JP3108233B2 - Disconnect control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disconnection control circuit used for disconnecting a terminal device from a communication line.

[0002]

2. Description of the Related Art When a failure is suspected in a terminal device connected to a communication line, the terminal device is disconnected from the communication line to test which side of the communication line or the terminal device has failed. Is performed.

As a conventional example of such a disconnection control circuit for disconnecting a terminal device from a communication line, a configuration shown in FIG. 2 is conceivable (see FIG. 1 of JP-A-3-226154 and FIG. 1 of JP-A-3-229557). (See FIG. 3). In FIG. 2, SCR silicon controlled rectifier, D _S is the diode, RL relay, r1 ₁ and r1 ₂ are contacts of the relays RL, R _F is the resistance, C _F capacitor, Z _S is a Zener diode, R _D is resistance, C _D capacitor, Z _L is a Zener diode, L ₁ and L ₂ are communication lines terminals,
T ₁ and T ₂ are terminals on the side to which the terminal device is connected.

At the time of an incoming call, the silicon controlled rectifier SC
Since the current flow is blocked by R, the relay RL
Is not driven, so that the contacts rl ₁ and r1 ₂ are closed and connected to the communication line and a terminal device not shown,
A DC voltage _VDC (48 V) from the central office is applied to the terminal device.

When disconnecting a terminal device from a communication line,
When a high voltage signal having the same polarity as the DC voltage _{VDC of} FIG. 2 is applied from the central office, the high voltage signal is applied to the gate G of the silicon controlled rectifier SCR via the Zener diode Z _S, and conduction between the anode A and the cathode K is performed. state, and current flows through the resistor R _D → relay RL → silicon controlled rectifier SCR → diode D _S. As a result, the relay RL is operated to contact r1 ₁ and r1 ₂ is opened, disconnecting from the communication line to the terminal device.

[0006] resistor R _D, a capacitor C _D and Zener diode Z _L constitute a circuit to prevent malfunction of the silicon controlled rectifier SCR. That is, when the terminal device is connected to the communication line and the voltage of the communication line sharply increases, a sharp voltage change occurs at both ends of the silicon controlled rectifier SCR. Upon receiving a sudden change in voltage, the silicon controlled rectifier SCR becomes conductive even if no signal is applied to the gate G. In order to prevent this malfunction, a sudden voltage change is applied to the resistor _RD and the capacitor _CD.
Is suppressed by the filter effect.

Further, the terminal device is disconnected from the communication line.
The capacitor C_DAnd Zener Daio
Do Z_LIs connected to the contact r1 of the relay RL₁Through
Line L₁Is connected to the Zener diode Z_Lof
Zener voltage is selected below the maximum allowable voltage of relay RL.
The Zener diode Z during the continuation of the disconnection signal. _L
And diode D_SThrough the relay RL
To protect.

[0008] The terminal device is connected to the communication line, when in communication, the impedance of the filter formed by the resistor R _F and the capacitor C _F is set high enough relative to the impedance of the terminal device, the communication It does not affect the signal and keeps high impedance.

A series circuit composed of a resistor R _D and a capacitor C _D also needs to have a high impedance with respect to a communication signal. However, the communication signal has a small amplitude. Zener diode Z _L
The current flow is blocked by the diode D _S and the high impedance is maintained.

[0010]

A high voltage impulse noise such as a call signal for calling a terminal device or lightning is applied to the above-mentioned disconnection control circuit via a communication line. That is, as shown in FIG. 3, a calling signal (16 Hz, 75 V) superimposed on a DC voltage of _VDC (48 V) is transmitted between the lines of the calling communication line. The ringing signal voltage alternately repeats a ring period (1 second) and a silent period (2 seconds). Since there is no synchronous relationship between the 16 Hz period and the intermittent period, the voltage at the end of the ring period is always different. If the ringing signal voltage ends at a high voltage V _N of the same polarity as the DC voltage V _DC , the line voltage drops sharply toward V _DC by V _N.

