JP4469228B2 - Security circuit for digital access device - Google Patents

Description

  The present invention relates to a security circuit for a digital access device used for suppressing a digital access device from entering an excessive self-protection state due to a lightning surge or the like entering through a communication line.

  In general, a digital access device is provided on the subscriber side and the switching center side to connect digital devices such as digital telephones, digital faxes, and TAs (Terminal Adapters) to digital lines such as ISDN. It plays the role of equipment interface with the station side.

  FIG. 10 is a block diagram schematically showing such a configuration. In FIG. 10, a subscriber side is shown, and a digital access unit (DSU) 115 on the subscriber side is provided on communication lines L1 and L2 that connect a switching center side and a subscriber side (not shown). A safety circuit 111 is provided between the two.

  The DSU 115 is provided with an overcurrent limiter 112. When a surge current such as lightning having a current value larger than the operating current of the overcurrent limiter 112 enters through the communication lines L1 and L2, the overcurrent limiter 112 is activated. Operate.

  However, when the overcurrent limiter 112 operates, the DSU 115 stops functioning and enters a self-holding state (this state is referred to as “stacking”), becomes a communication impossible state, and returns from a communication impossible state. It is necessary to disconnect the DSU 115 from the communication lines L1 and L2 by manual work, or to restore the polarity of the voltages of the communication lines L1 and L2 from the exchange.

  In order to suppress the stacking of the DSU 115, a safety circuit 111 having a voltage operation type lightning protection element is provided. When a surge exceeding the operation voltage value of the lightning protection element enters, the communication line L1 and the communication line L2 are connected. The operation of the overcurrent limiter 112 is restricted by short-circuiting and restricting the surge from entering the DSU 115.

  However, since the overcurrent limiter 112 is current sensitive, the lightning protection element of the safety circuit 111 is voltage sensitive, so that the surge does not reach the operating voltage of the lightning protection element. In such a case, a surge enters the DSU 115 and the DSU 115 stops functioning.

For such inconvenience, by connecting a constant current diode to the communication line and regulating the current flowing into a certain termination device regardless of the surge current value, the device can be protected from surge and the DSU A configuration for suppressing stacking has been proposed (see Patent Document 1).
JP 2002-223327 A

  However, in the configuration according to the above-mentioned publication, there is a concern that when a large surge is input, the constant current diode is destroyed, and replacement requires parts replacement or the like, which requires a great deal of cost and labor. .

  That is, in general, surges of various current values and voltage values enter the communication line, but all such surges pass through the constant current diode or may pass through. However, the constant current diode realizes the current limiting function by increasing / decreasing the internal resistance (increasing / decreasing the depletion layer on the cathode side). Therefore, when a large voltage is applied, it causes an avalanche phenomenon, etc., which causes destruction due to thermal burning. End up.

  In the above publication, it is inferred that a separate safety device is provided so that a large surge voltage is not applied to the constant current diode. However, in this case, the cost of the separately provided safety device is required, which is large. This is a factor of cost increase.

  Accordingly, an object of the present invention is to provide an inexpensive security circuit for a digital access device that does not burn out even when various surges enter and can suppress an excessive stack of DSUs.

In order to solve the above problems, the invention according to claim 1, together form an interface function of the device on the subscriber side and exchange station side, when a predetermined limit current value or more surge current through the communication line has penetrated In a digital access device security circuit that is attached to a digital access device that attempts self-protection by stopping the function to suppress excessive self-protection of the digital access device by operating at a current value lower than the limit current value, A thyristor comprising an anode terminal, a cathode and a gate terminal, the cathode terminal and the gate terminal being connected to at least one communication line, and being connected in the communication line between the cathode terminal and the gate terminal; A resistor that converts the current flowing through the wire into a voltage, and a protection die that is connected in parallel with the resistor and prevents a reverse bias from being applied to the thyristor When the surge current that has entered through the communication line has a predetermined current value smaller than the limit current value, the thyristor is turned on by the voltage generated by the resistor, and the surge The current flows between the cathode terminal and the anode terminal.

