JP4160706B2 - Subscriber circuit power supply system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a subscriber circuit power supply system, and more particularly to a subscriber circuit power supply system using a DC-DC converter capable of both analog terminal system and digital terminal system power supply.
[0002]
[Prior art]
There are an analog terminal system and a digital terminal system as power supply systems for subscriber terminals such as telephones. Conventionally, the analog terminal system power supply and the digital terminal system power supply are realized by using different circuits because required power supply characteristics are greatly different. Next, each power feeding method will be described.
[0003]
A block diagram of a power feeding circuit in an analog terminal system is shown in FIG. The power source 1 is connected to the DC-DC converter 9 and supplies power to the power feeding circuit 2. An output transistor 3 (3a, 3b) is connected to the power feeding circuit 2, and an output is connected to a current / voltage detection circuit 7 for detecting a current flowing through the subscriber line and a voltage between the subscriber lines.
[0004]
The output of the current / voltage conversion circuit 7 is input to a power supply controller 6 that controls the DC-DC converter 9. The output of the feeder circuit 2 is connected to a subscriber line resistor 12 (12a, 12b) and a subscriber terminal 11. The value of the subscriber line resistance 12 is RL.
[0005]
The power supply circuit 2 has a voltage drop (the difference between the output voltage Vout of the DC-DC converter 9 and the voltage drop of the subscriber line load (the product of the current IL flowing through the subscriber line and the value RL of the subscriber line resistance 12)). Vout-IL · RL) occurs.
[0006]
However, the power feeding circuit 2 is composed of an electronic circuit, and does not necessarily require a large voltage drop. It is sufficient to supply a minimum voltage drop (VCEM) that does not saturate the output transistor 3 (Vout = RL · IL + VCEM).
[0007]
The current / voltage detection circuit 7 inputs the detection result to the power supply controller 6 to control the output of the DC-DC converter. These control operations are shown in Japanese Patent Application Laid-Open No. 57-124962 and will not be described in detail.
[0008]
Next, the power feeding characteristics are shown in FIG. The current IL flowing through the subscriber circuit in the analog terminal system power supply is expressed by the following equation.
[0009]
IL = VBB / (RL + Rin)
Here, VBB is a power supply voltage, RL is a subscriber line resistance, and Rin is an internal resistance of the power feeding circuit. Generally, VBB = −48V, RL = 0 to 1720Ω, and Rin = 440Ω.
[0010]
FIG. 4 shows a block diagram of a power supply circuit in the digital terminal system. The power source 1 is connected to the DC-DC converter 9, and the current detection circuit 13 connected to the output of the DC-DC converter 9 inputs the detection output to the power supply controller 6. The power supply controller 6 controls the DC-DC converter so that the current value flowing through the subscriber terminal 11 becomes a constant current value (for example, 39 mA). The power supply characteristics are shown in FIG.
[0011]
[Problems to be solved by the invention]
As shown in FIGS. 3 and 5, the analog terminal system requires constant resistance power supply characteristics, and the digital terminal system requires constant current power supply characteristics. Providing independent circuits for both the analog terminal system and digital terminal system power supply is disadvantageous from the viewpoint of miniaturization of mounting area and economy.
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to provide a subscriber circuit power feeding system capable of realizing both an analog terminal system and a digital terminal system that achieve a reduction in mounting area and economy.
[0013]
[Means for Solving the Problems]
The purpose is to share the DC-DC converter between the analog terminal system power supply and the digital terminal system power supply. In the case of the analog terminal system power supply, the power is supplied to the subscriber terminal via the power supply circuit. This is achieved by bypassing the power supply circuit, switching control to supply power, and providing power supply characteristics suitable for each power supply.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0015]
First, FIG. 1 shows a block configuration of an example of a subscriber circuit power feeding system according to the present invention. As shown in the figure, the power source 1 is connected to a DC-DC converter 9, and the output of the DC-DC converter 9 is connected to a current / voltage detection circuit 7. The detection output of the current / voltage detection circuit 7 is input to a power supply controller 6 and an analog / digital switching control signal 5 is used to determine whether to supply power in an analog terminal system or a digital terminal system so that desired power supply characteristics can be obtained. The DC-DC converter 9 is controlled. The current / voltage detection circuit 7 is connected to a switch 4 (4a, 4a, 4a, 4b, 4c, 4c, 4c) so as to be connected directly to the subscriber line in the case of digital terminal type power supply and to the subscriber line via the power supply circuit 2 in the case of analog terminal type power supply. Connect to 4b). The power supply circuit 2 is connected to an output transistor 3 (3a, 3b), and the output transistor 3 (3a, 3b) includes a detection circuit 8 (8a, 8b) for the VCE (collector-emitter voltage). The detection result is input to the power supply controller 6.
