JPS637068B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a circuit for connecting a data collection terminal device to a subscriber telephone line, and in particular, the present invention relates to a circuit for connecting a data collection terminal device to a subscriber telephone line. Regarding a terminal connection device that is not provided.

[Technical background of the invention and its problems]

In recent years, data collection systems have been planned in which a terminal device that operates solely on the power supply of an exchange is connected in parallel with a telephone to a subscriber telephone line (hereinafter referred to as the telephone line), and data is transmitted to a central device. When configuring this type of system, the first thing to keep in mind is that it should not affect telephone calls, that it should exhibit high resistance during insulation tests, and that it should not waste power from the exchange. It is. Therefore, it is desirable to operate the terminal device only during the data collection period (an extremely short period of time for each terminal device), and for this purpose, it is necessary to activate and call the terminal device by some means.

In order to realize this, it is first possible to start up the terminal device by applying a DC voltage different from the normal state to the telephone line. However, this type of method requires a separate voltage to be applied to the telephone line, which is undesirable as it would significantly change the current specifications.

Therefore, it is currently being considered to start up the terminal device by reversing the polarity of the currently used DC voltage (approximately 48 volts) without changing the voltage value. By the way, the above polarity reversal is generally also performed when a 16Hz ringing signal arrives at the telephone. Therefore, if no means is provided to ensure that the terminal equipment is substantially disconnected when this 16Hz ringing signal arrives, the waveform of the 16Hz ringing signal will be distorted due to impedance fluctuations. There is a problem with this.

[Purpose of the invention]

An object of the present invention is to provide a terminal connection circuit that does not affect a calling signal to a telephone.

[Summary of the invention]

The present invention provides an analog device that exhibits a cut-off state when the voltage supplied via a telephone line is equal to or higher than a predetermined voltage, and maintains the cut-off state for at least a predetermined time irrespective of subsequent decreases in the supply voltage. The switch is arranged between the telephone line and the terminal device, thereby achieving the above object.

[Embodiments of the invention]

FIG. 1 is a block diagram showing the configuration of a terminal connection circuit including a terminal device. This embodiment also has a configuration for exhibiting high resistance during insulation testing and for preventing it from affecting the insulation testing. In the same figure, telephone line connection terminals 1a, 1
One terminal 1a of b is connected to the DC input side of the high voltage analog switch 2, and the other terminal 1b is connected to the common return end of the high voltage analog switch 2 via a reverse current blocking diode 3. ing. This high voltage analog switch 2 first shifts from a conductive state to a cutoff state when the voltage appearing on the telephone line exceeds a predetermined voltage ₁ set in advance. Once in the cutoff state, even if the voltage drops, the cutoff state is maintained for a predetermined period of time. Further, the high voltage analog switch 2 receives a release signal 6 from a terminal device 5, which will be described later.
It also enters the cutoff state when is supplied, and thereafter maintains the cutoff state for a predetermined period of time similarly to the above case. Note that the predetermined voltage ₁ is set to an arbitrary value between the voltage after polarity inversion (48) and the 16 Hz calling signal (effective value 75). In addition, the above prescribed time is
As will be described later, it is determined to be approximately one signal period of a 16Hz calling signal.

The voltage that appears on the output side of the high-voltage analog switch 2 is supplied to the low-voltage analog switch 4, where it is determined whether the supplied voltage is sufficient for the operation start voltage of the terminal device 5. will be done. In other words, the low voltage analog switch 4 maintains a cutoff state when the supply voltage is less than the predetermined voltage ₂ , and becomes conductive when the supply voltage _{is 2} or more. The above-mentioned conductive state is maintained even if

A terminal device 5 for data collection is connected to the output side of the low voltage analog switch 4. This terminal device 5 receives operating power from the exchange when the low-voltage analog switch 4 is turned on, and when collecting data, after polarity reversal by the exchange, reception of a specific terminal call signal sent from a central device (not shown) is detected. It is determined whether it is a call based on the presence or absence, and if it is not a call, a release signal 6 is sent to the high voltage analog switch 2 after a certain period of time has elapsed.
It has the function of supplying

FIG. 2 is a block diagram embodying the terminal connection circuit of FIG. 1. In the figure, the high voltage analog switch 2 includes a main switching section 21 consisting of a transistor Q ₂₁ , a switching control section 22 consisting of a transistor Q ₂₂ , a transistor Q ₂₃ , a constant voltage diode ZD ₂₁ , and a diode D ₂₃ . voltage detection section 2
3 and a time constant section 24 consisting of a resistor R ₂₄ and a capacitor C ₂₄ are connected together with resistors R ₂₁ , R ₂₂ and R ₂₃ as shown in the figure. In addition, as will become clear in the explanation of the operation described later, the resistor R ₂₄ and capacitor C ₂₄ in the figure
If these elements are removed, only the circuit configuration for dealing with the insulation test is left, and the circuit shown in the figure partially utilizes the circuit that deals with the insulation test, that is, works together to influence the ringing signal. This circuit is designed to prevent this from occurring.

