Background Art] In a data communication method utilizing a balanced cable that can be applied as telephone class lines, in particular, a communication method using x Digital Subscriber Line (xDSL), in which telephone

signals and data signals are overlapped, and a balanced cable, there are a low voice signal reaching several dB and a 20 Hz, 80 V ring signal and a 48 V DC current on a telephone side, thus utilizing a ring signal ranging from 16 Hz to 20 Hz and a small frequency range from 300 Hz to 3,400 Hz. In contrast, the communication method is characterized by a wide voltage level described above.

In the case of data, ADSL utilizes a range of 30 KHz to 1 MHz and VDSL utilizes a wide range frequencies ranging from the ADSL range to 12 MHz, and only data signals are used, so that it can be mentioned that a voltage range is more stable than a voltage level.

In xDSL in which two types of signals having different characteristics coexist, there exists a historical background on which the telephone technology developed along with the communication history is combined with the data technology recently put to practical use, and technologies applied to xDSL are very different, in addition to the characteristics of the used signals.

Accordingly, unlike the conventional technology, the necessity of special demand for protection against lightning and surges with respect to data is described in detail below.

In accordance with the telephone technology, telephones can be constructed using a handset based on a carbon material, hybrid coils for performing matching and transmission, and a circuit used to construct a bell. It is prescribed that a protective discharge tube on a telephone side"must not discharge at 179 V, but must discharge at lower than 600 V (KT- 5805-0761)."In accordance with the ITU-T recommendation K. 12, it is prescribed that, in the case of a standardized gas discharge tube for 250 V/3 P, a maximal impulse discharge initiation voltage is in the range of 1000 V/u. s to 900 V/ps.

In accordance with the above-described prescription, an installed lightning and surge protection apparatus has a margin of 180-300 V between the line and the ground, and a margin of 600 V between the lines. Generally, in the field, two gas discharge tubes having a standard of 230 V are configured in series and are then used. When the standard is tested based on the above-described prescription and the test method (IEC 61000-4), tests proved that a residual voltage higher than 1,500 V existed when a surge voltage of 4,000 V is applied.

FIG. 1 is a diagram showing the construction of the circuit of a conventional protection apparatus for telephone lines, which employs gas discharge tubes. As

shown in the drawing, two gas discharge tubes GA1 and GA2 are connected in series between telephone lines Li and L2, the connection point between the gas discharge tubes GA1 and GA2 is connected to a ground G, and the telephone lines Li and L2 are connected to tip and ring signal input terminals, respectively.

FIG. 2 is a circuit diagram of an ADSL modem that uses telephone lines as communication lines while sharing the telephone lines. As shown in the drawing, two telephone lines Li and L2 are connected to a modem 4 through a primary protection unit 1 composed of a gas discharge tube GAI a current limiting unit 2 using a resistor, a PTC element or a common mode choke coil 2, and a secondary protection unit 3 composed of a single surge limiting element TNR3 connected in parallel between the lines and two surge limiting elements TNR1 and TNRZ connected in series between the lines.

In the conventional lightning and surge protection circuit constructed as described above, the gas discharge tube GA of the primary protection unit 1 functions to block an overvoltage high than several hundred V, and one of a resistor, a PTC element or a choke coil may be used as the current limiting unit 2.

Furthermore, the secondary protection unit 3 functions as a limiter that blocks a high voltage higher than

several hundred volts generally using three surge limiting elements TNR1, TNR2 and TNR3.

Meanwhile, in the prior art, equipment, such as the protection apparatus employing gas discharge tubes or the ADSL modem, generates high frequency pulses (discharge pulses) of several volts according to the discharge characteristics of the gas discharge tubes in which a discharge and a recovery are repeated at the time of AC contact or the inflow of a ground fault. The equipment acts as an oscillator for a high frequency and a high voltage that can easily pass through the coupling transformer of a modem or the like through which a commercial AC voltage cannot pass, so that it becomes a factor in the breakage of the modem. Even though the secondary protection unit is added, as shown in FIG. 2, the discharge pulses cannot be prevented. When lightning or a surge at a several thousand level is applied, a residual voltage of server hundred volts exists, so that the conventional protection apparatuses are insufficient for the protection of the modem.