[0016]
FIG. 6 shows a block diagram of the power supply controller 6. The power supply controller 6 includes an output of a current / voltage conversion unit 15 that converts a current detection result of the current / voltage detection circuit 7 connected to an output of the DC-DC converter 9, and the current / voltage detection circuit 7. The maximum value selection circuit 16 that compares the output of the voltage detection unit and selects and outputs a large value, the output of the voltage detection unit of the current / voltage detection circuit 7, and the output transistors 3a and 3b of the power supply circuit 2 in FIG. The output of the VCE detection circuit 8 that detects the VCE is compared, the minimum value selection circuit 17 that selects and outputs a small value, and the output of the maximum value selection circuit 16 when the analog / digital control signal 5 supplies the digital terminal system. In the case of analog terminal system power supply, the power supply is configured from an error amplifier 18 having a reference voltage Vref to receive the output of the minimum value comparison circuit 17 and to obtain a required characteristic. The output of the controller 6 is input to the DC-DC converter 9.
[0017]
An example of an embodiment of the DC-DC converter 9 is shown in FIG. The DC-DC converter 9 includes a PWM generation circuit 19 that performs pulse width modulation on the output of the power supply controller 6, a transistor 21 that performs switching by receiving the output of the PWM generation circuit 19, and one of the transistors 21 is The secondary winding output of the switching transformer 22 is connected to a rectifying diode 23 and a capacitor 24 and output through a filter composed of a coil 25 and a capacitor 26.
[0018]
Next, the power supply mechanism in the digital terminal system and the analog terminal system will be described with reference to FIGS.
[0019]
First, digital power supply will be described. In FIG. 1, when the analog / digital switching control signal 5 sends a signal for the digital terminal system, the selector switch 4 (4a, 4b) is switched to the D side. In the case of the digital terminal system, the current detection unit of the current / voltage detection circuit 7 detects the current flowing in the subscriber line, and the voltage detection unit detects the voltage generated between the subscriber lines. The current detected by the current detection unit of the current / voltage detection circuit 7 is converted into a voltage by the current / voltage conversion unit 15 shown in FIG. Let the detected value be Vid. A detection value detected by the voltage detection unit of the current / voltage detection circuit 7 is defined as Vvd. Adjustment is made so that Vid = Vvd when the corner characteristic of the power feeding characteristic shown in FIG. 5 (IL = 39 mA, VL = 60 V). In the constant current region (IL = 39 mA), that is, 0 <VL <60V, Vvd <Vid, so the maximum value selection circuit 16 selects Vid. Vid is input to the error amplifier 18, and an error from Vref is output to the DC-DC converter 9. Here, when Vid <Vref, that is, when the current value is smaller than a desired value (for example, 39 mA), the PWM generator circuit 19 shown in FIG. 7 receiving the output from the error amplifier 18 increases the on-time of the transistor 21. Thus, when the output of the DC-DC converter 9 is increased, and when Vid> Vref, the on-time of the transistor 21 is shortened to decrease the output of the DC-DC converter 9, thereby making the constant current characteristic. Is realized. Further, in the constant voltage region (VL = 60 V), that is, 0 <IL <39 mA, Vvd> Vid, so the maximum value selection circuit 16 shown in FIG. 6 selects Vvd. The DC-DC converter 9 realizes constant voltage characteristics in the same manner as when Vid described above is selected.
