JPS63314471A - Power supply current monitoring circuit - Google Patents

Abstract

PURPOSE:To enable detection of both forward and backward currents, by employing currents through first and second emitter follower circuits as detection current. CONSTITUTION:When a normal forward feeder current If flows, voltage V0 and V1 (V1>V0) are generated across a detection resistance 11 and appear across a conversion resistance 21 (resistance R2) as intact through first and second operational amplifiers 22 and 23 with a high impedance. Here, a detection current if=(V1-V0)/R2 is applied to a detection current processing section 30 through NPN transistors 26 and 28 at first and second emitter-follower circuits 24 and 27. On the other hand, when a backward feeder current Ir flows, the voltages V0 and V1 developing across the resistance 11 shifts inversion of V1<V0 and the detection current flowing through the resistance 21 is also inverted from if to ir. At this point, the detection current ir is applied to the processing section 30 through NPN transistors 25 and 29 in the circuits 24 and 27, thereby enabling detection of both forward and backward currents.

Description

[Detailed Description of the Invention] [Summary] A power supply current monitoring circuit for monitoring a power supply current from a power supply circuit, in which a power supply current detection section essential for the monitoring detects that a power supply current is being supplied. A resistor, a pair of operational amplifiers whose non-inverting inputs take the voltage across the detection resistor, and an NPN transistor and a PNP transistor whose bases are commonly connected to the output of each operational amplifier and whose emitters are commonly connected. a pair of emitter follower circuits, each of which is also connected to an inverting input;
By detecting the feeding current using the collector current of each NPN transistor, it is possible to detect current in both forward and reverse directions.

[Industrial application field]

The present invention relates to a power supply current monitoring circuit, and more particularly to a power supply current monitoring circuit for monitoring 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 exchange side, and its main purpose is to supply direct current to each subscriber's telephone to operate it through the telephone line. Since this power feeding circuit is connected to the ends of the A line and B line forming the telephone line, it must be designed so that the input impedance to the AC signal seen from the A line and B line becomes a predetermined value. There are two types of input impedance (Zot
.

It is broadly classified into ZC a) and must satisfy the following conditions.

(2) The AC impedance ZDT for differential signals (audio signals) is high, and (2) The AC termination impedance ZCt for common mode signals (harmful AC signals such as AC induction) is low. In addition, (1) The DC power supply resistance must have a value that can supply the DC current required by the telephone, for example several hundred ohms.

AC termination impedance zoy for the above differential signal
is desirably high so as not to attenuate it, and on the other hand, the AC termination impedance ZCT for the above-mentioned common mode signal is desirably low so as to attenuate it as much as possible.

Furthermore, in recent years, the conditions for common-mode signals have become stricter.
Even if the common-mode signal current becomes thicker than the DC power supply current, it is required that the audio signal not be distorted, and power supply circuits that meet this requirement have also been proposed.

By the way, the power supply current monitoring circuit (hereinafter also simply referred to as a monitoring circuit) referred to in the present invention monitors the power supply current from the power supply circuit, thereby detecting an off-footer, on-hook or dial pulse in cooperation with a scanning device (SCN). It works with an alarm device (ALM) to detect abnormalities such as ground faults and cross-contact. It performs a wide range of functions, such as detecting this when the current is short (when the current is short) and suppressing the current.

The most important part of this monitoring circuit is the part that detects the power supply current, and in this power supply current detection section, it is necessary to detect not only the forward direction but also the reverse direction of the current. This is because, as described above, it is necessary to ensure that the normal audio signal does not deteriorate even if the common-mode signal current becomes larger than the power supply current. For this purpose, the power supply circuit itself must not only be capable of supplying power in both forward and reverse directions, but also
At the same time, the monitoring circuit must also be capable of detecting current in both forward and reverse directions. In addition, Reverse (described later)
) When considering the time of power supply, it is necessary to detect current in both forward and reverse directions.

[Conventional technology]

FIG. 8 is a diagram schematically showing a general switching system, in which a power supply current I is sent from power supply terminals 011TI and 0UT2 to a subscriber's telephone device via A line 13 and B line 14. This is the power supply circuit 15.

This power supply circuit 15 is generally configured to include an operational amplifier, and for its proper operation, bias input terminals B1 and B
2 receives the bias voltage from the bias circuit 16. Note that the original input/output section for the audio signal AC is selected as appropriate, but in the figure, the section drawn as a transformer on the right side of the bias circuit 16 is the human output section.