From tests in which a surge voltage of 150 V is continuously applied to live telephone lines on which ADSL is installed based on the conventional technology (the gas discharge tubes do not discharge at a voltage of 180 V), it was found that an ADSL modem lost memory

values and set profile values and settings were changed to values set at the time of manufacture. That is, in the circuit of FIG. 2, the surge limiting elements TNR1, TNR2 and TNR. 3 do not perform a limit function on a low voltage, but performs a limit function on a high voltage at a 270 V level. With respect to a strong surge of 1000 V/ps, a residual surge of several hundred volts remains, so that only a protection effect at a low level is expected.

Accordingly, although many attempts to lower the limiting voltage of the secondary protection unit have been made, interference with a ground or frame ground occurs, so that a problem occurs in that noise occurs in telephone lines due to the correlation between equipment connected to the frame ground and an EMI filter.

From tests for proving the above description, it could be frequently found that the ADSL modem stopped its function due to the loss of a process and a ping test was discontinued. A power voltage of +5 V in the ADSL modem was lowered to negative several volts due to the inflow of a surge. Additionally, the cases of damage caused by the above-described factors include frequently occurring failures in which the Internet is disconnected in ADSL and VDSL, failures in which a connection is not made and a normal operation is

performed by a reset operation, and failures in which settings must be reset by a reset operation.

Such a failure pattern can be verified by the failure statistics of a company that is providing an ADSL service in Korea. More than 14 % of users (reports: 1185/lines: 8213, samples in a specific region in May, 2002) reported failures on a monthly basis, and more than 70% of the reports (853/1185) were disconnections and defective connections, which showed seriousness.

Although the disconnections and the defective connections cannot be considered to be due to lightning or surges, factors must be found in a reproducible range in test and verification environments, so that weight is given to the factors.

Problems are serious in ordinary times. Damage caused by weather conditions at the time of lightning is clearly verified by damage caused by lightning in October, 2002. The numbers of lines damaged by lightning in a specific region having 40 thousand telephone facilities and 8 thousand ADSL facilities include 197 failed telephone lines and 2138 failed ADSL lines, which shows that data facilities have vulnerability to lightning.

The above-described cases of damage to data communication are caused by the problems of the prior

art and by field circumstances that take care of such damage.

In the case of a searchable arbitrary region to be investigated, in 283 homes that were investigated, only 37 had ground facilities and 31 homes had protection apparatuses therein. Urban architectures that were investigated had circumstances that had no ground and in which government recommendation or the IEE subscriptions could not be discussed.

[Disclosure] [Technical Problem] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an apparatus for protecting communication equipment from lightning and surges, in which a protection device, which must be installed in a communication inlet part, is provided in the lightning and surge protection apparatus, so that protection against lightning and surges can be achieved in regions relatively vulnerable to lightning and surges, such as farming and fishing villages and small towns having insufficient ground and protection facilities.

A detailed object of the present invention is to provide a technology that provides a fundamental

measure for protection against ground faults, power line contact and incoming surges by preventing the generation of a residual voltage and discharge pulses after the discharge of a gas discharge tube, transmits effective telephone signals to a telephone in a range that gives influence, such as attenuation, and gives protection against lower electrical potential for precise protection for a data side.

A further object of the present invention is to provide an optimal measure for protection against lightning and surges in a non-ground mode when providing a technology that blocks a 48 V DC voltage, a 80 V ring AC signal and a voice signal without attenuation, effectively limits surge components without causing the attenuation of data signals, and overcomes the potential difference between communication lines and power lines by implementing a pseudo-ground between all elements as well as communication lines.