  As a result, the current flowing through the communication line is detected as a voltage converted by a resistor, and the thyristor is turned on by a voltage at a predetermined current value lower than the limit current value at which the digital access device stops functioning. The surge current of the value does not enter the digital access device, it can prevent excessive self-protection operation of the digital access device, and suppress the communication on the subscriber side or the switching center side from falling into a communication disabled state. Will be able to.

In the invention according to claim 2 , the protection units are provided symmetrically on the two communication lines, and the anode terminals of the thyristors in each protection unit are connected to each other and grounded.

  As a result, the current flowing through the communication line is detected as a voltage converted by a resistor, and the thyristor is turned on by a voltage at a predetermined current value lower than the limit current value at which the digital access device stops functioning. The surge current of the value flows to the ground through the protection unit provided symmetrically and does not flow through the digital access device, so that excessive self-protection operation of the digital access device can be prevented. In addition, it is possible to prevent the exchange side device from falling into a communication disabled state.

In the invention according to claim 3 , the two communication lines are two communication lines in a plurality of communication lines.

  As a result, the present invention can be applied not only in the case of the two-wire system but also in the case of the four-wire system or the like, and the use range is expanded.

The present invention has an anode terminal, comprises a cathode and a gate terminal is connected to the thyristor and the cathode terminal and a gate terminal to at least one communication line is connected, during communication line between the cathode terminal and a gate terminal And a protection unit comprising a resistor for converting the current flowing through the communication line to a voltage , and a protection diode connected in parallel with the resistor to prevent a reverse bias from being applied to the thyristor. When the surge current that has entered is a predetermined current value smaller than the limit current value, the thyristor is turned on by the voltage generated by the resistor, and the surge current flows between the cathode terminal and the anode terminal. The current flowing through the device is detected as a voltage converted by a resistor, and the resistance when the current value is lower than the limit current value at which the digital access device stops functioning Voltage since the conduct thyristor in that, the surge current of the current value will not invade the digital access device, it is possible to prevent excessive self-protection operations of the digital access device, the subscriber and switching center side device Can be prevented from falling into a communication impossible state.

  Embodiments of the present invention will be described with reference to the drawings. When digital transmission is performed through an existing telephone line such as the INS network 64, a digital access device is required on both the subscriber side and the exchange side, and the digital access device on the subscriber side is a DSU (Digital Service). The switching center side is called OCU (Office Channel Unit). The present invention can be applied to both the DSU and the OCU. In the following description, a case where the present invention is applied to a DSU will be described as an example. Further, the security circuit for the digital access device is abbreviated as a security circuit.

The safety circuit converts the current that enters through the communication line into a voltage, and when the voltage exceeds a predetermined voltage, the current is such that at least the DSU overcurrent limiter operates by short-circuiting the communication lines. This prevents the DSU from stopping and entering an excessive self-protection function state.
In the present embodiment, the case of 1-line 2-wire type will be described. However, it is added in advance that the present invention is not limited to this and can be applied to the case of 4-wire type.

Reference example 1

  FIG. 1 is a diagram showing a circuit network using such a security circuit 10. The exchange side and the DSU 15 are connected by communication lines L1 and L2, and a user terminal 16 as a subscriber side device is connected to the DSU 15. ing. A security circuit 10 is provided on the lines L1 and L2 between the DSU 15 and the exchange.

  The security circuit 10 is provided between the communication lines L1 and L2 by connecting two protection units 11 and 12 having the same specification in series. Each of the protection units 11 and 12 includes resistors R1 and R2 and triacs Tr1 and Tr2 that are bidirectional semiconductor switching elements.

  As is well known, the triacs Tr1 and Tr2 have three terminals (G, T1, and T2). When the voltage at the G terminal (gate) becomes equal to or higher than a predetermined voltage (hereinafter referred to as a turn-on voltage), the terminals T1 and T2 are connected. It is an element that conducts, and thereafter keeps the conducting state unless the current flowing through the terminal T1 and the terminal T2 becomes equal to or lower than the ON maintaining current.

