JP2948417B2 - Lightning surge protection 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 lightning surge protection circuit for protecting a subscriber circuit connected to a telephone set by a lightning surge.

[0003] In a subscriber of an electronic exchange, a protection circuit capable of withstanding a lightning surge is provided in order to protect an electronic device or the like from lightning damage due to an induced lightning intruding into a subscriber circuit (SLC) depending on the usage environment. Has been requested.

FIG. 4 is a block diagram showing a conventional configuration example of a subscriber circuit. In the figure, reference numeral 1 denotes a telephone connected between an A terminal (ring line) and a B terminal (chip line). 2,
Reference numeral 3 denotes a power supply unit for supplying a telephone current to the telephone 1 at the time of off-hook. SW1 and SW2 are relay switches.

Reference numeral 4 denotes a ringer generator for generating a ringer for ringing the telephone 1, and reference numeral 5 denotes a ring trip circuit for detecting an overcurrent when the ringer generator 4 rings the telephone 1. Reference numeral 6 denotes an overvoltage protection circuit provided between the terminal A and the terminal B. In practice, for example, a diode bridge as shown in the figure is used. Reference numeral 7 denotes a hybrid unit having a function of converting 4-wire to 2-wire, and a hybrid transformer as shown in the figure is actually used.

Reference numeral 8 denotes a balanced network provided on the secondary side of the hybrid transformer. Amplifiers 9 and 10 are connected to the transformer secondary side, respectively. These amplifiers 9 and 10 are connected to a codec unit 11. The codec has a function of converting an analog signal into a digital signal and converting a digital signal into an analog signal. That is, a digital signal sent from the other party via the network is converted into an analog signal by the codec 11 and notified to the telephone 1, and conversely, the telephone 1
Is converted into a digital signal by the codec 11 and then transmitted to the network.

The power supply units 2 and 3 supply power to the telephone 1 when the telephone 1 is off-hook. That is, when the switches SW1 and SW2 are in the state shown in the figure, a current flows from the power supply unit 2 to the power supply unit 3 in the telephone 1, and the telephone 1 is operated. When an incoming call is received, the ringer generator 4 causes the switches SW1 and SW2 to be in a break state, sends the ringer to the bell of the telephone 1, and makes the telephone 1 ring. The overvoltage protection circuit 6 protects the subscriber circuit from lightning surge,
This will be described below.

FIG. 5 is a diagram showing a lightning surge voltage application state. (A) shows the case of a positive surge, and (b) shows the case of a negative surge. First, the case of applying a positive surge will be described. When a lightning surge voltage as shown in the figure is applied to the T line and the R line in the same phase, the surge current generated by the positive surge flows through the protection resistor RP and the diode bridge 6 in the direction shown in the figure and to the ground. Inflow. In this case, there is no effect on the system power supply VBB (−48 V). Therefore, there is no effect on the electronic device / circuit 20 connected between the T line and the R line. Here, the electronic device / circuit 20 is a general term for circuits such as a balanced network and a codec as shown in FIG.

Next, the operation when a negative surge voltage is applied will be described. When a negative surge voltage as shown in the figure is applied to the T line and the R line, a surge current flows in the direction shown in the figure from the system power supply of the apparatus. That is, the current flows from the system power supply VBB to the T line and the R line through the diode bridge 6 and the respective protection resistors RP.

[0009]

There is no problem when a positive surge voltage is applied, but when a negative surge voltage is applied, the voltage VBB of the system power supply has an amplitude of 100 V as shown in FIG. Reach. As a result, the withstand voltage of the electronic device / circuit 20 to which the system power supply is connected is at most 60 to
It is about 70 V, and as a result, there is a possibility that the electronic device / circuit 20 may be destroyed by pressure. VB when this surge is applied
The B amplitude increases as the steepness increases.

For example, assuming that the inductance of a wiring pattern or the like in a circuit is L, the voltage VL due to this inductance is: VL = L · di / dt di is a current change, and dt is a time change. And the system power supply VBB
In this case, an instantaneous voltage drop exceeding the withstand voltage of the electronic device / circuit 20 occurs, causing breakdown of the electronic circuit such as the LSI in the subscriber circuit.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a lightning surge protection circuit capable of preventing the destruction of an electronic device / circuit even when a negative lightning surge voltage is applied. The purpose is.

