage. DC-DC converter power supply subscriber circuit. The power supply circuit stops the operation of the DC-DC converter based on a current limit switching signal given from the outside, and in a constant voltage power supply mode to a near-end subscriber with a short subscriber line to the subscriber terminal. 2. The DC-DC converter-fed subscriber circuit according to claim 1, wherein a long-term subscriber line to a subscriber terminal operates in a constant resistance feed mode for a long-end subscriber.

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