JP2859908B2 - Network controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a terminal device connected between a telephone line and a terminal device without ringing a bell of a telephone connected in parallel. The present invention relates to a network control device for detecting a ringing incoming call to connect a terminal device to a telephone line.

(Prior Art) This kind of network control device is applied to a data transmission system constituting an automatic meter reading system as shown in FIG. 2, for example, which collects the usage of electricity, water, gas and the like via a telephone line. You. The data transmission system shown in FIG. 2 includes a center device 1 for collecting data, a center-side network control device 2, a telephone line 3, an exchange 4, a telephone line 8, a terminal-side network control device 5,
It comprises a terminal device 6 and a telephone 7.

In order to collect data from the terminal device 6, the center device 1 receives a call to the terminal-side network control device 5 connected in parallel to the telephone 7 through the center-side network control device 2, the telephone line 3, the exchange 4, and the telephone line 8. Thus, the terminal device 6 is connected to the terminal device 6 via the terminal-side network control device 5 and collects data from the terminal device 6. In this case, the incoming call to the terminal-side network control device 5 is designed so as not to hinder the use of the telephones 7 connected in parallel, that is, to make a ringing incoming call so as not to ring the bell of the telephone 7.

The network control device of the present invention relates to the terminal-side network control device 5. The network control device 5 has a function of detecting a no-ringing incoming call and has a sufficiently high impedance state for an insulation test of the telephone line 8. It is necessary to have.

FIG. 3 is a circuit diagram showing a switch circuit section of a conventional network control device. This switch circuit section has a high-voltage switching transistor 21 connected in series to the telephone line L, and switches the high-voltage switching transistor 21 between a base of the high-voltage switching transistor 21 and ground and a zener diode. It is controlled by a control transistor 23 connected via a resistor.

The control transistor 23 is turned on by the voltage supplied from the telephone line L via the resistor 25 connected to the base circuit of the transistor, thereby turning on the high voltage switching transistor 21 and maintaining the turned on state. , This conducting high voltage switching transistor 21
The telephone line L is connected to the terminal device 6 through the terminal.

Further, the switch circuit of the network control device shown in FIG.
By supplying an external signal to the base of the transistor 27 via a diode, the operation stop transistor 27 is operated, whereby the control transistor 23 is turned off and the high breakdown voltage switching transistor 21 is also turned off. When the operation stop transistor 27 is operated by an external signal, the operation stop transistor 27 continues to operate with the base current via the resistor 29, thereby preventing the control transistor 23 and the high breakdown voltage switching transistor 21 from operating. When the operation stop transistor 27 is activated and the high breakdown voltage switching transistor 21 is off, the collector current of the operation stop transistor 27 flows through the resistor 25. In this case, the network control seen from the telephone line L side is used. The impedance of the device is determined by the resistors 25 and 29 through which the collector and base currents flow, since only the deactivation transistor 27 is activated.

(Problems to be Solved by the Invention) In the switch circuit of the conventional network control device described above, the impedance at the time of off is determined by the resistances 25 and 29 as described above.
On the other hand, the conduction state of the high-voltage switching transistor 21 connected in series with the telephone line L to connect the telephone line L to the terminal device 6 is maintained by the conduction of the control transistor 23. Is maintained by the base current via the resistor 25, the resistor 25 cannot be made too large, and as a result, there is a problem that the off-state impedance of the network control device cannot be made sufficiently high.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a network control device of the present invention is connected between a telephone line and a terminal device and supplied from an exchange via the telephone line. A network control device activated by a no ringing call signal to connect a terminal device to a telephone line, the switching transistor being connected in series to the telephone line to connect the telephone line to the terminal device, and a telephone line side of the switching transistor. And a control transistor activated by a current supplied from the telephone line to the base terminal via the first high resistance to form a base current path of the switching transistor for operating the switching transistor; When the switching transistor is activated via the transistor, the activated switching An operation maintaining means for supplying a current from the telephone line via the transistor to the base terminal of the control transistor; a base terminal connected to the telephone line via the second high resistance and connected to ground via a capacitor; A deactivation transistor for stopping the supply of current to the base terminal of the control transistor during operation to stop the operation of the control transistor; and, when the control transistor is activated, a base of the deactivation transistor via the second high resistance from the telephone line. An operation stop maintaining means for causing a current to flow to the terminal to flow through the control transistor is provided.

