JPH0993311A - Dc load protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely protect a switch element of a DC load circuit even when a terminal connector is connected to a wrong line connector. SOLUTION: A line holding DC load circuit 40 is provided with a Zener diode 62 and a photocoupler 64 being a line detection means. In the case of connecting a terminal equipment side connector 12 to a line connector 82 with a low impedance, since the output impedance of a digital line is low, the Zener diode 62 is conductive and a detection signal is obtained from the photocoupler 64. The signal is fed to a control section 20 and a low level relay control signal is generated and a hook switch 14 is forcibly hooked on. Since no line voltage is applied to the DC load circuit 40, the switch element 48 is surely protected. When connection is wrong, it is displayed by a display section 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC load protection circuit provided in a communication terminal using a public line. For details, when the wrong terminal connector is connected to the installed line side connector, the drop voltage difference corresponding to the difference in the output impedance of the line and the line voltage on the non-line side are detected and the terminal is connected to the corresponding line. When it is determined that the connector is not connected, open the line and D
The C load circuit is protected.

[0002]

2. Description of the Related Art Recently, digital lines such as ISDN lines are becoming popular as public lines installed in offices and homes, and not only analog lines but also digital lines are being installed in many cases.

In contrast to these line connectors, particularly the line connectors used for digital lines and ISDN lines, the terminal side connectors (terminal connectors) are for ISDN lines (digital lines) even if they are analog line terminal connectors. Both of the terminal connectors can be connected (attached) to the line connector.

Therefore, although the line connector is an ISDN line connector, for example, an analog line terminal connector (for example, a modem terminal connector) is connected to this line connector.
It may be worn incorrectly or the other way around.

[0005]

A DC voltage is applied to the public line as a line voltage for establishing a call. This DC voltage is almost the same in both the analog line and the digital line, but the output impedance of the analog line is several hundred Ω to several kΩ, whereas it is very small in the digital line such as ISDN line, and several Ω to several Ω. It is about 10 Ω.

On the other hand, on the analog line terminal side such as a modem, a line holding DC load circuit is provided in an NCU (line control unit). The DC load circuit has a constant voltage source configuration, and when the terminal connector of the analog line terminal is connected to an analog line with high output impedance in a normally mounted state, a large voltage drop (voltage drop) due to the output impedance of the line causes The switching transistor provided in the load circuit and functioning as a line holding element performs normal operation (line holding operation) without being destroyed.

However, when the terminal connector is erroneously connected to a digital line such as an ISDN line, the output impedance of the line is very small, so that there is almost no voltage drop due to this output impedance. As a result, the line voltage is directly applied to the above-mentioned switching transistor. If the line voltage is applied directly, it may exceed the capacity (rating) of the switching transistor.
In such a case, this switching transistor may be destroyed and cause failure of the entire DC load circuit.

When the ISDN line terminal connector is erroneously connected to the analog line connector, a predetermined signal cannot be obtained at each of the transmission signal terminal and the reception signal terminal provided on the terminal connector side. Do not work. Moreover, since the output impedance of the analog line is high, the DC load circuit of the terminal is not destroyed by the line voltage.

Therefore, the present invention solves such a conventional problem, and even if a terminal connector which does not correspond to the line is erroneously connected to the line having a low output impedance, the terminal is provided in this terminal. The DC load circuit provided can be surely protected.

[0010]

In order to solve this problem, in the DC load protection circuit according to the present invention described in claim 1, line detecting means is provided in association with the DC load circuit for holding the line, When the terminal side connector is connected to the line connector having a low output impedance, the line opening means is operated based on the detection output from the line detecting means to protect the DC load circuit.

In the DC load protection circuit according to claim 1, the line voltage detecting means comprises an overvoltage detecting element, a light emitting element and a light receiving element, and when the light receiving element receives the optical output of the light emitting element, the output Is supplied to the hook switch control unit.

In the DC load protection circuit according to the present invention, a Zener diode is used as the overvoltage detecting element.

In the DC load protection circuit according to the present invention, the line voltage detecting means is connected to the signal line side terminal of the terminal connector.

In the DC load protection circuit according to claim 1, the line opening means is also used as a hook switch control means.