[Technical Solution] The present invention provides an apparatus for protecting communication equipment from lightning and surges, including a primary protection unit 11 for protecting circuits from an overvoltage that enters through an inlet side telephone line; a current

limiting unit 12 for limiting the overvoltage having passed through the primary protection unit 11 to a predetermined value; a high-pass filter unit 13 for separating only high frequency data signals from various signals that enter through telephone lines; an interface unit 14 connected to the high-pass filter unit 13 to eliminate line noise, adapted to implement a pseudo-ground by realizing equal potentials between the lines and a ground, and adapted to transmit the data signals to an output unit; a secondary protection unit 15 for blocking surge voltages transmitted to a modem 16 and a computer 17 by suppressing the residual potential of the primary protection unit 11 behind the interface unit 14; a low-pass filter unit 22 for separating only low frequency voice signals from various signals that enter through telephone lines while selectively connecting behind the primary protection unit 11 or current limiting unit 12 and transmitting the separated signals to a telephone 24; a voice protection unit 23 for protecting telephone side equipment; and a pseudo-ground 21 for forming an equal potential by commonly connecting the grounds of the primary protection unit, the secondary protection unit, the interface unit and the voice protection unit to the grounds of a modem and a computer.

The high-pass filter unit 13 includes two

condensers Cll and C12 connected in series to tip and ring lines, respectively, and a single coil L21 connected in parallel between the tip and ring lines.

Further, although the current limiting unit 12 is represented by two coils LZll and LZ12 in the drawing, which have characteristics effective to the reduction of common mode noise entering through lines and a current limiting function with respect to a surge level as common mode choke coils, and may be replaced with two resistors if common mode noise does not cause a problem.

Furthermore, the coil L21 of the high-pass filter unit 13 is characterized by being replaced with the coils L22 and L23 of the interface unit 14 and being omitted.

Furthermore, the two coils L22 and L23 of the high-pass filter unit 14 may be replaced with a single coil having both terminals and a neutral point, which may be used as an element, that is, the above- described high-pass filter unit, and eliminates noise entering through the lines by short-circuiting the lines and a ground using low impedance with respect to high frequency components, that is, 60 Hz 110 V components and their harmonic components induced to the ground or frame ground. This causes a line potential to be equal to individual devices and the

ground using a pseudo-ground, thus eliminating a cause that prevents a second limiting voltage from being low.

Furthermore, the present invention is characterized by suppressing lightning and surges to a low potential level lower than a commercial signal level on a telephone side by separating only high frequency signals while blocking ineffective telephone level signals without loss using the high-pass filter unit and the limit elements of a secondary protection unit.

Furthermore, the present invention is characterized in that a power source side surge protection unit 20 is further included on the power inlet side of the computer 17 and the ground of the power source side surge protection unit is connected to the pseudo-ground 21.

Advantageous Effects] As described above, the present invention provides a lightning and surge protection method in regions relatively vulnerable to lightning and surges, such as farming and fishing villages and small towns having insufficient ground and protection facilities, and provides a fundamental measure for protection against ground faults, power line contact and

continuously incoming surges.

Furthermore, the present invention provides a precise surge protection technology to a data communication equipment side sensitive to surge protection compared to a telephone side, and provides a technology capable of eliminating the potential difference between communication lines and power lines using a coil connection circuit for the balance of a pseudo-ground and the lines as well as a protection function for the communication side and the power source side, thus providing an optimal measure for protection against lightning and surges in a non- ground mode.

The present invention provides a fundamental measure for protecting communication equipment from lightning and surges regardless of whether a communication ground and a power source side ground is present, and improves a home ground environment using common ground distribution and provides a surge protection and ground method for a modem or SMPS for small-sized equipment, thus implementing an economical and stable communication environment and allowing a high-quality data communication environment without disconnections and defective connections.

[Description of Drawings

FIG. 1 is a diagram showing the construction of a conventional basic lightning and surge protection apparatus for conventional telephone lines; FIG. 2 is a diagram showing the construction of a conventional lightning and surge protection apparatus for conventional xDSL lines; FIG. 3 is a block diagram of a lightning and surge protection apparatus for communication equipment in accordance with an embodiment of the present invention; FIG. 4 is a circuit diagram of the lightning and surge protection apparatus for communication equipment in accordance with the embodiment of the present invention; FIG. 5 is a view illustrating a ground implementation method using common ground distribution that is applied to the present invention; FIG. 6 is a view showing the construction of SMPS that is used for xDSL according to the present invention; and FIGS. 7 (a) to 7 (c) are diagrams showing the characteristics of surge waveforms to illustrate the present invention.

