JP2552739B2 - Subscriber circuit overvoltage protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] With respect to an overvoltage protection circuit for a subscriber circuit of a time-division switch, circuit breakdown due to voltage rise of a communication power supply that occurs when a subscriber circuit package is hot inserted is prevented by a simple configuration. With the purpose of providing an overvoltage protection circuit for a subscriber circuit that can be used, a plurality of subscriber circuits equipped with capacitors for holding each subscriber line at the power supply voltage in a non-communication state, and a circuit power supply for each subscriber circuit , The power supply for communication and the circuit power supply line for supplying ground power, the power supply line for communication and ground power line are respectively connected to the external power supply section, and the bypass capacitor is connected between the power supply line for communication and the ground power line. The subscriber circuit package is provided, and a diode is provided on the power supply line for communication in the subscriber circuit package, the polarity of which is higher than that of a normal communication power supply from an external power supply unit. From the capacitor of the subscriber circuit of the subscriber circuit package that has been supplied with the existing power supply, against the rise of the power supply voltage due to the inrush current when the new subscriber circuit package is connected to the power supply unit with the polarity that blocks the current The discharge current generated is blocked by the diode.

TECHNICAL FIELD The present invention relates to an overvoltage protection circuit for a subscriber circuit of a time division switch.

The subscriber circuit of the time division exchange has a structure in which a plurality of subscriber circuits are mounted in one package. When the exchange is operating, the package is pulled out due to a failure of the subscriber circuit,
When replacing the package with another normal circuit or adding a subscriber circuit, the package of the subscriber circuit is inserted and operated while the exchange is operating. When a new circuit is inserted into the device driven by the power supply in this way (this is called active insertion), a charging current flows through the inserted circuit, the power supply voltage is temporarily changed, and the circuit is changed. There is a problem of destruction, and its solution is desired.

[Prior Art] FIG. 3 is a configuration diagram of a first conventional example.

In FIG. 3, 30 is a power supply unit provided on the back panel of the exchange, 31 to 33 are power lines provided in the package of the subscriber circuit, 31 is a circuit power (Vcc: + 5V) line,
32 is a ground line (GND), 33 is a power supply for communication (VBB: eg -48
V) represents a line. Reference numeral 34 is a subscriber circuit (indicated by BSH-LSI) provided corresponding to the subscriber lines 1 and 12.

The power supply Vcc, VBB and GND are input to the subscriber circuit 34, and a call current supply function (Battery feed:
B) and loop monitoring function (Supervision: S) and hybrid function (Hibrid: H) (represented by BSH).

A plurality of (e.g., eight) subscriber circuits 34 are provided in one package, and each line 31 to 33 is connected to each of those subscriber circuits in a multiple manner. Further, diodes D1 and D for preventing electrostatic breakdown are connected to the subscriber lines 1 and 12 to which the subscriber circuit 34 is connected.
2 is provided, and a capacitor C2 is connected to the subscriber circuit 34.

In the configuration of FIG. 3, when the exchange is operating, in the subscriber circuit 34 of the subscriber circuit package connected to the power supply unit 30, the capacitor C2 does not flow a call current (when the subscriber uses a telephone. If not) it is charged to about -44V.

In this way, when the power is turned on, another subscriber circuit package with the same structure is inserted into this frame (active insertion).
Then, an inrush current is generated in the bypass capacitor C1 of the package, and VBB of the power supply section rises transiently.

FIG. 5 shows a waveform diagram of VBB at that time. As shown in the figure, the rise of the call power supply VBB at this time reaches several tens of volts (V).

Then, in another adjacent subscriber circuit package that was driven by the same power supply unit 30 until then,
Charging voltage of capacitor C2 (-44V) due to voltage rise of VBB
The voltage at both ends becomes smaller due to the increase in VBB voltage, and the charge charged in the capacitor C2 is discharged.

This discharge current flows through the destruction prevention diode of the terminal of the subscriber circuit BSH-LSI, passes through the route of VBB → diode D2 → capacitor C2 → diode D1 → G, and its current value
Since I1 is several amperes as shown in FIG. 5, the diodes D1 and D2 of the subscriber circuit 34 (BSH-LSI) are destroyed and the entire circuit becomes unusable.

To prevent this, the configuration of Conventional Example 2 shown in FIG. 4 has been proposed.

In Fig. 4, Vcc, G, VBB and BSH-LSI represent the same as in Fig. 3, respectively, TR1 and TR2 are transistors, RL is a relay, r1 and rl2 are relay RL contacts, and R1 to R3 are resistors. Represent

When the package shown in FIG. 4 is inserted into the exchange, the transistors TR2 and TR1 are turned on and the relay RL is driven. As a result, the relay contacts r1 and rl2 are turned on after a predetermined time determined by the delay time characteristic of the relay RL. Therefore, the charging current generated when the package is inserted is
Resistor connected in series between VBB and subscriber circuit BSH-LSI
It flows according to the characteristics of the RC filter composed of the capacitor C1 connected between R3 and the ground G. Then, a rapid inrush current is suppressed within the time determined by the time constant of the circuit.