Further, if there is a lightning strike near the calling communication line, a lightning surge voltage is generated between each line of the communication line and the ground, and a three-pole lightning arrester in the subscriber protector is activated. Although the discharge protects the line and the terminal device in the subscriber's house, a pulse voltage that cannot be completely removed between the lines is generated at the wave front and the tail of the lightning surge voltage. If the pulse voltage is generated at the same polarity as the DC voltage V _DC during calls, when raised to a high voltage V _N is line voltage V _N by abruptly falls toward the V _DC.

In FIG. 2, when only DC voltage _VDC is applied between communication lines, the capacitor C _F
DC and the capacitor C _D are charged to a voltage lower than that by the zener voltage V _Z.ZL of the zener diode Z _L , respectively. In this state, when the calling signal voltage or noise voltage is applied by superimposing on a DC voltage V _DC, the voltage V _CF of the capacitor C _F is slightly because time is long constant determined by the capacitor C _F and the resistor R _F Although only change, the voltage V _CD of the capacitor C _D is relatively fast following the change of the paging signal voltage or noise voltage due to the short time constant determined by the capacitor C _D and the resistor R _D, ring signal voltage or noise Immediately before the disappearance of the voltage, the voltage rises by V _N and becomes V _CD = V _DC + V _N -V _Z.ZL. The charging path of the capacitor C _D is 2
As indicated by solid arrows.

In this state, the calling signal voltage or the noise voltage disappears, and the line voltage drops sharply by V _{N to} reduce the DC voltage V _DC.
Returning to the capacitor C _D the voltage V _CD is not possible sudden change of the voltage V _CD Zener diode Z of the capacitor C _D
If the Zener voltage V _{Z.ZS of S} is larger than the capacitor C _D , the capacitor C _D is discharged through a discharge path indicated by a broken arrow in FIG.
Through to the cathode terminal K. At this time, since the voltage polarity between the anode terminal A and the cathode terminal K is in the forward direction, the silicon controlled rectifier SCR is triggered and becomes conductive, and the relay RL malfunctions.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a disconnection control circuit improved so as to eliminate a malfunction of disconnecting a terminal device from a communication line by a call signal or noise.

[0015]

Means for solving the above problems will be described. The principle is that even if there is a sudden voltage change due to a ringing signal or noise, the control current does not flow through the electronic switch that operates the relay.

That is, a series circuit including at least a series connection of a relay, an electronic switch, and a first diode;
A low-pass filter composed of a series connection of a first resistor and a first capacitor is connected between two lines constituting a communication or monitoring control line, and supplied from the upstream side of the two lines. A first constant voltage element for discriminating a voltage of the first capacitor charged by the disconnection signal is provided between a connection point between the first resistor and the first capacitor and a control terminal of the electronic switch. A disconnection control circuit configured to disconnect and, when the relay operates by application of the disconnection signal, to disconnect a contact point of the relay connected in series to the two lines downstream of the two lines, A second resistor is connected in series to a series circuit including a series connection of the relay, the electronic switch, and the first diode, and a series circuit including a second capacitor and a second constant voltage element is connected in parallel. And third Wherein the constant voltage element and the second resistor, a second
Are connected in series to a series connection circuit composed of a capacitor and a second constant voltage element.

[0017]

For a series circuit of a relay, an electronic switch, and a first diode, the second resistor is connected in series with the second resistor.
The series circuit consisting of the capacitor and the second constant voltage element is connected in parallel, and the third constant voltage element is connected to the series connection circuit consisting of the second resistor and the second capacitor and the second constant voltage element. Connected in series.