(Operation) In the network control device of the present invention, the control transistor is activated by the voltage signal from the telephone line side, and when the switching transistor is turned on via the control transistor, the voltage signal from the telephone line side via the switching transistor is turned on. Maintains the operation of the control transistor.

(Example) Hereinafter, an example of the present invention is described using a drawing.

FIG. 1 is a circuit diagram of a switch circuit section of a network control device according to one embodiment of the present invention. The network control device shown in FIG.
In the network control device shown in FIG. 3, a current supply circuit 30 including a resistor 31 and a backflow prevention diode 33 for maintaining the operation of the control transistor 23 is provided on the terminal device side behind the high breakdown voltage switching transistor 21. Are different.

Describing the circuit configuration in more detail, the base of the high breakdown voltage switching transistor 21 is connected to the collector of the control transistor 23 via the Zener diode 35 and the resistor 37. The emitter on the telephone line L side of the high breakdown voltage switching transistor 21 is connected to the collector of the operation stop transistor 27 via the resistor 25, and
It is connected in common to the anodes of backflow prevention diodes 39 and 40 via 29. One backflow prevention diode
The cathode of 39 is the collector of the control transistor 23 and the resistor 37.
And the other diode 40 for reverse current prevention
Is grounded via a capacitor 43.
The connection point between the capacitor 43 and the diode 40 is connected to the base of the operation stop transistor 27, and is connected to the cathode of the backflow prevention diode 44.
An external signal is supplied to the base of the deactivation transistor 27 via The high-voltage switching transistor 21, the Zener diode 35, and the resistor 37 constitute a high-voltage switch circuit 20, and include a control transistor 23, an operation stop transistor 27, and the like, excluding the current supply circuit 30 and the high-voltage switch circuit 20. The circuit constitutes the control circuit 50.

 Next, the operation will be described.

First, when gentle reversal occurs due to no ringing incoming, a voltage is applied from the telephone line L by the operation of a polarity reversal detection circuit (not shown). When a voltage is applied to the telephone line L, a current flows through the base of the control transistor 23 via the resistor 25, and the control transistor 23 becomes conductive. Along with this operation, the base power supply also tries to flow to the operation stop transistor 27 via the resistor 29 and the backflow prevention diode 40. However, since this current is charged in the capacitor 43, the base potential of the operation stop transistor 27 Gradually rises and the deactivation transistor 27 does not conduct immediately. In this state, the control transistor 23 is turned on by the base current via the resistor 25, and the current that is going to flow to the base of the operation stop transistor 27 via the backflow preventing diode 40 is supplied from the resistor 29 to the backflow preventing diode 39 , And is turned off by the control transistor 23, and the operation stop transistor 27 is turned off.

In this state where the control transistor 23 is turned on and the operation stop transistor 27 is turned off, the telephone line L
When the voltage applied to the high-voltage switch circuit 20 becomes equal to or higher than the zener voltage of the zener diode 35 of the high-voltage switch circuit 20, the emitter line of the high-voltage switching transistor 21 from the telephone line L,
The current flowing to the control transistor 23 via the Zener diode 35 and the resistor 37 is
High-voltage switching transistor
21 conducts, whereby the voltage from the telephone line L is supplied to a determination circuit and the like and a current supply circuit 30 provided after the high voltage switching transistor 21.

The current supply circuit 30 is a high-voltage switching transistor
When a voltage is supplied from the telephone line L through the resistor 21, a current based on the voltage flows as a base current of the control transistor 23 through the resistor 31 and the backflow preventing diode 33, whereby the control transistor 23 is connected to the resistor 25. It becomes completely conductive with the base current via the current supply circuit 30 in addition to the base current. As described above, since the control transistor 23 conducts more completely with the base current from the current supply circuit 30,
The value of the resistor 25 may be such that it simply conducts at first, and the resistance value of the resistor 25 can be made larger than that of the related art.
Therefore, the impedance formed by the resistor 25 and the resistor 29 when the circuit is off can be increased as compared with the related art.