By the way, the power supply current monitoring circuit according to the present invention is designated by reference number 1.
0 block, and has detection resistors 11 and 12 at their inputs to which a power supply current I is applied. As mentioned above,
The monitoring circuit 10 performs various functions in cooperation with other devices, which are shown as a scanning device 17, an alarm device 18, etc.

FIG. 9 is a circuit diagram showing an example of a conventional monitoring circuit.
Only the line side is shown. The B line side also has the same configuration. As shown in this figure, a conventional monitoring circuit 10 includes two transistors Ql and Q2, a constant current source CI, a detection resistor 11, and a voltage/current conversion resistor 21. Around it, there is a power supply circuit 15, a power supply end 0UT1, an A line 13, etc. shown in FIG. When a normal positive power supply current 1 flows through the detection resistor 11, the voltage V generated here is detected at high impedance by the transistor Q1, and after compensating its emitter-base voltage with the transistor Q2,
The above voltage ■ is produced at the emitter of . As a result, the voltage/current conversion resistor 21 has a detection current 1 proportional to the voltage
．． flows. This is yet another group of devices to cooperate 17
, 18 etc. In addition, the power supply voltage ■. For example, -
The voltage is 48V, and a current flows from the constant current source CI to keep the transistor Q1 in operation at all times. Also, if the resistance values of resistors 11 and 12, respectively).

[Problem that the invention seeks to solve]

In the monitoring circuit 10 shown in FIG. 9, a detection current if flows from the collector of the transistor Q2 through the emitter, so that the desired monitoring can be performed. However, if there is a large AC induction and the common-mode signal current based on this becomes larger than the supply current ■,
This time, current 1 flows in the opposite direction. Then, transistor Q2 must conduct a detection current ir, which is opposite to i. However, since the transistor can only flow current in one direction, 17 cannot be detected.

If the current is to flow in the opposite direction, Ql.

Even if a transistor or the like other than Q2 etc. is provided, it is actually not practical because it is limited by the voltage range. As a result, conventional monitoring circuits have a problem in that it is difficult to detect current in both forward and reverse directions.

The present invention has been made to address the above-mentioned problems, and an object of the present invention is to provide a power supply current monitoring circuit that can handle power supply currents in both forward and reverse directions.

[Means for solving problems]

FIG. 1 is a diagram showing the main parts of a power supply current monitoring circuit based on the present invention. In this figure, the power supply current monitoring circuit lO is
It consists of a feeding current detecting section 20, which is the main part thereof, and a detected current processing section 30, which performs certain processing necessary for monitoring the detected current detected here. Power supply current detection section 2
0 is the first operational amplifier 22 and the second operational amplifier 23 whose non-inverting inputs are connected to both ends of the detection resistor 11, respectively, and the first common connection connected to the output of the first amplifier 22.
NPN with base and common connected first emitter
A first emitter follower circuit 24 consisting of a transistor 25 and a PNP transistor 26, and a second amplifier 23
a second emitter follower circuit 27 consisting of an NPN transistor 28 and a PNP transistor 29 having a commonly connected second base and a commonly connected second emifter connected to the output of the first operational amplifier 22; Commonly connected first emitter and second operational amplifier 23
a voltage/current conversion resistor 21 connected between the second emitter of the common connection connected to the inverting input of the NPN, and converting the voltage between the first and second emitters into a current; A positive detection current i is obtained through the transistor 28 and the PNP transistor 26, and the PN
P transistor 29 and NPN transistor 25
A detection current i in the opposite direction is obtained through the detection current 'f +i, and these detection currents 'f +i' are supplied to the detection current processing section 30.

[For production]

Normal positive feed current 1. flows, the detection resistor 1
Voltages v0 and V+ (Vl > VO) are generated across 1. These voltages V0 and V are directly applied to the conversion resistor 21 and the transistors 28 and 26 in the second emitter follower circuits 24 and 27 via the high impedance first and second operational amplifiers 22 and 23.
obtained through.

-m, the emitter follower circuit has no voltage gain but high current gain, and its collector is directly connected to the power supply. In the present invention, the collector is not directly connected to the power source, but directly connected to the current processing section 30.

On the other hand, when the reverse direction supply current 1 flows, a voltage ■ appears across the detection resistor 11. and ■1 is reversed to V, <V, and the detection current flowing through the conversion resistor 21 also changes from i to i,
The reverse is true. At this time, the detection current ir flows through the transistors 25 and 29 in the first and second emitter follower circuits 24 and 27.