Therefore, when the line voltage drops sharply, the electric charge charged in the second capacitor is reduced by the second resistor and the second capacitor.
And the third constant voltage element is discharged, so that malfunction of the electronic switch can be prevented.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram of the present invention. In FIG. 1, a silicon controlled rectifier SCR, a diode D _S , a relay R
L, contacts r1 ₁ and r1 ₂ relay RL, the resistor R _F,
A capacitor C _F , a Zener diode Z _S , a resistor R _D ,
The capacitor C _D , the Zener diode Z _L , the communication line side terminals L ₁ and L ₂ , and the terminal device side terminals T ₁ and T ₂ are as described in FIG.

Further, Z _H1 and Z _H2 are Zener diodes for preventing the inflow of communication signals, and are no longer used as the Zener diodes Z _L and D _S described in the conventional example shown in FIG. To be provided. The operation of the embodiment is as described in the conventional example and will not be described.

[0021] terminals L ₁ and L _2, when the voltage having a rapid voltage changes as described in Figure 3 is inputted, the electric charge charged in the capacitor C _D is the path indicated by the broken line in FIG. 1 Discharged. Therefore, the silicon controlled rectifier SC
No discharge current flows through the gate G of R, and no malfunction occurs.

In the embodiment, the Zener diode Z _H2 is connected between the Zener diode Z _H1 and the terminal L _2. However, the Zener diode Z _H2 may be connected to any point in the discharge path excluding the communication line shown by the broken line in FIG. The same effect can be obtained.

[0023]

As described above, according to the present invention,
The diode for preventing the inflow of the communication signal is separated and independent, so that the silicon controlled rectifying element SC that operates the relay even when a voltage with a sudden voltage change is input.
No current flows to the control terminal of R, and malfunction of the relay can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of the present invention.

FIG. 2 is a configuration diagram of a conventional example.

FIG. 3 is an explanatory diagram of a calling signal and a noise voltage.

[Explanation of symbols]

L _1, L ₂ communication line terminals T _1, T ₂ terminal apparatus-side terminals RL relays r1 _1, r1 ₂ relay contacts SCR silicon controlled rectifier R _D, R _F resistance C _D, C _F capacitor D _S diode Z _S, Z _L , Z _H1 , Z _H2 Zener diode

──────────────────────────────────────────────────続 き Continuing on the front page (73) Patent holder 000004226 Nippon Telegraph and Telephone Corporation 2-3-1, Otemachi, Chiyoda-ku, Tokyo (72) Inventor Tamio Motomitsu 1-1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Tsunetaka Ema 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Yoshihiro Sawada 1-130-13, Narimasu, Itabashi-ku, Tokyo Shares (72) Inventor Shigeru Fukushima 3-12-15 Chuo, Warabi City, Saitama Pref. Nikko Electric Works, Ltd. (72) Inventor Tomoji Ogata 108-3 Oyamagahara, Iruma City, Saitama Prefecture Nisatsu Corporation Inside Electric Works (72) Inventor Takahiro Ami 1 Shinko, Hanno City, Saitama Prefecture Inside Hakusan Works (56) References JP-A-3-226154 (JP, A) Open flat 3-229557 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) H04M 3/22 H04M 11/00 - 11/10

Claims (1)

(57) [Claims] At least a relay, an electronic switch and a first
A series circuit including a series connection with a diode and a low-pass filter including a series connection of a first resistor and a first capacitor are connected between two lines constituting a communication or monitoring control line. The first constant voltage element for discriminating the voltage of the first capacitor charged by the disconnection signal supplied from the upstream side of the two lines is provided by the first resistor and the first capacitor. When the relay operates between the connection point of the electronic switch and the control terminal of the electronic switch and the disconnection signal is applied, the contact point of the relay connected in series with the two lines downstream of the two lines A disconnection control circuit, wherein a second resistor is connected in series to a series circuit including a series connection of the relay, the electronic switch, and the first diode, and a second capacitor is connected to the second capacitor. Constant voltage element And a third constant voltage element connected in series to a series connection circuit composed of the second resistor, the second capacitor, and the second constant voltage element. Characteristic disconnection control circuit.