JPH0638625B2 - Supply current control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A power supply current control circuit for controlling a power supply current from a power supply circuit, wherein the power supply current is monitored, and when it exceeds a predetermined value, an excess of a predetermined value or more is detected. By detecting the current component and changing the bias voltage to be supplied to the power supply circuit according to this overcurrent component, the power supply current is prevented from exceeding the specified value. Make sure that the supply current does not flow too much even if the distance is short.

[Industrial application field]

The present invention relates to a power supply current control circuit, and more particularly to a power supply current control circuit for controlling a power supply current from a power supply circuit provided in a subscriber circuit of an exchange.

Generally, the power supply circuit is placed on the side of the exchange, and its purpose is to supply direct current power for operating the telephone of each subscriber through so-called A line and B line (telephone line). This power supply circuit receives a bias voltage on the A line side and a bias voltage on the B line side which are supplied from the outside, and supplies a power supply current on which the bias voltages are superimposed to the A line and the B line. A bias circuit is provided to generate this bias voltage. As will be described later, this bias circuit normally sets the B line side to a value several V lower than ground (zero V) and the A line side to a value several V higher than the power supply voltage (-48 V). In some cases, the presence of this bias voltage of several V makes it necessary to control the power supply current according to the distance of the telephone lines (A and B lines) to the subscriber's telephone. occured. The present invention refers to circuits that can meet this need.

[Conventional technology]

FIG. 5 is a diagram showing a general concept of a power feeding system, in which TEL is a subscriber's telephone, _RL is a telephone and a telephone T.
This is the resistance of EL, so-called load resistance. This load resistance R
_A power supply circuit supplies power to _L , and its DC power supply resistance is 220Ω, for example. Note that I in FIG. Is a DC power supply _{current, V BB} is, for example, the supply voltage of -48V.
Although there is no description about the bias voltage in FIG. 5, power supply can be performed in principle without the bias voltage.

By the way, generally, the following can be said regarding the power supply circuit. This power supply circuit is composed of the above-mentioned telephone lines A and B.
In order to be connected to the ends of the lines, the input impedance for the AC signal viewed from the A and B lines must be designed to have a predetermined value. This input impedance is roughly classified into two types (Z _DT and Z _CT ) and must satisfy the following conditions.

AC impedance Z for differential signals (voice signals)
_{The DT} is high, and the AC termination impedance Z _CT for a common-mode signal (a harmful AC signal such as AC induction) is low. Also, the DC power supply resistance must be a value that can supply the DC current required by the telephone TEL, for example, several hundred Ω.

AC termination impedance Z _DT for the above differential signal
Is preferably high in order not to attenuate it, while the AC termination impedance Z _CT for the in-phase signal is preferably low in order to attenuate it as much as possible. Furthermore, in recent years, the conditions for in-phase signals have become stricter, and even if the in-phase signal current becomes larger than the DC power supply current I, it is required that the audio signal is not distorted. The fact that the in-phase signal becomes larger than the DC power supply current I means that the current I may flow in the opposite direction to the normal case, and such a reverse current may also flow. It is practiced to set the bias voltage inside a few V (for example, 2 V) (described later).

FIG. 6 is a diagram showing a concept of a general power feeding system which is a premise of the present invention, and the above-described bias voltage set inside several V is schematically illustrated as a battery of −2 V (B line side) and +2 V. Is shown in. The point to be noted in this figure is that the DC power supply resistance is, for example, 100Ω, which is smaller than that in the case of no bias in FIG. 5 (220Ω → 1).
00Ω). The reason for this is that only the bias voltage of 2V, telephone TEL
This is based on the fact that the resistance has to be low in order to compensate for the attenuation of the power supply current I to the.