[Best Model Embodiments of the present invention are

described in detail with reference to the accompanying drawings below.

FIG. 3 is a block diagram showing an apparatus for protecting communication equipment from lightning and surges. As shown in this drawing, telephone lines L1 and L2 are connected to a primary protection unit 11, a current limiting unit 12 for limiting current, a high-pass filter unit 13 for passing only a data communication signal therethrough, an interface unit 14 for maintaining equal electrical potential between a line and a ground wire, removing noise from a ground wire or virtual ground wire, and coupling a data signal to an output terminal, and a secondary protection unit 15 for suppressing surge potential to a protection level at which a modem 16 can operate safely. The modem 16 is connected to the output sides of the telephone lines Ll and L2.

A Personal Computer (PC) 17 is connected behind the modem 16. The power supply is designed so that power can be supplied from power lines through a power source side surge protection unit, that is, a distribution panel, to the PC 17 and through an adaptor 19 to the modem 16.

Furthermore, a low-pass filter 22, a voice protection unit 23 and a telephone 24 are connected in parallel behind the primary protection unit 11 or the

current limiting unit 12, thus protecting against surges transferred from the low-pass filter 22 and the voice protection unit 23 to the telephone.

Meanwhile, the ground wires of the primary protection unit 11, the interface unit 14, the secondary protection unit 15, the modem 16, the PC 17, the voice protection unit 23 and a power source side surge protection unit 20 are connected in common to a pseudo-ground 21, so that they are in an equipotential state.

FIG. 4 is a detailed circuit diagram of the apparatus for protecting communication equipment from lightning and surges. As shown in this drawing, the apparatus includes two gas discharge tubes GA1 and G that are connected in series between telephone lines L1 and L2 and are connected to a virtual ground G at a central connection point between them, a primary protection unit 11 that is composed of a gas discharge tube GM connected between the ends of the lines, and a current limiting unit 12 that is connected behind the primary protection unit 11 and is composed of common mode choke coils Lzll and Lzl2, so that the balancing of the two lines, the attenuation of in-phase noise and the restriction of surge-level current can be achieved.

A high-pass filter unit 13 for blocking Direct

Current (DC) components and low frequency components is composed of a structure in which two condensers Cil and C12 and a coil L21 are connected in a differentiator form. An interface unit 14 is composed of two coils L22 and Las and a transformer T1. The two coils L22 and L23 may be replaced with a single coil having a positive terminal and a neutral point. The coil may include the function of the coil L21 that is a component of the high-pass filter unit 13. The transformer T1 is necessary in terms of a function but may be omitted in practice.

A secondary protection unit 15 to be connected to the modem 16 is connected behind the transformer T1, and protects the modem 16 by suppressing residual voltage after discharge in the primary protection unit 11 to such a low level so as not to influence the modem.

The low-pass filter unit 22 includes coils Ll, and L12 and a condenser C1 that are connected to two lines behind the current limiting unit 12, and the voice protection unit 23 includes two surge limiting elements MI and M2.

In the present invention constructed as described above, the primary protection unit 11 composed of the gas discharge tubes CAl, GA2 and GA3, that is, elements for protecting against transient

voltage that may be input to telephone signals and data through the telephone lines L1 and L2, is provided in the protection apparatus, so as to provide for the case where telephone protection apparatuses are not installed, as in farming and fishing communities and small towns.

Furthermore, a power source side surge protection unit 20 is provided to cope with the ingress of a surge from a power source side, and the pseudo-ground 21, in which the ground wires of the respective components are connected in common, so that a ground function is achieved using only a chassis ground, is constructed in a ground mode to allow smooth operation.

In the present invention, if a customer premise protector used for telephones exists, the customer premise protector is used. Otherwise the primary protection unit 11 provided in the protection apparatus performs such a function.

Furthermore, the low-pass filter unit 22 for identifying effective signals from the point of view of the telephone 24 is constructed. The low-pass filter unit 22 employs a low-pass filter technology.

The low-pass filter unit 22 is implemented in a combination limiting technology and filter technology form. In this case, the limiting technology acts as a

surge suppression technology, and is invented to coincide with a data level surge protection technology and achieve the purpose of the present invention.