  Therefore, the resistors R1 and R2 are inserted into the communication line L1 and the communication line L2, and the G terminal and the T1 terminal are connected so as to sandwich the resistors R1 and R2. The T2 terminals of the triacs Tr1 and Tr2 are connected to each other.

  The operation when a surge such as lightning enters from the communication line L1 with such a configuration will be described as an example. In this case, when the surge current flows through the resistor R1, a voltage corresponding to the current value is applied to the G terminal of the triac Tr1, and when this voltage becomes equal to or higher than the turn-on voltage, the triac Tr1 is turned on and the T1 terminal and the T2 terminal are connected. Conduct. The current value at this time is set to a current smaller than the limit current of the overcurrent limiter 14 in the DSU 15 and larger than the normal communication current.

  Further, when a surge current flows through the communication line L2 via the DSU 15, the triac Tr2 is turned on by the voltage at the resistor R2, and the triac Tr2 is turned on.

  When both the triac Tr1 and the triac Tr2 are turned on, the communication line L1 and the communication line L2 form a loop of these two triacs Tr1 and Tr2, and a surge current flows through the triacs Tr1 and Tr2. Triac has a higher withstand voltage than a constant current diode, and is more resistant than the case where the constant current diode is used.

  Although it is temporary, the surge current flows through the DSU 15 until the two triacs operate, but since this time is very short, it is possible to form a triac loop before stacking the DSU 15. is there.

  Thereafter, when the surge current decreases and becomes equal to or less than the ON maintaining current of each of the triacs Tr1 and Tr2, the triacs Tr1 and Tr2 are turned off, and the T1 terminal and the T2 terminal become non-conductive and communication is possible.

  FIG. 2 is a diagram showing the intrusion current at which the DSU 15 is stuck, and the region where the DSU 15 is stuck is indicated by hatching. The dotted line indicates the operating current (corresponding to the turn-on voltage) of the safety circuit 10, and in this figure, the case where the circuit is turned on with a surge current of 130 mA or more is shown. This current is referred to as a regulated current.

  Since the turn-on voltage is a characteristic value of the triacs Tr1 and Tr2, the values of the resistors R1 and R2 are set so that the voltage when the regulation current flows becomes the turn-on voltage. The value of the resistance R may be set by the user in accordance with the time of frequent lightning and the usage situation in the area. For example, a plurality of resistors having different resistance values are provided, and the user selects one of the resistors according to the usage situation.

  As described above, before the overcurrent limiter 14 of the DSU 15 operates, a loop can be formed between the communication lines L1 and L2 by the triac, and even if various surges enter, the DSU 15 does not burn out. Excessive stacking can be prevented.

In the above description, a case has been described in which the protection unit 11, 12 are connected in series, is not limited to this, may be a 3 or as shown in FIG. 4 configuration example.

  The configuration shown in FIG. 3 is a configuration in which the T2 terminal of one protection unit is connected to the T1 terminal of the other protection unit. In FIG. 4, two protection units 11 and 12 are connected in series. The connection point (T2 terminal) is grounded.

  With such a configuration, the triacs Tr1 and Tr2 of any of the protection units 11 and 12 can be turned on so that a surge current can be released. Therefore, as shown in FIG. The surge current can be released with a quicker operation than when a loop is formed when the triacs Tr1 and Tr2 are turned on.

Reference example 2

Next, Reference Example 2 will be described. In order for the triac to turn off, it is necessary that no current flow. However, if the surge current input to the DSU 15 is a small current value, the DSU 15 does not stack and does not adversely affect the user terminal 16.

For example, assuming a digital phone as the user terminal 16, the normal power supply current of the digital phone is because it is 39 mA, there is no need to turns on the triac until the current follows. Further, in a situation where the surge current and the line signal enter at the same time (multiplied), the triac turn-on state may continue due to the signal current even if the surge current becomes zero.