FIG. 7 is a graph showing the relationship between the load resistance R _L and the power supply current I. R _L increases as the distance of the telephone line increases, but if R _L at the longest possible distance is 1900Ω, the minimum guaranteed value of the power supply current at this time is 20 mA, for example.
Is set to. This 20 mA is secured by the resistance reduced to 100 Ω in FIG. However,
For subscribers with shorter telephone line distances, R _{L in} this graph shifts to the left in the figure, and the power supply current I rapidly increases in proportion to 1 / R _L (dashed-dotted curve P). For this reason, there arises an inconvenience that the power supply current flows excessively to subscribers at a short distance. Therefore, in order to eliminate this inconvenience, it has been attempted to modify the characteristics of the power supply current I in this graph as shown by the solid curve Q. That is, the power supply current I is suppressed to, for example, about 50 mA for subscribers in a short distance. This eliminates the above-mentioned inconvenience of excessive flow of the power supply current.

[Problems to be solved by the invention]

Based on the above background, in order to control the power supply current I to be larger or smaller depending on the magnitude of the load resistance R _L , the power supply resistance in the power supply circuit (corresponding to each 100Ω in FIG. 6) should be variable. Was previously tried. However, the inside of the power feeding circuit is complicatedly configured so as to simultaneously satisfy the above conditions and, and there is a problem that the method of changing the power feeding resistance is practically difficult.

The present invention has been made in view of the above-mentioned problems, and the above 50
You can easily and reasonably limit the current at about mA, and add other functions (such as reversing power supply and balance-
It is an object of the present invention to provide a power supply current control circuit that can easily have an unbalanced mode).

[Means for solving problems]

FIG. 1 is a diagram showing a principle configuration block of a power supply current control circuit according to the present invention and its peripheral circuits. As the peripheral circuits, a power supply circuit 10, a bias circuit 13 and the like are shown. The power feeding circuit 10 uses the bias voltages V _B1 and V _B from the bias circuit 13.
Bias input terminals B1 and _B2 for receiving B2 and power supply terminals OUT1 and OUT2 for supplying a power supply current I to the telephone TEL via A line 14 and B line 15 are provided. Also the power supply circuit
11 and 12 in 10 represent the above-mentioned power feeding resistance. However, description of the original input / output portion (transformer or the like) of the audio signal is omitted.

The power supply current control circuit 20 which is the subject of the present invention,
A detection unit 21 for detecting a power supply current when I becomes the predetermined value I _th or more, the detecting unit 22 for detecting the over-current component (I-I _th), the bias voltage V from the bias circuit 13
_B1, and _{V B2,} consisting of the over-current component _{(I-I th)} bias voltage control unit 23 that is changed according to.

[Action]

As described above, the conventional power supply resistors 11 and 12 shown in FIG.
I tried to change the power supply current I by changing the resistance value of
In the present invention, the power supply current I is changed by changing the bias voltages V _B1 and V _B2 . This makes it possible to easily realize the circuit and also realize the additional function.

FIG. 2 is a graph for explaining the operation according to the present invention, and the upper half thereof corresponds to the graph of FIG. The lower half shows that the bias voltage V _B is controlled by the present invention. The potential (zero V) of the ground E is indicated by the dashed-dotted line E, and the power supply voltage V _BB is made to coincide with the horizontal axis. Higher the subscriber is in a short distance, the load resistance R _L is small, the supply current I is increased, the power supply current control circuit 20, when I exceeds a predetermined value I _th, the bias voltage of the line B side V
_At least one of the bias voltage V _B1 on the _B2 side and the A line side is changed so as to approach each other, and the feeding current I is controlled to be reduced. In FIG. 2, V _B1 and V
_The case where both _B2 approach each other is shown.

〔Example〕

FIG. 3 is a diagram showing an embodiment of the power supply current control circuit and its peripheral circuits according to the present invention. First, looking at the overall configuration of the circuit shown in this figure, the power supply circuit 10 includes power supply resistors 11 and 12, an operational amplifier OP1 on the A line side (corresponding to the triangle shown in the lower side of the power supply circuit 10 in FIG. 1), and a B line. Side operational amplifier OP2 (corresponding to the triangle shown on the upper side in the power feeding circuit 10 in FIG. 1), and the power feeding end OUT
1, OUT2 as well as bias inputs B1, B2. The bias circuit 13 has reference numerals 130 to 134 and 130 'to 13
4 ', 135-139 and 33-35. The power supply current detector 21 is represented by the components with reference numerals 211 to 215. The overcurrent detection unit 22 has a reference number 221.
Represented by components labeled with ~ 224. Further, the bias voltage control unit 23 is represented by the components denoted by reference numerals 231-237 and 36-39.

