JPH0254663A - Feeder circuit - Google Patents

Abstract

PURPOSE:To improve the reliability of an overcurrent protective function by interrupting a drive current by a protection operation signal when a monitor circuit detects an overcurrent in the feeder circuit. CONSTITUTION:A switch SW4 controller with a switch SW3 by a monitor circuit 32 and acting like a control circuit is provided between a gate and a terminal 5 of the switch SW2. When a terminal 2 is opened or terminals 1, 7 are short-circuited and a difference between a current flowing to a resistor R1 and a current flowing to a resistor R3 is increased, since the monitor circuit 32 opens the switches SW3, 4 the drive current of the switch SW2 is interrupted and the feeder enters the protective operating state. Thus, a drive current via a resistor R8 is interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power supply circuit for a subscriber circuit connected to a telephone exchange.

(Prior Art) Various external noises such as lightning surges are applied to subscriber circuits that are directly connected to subscribers, and short circuits and the like occur.

Therefore, when integrating the power supply circuit of the subscriber circuit,
Things like this need to be taken into consideration.

Conventionally, as a power supply circuit for this type of subscriber circuit, there has been a study published by Tahara et al., entitled "A Structure of a Common-Mode Noise Elimination Circuit," 1981 IEICE General Conference No. 343J Report, pp. 2-279. This report describes one configuration of a common mode noise removal circuit that includes a subscriber circuit power supply circuit.

Also, although I will only quote it here,
There is also a technique described in Japanese Patent No. 19674.

Furthermore, IEICE's 70th Anniversary National Conference (written by Kitano et al., "Study of rIC current detection circuit")
1985)'' report, page 2-163, FIG. 2 shows a ``current detection circuit'' with improved detection accuracy. According to this current detection circuit, it has been reported that ground faults and electrical layers can be detected in off-hook conditions by detecting line current based on the voltage drop across the feedback resistor of the balanced current output amplifier for supplying communication current. has been done.

Furthermore, as a power supply circuit element that can be used in this type of subscriber circuit, "Telecommunications e-Data" published by Motorola Corporation is used.
onsDevice Data)J includes "Telephone line power supply and 2-wire 4-wire conversion circuit
FEED AND 2-To 4-WIRE C0N
VER3ION CIRCUIT) J is shown in the tail.

There is also a conventional power supply circuit shown in FIG.

FIG. 2 will be explained below.

In FIG. 2, 1 to 4.67 are terminals of the power supply circuit. Terminal 1 connects one line of a telephone line TL consisting of a pair of lines to the cathode of a switch SWI consisting of a thyristor. The anode of the switch SW1 is connected to the positive terminal of the power source E via the terminal 3, the transistor Q1, the resistor R1, and the terminal 6.

The transistor Q1 has its base connected to the output terminal of the operational amplifier OPl, its emitter connected to the terminal 6 through the resistor R1, and connected to the negative input of the operational amplifier OPI through the resistor R2.

The positive input of operational amplifier OPI is connected to terminal 6 through resistor R5.
It is connected to one end of the current source circuit 1 and the current source circuit 3. The negative input of operational amplifier OPI is connected to the emitter of transistor Q1 via resistor R2 and to one end of current source 2.

The switch S is symmetrical to the circuit including the switch 1, the transistor Q1, and the operational amplifier OPI described above.
A circuit is provided including W2, transistor Q2 and operational amplifier OP2.

That is, terminal 2 connects the other line of telephone line TL to switch 1.
Similarly, it is connected to the anode of switch SW2 made of Cyrisk. The cathode of switch SW2 is terminal 4,
Power supply E via transistor Q2, resistor R3 and terminal 7
connected to the negative terminal of.

Transistor Q2 has its base connected to the output terminal of operational amplifier OP2, its emitter connected to terminal 7 via resistor R3, and connected to the negative input of operational amplifier OP2 via resistor R4.

The positive input of the operational amplifier OP2 is connected to a terminal 7 via a resistor R6, and is also connected to the other end of the current source I3 via a current source 2 and a switch SW3. The negative input of the operational amplifier OP2 is connected to the emitter of the transistor Q2 via a resistor R4, and to the other end of the current source 1.

The control inputs or gates of switches SWI and SW2 are:
Both are connected to a drive current control device 5. The drive current control device 5 connects in series a switch 5a whose one end is connected to the gates of the switches SWI and SW2 and which is controlled as described below, a current source 5b, and a power source 5c whose negative terminal is grounded. These components are easily realized, for example, by integrated circuits with TTL level interfaces.

Here, resistors R7 and 8, current source 11,
Sections 2, 3, and switch SW 3 (f) schematically illustrate a current supply circuit 31 having a configuration as shown in FIG. 3, for example. Also, the resistance R surrounded by the dotted line
1 and R3 are the monitoring circuit 32 shown in detail in FIG.
This is an overview.