Next, an operation when the high breakdown voltage switching transistor 21 is turned off will be described. As mentioned above, high-voltage switching transistor
21 is turned on, and the voltage from the telephone line L is supplied to a determination circuit (not shown) provided at the subsequent stage through the high-voltage switching transistor 21. The determination circuit detects a no-ringing incoming signal and detects an abnormal line voltage. When the operation is performed and an abnormality is detected, an external signal is supplied to the base of the operation preventing transistor 27 through the backflow preventing diode 44 in order to turn off the high voltage switching transistor 21. Since the capacitor 43 is connected to the base of the deactivation transistor 27, the deactivation transistor 27
Does not conduct immediately, but conducts after charging the capacitor 43. When the operation stop transistor 27 is turned on, the current flowing to the base of the control transistor 23 via the resistor 25 and the current flowing to the base of the control transistor 23 via the current supply circuit 30 flow via the operation stop transistor 27. Thus, the base current of the control transistor 23 disappears, and the control transistor 23 is turned off. As a result, the high withstand voltage switching transistor 21 is also turned off, and the voltage supply to the circuit subsequent to the high withstand voltage switching transistor 21 is also stopped, whereby the external signal from the determination circuit and the current via the current supply circuit 30 are also eliminated. However, the operation stop transistor 27 is a resistor 29 and a backflow prevention diode.
The conduction state is maintained by the base current through 40, and thereby the off state of the high breakdown voltage switching transistor 21 is maintained.

The impedance of the circuit in this off state is
25 and the resistor 29, in this case the resistor 25
Since the supply of the base current of the control transistor 23 by the control transistor 23 is assisted by the current supply circuit 30, the resistance value of the resistor 25 may be a value that simply causes the control transistor 23 to conduct first, and the resistance value of the resistor 25 is It can be set to a large value in comparison. Therefore, the impedance formed by the resistor 25 and the resistor 29 when the circuit is off can be increased as compared with the related art.

[Effects of the Invention] As described above, according to the present invention, when the control transistor is activated by the voltage signal from the telephone line side and the switching transistor is turned on via the control transistor, the telephone via the switching transistor is turned on. The operation of the control transistor is maintained by the voltage signal from the line side, and the operation of the control transistor is not maintained by the direct voltage signal from the front side of the switching transistor, that is, the telephone line side. can do. In addition, when the control transistor is activated, the current to flow to the base terminal of the deactivation transistor for deactivating the control transistor is caused to flow out through the control transistor, so that stable deactivation of the deactivation transistor can be ensured. Thus, malfunction of the control transistor and the switching transistor can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a switch circuit section which is a main part of a network control device according to an embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a data transfer system to which the present network control device is applied. FIG. 3 is a circuit diagram of a switch circuit section of a conventional network control device. 20 high-voltage switch circuit 21 high-voltage switching transistor 23 control transistor 27 deactivation transistor 25,29 resistance 30 current supply circuit 31 resistance 50 control circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04M 11/00-11/10

Claims (1)

(57) [Claims] 1. A network control device connected between a telephone line and a terminal device, the network control device being activated by a no-ringing call signal supplied from an exchange via the telephone line to connect the terminal device to the telephone line. A switching transistor connected in series with the telephone line to connect the line to the terminal device, and a telephone connected to the telephone line side of the switching transistor to form a base current path of the switching transistor for operating the switching transistor. A control transistor activated by a current supplied from the line to the base terminal via the first high resistance; and a current from the telephone line via the activated switching transistor when the switching transistor is activated via the control transistor. To the base terminal of the control transistor And the dynamic stabilizing means, a base terminal second
A deactivation transistor that is connected to the telephone line via a high resistance and connected to the ground via a capacitor, and when activated, stops the supply of current to the base terminal of the control transistor and stops the operation of the control transistor;
A deactivation maintaining means for causing a current to flow from the telephone line to the base terminal of the deactivation transistor via the second high resistance when the control transistor is activated, through the control transistor. .