According to the sixth aspect of the DC load protection circuit of the present invention, the terminal connector on the analog terminal side is the non-signal line side terminal and the line connector is ISD.
When the line is an N line, line voltage detection means is connected between the terminals corresponding to the transmission signal terminal and the reception signal terminal,
The detection output of the line voltage detection means is supplied to the control unit constituting the NCU, and when the detection output is obtained, the line opening means for opening the line on the analog terminal side is operated.

In a DC load protection circuit according to a sixth aspect of the present invention, a photocoupler is used as the line voltage detecting means, and the photocoupler uses a photodiode as a light emitting element and a phototransistor as a light receiving element.

Since the output impedance on the analog line side is high when the correct terminal connector is attached to the line connector, that is, when the terminal connector of the analog terminal is connected to the line connector for the analog line, A voltage lower than the line voltage is applied to the DC load circuit. Therefore, there is no possibility that the switching transistor of the DC load circuit is destroyed by the applied line voltage. The Zener diode does not conduct depending on the line voltage applied at that time.

However, when the terminal connector for the analog terminal is inserted into the line connector for the ISDN line, the line side output impedance at that time is low,
Since the line voltage itself is applied to the switching transistor of the DC load circuit, the switching transistor may be destroyed if this is left unattended.

As described above, the line voltage which is almost unchanged is DC.
When it is applied to the load circuit, the voltage becomes equal to or higher than the reverse voltage of the Zener diode provided in the line detecting means, so that it becomes conductive. Along with this conduction, a photodiode, which is a light emitting element, is turned on, and the light is received by a phototransistor, which is a light receiving element, and is turned on.

When the phototransistor turns on, the detection signal at that time is supplied to the control section. The control section discriminates the voltage change of this detection signal and generates a relay control signal (low level) which is applied to the control transistor which is the line opening means. As a result, the relay is deenergized, the hook switch is turned on hook, the line is opened, and the DC load circuit is protected.

When the digital line is an ISDN line, the non-signal line terminal of the terminal connector for analog terminal is used as each terminal of the transmission signal and the reception signal. In this case, between the non-signal line terminals. It is only necessary to connect a photo coupler as a line voltage detecting means to the.

This is because the analog terminal is connected to the wrong line when the output of the photocoupler is obtained. In that case, the output (detection output) of the photocoupler is given to the control section, whereby a relay control signal is generated and forced to be on-hook.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Next, one embodiment of a DC load protection circuit according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a case where the DC load protection circuit according to the present invention is applied to a modem 10 which is an analog terminal. The terminal connector 12 connected to the modem 10 is a 4-terminal 2-wire type, and the signal line 16 (signal lines L1 and L2) is connected to the two terminals located at the center. The hook switch 14 is connected to one of the signal lines L1, and the signal lines L1 and L2 are connected to the isolation transformer 1.
A signal modulator / demodulator 19 which is terminated by
Is connected.

Input / output signals to / from the modulator / demodulator 19 are CPU
The input / output is controlled by a control unit 20 having a built-in controller. As is well known, the control unit 20 includes a memory 22 in which a control program and the like are incorporated, and a display device 2 for displaying modes and the like.
4, a sounding device 26 using a buzzer, etc., and a serial interface for exchanging signals with a personal computer, etc.
Input / output interface (SIO)
28 are provided. 30 is a drive power source for them.

The on / off state of the hook switch 14 is controlled by the relay 32, and therefore the control unit 20
The high-level relay control signal from is supplied to the control transistor 34, and the relay 32 is controlled by this.

A DC load circuit 40 for holding a line is provided between the signal lines L1 and L2 via a diode bridge circuit 42 which is a part of the NCU. The diode bridge circuit 42 uses the signal lines L1. This is for rectification so that the line voltage in the same direction is given to the DC load circuit 40 even if the polarity of the line voltage given to L2 is reversed.

The DC load circuit 40 is composed of a pair of voltage dividing resistors 44 and 46 and a line holding switching transistor 48 to which the divided voltage is supplied.
The on / off of the transistor 48 is controlled by detecting the voltage drop between q. The capacitor 50 is for smoothing.