With reference to FIG. 4, the present invention is described in detail below.

The low-pass filter unit 22, which is a voice filter circuit handling voice level signals, is a low- pass filter that is composed of the coils Lll and L12 and a condenser C1. The pass frequency band of the low-pass filter unit 22 corresponds to DC and ring and voice signals, the frequencies of which are each less than 4 KHz. Accordingly, it can be understood that DC 48 V, that is, a voice level signal, and ring and voice signals can be coupled to the telephone 24.

Meanwhile, when discharge is performed in the gas discharge tubes GA1, GA2 and G of the primary protection unit 11, a discharge residual voltage in a range of several hundreds V to 1,500 V may remain. The discharge residual voltage is limited to a predetermined range (approximately 15 V) by the limit elements Zll, Z12 and Z13 of the secondary protection unit 15.

In this case, the limitation is exerted from an electrical potential lower than the limiting voltage of the limit elements Zlll Z12 and Z13, that is, approximately 15 V, by the coils Lzll and Lzl2 of the

current limiting unit 12.

The high-pass filter unit 13 passes only the data signals, that is, harmonic signals, of signals that are input through the telephone lines, therethrough. When a data line side is normal, a problem does not occur. When the line status is abnormal, the distortion of a waveform occurs and a pulse form having a high through rate enters, which may damage the modem. In order to prevent this problem, the present invention enables a limitation in a range of several mV using the high-pass filter.

The voltage limiter of the secondary protection unit 15 has a function of suppressing all the signals, which have passed through the high-pass filter, to a standard voltage level. When a level is lower than a reference level of several V, the limiter does not operate. However, if a voltage higher than the reference voltage is applied, the limiter is operated and, therefore, suppression to a level lower than the reference level is performed, thus preventing a surge higher than the reference level from being output.

Accordingly, a ring signal can be eliminated up to several hundred mV while a voltage lower than the voltage limit range (here, 15 V) of the secondary protection unit 15 is high-pass filtered through the condensers Cll and C12 of the high-pass filter unit 13

and the coil L21.

That is, a DC voltage of 48 V is blocked by the condensers Cl, and C12, a voice signal is blocked by the high impedance of the high-pass filter unit, and a ring signal passed through with high impedance and input to the data side is checked by the high-pass filter unit.

According to the same principle, although high voltage lightning, a surge, a ground fault current, a power line contact current, a discharge residual voltage or a discharge pulse enters, it is blocked by the limiter function, so that the communication equipment can be protected.

Meanwhile, when the entire system along with the communication device of the present invention is entirely constructed using the pseudo-ground 21, an AC 110V component may be induced from the power source side to the line of the pseudo-ground 21 due to a frame connection. That is, equal potential is formed by the pseudo-ground 21, so that trouble with the EMI filter of the power source side occurs, so that AC 110V can be induced to the telephone lines through the line of the pseudo-ground.

AC 110V induced as described above is blocked by the limit elements Zn, Z12 and Z13 of the secondary protection unit 15. The reason why a rated voltage is

limited to a high voltage (for example, 270 V) in a conventional limit unit is that the noise of the ground wire or frame ground wire causes a problem.

Even in the present invention, a potential difference is generated between tip-ring lines by the end voltage of the two limit elements Zll and Z12, and is induced to the telephone lines L1 and L2 through the condensers Cl, and C12 in the form of noise, and, therefore, may cause noise in telephones.

Accordingly, in the present invention, noise, that is, a low frequency component (60 Hz and its harmonic component) induced from a pseudo-ground line, is eliminated by short circuit.

In the meantime, the present invention is described in detail below on a theoretical basis. A representative waveform of a surge is as defined in IEC62-41, which is represented by the following equation.

FIGS. 7 (a) to 7 (c) are example views of a surge waveform.