It suffices for the power supply current detector 21 to know the magnitude of the power supply current I. In the present embodiment, the voltage drop caused in the detection resistors 214 and 215 by the current I is detected by the voltage / current exchanger (VI). Converted to current value by 211 and 212,
Further, a combination of these by the current mixer (CMIX) 213 is set as a detection current i, and this i is proportional to the feeding current I. This detection current i is caused to flow out from the first terminal 224 of the current mirror circuit 222 (upper right end of the figure). The reason why the voltage / current converters 211 and 212 are provided on the A line 14 and B line 15 sides and they are combined by the mixer 213 is to cancel the in-phase signal described above.

The detection current i is applied to the first terminal (224) of the sixth current mirror circuit (CM6) 222 which is a part of the overcurrent detection unit (22). A constant current source 221 is connected to the second terminal (223),
The constant current i _{th, which} is proportional to the above-described predetermined value I _th of the power supply current (I), is constantly caused to flow out. And power supply current (I)
_{Exceeds the} predetermined value I _th by an overcurrent (ΔI) (= I−I _th ), the corresponding overcurrent Δi (= i−i)
_th ) occurs. This Δi becomes a control factor for bias voltage control, that is, power supply current control. The reason why the current mirror circuit is adopted is that it has a high output impedance and is effective in suppressing power source noise from entering the bias circuit side.

The overcurrent Δi is processed as follows to control the bias voltage. First, the first terminal 234 of the fifth current mirror circuit (CM5) 231 forming a part of the bias voltage control unit 23.
The overcurrent Δi is drawn in. A current equal to this Δi is drawn into the second terminal 232 as a control current i _c , and changes the current / voltage state in the bias circuit (13).

The bias circuit (13) has a third current mirror circuit (CM3) 135 forming a current source, a transistor 138, a resistor 139, and a buffer transistor 33 on the bias voltage control section (23) side, and the power supply circuit (10). On the side, a first current mirror circuit (CM1) 130, a resistor 133, a voltage follower circuit 134 (all for A line), and components 130 'and 133 similar to these components.
And 134 '(both for B line). Line A (14)
As for the side, one end of the resistor 133 has a reference voltage V _BR.
Of the reference voltage source is connected, and this V _BR is held at a constant value between −2 and −3 V, which is 2 to 3 V lower than the ground potential.
Here, if the resistance value of the resistor 133 is R, I _{B can be calculated} from V _BR.
The value dropped by × R becomes the bias voltage V _B1 ,
The voltage is applied to the bias input terminal B1 via the voltage follower circuit 134. The current I _{B at} this time is the current mirror circuit 13
0 is the current flowing into the second terminal 131 and its first terminal 13
Equal to the current flowing into 2. The current flowing into the first terminal 132 is the transistor 34 (the transistor 35 is off).
And through 33, a current I _B sent from the second terminal 136 of the third current mirror circuit 135, the current is a current with an equal volume made at the first terminal 137 side. This is a current flowing through the transistor 138, and its magnitude is V _BR / R _r (R _r is the resistance value of the resistor 139). The above is the description on the A line 14 side, but on the B line 15 side, the transistor 35 is now off, and no current flows through the first terminal 132 'of the second current mirror circuit 130'. No current flows through the two terminals 131 ', there is no voltage drop across the resistor 133', and the voltage V _BR remains the bias voltage V
It becomes _B2 . This state is equal to the state where V _B1 and V _B2 maintain a predetermined constant value (when I is smaller than I _th ) in the lower half of the graph of FIG.

Here, the load resistance R _L becomes small and the feeding current (I) becomes I
_If ΔI becomes larger than _th , the control current i _{c described} above is drawn into the bias voltage control unit 23. Therefore, the current I from the current mirror (CM3) 135
_B is reduced to _I B -i _c. Reduced current I _B −i
_c reaches the current mirror circuit 130 from the transistor 34, and the voltage drop in the resistor 133 becomes smaller by i _c × R than before. That is, the bias voltage V _B1 increases by i _c × R (see the increase of V _B1 in FIG. 2).