The contacts of the relay RL are driven after the delay time (several milliseconds) of the relay, so that the resistors R3 and R2 are short-circuited respectively, and the resistors are removed from the ground line and the power supply VBB line.
L then holds the driving state while power is supplied.

[Problems to be Solved by the Invention] According to the conventional example 2 shown in FIG. 4 described above, a relay is used to prevent a large inrush current by utilizing its delay time. It has a characteristic that chattering occurs because it is driven mechanically, and when chattering occurs in FIG. 4, there is a problem that the inrush current cannot be sufficiently suppressed. Further, it is difficult to precisely adjust the delay time of the relay, and there is a problem that a complicated circuit configuration is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an overvoltage protection circuit for a subscriber circuit, which can prevent the circuit from being destroyed by a voltage rise of a power supply for communication which occurs when a subscriber circuit package is hot inserted, by a simple configuration.

[Means for Solving the Problems] FIG. 1 is a principle configurational diagram of the present invention.

In FIG. 1, 10 is a subscriber circuit package 100 is a circuit power line, 101 is a ground line, 102 is a power line for communication, 11 is a diode provided by the present invention, 12 is a bypass capacitor,
Reference numeral 13 represents a plurality of subscriber circuits.

According to the present invention, a diode is provided in the telephone power supply line of the subscriber circuit package to prevent the subscriber circuit in the package from being destroyed when the telephone power supply on the power supply side rises.

[Operation] Each power is supplied from the power supply unit 14 to each subscriber circuit 13
When another package (not shown) is inserted into the power supply unit 14 when the
The voltage of the power supply VBB for communication rises rapidly due to the current supplied to 12. The increased voltage of the power source VBB appears on the power supply line 102 for communication of the active subscriber circuit package 10. However, since the diode 11 blocks the passage of current, a large current does not flow in the subscriber circuit 13. Therefore, the protection diode in the subscriber circuit 13 can perform normal operation without being destroyed.

[Embodiment] FIG. 2 is a block diagram of an embodiment.

In FIG. 2, 20a and 20b are subscriber line terminals connected to a subscriber terminal, 21 is a subscriber capacitor C2, 22 is a subscriber circuit (BSH-LSI), and 23 is a diode D1 added by the present invention.
And an overvoltage protection circuit composed of a bypass capacitor C1. Although only one subscriber circuit 22 is shown in FIG. 2, a total of eight subscriber circuits are actually mounted in the subscriber circuit package. The circuit including the transistor and the resistor shown on the left side of the subscriber circuit 22 has the same configuration as the conventional one and realizes the function of supplying the call current to the subscriber terminal.

When the subscriber circuit package shown in FIG. 2 is connected to a power source and is operating, if another subscriber circuit package is inserted in an adjacent position, the voltage of the communication power source VBB rises due to the inrush current. Then, the risen power supply for call VB
B is fed to the subscriber circuit of FIG. As a result, a voltage shown as a waveform VBB 'at the bottom of the figure is generated in the subscriber circuit 22 of FIG. 2 (the level of this rising voltage is the diode
It is kept lower than the conventional example by D1).

Then, in response to this, the voltage across the capacitor C2 decreases, so that discharge is attempted. However, since the diode D1 is provided in the discharge path, only a weak current flows. The waveform of the discharge current I at this time is shown in the lower part of FIG.

〔The invention's effect〕

According to the present invention, it is possible to suppress the rise of the communication power source VBB and prevent the destruction of the integrated circuit used in the subscriber circuit with a simple configuration of simply adding one diode.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment, FIG. 3 is a block diagram of Conventional Example 1, FIG. 4 is a block diagram of Conventional Example 2, and FIG. It is a waveform diagram. In Fig. 1, 10: Subscriber circuit package 100: Circuit power line 101: Ground line 102: Communication power line 11: Diode 12: Bypass capacitor 13: Subscriber circuit

Claims (1)

(57) [Claims] 1. An overvoltage protection circuit for a subscriber circuit of a time-division switch, wherein a plurality of subscriber circuits each having a capacitor for holding each subscriber line at a power supply voltage in a non-communication state and a circuit for each subscriber circuit are provided. Power supply, telephone power supply, and power supply line for the circuit that supplies the earth.
A subscriber circuit package in which a call power line and a ground line are respectively connected to an external power supply unit and a bypass capacitor is connected between the call power line and the ground line; A diode is provided on the power supply line for communication of the above, and the polarity is such that the current is blocked when a voltage higher than that of the normal power supply for communication is generated from the external power supply unit, and a new subscriber circuit package is connected to the power supply unit. In the subscriber circuit, the diode prevents the discharge current generated from the capacitor of the subscriber circuit of the subscriber circuit package supplied with the existing power source against the rise of the power supply voltage due to the inrush current. Overvoltage protection circuit.