In the case where f=l/t and the waveform of a surge (IEC 60-1) is 1.25/50 asz with regard to a voltage waveform, the frequency Fl=1/1. 25 ps=800 KHz in the case of 1.25 pus, and the frequency F2=1/50 ps=20 KHz in the case of 50 , s, as shown in FIG. 7 (a). With regard to a current waveform, the frequency F3=1/8

pu=125 KHz in the case of 8 jjLs, and the frequency F4=1/20 pu=50 KHz in the case of 20 jj. s, as shown in FIG. 7 (b). With regard to a voltage waveform at 10 J. s or 700 ps, the frequency F5=1/10ps=100 KHz in the case of 10 ps, and the frequency F6=1/700 pus=1, 429 Hz, as shown in FIG. 7 (c).

The telephone 24 connected to the low-pass filer unit 22 has a high surge impedance, so that no problem is caused. The data side circuit having the high-pass filter unit 13 produces results that are still influenced by a surge.

The above description is examined in conjunction with the characteristics of the surge below.

In the case of the xDSL overlapping a balanced cable that are used as telephone lines, it is constructed as shown in FIG. 3, so that it is characterized in that the danger of lightning or a surge is relatively low, but inflow from communication lines and power lines is high.

In the case of a surge induced between the lines L1 and L2, the level at which the primary protection unit 11 operates is theoretically 460 V. In the case of a surge lower than the above-described surge, there is no discharge of the primary protection unit 11, so that the surge is applied both to a telephone and to data. When lightning, a surge, a ground fault or an AC

contact having a voltage ranging from a discharge voltage up to several thousand V enters, a discharge is generated in the primary protection unit 11.

A voltage before a discharge (a discharge residual voltage) and a pulse (a discharge pulse) voltage during a discharge are high frequency voltages, and enter through telephone side and data side paths.

Since the telephone side low-pass filter unit 22 composed of coils Lll and L12 and a condenser Cl has high surge impedance, a high frequency voltage is blocked. In the case of the data side, the high frequency voltage is passed through the condensers Cil and C12, so that the high frequency voltage is limited to a reference voltage by the limit elements Zll, Z12 and Z13 or is limited to the surge impedance level of the elements.

The limit elements Zll, Z12 and Z13 may have a limit function or a trigger function. Output characteristics are limited by a reference voltage or the internal resistance of the elements with respect to the transient characteristics of the elements. A residual voltage appearing on an output side is determined by the following Equation. In this case, Vi refers to a voltage on the input sides of the limit elements, that is, a voltage on a high-pass filter

side, and Vo refers to a voltage on the output sides of the limit elements, that is, a voltage on a modem side.

If Vi is lower than the sum of the limit voltages of Zll and Z12, Vo=Vi.

If Vi is higher than the sum of the limit voltages of Zll and Z12, Vo=VZ11+VZ12.

VZll=VZ12=the limit voltage rating of Zll and Z12 If Vi is higher than the sum of the limit voltages of Zll and ZI. 2 and is the transient characteristics of Zll and Z12, Vo=Vi* (RZ11+RZ12) /Vi* (RC11+RZ11+RZ12+RC12) where Vo: output voltage, Vi: input voltage, RZI, : surge resistance of Zll, RZ12 : surge resistance of Z12, RCll : surge resistance of C11, RC12 : surge resistance of Cl2 Accordingly, there occurs a phenomenon in which an actual voltage limit value becomes higher than a desired voltage limit value (for example, 15 V) (by approximately 20-30 V) due to an internal resistance in the range of several ten mu-several hundred m#.

In order to solve the above-described problem, in the present invention, the current limiting unit 12 is provided to the lines L1 and L2, so that a phenomenon in which a limiting voltage increases due to the internal resistance values of the limit

elements Zll, Z12 and Z13 and the internal resistance values of the elements of the high frequency filter unit can be compensated for.

Meanwhile, when a surge between the lines is applied to the power source side, the PC 17 is protected by the operation of the power source protection unit 20. Furthermore, when an excessive potential difference, that is, lightning or a surge, enters between the communication line L1 and the earth, no current passes through equipment having no power source, such as a telephone, in the case where there is no appropriate discharge route, and, therefore, the equipment is not damaged.

In contrast, in the case of data communication equipment, a power source is connected to the equipment due to its characteristics and, therefore, a potential difference between the power source or communication lines is caused, so that a discharge occurs in the portion of the equipment that is connected to the power line and the communication lines, resulting in damage to the equipment.