The current supply circuit 31 shown in FIG. 3 includes a transistor Qll whose collector is connected to the negative input of the operational amplifier OPI, a transistor Q12 whose collector is connected to the positive input of the operational amplifier OP1, and a transistor Q12 whose collector is connected to the negative input of the operational amplifier OP2. and a transistor Q14 whose collector is connected to the positive input of the operational amplifier OP2. The emitters of transistors Qll and Q14 are connected to each other via a resistor R12. transistor Q
The emitters of Q12 and Q13 are connected to each other via a resistor R11.

Further, the current supply circuit 31 includes a current mirror circuit 41 connected to terminal 3 via a resistor R7 and to terminal 6, and a current mirror circuit 41 connected to terminal 4 via a resistor R8 and connected to terminal 7. A current mirror circuit 42, a current mirror circuit 43 connected to the positive inputs of operational amplifiers OPI and OF2, and a current mirror circuit 44 connected to the current mirror circuit 43 via the switch SW3 and connected to the terminal 7. have

Here, if there is a relationship of 111>112 between the current Ill flowing through the resistor R7 and the current 112 flowing through the resistor R8, then the current from the positive terminal of the power supply E is connected to the operational amplifier op.
i flows through the positive input of transistor Q12, resistor R11, transistor Q13 and the negative input of operational amplifier OP2.

On the other hand, if there is a relationship of Ill<112, the current from the positive terminal of the power supply E flows to the negative input of the operational amplifier OPI, the transistor Qll, the resistor R12, the transistor Q14, the positive input of the operational amplifier OP2, and the negative terminal of the power supply E. .

Further, a current (I
11+I l 2) is switch SW3, operational amplifier op
i and the positive input of operational amplifier OP2.

FIG. 4 is a detailed circuit diagram of the monitoring circuit 32 shown in FIG. 2. The monitoring circuit 32 includes a transistor Q21 whose base is connected to the emitter of the transistor Q1, which is connected to the power supply E shown in FIG. 2 through a resistor R1, and whose emitter is connected to the power supply E through a resistor R21, Connected to the emitter of Q2 and connected to the power supply E via resistor R3,
A transistor Q22 whose emitter is connected to the power supply E via a resistor R22, transistors Q23 and Q24 whose emitters are connected to each other and whose bases are also connected to each other, a transistor Q25 whose collector and base are connected to the collector of the transistor Q24, and a transistor Q25 whose collector and base are connected to the collector of the transistor Q24. A voltage comparator VCOMP has a positive input connected to the collector of the transistor Q23 and the collectors of the resistors R23 and Q26.

The monitoring circuit 32 determines that I21>I2 between the current I21 flowing through the resistor R1 and the current I22 flowing through the resistor R3.
If there is a relationship of 2, the resistor R21, the transistor Q21,
Current flows through the path of transistor Q24 and transistor Q25. On the other hand, if there is a relationship of I21<I22, resistor R23, transistor Q23, transistor Q
22, a current flows through the resistor 22. voltage comparator VC
The OMP introduces the voltage due to this current to its positive input, the reference voltage to its negative input, and controls the switch SW3 with an output consisting of the comparison result.

The power supply to the telephone line TL is such that current from the positive terminal of the power supply E flows through terminal 6, resistor R1, transistor Ql, terminal 3, switch SWI in the on state, terminal 1, terminal 30, terminal 2,
Switch SW2 in on state, terminal 4, transistor Q2
and the negative terminal of the power source E through the resistor R3. At this time, the DC impedance between the terminals 3 and 6 is determined by the resistors R1, R5, R7 and the current source I3. Also, terminal 4 and terminal 7
The DC impedance between the resistors R3, R6, and R8
and current source I3.

Also, if the voltage ■1 between the terminals 3 and 6 and the voltage ■2 between the terminals 4 and 7 are not equal, that is, ■1≠v2
In this case, if Vl>V2, resistor R7 and resistor R8
The current of the current source 1 is increased according to the difference in the current flowing through the current source 1, and if Vl<V2, the current of the current source 2 is increased according to the difference.
The current is increased, and both operate so that Vl=V2.

However, if V1=V2 is not achieved even with the above operation due to a failure in the telephone line TL, etc., the monitoring circuit 32
The switch SW3 is opened to stop the operation of the current source I3, thereby limiting the currents of the current source 11 and the current source I2. Such protection operation prevents the current supplied to the telephone line TL from becoming an overcurrent. This operation continues until the difference in current flowing through resistors R1 and R2 becomes sufficiently small.

(Problem to be Solved by the Invention) However, in the conventional power supply circuit, when there is a short circuit between the terminals 1 and 7, the power supply E, the resistor R1, the transistor Q1.
Since current flows through terminal 3, switch SWI, terminal 1, terminal 7, and electric current ME, the current difference between resistor R1 and resistor R3 becomes large (becomes a protective operation. However, the drive current control device Since the drive current flows through terminal 4 and resistor R8, the difference in current flowing through resistor R7 and resistor R8 is reduced, reducing the current of current source 11, and further reducing the current flowing through resistor R1 of monitoring circuit 32. Therefore, the power supply circuit operates to cancel the protective operation, and when the protective operation is canceled, the short circuit is not removed, so the power supply circuit operates again to cancel the protective operation. There was a problem in that this was repeated and the operating state became unstable.