When the voltage applied between points A and C reaches a predetermined voltage _{of 1} or more, the voltage is applied to the base-emitter of the transistor Q 22 of the opening/closing control section 22 via the constant voltage diode ZD ₂₃ and the resistor R ₂₁ of the voltage detection section ₂₃ . A Zener current flows between them, which turns on transistor _Q22 . This transistor Q ₂₂
When turned on, the transistor of the main switching section 21
Since base current no longer flows through Q ₂₁ , transistor Q ₂₁ shifts to the off state. Furthermore, when the transistor Q ₂₂ of the opening/closing control section 22 is turned on,
The emitter of the transistor Q ₂₃ of the voltage detection section 23
Current flows between the bases and transistor _Q23 is turned on. When the transistor Q ₂₃ is turned on, the base current of the transistor Q 22 of the opening/closing control section ₂₂ flows through the transistor Q 23 of the voltage detection section ₂₃ and the diode.
D ₂₃ flows through the resistor R ₂₁ , so even if the voltage between points A and C drops below the predetermined voltage ₁ , the ON state of the transistor Q ₂₂ of the switching control section 22 and, by extension, the ON state of the main control section 21 is maintained. The off state of transistor _Q21 is maintained. In addition, the voltage detection section 2
By turning on transistor Q ₂₃ of No. 3,
Since the capacitor C ₂₄ of the time constant section 24 is charged,
Even if the voltage between points A and C drops and transistor Q ₂₃ turns off, the opening/closing control section 22
At the base of the transistor Q ₂₂ is a diode D ₂₃ ,
The discharge current of the capacitor C ₂₃ is supplied via the resistor R ₂₁ . Therefore, the on state of transistor _Q22 is
It is held for a predetermined time determined by the time constant of the capacitor C ₂₄ and the sum of resistors R ₂₄ and R ₂₁ .

Note that when the voltage applied between points A and C is less than the predetermined voltage ₁ , no current flows through the constant voltage diode ZD ₂₃ of the voltage detection section 23, so the transistor Q ₂₂ of the switching control section 22 is in the off state. As a result, the transistor Q ₂₁ of the main switching section 21
remains on.

On the other hand, when the transistor Q ₂₂ of the switching control unit 22 is in an off state, that is, the transistor Q ₂₁ of the main switching unit 21 is in an on state, when a release signal 6 that is sufficiently higher than the potential at point C is supplied from the terminal device 5, Resistance R ₂₃
The base current flows through the transistor Q ₂₂ of the opening/closing control unit 22, and the transistor Q ₂₂ turns on. When this transistor Q ₂₂ is turned on, the transistor Q 23 of the voltage detection section 23 is also turned on, as described above, while the transistor Q ₂₁ of the main switching section ₂₁ is turned off. Thereafter, even if the release signal 6 is cut off or the voltage between points A and C drops, the transistor Q 22 of the opening/closing control section 22 is activated by the transistor Q ₂₃ of the voltage detection section ₂₃ .
remains on. In addition, when the voltage between points A and C further decreases and the transistor Q ₂₃ of the voltage detection section 23 turns off, the opening/closing control is performed by the discharge current of the capacitor C ₂₄ of the time constant section 24 as described above. Transistor _Q22 of section 22 remains on for a predetermined period of time.

In addition, in this way, the transistor of the main switching section 21
When Q ₂₁ is off, that is, when high voltage analog switch 2 is cut off, the DC resistance value seen from the telephone line side is the resistance R ₂₁ and the resistance R ₂₂ .
The parallel combined resistance value of

Next, the low voltage analog switch 4 has a main switching section 41 consisting of a transistor Q ₄₁ , a voltage detection section 42 consisting of a transistor Q ₄₂ , and a constant voltage diode ZD ₄₂ , and these sections are connected to each other by a resistor R _41. They are connected as shown in the figure. Therefore, the voltage between point B and point C in the figure is the predetermined voltage ₂
If this is the case, the transistor Q ₄₁ of the main switching section 41
A constant voltage diode is connected between the emitter and base of
Zener current flows through ZD ₄₂ . Therefore,
Transistor _Q41 is turned on. When transistor Q ₄₁ is turned on, through resistor R ₄₁ ,
Since current flows between the base and emitter of the transistor Q ₄₂ of the voltage detection section 42, the transistor Q ₄₂
turns on. Therefore, the base current of the transistor Q ₄₁ of the main switching section 41 is
Since the current flows through the transistor Q ₄₂ of the main switching section 41, the on state of the transistor Q ₄₁ of the main switching section 41 is maintained even if the voltage between the point B and the point C decreases thereafter. Note that the on state of the transistor Q ₄₁ returns to the off state when the voltage between the point B and the point C further decreases and the transistor Q ₄₂ of the voltage detecting section 42 turns off.