[0012]

FIG. 1 is a block diagram showing the principle of the present invention. The same components as those in FIG. 5 are denoted by the same reference numerals. The circuit shown in the figure has a terminal A (R line) and a terminal B (T
Line) constitutes a subscriber circuit to which a telephone is connected. Reference numeral 6 denotes an overvoltage protection circuit provided between the terminals A and B and the system power supply and ground. Reference numeral 20 denotes an electronic device / circuit for the subscriber circuit connected between the terminals A and B. An integration circuit 30 is connected between the system power supply and the electronic device / circuit 20. That is, the system power supply supplies power to the electronic device / circuit 20 via the integration circuit 30.

[0013]

When a negative lightning surge voltage is applied to the terminals A and B, a surge current flows from the system power supply VBB through the diode bridge 6 and the protection resistor RP to the terminals B and A.
Flows to the side. At this time, the system power supply VBB causes an instantaneous voltage drop as described above due to parasitic inductance in the circuit. However, a steep change in the amplitude of the system power supply VBB is also reduced by the integration circuit 30 and supplied to the electronic device / circuit 20. This will be described with reference to FIG. It is assumed that the system power supply VBB significantly changes as shown in FIG. When the power supply amplitude also passes through the integrating circuit 30, the amplitude is reduced as shown in FIG. Electronic equipment / circuit 2
Since what is supplied to 0 is the output of the integrating circuit 30,
The electronics / circuit 20 can survive the breakdown.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 3 is a configuration block diagram showing one embodiment of the present invention. 1 are denoted by the same reference numerals. In the embodiment shown in FIG.
And a capacitor C to form an integrating circuit using passive elements. The rapid change of the system power supply VBB due to the lightning surge also passes through the integration circuit 30, so that its amplitude is suppressed. In other words, the steep voltage drop as shown in FIG. 2A also passes through the integration circuit 30 so that its amplitude is suppressed as shown in FIG.
It is possible to prevent breakdown of the electronic device / circuit 20 composed of I or the like.

In the above description, a case where a low-pass filter circuit including a resistor R and a capacitor C is used as the integration circuit 30 is taken as an example. However, the present invention is not limited to this. If the power supply voltage VBB can be suppressed from a steep voltage drop due to a lightning surge, the present invention is not limited thereto.
Any form may be used.

[0016]

As described above in detail, according to the present invention, it is possible to provide a lightning surge protection circuit capable of preventing the destruction of an electronic device / circuit even when a negative lightning surge voltage is applied. . Also, the overvoltage protection circuit 6 is not limited to the diode bridge described above, and other circuits can be used.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram showing an example of operation waveforms of a power supply VBB.

FIG. 3 is a configuration block diagram showing one embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional configuration example of a subscriber circuit.

FIG. 5 is a diagram showing an applied state of a lightning surge voltage.

FIG. 6 is a diagram showing a voltage change of a system power supply of the apparatus.

[Explanation of symbols]

 6 Overvoltage protection circuit (diode bridge) 20 Electronic equipment / circuit 30 Integrator circuit RP Protection resistor

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshinobu Imai 3-9-1-18 Shin-Yokohama, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Inside Fujitsu Communication Systems Limited (72) Inventor Kenji Takato Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture 1015 Address Fujitsu Limited (72) Inventor Kazuhiro Yoshida 1015 Kamikodanaka Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Takeshi Nishioka 1015 Kamodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (56 References JP-A-63-215249 (JP, A) JP-A-3-139090 (JP, A) JP-A-60-118024 (JP, A) JP-A-58-195428 (JP, A) 6-62445 (JP, A) Special Table 57-502148 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04Q 3/42-3/42 107 H04M 19/00-19 / 0 8

Claims (3)

(57) [Claims] An overvoltage protection circuit (6) provided between a terminal A, a terminal B, a system power supply, and a ground, a subscriber circuit having a telephone connected to the terminals A and B, An electronic device / circuit (20) for a subscriber circuit connected therebetween, so that power supply from the system power supply to the electronic device / circuit (20) is provided through an integrating circuit (30). Characterized by a lightning surge protection circuit. 2. The lightning surge protection circuit according to claim 1, wherein said integration circuit comprises a passive circuit of a resistor and a capacitor. 3. An electronic device / circuit (20) wherein, when a negative surge voltage is applied between the terminals (A) and (B), fluctuations in a system power supply are moderated by the integration circuit (30).
2. The lightning surge protection circuit according to claim 1, wherein the lightning surge is prevented from being destroyed by pressure.