Therefore, in the second reference example, the triac is turned off when the surge current falls below a range that does not affect the user terminal 16 as described above. FIG. 5 is a diagram showing a circuit network using such a security circuit 10, which is generally the same as the configuration shown in FIG. 1, except that an off-adjusting element 13 composed of a PNPN element is provided between the protection units 11 and 12. Is different.

  The PNPN element has a characteristic that it conducts when the inter-element voltage becomes equal to or higher than a predetermined voltage, and the ON maintaining current is set to a value larger than the normal supply current 39 mA. Therefore, when the surge current is reduced to be equal to or lower than the on-maintaining current, a non-conduction state occurs and the triac is turned off.

  The purpose of using the off-adjustment element 13 is to cut off the current flowing through the triac when the surge current is equal to or less than the current value allowed by the user terminal 16 as described above. The element 13 may be provided between the T1 terminal and the communication line L1 or the communication line L2. Furthermore, a Zener diode can be applied as the off-adjusting element 13.

Next, examples of the present invention will be described. In the security circuit described so far, a triac is used. In contrast, in this embodiment , a thyristor is used.

  FIG. 6 is a diagram showing a line network using such a security circuit 10. The exchange side and the DSU 15 are connected by communication lines L 1 and L 2, and a user terminal 16 is connected to the DSU 15. A security circuit 10 is provided on the lines L1 and L2 between the DSU 15 and the exchange.

  In the security circuit 10, two protection units 11 and 12 having the same specifications are provided on the communication lines L1 and L2. Each of the protection units 11 and 12 includes resistors R1 and R2, protection diodes D1 and D2, and thyristors S1 and S2.

  As is well known, the thyristor has three terminals (G; gate, A; anode, K; cathode), and when the voltage at the G terminal (gate) exceeds a predetermined voltage (hereinafter referred to as turn-on voltage), the A terminal and the K terminal. And become self-holding.

  Therefore, the resistors R1 and R2 are inserted into the communication line L1 and the communication line L2, and the K terminal and the G terminal are connected so as to sandwich the resistors R1 and R2, and the protective diodes D1 and D2 are connected in parallel with the resistors R1 and R2. Is connected. Each A terminal of each thyristor S1, S2 is connected to the opposing communication line L1 and communication line L2.

  The protective diodes D1 and D2 function to protect the thyristors S1 and S2 by acting so that no reverse bias is applied between the G terminal and the A terminal of the thyristors S1 and S2.

  That is, consider a case where surge current enters from the communication line L1. In this case, if the protective diode D1 is not provided, a gate current flows to the G terminal due to a voltage caused by a surge current flowing through the resistor R1, and the thyristor S1 is turned on. When the thyristor S1 is turned on, the K terminal and the A terminal are in a reverse bias state, and a surge current tends to flow from the K terminal of the thyristor S1 to the A terminal. Therefore, a situation occurs in which the thyristor S1 is broken due to the magnitude of the reverse bias, that is, the magnitude of the surge voltage.

  Therefore, when a surge current enters from the communication line L1, the thyristor S1 is prevented from being turned on by flowing the surge current through the protective diode D1. For this reason, the anode terminal of the protection diode D1 is connected to the switching station side (the cathode side of the thyristor S1), and the cathode terminal of the protection diode D1 is connected to the user terminal side (the gate terminal side of the thyristor S1). Thus, a forward bias is applied to the surge current flowing into the DSU 15 via (the protective diode D2 is also set to the same connection relationship).

  If the thyristor S1 is not turned on by the protection diode D1, the surge current flows to the communication line L2 via the DSU 15. At this time, since the protection diode D2 is reverse-biased, a surge current flows through the resistor R2, and the thyristor S2 is turned on.

  When the thyristor S2 is turned on, a surge current flows from the communication line L1 to the communication line L2 via the A terminal and the K terminal of the thyristor S2, so that no reverse bias is generated. Therefore, it is possible to suppress a situation in which the surge current operates the DSU 15 without damaging the thyristors S1 and S2.