On the other hand, looking at the bias voltage V _B2 side, the current (Δ _i , that is, Δ _i , which flows out from the first terminal 237 of the fourth current mirror circuit (CM4) 235 to the third terminal 233 of the fifth current mirror circuit (CM5) 231, equal to i _c ) flows in through transistor 39 (transistor 38 is off).
Therefore, from the second terminal 236 of the current mirror circuit 235, i
_c flows out and flows into the current mirror circuit 130 'in the bias circuit (13) through the transistor 36 (transistor 37 is off). Therefore, the resistance 133 '(resistance value R)
A voltage drop of i _c × R occurs and V of the graph of FIG.
_B2 is lowered.

The above is the basic operation of the present invention. In addition to this, it is also possible to support reversal power supply and balanced-unbalanced mode. Reverse feeding is usually the B line (15) to the A line (1
The DC power supply current I is made to flow toward 4), but the direction of the current is reversed (A → B), which is used for providing advanced services such as automatic incoming calls. Thus, to reverse the current I, the transistors 34 and 3
5 forms a current switch, and these are N / R
(Normal / Reverse) input turns on or off alternatively. During normal (N) power feeding, N / R = “L”, the transistor 34 is on (transistor 35 is off), and during revers (R) power feeding, the transistor 35 is on (transistor 34 is off). , The levels of V _B1 and V _{B2 in} the graph of FIG. 2 are reversed.

To support this reversal power supply, the bias voltage controller
Also in (23), the transistors 36 and 37 forming a current switch are formed, and the above-described current i _c flowing through the transistor 36 can be switched to the transistor 37 during the reversal power supply (the transistor 36 is off). .

Next, the balanced-unbalanced mode means whether the bias voltages V _B1 and V _B2 are balanced or unbalanced, and all the above operations are described in the balanced mode.

FIG. 4 is a graph for explaining the unbalance mode and corresponds to FIG. 2 described above. In the graph of Figure 2,
Although the bias voltages V _B1 and V _B2 are changed in the same manner, in the unbalanced mode shown in FIG. 4, the bias voltage V _B2 remains unchanged and only the bias voltage V _B1 is increased to supply the power supply current (I). Is suppressed to a predetermined value I _th . To achieve this imbalance mode, will be described with a case of the normal power supply, the current through transistor 34, the I _B -i _c in balance mode described above, it may be set to I _B -2i _c. That is, the amount of voltage increase due to the resistance 133 is _calculated from i _c × R to 2 i _c
It may be raised to × R. On the other hand, on the B line side, the inflow current to the current mirror 130 'in the balance mode described above may be set to 0, which was i _c . That is, the voltage drop due to the resistor 133 'may be set to zero. To this end, the transistors 38 and 3 forming the current switch
9 is provided, and these are selectively turned on and off by U / B (Unbalance / Balance) input. U in balance mode
The / B input is U / B = “L”, the transistor 39 is on, and the transistor 38 is off, which is the same as the above-described conditions for the operation description. On the other hand, when U / B = "H" and the unbalance mode is entered, the transistor 38
Is turned on and the transistor 39 is turned off. Since the transistor 39 is turned off, the current mirror circuit (C
The current (Δ _i , that is, the same amount as i _c ) flowing out from the first terminal 237 of M4) 235 becomes 0, and the supply current to the current switch (36, 37) becomes 0. As a result, the above-described condition that the voltage drop due to the resistor 133 'is set to 0 is satisfied. Since the transistor 38 is turned on when the transistor 39 is turned off, the control current from the current mirror 135 flows into the third terminal 233 of the current mirror 231 i _c and originally flows into the second terminal 232 thereof i _c . , I.e., 2 _ic . Therefore, the current flowing through the transistor 33 and transistor 34 (when normal power supply) from the _I B -i _c at balance _mode, decreases to I B -2i _c. As a result, the above-described condition of I _B -2 _ic is satisfied, and the unbalanced mode is formed. In the unbalanced mode, the bias voltage V _B1 of the A line and the power supply voltage V _BB
Can yield the corresponding large voltage difference between the case of FIG. 4, with respect to supply voltage V _{BB (-48V),} can raise the levels eg up to -24V. This results in a reduction in power consumption in the power supply circuit and the like. However, if the reduction from -48V to -24V (decrease in voltage value) is performed by resistance voltage division, power loss (heat generation) occurs in this voltage division resistance, which is meaningless. Therefore -48V
To -24V requires the use of low loss converters such as so-called DC-DC converters.