According to the present invention, the DC load protection circuit 60 is provided in addition to the conventionally known DC load circuit 40.
Is provided. In this example, a Zener diode 62 as an overvoltage detecting element and a photocoupler 64 are provided between terminals p and q.
A series circuit of a light emitting element and a photodiode 66 constituting the above and a current limiting resistor 70 is connected. The Zener diode 62 is connected so that the terminal q side serves as a cathode in order to detect an overvoltage between the terminals p and q.

A control transistor 74 is connected to the collector side of a phototransistor 68 which is a light receiving element constituting the photocoupler 64, and its emitter side is connected to a power supply Vcc via a resistor 76 and also to the control section 20. It The photocoupler 64 is used in the DC load protection circuit 60 in order to electrically insulate the control unit 20 side from the signal lines L1 and L2 side. The control transistor 34 and the relay 32 described above are also used as the line opening means 80.

In the modem 10 having the DC load protection circuit 60 thus constructed, the terminal connector 12 of the modem 10 is a line connector 82 embedded in a room wall or the like.
Used by being plugged into.

When the line connector 82 is a line connector for analog lines, the line voltage is applied to the signal lines L1 and L2 from the analog line side by off-hooking. The switching transistor 48 is turned on by the line voltage, the signal lines L1 and L2 are connected, and the relay station side determines that the off-hook state is established. At the same time, the line signal is supplied to the control unit 20 to detect the off-hook state, and a relay control signal (high level) is generated by the detection. This relay control signal turns on the control transistor 34,
Relay 32 is energized and hook switch 14 is held in the off-hook state.

Since the line side output impedance when the line is connected is as high as several hundreds to several kΩ, the line voltage drop becomes large, and at the line voltage at that time, a voltage higher than the Zener voltage VZ between the terminals p and q is generated. Not applied. Therefore,
The DC load protection circuit 60 does not operate.

Next, the operation when the above-mentioned analog line terminal connector 12 is inserted into a line connector other than the analog line connector, that is, a digital line connector will be described.

FIG. 1 shows an example of a line connector 82 used for a digital line such as an ISDN line.

As is well known, the line connector 82 is a 6-terminal 4-wire type, and the ISDN line is connected to the central 4 terminals and the remaining 2 terminals are unconnected. Here, TA and TB are terminals for transmission signals, and RA and RB are terminals for reception signals. There are four possible patterns of signals applied to these four terminals, as shown in FIG.

When the terminal connector 12 is erroneously inserted into the line connector 82, the line voltages applied to the signal lines L1 and L2 in the patterns 2 and 3 have the same potential, so there is no particular problem at this time. However, in the case of patterns 1 and 4, since the line voltage is applied to the signal lines L1 and L2,
The DC load circuit 40 operates to connect between the signal lines L1 and L2, and the line is held.

On the other hand, the ISDN line has an output impedance of several Ω to several tens Ω, which is much smaller than that of the analog line, so that the voltage drop due to the output impedance is negligibly small. Therefore, almost the line voltage itself is applied to the DC load circuit 40. When the line voltage itself is applied, the terminals p of the DC load circuit 40,
Since a voltage equal to or higher than the Zener voltage VZ is applied to both ends of the Zener diode 62 during q, the Zener diode 62 becomes conductive and the photodiode 66 emits light. This light is received by the opposing phototransistor 68, which turns on. When the phototransistor 68 is turned on, the control transistor 74 is also turned on. Therefore, the low-level collector voltage at this time is supplied to the control unit 20 as a detection signal.

The control section 20 generates a relay control signal (low level) based on this detection signal, whereby the transistor 34 is turned off, the relay 32 is deenergized, and the hook switch 14 is forcibly turned on hook. As a result, the line is cut off and the switching transistor 4
8 is certainly protected.

The control unit 20 uses the switching transistor 4
8 can be protected, and at the same time, when an incorrect connector connection is made, it can be displayed on the display device 24. Alternatively, the sounding device 26 can be operated to give an audible notification to that effect. By adopting such a means, the user can immediately know the cause of the failure in which the modem 10 cannot be used, and it is very preferable that both the user and the service person can save waste.

Once the control unit 20 has obtained the detection signal,
The relay control signal is continuously generated until the driving power is turned off or the control unit 20 is reset. Therefore, even if the photodiode 66 is turned off by the on-hook, the control state (on-hook control state) for the hook switch 14 does not change.

