JPH0638252A - Lightning surge protection circuit - Google Patents

Abstract

PURPOSE:To prevent destruction of an electronic device and a circuit against a negative surge voltage by adopting the configuration such that a power is supplied from a system power supply to the electronic device and the circuit through an integration circuit. CONSTITUTION:When a negative lightening surge voltage is applied to terminals A, B, a surge current flows from a system power supply VBB to terminals B, A through a diode bridge 6 and a protection resistor RP. In this case, a momentary voltage drop is caused in the power supply VBB due to a parasitic inductance in the circuit, a steep change in the amplitude of the power supply VBB is relaxed by an integration circuit 30 and the resulting voltage is fed to an electronic device/circuit 20. Thus, destruction of the circuit 20 is prevented even when a lightning surge of negative is impressed to the circuit 20.

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 from a lightning surge.

A subscriber of an electronic exchange has a protection circuit capable of withstanding a lightning surge in order to protect electronic devices and the like from a lightning damage due to a guided lightning invading the subscriber circuit (SLC) side depending on its usage environment. Is required.

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

Reference numeral 4 denotes a ringer generation section for generating a ringer for ringing the telephone 1, and 5 a ring trip circuit for detecting an overcurrent when the ringer generation section 4 rings the telephone 1. Reference numeral 6 is an overvoltage protection circuit provided between the terminals A and B, and actually uses, for example, a diode bridge as shown in the figure. Reference numeral 7 is a hybrid section having a conversion function from 4 lines to 2 lines, and in practice, a hybrid transformer as shown in the figure is used.

Reference numeral 8 is a balanced circuit network provided on the secondary side of the hybrid transformer. Amplifiers 9 and 10 are connected to the secondary side of the transformer, respectively. The amplifiers 9 and 10 are connected to the codec section 11. The codec has a function of converting an analog signal into a digital signal and a digital signal into an analog signal. In other words, the 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 vice versa.
The voice analog signal from 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 drawing, a current flows from the power feeding unit 2 to the power feeding unit 3 in the telephone 1 to operate the telephone 1. When an incoming call arrives, the ringer generation unit 4 switches the switches SW1 and SW2 to a break state, sends a ringer to the bell of the telephone 1, and causes the telephone 1 to ring. The overvoltage protection circuit 6 protects the subscriber circuit from lightning surge,
This will be described below.

FIG. 5 is a diagram showing the applied state of the lightning surge voltage. (A) shows the case of a positive surge, (b) has shown the case of a negative surge, respectively. 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 protective resistor RP and the diode bridge 6 in the direction shown in the figure to the ground. Inflow. In this case, the system power supply VBB (-48V) is not affected. Therefore, there is no influence 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 circuit 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 from the system power supply of the device in the directions shown in the figure. That is, the current flows from the system power source VBB to the T line and R line sides 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 system power supply voltage VBB has an amplitude of 100 V as shown in FIG. Reach As a result, the breakdown voltage of the electronic device / circuit 20 to which the system power supply is connected is at most 60-
The voltage is about 70V, and as a result, the electronic device / circuit 20 may be broken down by withstand voltage. VB when this surge is applied
The B amplitude increases as the steepness increases.

For example, assuming that the inductance of the wiring pattern in the circuit is L, the voltage VL due to this inductance is: VL = Ldi / dt di is the change in current and dt is the change in time. System power supply VBB
In addition, an instantaneous voltage drop occurs that exceeds the withstand voltage of the electronic device / circuit 20, causing breakdown of the withstand voltage of an electronic circuit such as an LSI in the subscriber circuit.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a lightning surge protection circuit capable of preventing damage to an electronic device / circuit even when a negative lightning surge voltage is applied. Has an aim.

[0012]

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

[0013]

When a negative lightning surge voltage is applied to the terminals A and B, the surge current passes from the system power supply VBB through the diode bridge 6 and the protection resistor RP to the terminals B and A.
Flowing to the side. At this time, the system power supply VBB causes the instantaneous voltage drop as described above due to the parasitic inductance in the circuit. However, the sharp amplitude change of the system power supply VBB is also alleviated 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 is significantly changed by the negative lightning surge as shown in (a). This change in power supply amplitude is also reduced to about several tens of volts when passing through the integrating circuit 30, as shown in (b). Electronic device / circuit 2
Since it is the output of the integrating circuit 30 that is supplied to 0,
The electronic device / circuit 20 can be protected from breakdown.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 3 is a configuration block diagram showing an embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals. In the embodiment shown in the figure, the resistor R is used as the integrating circuit 30.
And a capacitor C constitute an integrating circuit by a passive element. A sudden change in the system power supply VBB due to a lightning surge also has its amplitude suppressed by passing through the integrating circuit 30. In other words, the sharp voltage drop as shown in FIG. 2A is suppressed by passing through the integrating circuit 30 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, the case where the low pass filter circuit including the resistor R and the capacitor C is used as the integrating circuit 30 is taken as an example. However, the present invention is not limited to this, as long as it can suppress a steep voltage drop of the power supply voltage VBB due to a lightning surge.
It may be in any form.

[0016]

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

[Brief description of 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 an 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 how a lightning surge voltage is applied.

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 Integration circuit RP Protection resistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinobu Imai 3-9-18 Shin-Yokohama, Kohoku-ku, Yokohama City, Kanagawa Prefecture, Fujitsu Communication Systems Ltd. (72) Kenji Takanaka Ueda, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Address 1015 in Fujitsu Limited (72) Inventor Kazuhiro Yoshida 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (72) Inventor, Goji Nishioka 1015, Kamiodanaka, Nakahara-ku, Kawasaki, Kanagawa Prefecture

Claims (3)

[Claims] 1. A subscriber circuit in which a telephone is connected to terminals A and B, an overvoltage protection circuit (6) provided between terminals A and B and a system power supply and ground, and terminals A and B. An electronic device / circuit (20) for a subscriber circuit connected in between, and a power supply from the system power source to the electronic device / circuit (20) is provided through an integrating circuit (30). Lightning surge protection circuit. 2. The lightning surge protection circuit according to claim 1, wherein the integration circuit (30) is composed of a passive circuit of a resistor and a capacitor. 3. When a negative surge voltage is applied between the terminal A and the terminal B, the fluctuation of the system power supply is moderated by the integrating circuit (30), and an electronic device / circuit (20) is provided.
2. The lightning surge protection circuit according to claim 1, wherein the lightning surge protection circuit is configured to be protected from breakdown.