〔The invention's effect〕

As described above, according to the present invention, it is possible to control the power supply current relatively easily without adding control to the power supply circuit itself, and it is possible to suppress the excessive flow of the power supply current that occurs particularly in the case of a short distance subscriber. it can. In addition, reversal power supply and balanced-unbalanced mode can be easily realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration block of a power supply current control circuit according to the present invention and its peripheral circuits, FIG. 2 is a graph for explaining the operation according to the present invention, and FIG. 3 is a power supply current according to the present invention. FIG. 4 is a diagram showing an embodiment of a control circuit and its peripheral circuits, FIG. 4 is a graph for explaining an unbalanced mode, FIG. 5 is a diagram showing the concept of a general feeding system, and FIG. 6 is a diagram showing the present invention. FIG. 7 is a diagram showing a concept of a general power feeding system as a premise, and FIG. 7 is a graph showing a relationship between a load resistance R _L and a power feeding current I. 10 ... Feeding circuit, 13 ... Bias circuit, 14 ... A line, 15 ... B line, 20 ... Feeding current control circuit, 21 ... Feeding current detection part, 22 ... Overcurrent detection part, 23 ... Bias voltage control part.

Claims (1)

[Claims] 1. A power supply current (I) supplied from a power supply circuit (10) to a subscriber's telephone (TEL) via an A line (14) and a B line (15), the A line (14) Side first bias voltage (V
_B1 ) and the second bias voltage (V
_B2 ) are respectively connected to a bias circuit (13) for superimposing them, and the predetermined feeding current (I) is applied to the feeding circuit (10).
In the feeding current control circuit (20) for controlling the bias circuit (13) so as to supply more power, the feeding current detection unit for detecting the magnitude of the feeding current (I)
(21) and the detected feeding current (I) is a predetermined value (I
_th ) or more, an overcurrent detection unit (22) for detecting the overcurrent component (ΔI), and the first bias voltage according to the magnitude of the detected overcurrent component (ΔI). At least one of the first bias voltage (V _B1 ) and the second bias voltage (V _B2 ) so that the levels of (V _B1 ) and the second bias voltage (V _B2 ) approach each other. The power supply current control circuit (20) is composed of a bias voltage control section (23) for changing, and (a) the power supply current (I) is supplied from the B line (15) to the A line (1).
4) In the case of normal power supply that energizes toward, the bias voltage controller (23) changes the first bias voltage (V _B1 ) and the second bias voltage (V _B2 ) in a balance mode. Under the condition, each level of the first bias voltage (V _B1 ) and the second bias voltage (V _B2 ) approaches each other according to the magnitude of the detected overcurrent component (ΔI). Under an unbalanced mode in which both the first bias voltage (V _B1 ) and the second bias voltage (V _B2 ) are changed, and only the first bias voltage (V _B1 ) is changed. , The level of the first bias voltage (V _B1 ) and the level of the second bias voltage (V _B2 ) approach each other according to the magnitude of the detected overcurrent (ΔI). First Configured so as to change the bias voltage only (V _B1), b) the line B the supply current (I) is from the A line (14) (1
In the case of the reversal power supply that energizes toward 5), the bias voltage control unit (23), in the balance mode, according to the magnitude of the detected overcurrent (ΔI), Of the first bias voltage (V _B1 ) and the second bias voltage (V _B2 ) of the first bias voltage (V _B1 ) are close to each other.
_B1 ) and the second bias voltage (V _B2 ) are both changed, and under the unbalanced mode, depending on the magnitude of the detected overcurrent (ΔI), The levels of the first bias voltage (V _B1 ) and the second bias voltage (V _B2 ) are close to each other.
Only in terms of the varying bias voltage (V _B1), to configure it to reverse the level of the said second bias voltage of the first bias voltage (V _B1) (V _B2) Characteristic power supply current control circuit.