JPH07307816A - Subscriber telephone interface circuit - Google Patents

Abstract

PURPOSE:To allow the integrated circuit to cope with a long distance subscriber line and to reduce the power consumption by supplying a comparatively large (small) current to the subscriber line when the distance of the subscriber line is long (short) and its line resistance is high (small). CONSTITUTION:A feeder circuit 1 detects hook-off with a threshold as a current sufficiently lower than a telephone set minimum operating current I1 and gives the information to a CPU 7. Since a monitor circuit 4 dose not activate a boosting circuit 4a when a feeding current is higher than a current I2(>I1), a -24V power supply supplied from a system power terminal 10 is supplied to the feeding circuit 1 as it is. When the feeding current is less than the threshold current I2, the CPU 7 activates the boosting circuit 4a via a control circuit 3 to supply a -48V power supply to the circuit 1. Thus, when the resistance of a subscriber line is small resulting from a short distance line, a minimum current is supplied and when the line resistance is high resulting form a long distance line, a required current is supplied. The CPU 7 does not activate the boosting circuit 4a in the on-hook state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber telephone interface circuit of an electronic exchange and, more particularly, to supplying power to a subscriber line.

[0002]

2. Description of the Related Art In recent years, electronic switchboards having a lower system power supply voltage are used because of low power consumption, low price, and the like. Especially, in a small capacity system, -48V is used instead of -48V.
A system power supply voltage of 24V is being adopted. Thus, in the subscriber telephone interface circuit of the electronic exchange whose system power supply voltage is -24V, when constant resistance power feeding is performed to the subscriber telephone, the power feeding voltage is also -24V.
Becomes However, in the subscriber telephone interface circuit with a power supply voltage of -24V, the power supply capability is naturally lower than in a system with a power supply voltage of -48V, so that it cannot be handled when the subscriber line becomes a long distance.

In order to solve this problem, a method of boosting only the power supply voltage supplied to the subscriber telephone interface circuit from -24V to -48V in an electronic exchange having a system power supply voltage of -24V can be considered. This configuration will be described with reference to FIG. 4. The booster circuit 4 boosts -24V supplied from the system power supply connection terminal 10 to -48V, and the power feeding circuit 1 adds this -48V voltage to the ringer sending circuit 6. Power is supplied to a subscriber line (not shown) and a subscriber telephone set via the subscriber telephone connection terminal 8. The 2-wire to 4-wire conversion circuit / codec 5 is connected between the power supply circuit 1 and the PCM highway connection terminal 9, and the CPU 7 controls this subscriber telephone interface circuit.

[0004]

However, in the above configuration, since the booster circuit 4 always boosts the voltage from -24V to -48V, it is necessary to cope with the case where the subscriber line has a long distance as shown in FIG. However, if the subscriber line is a short distance and the line resistance is small, an unnecessarily large amount of current will be supplied to the subscriber line, and there is a problem that low power consumption cannot be realized.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide a subscriber telephone interface circuit capable of coping with long distance subscriber lines and realizing low power consumption. To do.

[0006]

In order to achieve the above-mentioned object, a booster circuit for outputting different voltages based on a power supply voltage, and an output voltage of the booster circuit for a subscriber telephone set are provided. Power supply circuit for constant resistance power supply, and the current supplied by the power supply circuit is detected, and the booster circuit outputs a relatively high voltage when the power supply current is small, and the booster circuit compares when the power supply current is large. Boosting control means for controlling so as to output a relatively low voltage.

According to a second aspect of the present invention, the booster circuit outputs the power supply voltage as it is or after boosting the power supply voltage, and the boosting control means outputs the power supply voltage as it is when the power supply current is small. Is large, the booster circuit controls to boost and output the power supply voltage.

According to a third aspect of the present invention, the booster circuit boosts and outputs the power supply voltage, and further, switching means for selectively switching the power supply voltage or the output voltage of the booster circuit to supply the power supply circuit. The boost control means controls the switching means so that the power supply voltage is supplied to the power supply circuit when the power supply current is small, and the output voltage of the booster circuit is supplied to the power supply circuit when the power supply current is large. It is characterized by doing.

The present invention may further comprise means for detecting an on-hook state and an off-hook state of the subscriber's telephone, wherein the boosting control means supplies a relatively low voltage from the boosting circuit to the power feeding circuit in the on-hook state. Is supplied, and in the off-hook state, a relatively high voltage is supplied when the power supply current is small, and a relatively low voltage is supplied when the power supply current is large.