FIG. 3 shows another embodiment of the DC load protection circuit according to the present invention. In this example, a control signal is formed by hardware. Therefore, the configuration other than the DC load protection circuit 60 is the same as that of FIG. 1, and the description thereof is omitted. As the analog terminal, a modem is illustrated as in FIG. In the DV load protection circuit 60 shown in FIG. 3, the flip-flop 86 is used as an element for holding the operation. This will be described with reference to the operation waveform chart of FIG.

Also in FIG. 3, the line voltage applied to the DC load circuit 40 is detected by the Zener diode 62, and the photodiode 66 is turned on by the current loop generated by turning on the Zener diode 62, which emits light. This light is received by the phototransistor 68 and a detection signal (FIG. 4C) flows.

The collector side of the phototransistor 68 is a flip-flop for holding the operation via the OR gate 84, and in this example, the clock terminal CK of the JK flip-flop 86.
Is supplied to. The Q terminal output of the flip-flop is used as the other input of the OR gate 84 described above, and the Q bar terminal output is given to the above-mentioned control transistor 34 for relay control via the AND gate 88.

As in the case of FIG. 1, the other input of the AND gate 88 is supplied with the relay control signal from the control section 20 composed of the CPU as described above.

Now, in the DC load protection circuit 60 thus constructed, when the terminal connector 12 is correctly inserted into the corresponding line connector (line connector for analog line), the zener is the same as in the case of FIG. The diode 62 does not turn on. Therefore, as shown in section I in FIG. 4, both the photodiode 66 and the phototransistor 68 are kept in the off state, and the detection signal remains at the high level (FIG. 4C). Therefore, the level of the clock terminal CK of the flip-flop 86 remains high level (D in the same figure), and the flip-flop 86 does not perform the inversion operation (E and F in the same figure).

That is, since the Q terminal output is "L" and the Q bar terminal output, and thus the relay control signal is "H", the hook switch 14 holds the off-hook state.

On the other hand, the line connector 12 is
When plugged into the line connector 82 for the SDN line, the line impedance (48V) is applied to both ends of the DC load circuit 40 because the output impedance on the line connector side is small. At this time, since a voltage higher than the Zener voltage VZ is applied to the Zener diode 62,
This becomes conductive and the photodiode 66 emits light.

The light is received by the phototransistor 68, and the detection signal (low level) at that time causes the clock terminal CK side to be inverted to the low level as shown in section II in FIG. 4 (C in the same figure). And flip-flop 8
The Q terminal output and the Q bar terminal output of 6 are also inverted, and the relay control signal becomes low level (D in the figure,
E, F). The relay control signal deenergizes the relay 32 and the hook switch 14 is on-hook, forcibly releasing the power supply to the DC load circuit 40. This release protects the switching transistor 48.

Since the Q terminal output of the flip-flop 86 is given to the clock terminal CK via the OR gate 84, the output of the flip-flop 86 is not inverted even if one input of the OR gate 84 becomes high level. Therefore, even if the line voltage to the DC load circuit 40 is cut off by going on hook, the mode of the flip-flop 86 retains the immediately preceding inversion mode. In other words, there is no fear that the relay control signal will be inverted every time on-hook or off-hook. This is the same when the terminal connector 12 is mistakenly reinserted. This is because the flip-flop 86 retains the previous operation mode unless the power is once turned off and the flip-flop 86 is restarted.

FIG. 5 shows a line connector 8 dedicated to the ISDN line.
This is a measure when the terminal connector is inserted into 2. FIG.
Dedicated line connector 82 and terminal connector 1 as shown in
2 means that the terminal connectors 12 corresponding to the two outer terminals to which the ISDN line is connected are non-connection terminals. Therefore, the line voltage between the terminals of the terminal connector 12 corresponding to these two outer terminals is directly detected.

Since the relationship between the terminals of the line connector 82 and the voltage pattern is as shown in FIG.
In both cases, both terminals have the same potential, but in other patterns, the line voltage can be obtained. At the same potential, there is no problem because the signal lines L1 and L2 also have the same potential. However, when the patterns 1 and 4 are applied with a predetermined line voltage, it is necessary to detect the line voltage in this case to protect the DC load circuit 40.