[0020]
Next, analog terminal system power supply will be described. First, in FIG. 1, when the analog / digital switching control signal 5 sends out a signal for the analog terminal system, the selector switches 4a and 4b are switched to the A side. In the case of an analog terminal system, the output of the DC-DC converter 9 is connected to the power feeding circuit 2. Further, it is used as a non-floating circuit by being grounded to VBB or ground by a ground switch. The detection result VCE of the VCE detection circuits 8a and 8b for detecting the VCE of the output transistors 3a and 3b of the power supply circuit 2 and the output Vvd of the voltage detection unit of the current / voltage detection circuit 7 are selected as the minimum value shown in FIG. The value is input to the circuit 17 and a small value is input to the error amplifier 18. In the case of VCE <Vvd, in other words, when the load resistance on the subscriber line side is large, the value of VCE is selected, and the error amplifier 18 is set to Vref which is the minimum VCE value (VCEM) necessary for the transistor to operate. Enter. The output of the error amplifier 18 is input to the DC-DC converter 9 and controlled so that VCE = VCEM. (The operation of the DC-DC converter 9 is the same as that of the digital terminal system.) When VCE> Vvd, in other words, when the load resistance on the subscriber line side is small, the output voltage from the DC-DC converter becomes low. The power feeding circuit 2 may not operate. In this case, the output of the voltage detection unit of the current / voltage detection circuit 7 is selected by the minimum value selection circuit 17 so that a voltage necessary for the operation of the power feeding circuit 2 is generated from the output of the DC-DC converter 9. It is a subscriber circuit power supply control system that can also be controlled.
[0021]
【The invention's effect】
As described above, in the subscriber circuit power supply system according to the present invention, the conventional analog terminal system and digital terminal system power supply can be realized by using a single DC-DC converter instead of using separate circuits. In addition, it is possible to provide a subscriber circuit power supply system that is low in power consumption and economical in terms of mounting area.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram of a conventional analog terminal type power supply circuit.
FIG. 3 shows power supply characteristics of a conventional analog terminal system.
FIG. 4 is a block diagram of a conventional digital terminal type power supply circuit.
FIG. 5 shows power supply characteristics of a conventional digital terminal system.
FIG. 6 is a block diagram of a power supply controller.
FIG. 7 is a circuit diagram showing an embodiment of a DC-DC converter.
[Explanation of symbols]
1: Power supply 3: Output transistor 4: Analog / digital switch 10: Conventional analog terminal type power supply block 11: Subscriber terminal 12: Subscriber line resistance 14: Conventional digital terminal type power supply block 21: Transistor 22: Switching transformer 23: Diode 24: Capacitor 25: Coil 26: Capacitor

Claims (3)

In a subscriber circuit power supply system for supplying power to a subscriber terminal such as a telephone, a DC-DC converter connected to the power supply and a current / voltage for detecting output current / voltage connected to the output side of the DC-DC converter. A voltage detection circuit; a power supply circuit for supplying power to the subscriber terminal; a power supply controller connected to the DC-DC converter and the current / voltage detection circuit to control power supply characteristics of the converter; and the current / voltage detection An analog terminal power feeding method side provided between the circuit output and the power feeding circuit and guiding the output of the current / voltage detection circuit to the power feeding circuit, and a digital terminal power feeding bypassing the power feeding circuit to the subscriber terminal A switch unit that switches between the system side, the switch unit and the power supply controller connected to the analog terminal power system side And a control unit for controlling one of the digital terminal power supply method side, and when the switch unit is switched to the analog terminal power supply method side, it is switched to the digital terminal power supply method side so as to have a constant resistance power supply characteristic. In this case, the subscriber circuit power supply system is characterized in that the DC-DC converter is controlled by the power supply controller so as to have constant current power supply characteristics. An output transistor is provided on the output side of the power supply circuit, and in the case of the analog terminal type power supply, a voltage between a collector and an emitter of the output transistor of the power supply circuit is detected, and the DC is passed through the power supply controller with the detected voltage. The subscriber circuit power supply system according to claim 1, wherein a power supply voltage is supplied to the power supply circuit so as to control the DC converter and to supply the collector-emitter voltage necessary for power supply. In the case of the digital terminal system power supply, a current flowing through a subscriber line is detected by the current / voltage detection circuit, and the DC-DC converter is controlled by the detection output via the power supply controller. The subscriber circuit power feeding method according to claim 1, wherein:

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