An object of the present invention is to provide a power supply circuit in which the operating state of the circuit is stable without being affected by the drive current that operates the switch as described above.

(Means for Solving the Problems) A power supply circuit of the present invention is connected in series to a pair of telephone lines, and is set to a conductive state when the drive current is energized, and is set to a conductive state when the drive current is deenergized. are first and second switches that are set to a cutoff state when the passing current becomes less than a certain value, and a first transistor and a first resistor that are connected in series between the first switch and one end of the power supply. and a second current flowing through a second transistor and a second resistor connected in series between the second switch and the other end of the power supply, the difference being a predetermined value. When the above occurs, a monitoring circuit that activates a protective operation signal and a third switch connected between the first switch and one end of the power supply
and a fourth current flowing through a fourth resistor connected between the second switch and the other end of the power source. a current supply circuit that controls the first and second transistors to flow a current and limit the current to the telephone line when the protection operation signal is activated; and protection of the monitoring circuit. The control circuit includes a control circuit that reduces the drive current of one of the first and second switches when the operating signal is activated.

(Function) In the power supply circuit configured as described above, the difference between the first current flowing through the first resistor and the second current flowing through the second resistor is equal to or larger than a predetermined value. At this time, the drive current is cut off by energizing the protection operation signal and opening the control input of at least one of the first and second switches, and the third and fourth currents are The difference is not affected by the drive current.

(Embodiment) FIG. 1 is a circuit diagram of a power supply circuit showing an embodiment of the present invention. In FIG. 1, the same parts as in FIG. 2 are given the same reference numerals. A switch SW4 is provided between the gate of the switch SW2 and the terminal 5, as shown by the arrow, and is controlled together with the switch SW3 by the monitoring circuit 32 and functions as a control circuit. Other parts are second
The configuration is similar to that shown in the figure, and the explanation will be repeated, so please refer to the above explanation.

Next, the operation of the above configuration will be explained. When terminal 2 is open and terminal 1 and terminal 7 are shorted,
When drive current flows to the gates of switches SW1 and SW2, switches SWI and SW2 are turned on, and current flows from the positive terminal of power supply E to resistor R1, transistor Q1, and terminal 3.
, through switch SWI, terminal 1 and terminal 7 to the negative terminal of power supply E.

However, as mentioned above, when the difference between the current flowing through the resistor R1 and the current flowing through the resistor R3 becomes large because the terminal 2 is opened or the terminals 1 and 7 are short-circuited. Since the monitoring circuit 32 opens the switches SW3 and SW4, the drive current of the switch SW2 is cut off, and the power supply circuit enters the protective operation state. This results in resistance R
The drive current via 8 is cut off. This protective operation is maintained until the voltage between terminals 1 and 7 increases and the current flowing through resistor R7 decreases.

Thereafter, when the short circuit between terminal 1 and terminal 7 is removed and the difference between the currents flowing through resistor R1 and resistor R3 decreases, the monitoring circuit 32 turns on switches SW3 and SW4 to perform a protective operation. Release.

(Effects of the Invention) As described above in detail, according to the present invention, when the monitoring circuit detects an overcurrent in the power supply circuit, the protection state is reliably maintained by a protection operation signal that cuts off the drive current. Therefore, the reliability of the overcurrent protection function can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a power supply circuit according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional power supply circuit, FIG. 3 is a circuit diagram showing details of the current supply circuit of FIG. 2, and FIG. The figure is a circuit diagram showing details of the monitoring circuit of FIG. 2. SWI to SW4...Switch, 31...Current supply circuit, 32...Monitoring circuit. Patent applicant Oki Electric Industry Co., Ltd. Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] Each is connected in series to a pair of telephone lines, and when the driving current is energized, it is set to a conductive state, and when the driving current is deenergized, the passing current is below a certain value. a first current flowing through first and second switches that are set to a cut-off state when the switch is turned off; a first transistor and a first resistor that are connected in series between the first switch and one end of the power source; A second voltage flowing through a second transistor and a second resistor connected in series between the second switch and the other end of the power supply.
When the difference between the current of A current is caused to flow through the telephone line according to a current corresponding to a difference between a third current that flows and a fourth current that flows through a fourth resistor connected between the second switch and the other end of the power source. and a current supply circuit that controls the first and second transistors so as to limit the current to the telephone line when the protection operation signal is activated, the power supply circuit comprising: protection of the monitoring circuit; A power supply circuit comprising: a control circuit that cuts off the drive current of at least one of the first and second switches when an operation signal is activated.