〔Example〕

FIG. 2 is a diagram showing an embodiment of the power supply current monitoring circuit according to the present invention, in which the power supply current detection section 2o shown in FIG. 20'. The sense resistor at its input is designated as 11'. Then, a positive direction detection current i□vff
b and the reverse direction detection current f, , 4+Lb are respectively given to the detection current processing section 30. The detected current processing section 3o is
7 current mirror circuits (CMI to CM7) 41 to 4
7, which performs predetermined addition and subtraction, and further includes absolute value circuits (ABSI, ABS2) 51,
52 and comparison circuits 53 and 54, the scanning device (
The added and subtracted detection current is supplied to the alarm device (SCN) and the alarm device (ALM).

Here, the meaning of the additions and subtractions performed by the current mirror circuits 41 to 47 will be explained. The reason why addition and subtraction are necessary is to eliminate the harmful common-mode signal current when it becomes excessive.

Figure 3 (1), (2), (3), (4) and (
5) is a diagram showing a detected current accompanied by a common-mode signal and its processed waveform. This shows that the currents are superimposed and a reverse direction detection current 10 and a forward direction detection current ifb appear. In the same figure (2), the above-mentioned excessive common-mode signal current is superimposed on the DC power supply current (detection current 1 m-) on the A line 13 side, and the forward direction detection current if and the reverse direction detection current 1
Indicates that 0 has appeared. These common-mode signal currents become an obstacle to accurately monitoring the power supply current, so ultimately,
As shown in (5) in the same figure, only the supply current component (L
+tb). For this process,
First, the detected currents of the A line 13 and the B line 14 in the positive direction are added. This addition (i□+i rb) results in the same figure (3
) to obtain the processed waveform. Among these processed waveforms, prominent waveforms (unnecessary waveforms) such as u, v, and w correspond to u, v, and w in (1) and (2) in the same figure.

Next, the reverse direction detection currents on the A line 13 and B line 14 sides are added. By this addition (1rm+'1 rb), the processing waveform shown in (4) in the same figure is obtained. These processed waveforms are exactly the above-mentioned unnecessary waveforms u, v, w, etc.

Therefore, the waveform of (4) in the same figure is extracted from the waveform of (3) of the same figure, and the desired feeding current component of (5) of the same figure is extracted. If we look at this as an addition/subtraction process, (1fa+I fb)
(l ra+1 rb) ... Equivalent to the operation (1). The detected current processing section 30 performs this operation, and the first term of the above equation (1), that is, (irm
+1rb) is output as the sum of currents flowing out from the respective second terminals 412 and 422 of the current mirror circuits 41 and 42 in FIG.
(1rm+1 rb) is output as the sum of currents flowing into the second terminals 462 and 472 of the current mirror circuits 46 and 47, respectively. In addition, each current mirror circuit is
A current equal to the current flowing out from or flowing into the first terminals 411 to 471 is transferred to the corresponding second terminal 412.
~472 or flow into these. Similarly, equal amounts of current are caused to flow out from the third terminals 413 , 423 , 443 and flowed into the third terminal 473 . Thus, port 56 has (i□+1rb)
(lrm” 1rb) appears, which is (lrm” 1rb) in Figure 3.
Corresponds to 5). The current at port 56 is the absolute value circuit 51
When the comparator circuit 53 detects that the absolute value is larger than a predetermined value, it is determined that the power supply current is present. The reason why the absolute value circuit 51 (52 is the same) takes the absolute value is to cope with reverse power feeding. Reverse power feeding refers to reversing the direction of the current (A-B), whereas normally the DC power feeding current I flows from the B line 14 to the A line 13. Used when providing a service.

Figure 4 (1), (2), (3), (4) and (
5) is a diagram showing a detected current accompanied by a ground fault and its processed waveform, and this figure shows an example in which a ground fault occurs on the A line 13 side. This current at the time of a ground fault appears at the port 55 in FIG.
Drives the alarm device ALM.

In Figure 4 (1), the feed current component is o (ib = 0)
However, only the in-phase signal component is visible.