[0010]

According to the present invention, a relatively high voltage is supplied when the power supply current to the subscriber telephone is small, and a relatively low voltage is supplied when the power supply current is large. If the line is short and the line resistance is small, a relatively low current is fed to the subscriber line, and if the line is long and the line resistance is large, a relatively high current is supplied to the subscriber. The line is powered. Therefore, it is possible to cope with the case where the subscriber line has a long distance, and it is possible to realize low power consumption.

In the fourth aspect of the present invention, a relatively low voltage is supplied in the on-hook state, a relatively high voltage is supplied in the off-hook state when the power supply current is small, and a relatively low voltage is supplied when the power supply current is large. Will be supplied,
Can handle long distance subscriber lines, and
It is possible to realize low power consumption even in the on-hook state.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a subscriber telephone interface circuit according to the present invention.

In FIG. 1, the power feeding circuit 1 includes a booster circuit 4a.
Power is supplied to a subscriber line (not shown) and a subscriber telephone set (not shown) through a -24V or -48V ringer sending circuit 6 and a subscriber telephone connection terminal 8 supplied from the monitoring circuit 2 by this power feeding circuit 1. The monitored current value I is monitored. Then, in this embodiment, the booster circuit 4a keeps -24V supplied from the system power supply connection terminal 10 as it is, or-
It is configured to boost the voltage to 48 V and supply it to the power supply circuit 1, and this selection is controlled by the boost control circuit 3 described later.

As is well known, when the subscriber's telephone is off-hook, a DC loop is formed between the subscriber's telephone and the feeder circuit 1 via the subscriber line by the current fed by the feeder circuit 1. . Further, the power feeding circuit 1 detects this off-hook by using a value Ioffhook sufficiently lower than the minimum current value I1 at which the telephone operates, and applies the off-hook detection information to the CPU 7.

When the power supply circuit 1 detects the off-hook and the detection information is applied to the CPU 7, the booster control circuit 3 detects that the power supply current monitored by the monitor circuit 2 is larger than the threshold value I2 (> I1). Is supplied from the system power supply connection terminal 10 without the booster circuit 4a operating-2
4 V is supplied to the power supply circuit 1 as it is, and on the other hand, when the power supply current is smaller than the threshold value I2, the booster circuit 4a is operated to control to supply a voltage of -48V. Further, since the power supply current does not flow in the on-hook state, the booster control circuit 3 judges that the power supply current is smaller than the threshold value I2. However, since the power supply circuit 1 does not detect the off-hook, the booster circuit 4
Do not operate a.

When receiving an incoming call to the subscriber's telephone, C
Under the control of the PU 7, a ringer is sent from the ringer sending circuit 6 to the subscriber's telephone, and the dial pulse from the subscriber's telephone is detected by the power feeding circuit 1 and the detection signal is applied to the CPU 7. In addition, this circuit includes a 2-wire to 4-wire conversion circuit / codec 5 for communication.
And a PCM highway connection terminal 9 and the like.

Therefore, in the above embodiment, when the feeding current is larger than the threshold value I2, the voltage of -24V is fed,
When the feeding current is smaller than the threshold value I2, the voltage of -48V is fed. Therefore, as shown in FIG. 2, when the subscriber line is close and the line resistance is small, the minimum required current is the subscriber line. In addition, when the subscriber line has a long distance and the line resistance is large, a sufficient amount of current is supplied.

Therefore, it is possible to cope with the case where the subscriber line has a long distance, and it is possible to realize low power consumption as shown by the broken line in FIG. Further, in the on-hook state where power is not supplied, the voltage of -24V is applied to the booster circuit 4.
Since the power is supplied to the power supply circuit 1 from a, low power consumption can be realized. The boost control circuit 3 can be configured by hardware or software of the CPU 7.

Next, a second embodiment will be described with reference to FIG. In FIG. 3, the same circuits as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the second embodiment, a resistor R is inserted in the power supply line between the power supply circuit 1 and the ringer sending circuit 6 to monitor the power supply current,
The voltage across the resistor R is applied to the operational amplifier (differential amplifier) 11
Is detected by. Then, the output voltage of the operational amplifier 11 is compared with the reference voltage Vref by the comparator 12, and when the output voltage of the operational amplifier 11 is less than or equal to the reference voltage Vref, that is, when the power supply current is smaller than the threshold value I2 in the first embodiment shown in FIG. An H-level signal is output to.