In the adaptation of a non-ground scheme, the present invention is provided with the pseudo-ground 21, as shown in FIG. 3, so that an equipotential loop extending from the communication line Ll, through the gas discharge tube GAI, the neutral point of the coils

L22 and L23 of the interface unit 14, the limit element Zll, the pseudo-ground G and the PC 17 to the power source side surge protection unit 20 can be provided, thus fundamentally preventing an excessive potential from resulting in a discharge in the equipment.

Meanwhile, FIG. 5 is a diagram illustrating a ground implementation method based on a common ground distribution scheme that is applied to the present invention.

As shown in the drawing, a communication line 103 suspended on a communication pole 101 branches off to a home from a terminal box 102. Generally, since a ground wire 104 is connected from the communication pole 101 to a ground rod 104a embedded in the ground, the ground wire 104 branches off and enters the home along with the communication line 103.

Furthermore, a ground wire 204 is connected from another communication pole 201 to a ground rod 204a embedded in the ground. In this case, a ground distribution terminal 202 is mounted on the communication pole 201, and the ground wire 204 is allowed to enter a home through the ground distribution terminal 202.

A method of compensating for home ground circumstances, in which a ground is not constructed or is weak, by connecting a ground, which is constructed

on an electric or communication pole or a distribution device, to a home is implemented by employing an idle core line for electricity or communication or adding a ground supply line, and connecting the idle core line or ground supply line to the pseudo-ground or the ground terminal of the equipment.

By connecting the ground wire, which is led as described above, to the line of the pseudo-ground 21 of the protection apparatus of the present invention, a ground effect can be reliably maintained.

FIG. 6 is a diagram showing the construction of an SMPS that is also used in xDSL. In accordance with the prior art, a surge protection method using MOV is applied only to both ends of power input. The conventional SMPS is provided with an outlet having no ground terminal, so that ground cannot be achieved. In the present invention, surge limiting elements MI, and M12 are additionally provided and connected to both ends of power lines, and the neutral point of the surge limiting elements Mil and M12 is connected to the (-) line of the DC output terminals of the SMPS.

When a power source is connected, a modem or equipment using DC power output is naturally connected not only to the ground side of equipment but also to the above-described pseudo-ground line, so that perfect protection for the SMPS can be achieved.

Using the ground for the SMPS, the correlation between a signal ground SG and a frame ground FG is not influenced by the filters that are employed in an EMI filter on the power source side of the entire equipment.

Furthermore, the coils Ll, and L23 of the interface unit 14 violates a separate ground method (IBM's recommendation for the ground of a PC) at the time of application of the above-described pseudo- ground method, so that a method for fundamentally coping with low frequency noise that may be induced to communication lines is provided. This method functions to balance a voltage difference when the voltage difference occurs between the two lines L1 and L2.

In such construction, the source of a surge, which may be induced to a home, includes a ring type transient phenomenon that occurs at the time of operation of an electrical motor. In this case, the surge is a surge (IEV 826-02-01) that the peak voltage and frequency thereof decreases and disappears from a period of 100 KHz, and may be interpreted by the above-described interpretation of a surge basic waveform. The sources of the potential difference in a communication cable section or between communication cables and power lines include lightning, a surge or a ground fault. Surges in communication and power line

sections are exemplified by a transversal current due to the balance of lines and a longitudinal current that is induced between the lines and the ground.

Accordingly, in the present invention, the coils L22 and L23 of the interface unit 14 are connected in series between the two lines, and the central connection point therebetween is connected to the pseudo-ground G, so that the balance between the lines can be achieved and an equipotential loop can be formed, thus overcoming the above-described voltage difference between the lines.

Industrial Applicability] The present invention relates, in general, to an apparatus for protecting communication equipment from lightning and surges that is capable of grounding balanced lines without the influence of noise at the time of realizing ground so as to improve the stability of a network by preventing various noise, lightning and surges in the network using a balanced cable, such as telephone lines or a UTP cable, and, more particularly, to an apparatus for protecting the terminals of x Digital Subscriber Line using a telephone signal and a data signal in an overlapped fashion and dedicated lines using a balanced cable from lightning and surges.