In (2) of the same figure, an in-phase signal component is superimposed on the power supply current (i@) as a ground fault current, and ffa, i, , a are formed. Take the difference between the positive direction currents (its Lb),
Obtain the waveform shown in (3) in the same figure and emphasize the in-phase signal component. Furthermore, taking the difference between the reverse currents (i rb = lrJ), (
In addition to the waveforms shown in (3) of the same figure, the in-phase signal component is further emphasized (see (5) of the same figure). This (5)
The occurrence of a ground fault can be detected by the waveform of Nfm 1rb) + (trb trm)...
- Detected by operation (2). The first term of this equation (2),
That is, (lfm 1rb) is the current 1fa from the third terminal 413 of the current mirror circuit 41 in FIG. 2 and the current Irb to the second terminal 452 of the current mirror circuit 45.
The second term of equation (2) above, that is, (
11'b 11''a) is obtained by combining the current Lb from the third terminal 443 of the current mirror circuit 44 in FIG. When the comparing circuit 54 detects that its absolute value (according to the circuit 52) exceeds a predetermined value, the alarm device ALM is notified.

Figure 5 is a diagram showing an example of a current mirror circuit (inflow type), Figure 6 is a diagram showing an example of a current mirror circuit (outflow type), and Figure 7 is an example of Figure 6 with more terminals. 5 shows the same configuration as in FIG. 5 even if the number of terminals is further increased.

〔Effect of the invention〕

As described above, according to the present invention, a power supply current monitoring circuit that can deal with power supply currents not only in the forward direction but also in the reverse direction is realized.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main parts of a power supply current monitoring circuit according to the present invention, FIG. 2 is a diagram showing an embodiment of a power supply current monitoring circuit according to the present invention, and FIGS. 3 (1), (2), (3), (4) and (
5) is a diagram showing the detection current accompanied by a common-mode signal and its processed waveform, Figure 4 (1), (2), (3), (4) and (
5) is a diagram showing a detection current accompanied by a ground fault and its processed waveform. Figure 5 is a diagram showing an example of a current mirror circuit (inflow type). Figure 6 is an example of a current mirror circuit (outflow type). Figure 7 is a diagram showing an example in which the number of terminals in Figure 6 has been further increased, Figure 8 is a diagram schematically showing a general switching system, and Figure 9 is an example of a conventional monitoring circuit. It is a circuit diagram. DESCRIPTION OF SYMBOLS 10... Power supply current monitoring circuit, 11... Detection resistor, 13... A line, 14...
...B line, 15...Power supply circuit, 20,
20'... Feed current detection section, 21... Voltage/current conversion resistor, 22... First operational amplifier, 23... Second operational amplifier, 24... First emitter follower circuit, 27... - Second emitter follower circuit, 30... detection current processing section. Fig. 3 Fig. 4 A diagram showing an example of a current mirror circuit (inflow type) Fig. 5 rr A diagram showing an example of a current mirror circuit (outflow type) Fig. 6 rr Fig. 7 1U A general exchange system Diagrammatically shown diagramCircuit diagram showing an example of a conventional monitoring circuitFig. 9

Claims (1)

[Claims] 1. A line (13) and B line (1
4), a power supply current detection unit (20
, 20') and a detection current processing section (30) that performs necessary processing for monitoring the detection current detected by the supply current detection section (20, 20'). , each of the feeding current detection units (20,
20') is a detection resistor (11) to which the power supply current is applied.
) with each non-inverting input connected to both ends of the first operational amplifier (
22) and a second operational amplifier (23), an NPN transistor whose emitters are connected to each other, and a P
consisting of NP transistors, each base of which is connected to the first transistor.
and a first emitter follower circuit (24) and a second emitter follower circuit (27) connected to the outputs of the second operational amplifiers (22, 23), and connect the connection points between the emitters to the first and second emitters. It is connected to each inverting input of the operational amplifier (22, 23), and the voltage/current conversion resistor (
21), wherein the detection current processing section (30) uses the current flowing through the first and second emitter follower circuits (24, 27) as the detection current. 2. The detected current processing section (30)
4 of the forward direction detection current and reverse direction detection current on the side, and the forward direction detection current and reverse direction detection current on the B line (14) side.
The power supply current according to claim 1, which has addition/subtraction means that inputs detected currents of seeds and adds and subtracts these detected currents in a predetermined combination, and performs the above-mentioned monitoring based on the addition/subtraction results. monitoring circuit. 3. A plurality of current mirror circuits wired such that the addition/subtraction means adds two predetermined ones of the four types of detected currents and subtracts the other two predetermined ones (
41, 42, 43, 44, 45, 46, 47). 4. Absolute value circuits (51, 52) are provided to take the absolute value of the addition/subtraction results by the addition/subtraction means, and the above monitoring is performed by detecting that the absolute value output exceeds a predetermined value. A power supply current monitoring circuit according to claim 3.