Further, the output signal of the comparator 12 and H when the power supply circuit 1 detects an off-hook
A logical product signal of level detection signals is output from the AND gate 13 to drive the relay 14. Further, the booster circuit 4 is configured to constantly perform an operation of boosting −24V supplied from the system power supply connection terminal 10 to −48V, and supplying the output voltage to the power feeding circuit 1 via the relay 14.

The relay 14 is controlled so as to supply -24V supplied from the system power supply connection terminal 10 to the power supply circuit 1 as it is in the off state, and to supply the output voltage of the booster circuit 4 to the power supply circuit 1 in the on state. .

Therefore, also in this embodiment, when the subscriber line is short distance and the line resistance is small, the relay 14 is controlled to be turned off and the minimum required current is supplied to the subscriber line. Further, when the subscriber line is a long distance and the line resistance is large, the relay 14 is controlled to be turned on and a sufficient amount of current is supplied from the booster circuit 4,
It is possible to cope with long-distance subscriber lines and to realize low power consumption.

Here, even in an electronic exchange whose system power supply voltage is -24V, the trunk circuit on the office line side operates at -48V, and therefore has a -48V booster circuit. Therefore, the booster circuit 4 shown in FIG. Since it is possible to use the one in the trunk circuit, it is not expensive.

[0024]

As described above, according to the inventions of claims 1 to 3, a relatively high voltage is supplied when the power supply current to the subscriber telephone is small, and a relatively low voltage is supplied when the power supply current is large. Therefore, when the subscriber line is short-distance and the line resistance is small, a relatively low current is supplied to the subscriber line, and when the subscriber line is long-distance and the line resistance is large. A relatively high current is supplied to the subscriber line. Therefore, it is possible to cope with the case where the subscriber line has a long distance, and it is possible to realize low power consumption.

In the invention according to claim 4, a relatively low voltage is supplied in the on-hook state, a relatively high voltage is supplied in the off-hook state when the power supply current is small, and a relatively low voltage is supplied when the power supply current is large. Will be supplied,
Can handle long distance subscriber lines, and
It is possible to realize low power consumption even in the on-hook state.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a subscriber telephone interface circuit according to the present invention.

FIG. 2 is a graph showing a supply current supplied by the subscriber telephone interface circuit of FIG. 1 for each line resistance range.

FIG. 3 is a block diagram showing a subscriber telephone interface circuit of a second embodiment.

FIG. 4 is a block diagram showing a conventional subscriber telephone interface circuit.

5 is a graph showing a power supply current supplied to each system by the subscriber telephone interface circuit of FIG. 4;

[Explanation of symbols]

 1 Feeding Circuit 2 Feeding Current Monitoring Circuit 3 Boost Control Circuit 4, 4a Boosting Circuit 8 Subscriber Telephone Connection Terminal

Claims (4)

[Claims] 1. A booster circuit that outputs different voltages based on a power supply voltage, a power supply circuit that supplies a constant resistance power to an output voltage of the booster circuit to a subscriber telephone, and a current supplied by the power supply circuit is detected. And a booster control means for controlling the booster circuit to output a relatively high voltage when the power supply current is small and to output a relatively low voltage when the power supply current is large. Interface circuit. 2. The booster circuit outputs the power supply voltage as it is or after boosting it, and the boosting control means boosts the power supply voltage when the power supply current is small and outputs it, and when the power supply current is large. 2. The subscriber telephone interface circuit according to claim 1, wherein the booster circuit is controlled so as to output the power supply voltage as it is. 3. The booster circuit includes a switching unit that boosts and outputs a power supply voltage and further selectively switches the power supply voltage or the output voltage of the booster circuit to supply the power supply circuit. Controls the switching means such that the power supply voltage is supplied to the power supply circuit when the power supply current is small, and the output voltage of the booster circuit is supplied to the power supply circuit when the power supply current is large. The subscriber telephone interface circuit according to claim 1. 4. A means for detecting an on-hook state and an off-hook state of a subscriber's telephone is further provided, wherein said step-up control means is supplied with a relatively low voltage from the step-up circuit to the power supply circuit in the on-hook state and is in the off-hook state. The control according to any one of claims 1 to 3, wherein a relatively high voltage is supplied when the power supply current is small, and a relatively low voltage is supplied when the power supply current is large. Person telephone interface circuit.