  With such a configuration, when a surge such as lightning enters from the communication line L1, the surge current flows through the protective diode D1 having a low resistance, passes through the DSU 15, and flows through the resistor R2. When a surge current flows through the resistor R2, the thyristor S2 is turned on, the surge current flows between the communication line L1 and the communication line L2, and the overcurrent limiter 14 in the DSU 15 can be prevented from being stacked.

  On the other hand, when a surge such as lightning enters from the communication line L2, the surge current flows through the protection diode D2 having a low resistance, passes through the DSU 15, and flows through the resistor R1. When a surge current flows through the resistor R1, the thyristor S1 is turned on, the surge current flows between the communication line L1 and the communication line L2, and the overcurrent limiter 14 in the DSU 15 can be prevented from being stacked.

The reference examples and embodiments described so far are not limited to one line, but can be applied to cases where a plurality of lines are mounted in one unit. 7 illustrates the case where the configuration shown in FIG. 1 is applied to four lines as one unit, FIG. 8 illustrates the case where the configuration shown in FIG. 5 is applied to four lines as one unit, and FIG. 6 illustrates the case where the configuration shown in FIG. 6 is applied as four units as one unit.

  That is, in the case of supporting four lines, four security circuits 10 each including the protection units 11 and 12 connected between the communication lines L1 and L2 are provided in one unit. By adopting such a configuration, even in the case of four lines, one unit can similarly prevent excessive self-protection operation of the digital access device, and the subscriber side and the exchange side devices are in a communication disabled state. It becomes possible to suppress falling.

It is a diagram that schematically a network using the coercive intrinsically safe circuits of Example 1 of the present invention. It is a figure which shows the stack | stuck area | region of DSU, and the operation | movement area | region of a protection unit. It is the figure which simplified the circuit network using the security circuit of the structure replaced with FIG. It is the figure which simplified the circuit network using the security circuit of the structure replaced with FIG. Is a diagram that schematically a network using the coercive intrinsically safe circuits of Reference Example 2 of the present invention. It is the figure which simplified the circuit network using the security circuit which concerns on invention of the Example of this invention. It is the figure which illustrated the case where the composition shown in Drawing 1 is applied to a 4-wire system. It is the figure which illustrated the case where the structure shown in FIG. 5 is applied to a 4-wire system. It is the figure which illustrated the case where the composition shown in Drawing 6 is applied to a 4-wire system. It is the figure which simplified the circuit network using the security circuit applied to description of a prior art.

DESCRIPTION OF SYMBOLS 10 Safety circuit 11,12 Protection unit 13 Off adjustment element 14 Overcurrent limiter 15 DSU
16 User terminal (equipment)
L1, L2 Communication line G, T1, T2, G, A, K Terminal Tr1, Tr2 Triac S1, S2 Thyristor D1, D2 Protection diode

Claims (3)

Attached to a digital access device that performs self-protection by suspending the function when surge current exceeding a specified limit current value enters through the communication line, as well as the interface function of the subscriber side and exchange side equipment In a security circuit for a digital access device that operates at a current value lower than the limit current value and suppresses excessive self-protection of the digital access device,
A thyristor comprising an anode terminal , a cathode and a gate terminal, wherein the cathode terminal and the gate terminal are connected to at least one communication line, and connected to the communication line between the cathode terminal and the gate terminal; A protection unit comprising a resistor that converts a current flowing through the communication line into a voltage , and a protection diode that is connected in parallel with the resistor and prevents a reverse bias from being applied to the thyristor ;
When the surge current that has entered through the communication line has a predetermined current value smaller than the limit current value, the thyristor is turned on by the voltage generated by the resistor, and the surge current is applied to the cathode terminal and the anode. A security circuit for a digital access device, characterized in that it flows between terminals . Said protective unit to two of the communication lines are provided symmetrically, the anode terminal of the thyristor in each protection unit are connected to each other, and, digital according to claim 1, characterized in that it is grounded Security circuit for access device. The two communication lines, digital access device Protective circuit according to claim 2, characterized in that the two communication lines in a plurality of communication lines.

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