In FIG. 5, according to the present invention, a line voltage detecting photocoupler 90 is connected between terminals located at both ends of the terminal connector 12. The photocoupler 90 is composed of a pair of photodiodes 92 and 94 connected between two terminals so as to have opposite polarities, and a phototransistor 96 which receives these lights in common, and the output thereof is controlled via the control transistor 74. It is supplied to the unit 20. Photo coupler 90
The reason for using is to electrically insulate the control unit 20 side and the DC load circuit 40 side.

As described above, the terminal connector 12 for the analog terminal is mistakenly used for the ISDN line dedicated line connector 8
When the pattern is inserted into the terminal 2 and the patterns 1 and 4, the predetermined line voltage is applied between the terminals 12a and 12b of the terminal connector 12. This line voltage causes either of the photodiodes 92 or 94 to conduct, and the light from them is received by the phototransistor 96. As a result, the detection signal is supplied to the control unit 20, and the relay control signal (low level) from the control unit 20 turns on the control transistor 34, which forces the hook switch 14 to go on-hook. The switching transistor 48 is protected by this operation and the failure of the DC load circuit 40 can be prevented.

In the above description, a modem is used as an example of the analog line terminal, but a DC load circuit element provided in the analog communication terminal such as a fax machine or a telephone can be effectively protected from being destroyed. IS as a digital line
It is not limited to the DN line.

[0056]

As described above, according to the present invention, the DC load is detected by detecting the difference in the output impedance of the lines or by detecting the line voltage applied between the unnecessary terminals provided in the terminal connector on the analog terminal side. The protection circuit is operated.

According to this, even if the terminal connector on the analog terminal side is mistakenly connected to the line connector for the digital line, the switching element of the DC load circuit can be surely protected from being destroyed.

By driving the display device and the sounding device at the same time as protecting the switching element, the cause of the terminal failure can be surely grasped, which is effective for both the user and the service person. Therefore, the present invention is extremely suitable when applied to the DC load circuit of analog terminals such as telephones, fax machines, and modems.

[Brief description of drawings]

FIG. 1 is a connection diagram of essential parts showing an embodiment of a DC load protection circuit according to the present invention.

FIG. 2 is a diagram showing a voltage relationship of an ISDN line.

FIG. 3 is a connection diagram of essential parts showing another embodiment of the DC load protection circuit according to the present invention.

FIG. 4 is an operation waveform diagram thereof.

FIG. 5 is a connection diagram of essential parts showing another embodiment of the DC load protection circuit according to the present invention.

[Explanation of symbols]

 10 modem 12 terminal connector 14 hook switch 20 control unit 24 display device 26 sounding device 42 diode bridge circuit 40 DC load circuit 60 DC load protection circuit 62 Zener diode 64 photocoupler 80 line opening means 82 line connector

Claims (7)

[Claims] 1. A line detecting means is provided in association with a line holding DC load circuit, and when a terminal side connector is connected to a line connector having a low output impedance, the line is opened based on a detection output from the line detecting means. A DC load protection circuit, characterized in that the means is operated to protect the DC load circuit. 2. The line voltage detecting means is composed of an overvoltage detecting element, a light emitting element and a light receiving element, and when the light receiving element receives an optical output of the light emitting element, the output is supplied to a control section for hook switch control. The DC load protection circuit according to claim 1, wherein the DC load protection circuit is configured to be performed. 3. The DC load protection circuit according to claim 1, wherein a Zener diode is used as the overvoltage detection element. 4. The DC load protection circuit according to claim 1, wherein the line voltage detecting means is connected to a signal line side terminal of the terminal connector. 5. The DC according to claim 1, wherein the line opening means is also used as a hook switch control means.
Load protection circuit. 6. The terminal connector on the analog terminal side, which is a non-signal line side terminal and the line connector is ISDN.
When it is a line, line voltage detecting means is connected between the terminals corresponding to the transmission signal terminal and the receiving signal terminal respectively, and the detection output from the line voltage detecting means is supplied to the hook switch control section to detect the line voltage. A DC load protection circuit characterized in that a line opening means for opening a line on the analog terminal side is operated when a detection output from the means is obtained. 7. The DC load protection circuit according to claim 6, wherein the line voltage detecting means uses a photocoupler, and the photocoupler uses a photodiode as a light emitting element and a phototransistor as a light receiving element.