Next, the operation of the terminal connection circuit as described above will be explained.

(i) When a voltage is applied between the telephone line terminals 1a and 1b, with the 1b side being positive, the resistance value seen from 1a and 1b is extremely high due to the reverse current blocking diode 3.

(ii) If the polarity of the voltage 48 applied from the exchange to the telephone line is reversed in order to start up the terminal device 5 and collect data, and then a specific terminal ringing signal is sent superimposed on this, the high voltage The low voltage analog switch 2 is conductive, and the low voltage analog switch 4 is conductive. As a result, terminal 1a - high voltage analog switch 2 - low voltage analog switch 4 - terminal device 5 - diode 3 - terminal 1b
A current flows through the terminal device 5 through the path. In other words,
When operating power is supplied, the terminal device starts operating and monitors whether reception of a specific terminal call signal is detected. When the terminal device 5 recognizes that it has been called, it thereafter performs predetermined data transmission with the central device.

(iii) Now, when a call is made to this telephone, which is connected to the telephone line in parallel with the terminal device,
When a 16Hz calling signal (effective value 75) is supplied to the telephone line terminals 1a and 1b, the following operation occurs.

First, when the 16Hz ringing signal AS is supplied at the same time as the polarity is reversed as shown in Figure 3, when the ringing signal AS reaches the predetermined voltage ₁ or higher, the high voltage analog switch 2 switches to the voltage BS shown in Figure 3. It becomes a cut-off state. Once the high-voltage analog switch 2 is in the cutoff state, even if the 16Hz call signal AS (instantaneous value) drops below ₁ , the high voltage analog switch 2 continues to discharge the capacitor C ₂₄ and the resistors R ₂₄ and R ₂₁ in the time constant section 24. The cut-off state is maintained for a predetermined time determined by a constant. The above predetermined time is the time _T0 or more from when the 16Hz ringing signal AS becomes less than ₁ until it exceeds ₁ again, but although this value depends on the setting value of _V1 ,
One period T ₁ of the ringing signal is sufficient, and this T ₁
It is stipulated in Therefore, even if the voltage of the 16 Hz calling signal AS changes repeatedly and passes through the conduction region each time, the high voltage analog switch 2 reliably maintains the cut-off state. Therefore, the above 16Hz ringing signal
During the supply period of AS, the high voltage analog switch 2 maintains a high resistance (more than the parallel combined resistance value of resistors R ₂₁ and R ₂₂ ), so that the waveform of the 16 Hz call signal AS is not distorted.

On the other hand, in some exchanges, after the polarity reversal occurs and the break period has passed, as shown in Figure 4, the 16Hz ringing signal AS
In this case, the analog switches 2 and 4 for high voltage and low voltage become conductive at the same time as the polarity is reversed, and the terminal device 5 is driven. However, in this case, since no specific terminal call signal arrives after activation, the terminal device 5 issues a release signal 6 after a certain period of time (T ₂ in FIG. 4). Therefore, the high voltage analog switch 2 shifts to the cutoff state as shown in FIG. 4 BS, and the terminal device 5
is equivalently disconnected from the telephone line. And thereafter 16
Even if the Hz call signal AS is supplied, as described above, the discharge current of the capacitor C24 of the time constant section ₂₄ causes the transistor _Q22 of the opening/closing control section 22 to operate for a predetermined time T1 _.
Since the high voltage analog switch 2 is kept in the on state, the high voltage analog switch 2 is kept in the cut off state. Note that the cut-off control using the release signal 6 here is mainly performed for insulation testing, and if this control were not present, the above-mentioned third signal would be activated when the 16Hz ringing signal arrives
It will operate in the same way as the case shown in the figure. Thus, influencing the 16Hz ringing signal is prevented. Note that CS in FIGS. 3 and 4 indicates the conduction state at the input end of the terminal device 5 in the case where only the circuit configuration is used to cope with the insulation test described above. Here, the "H" level of the BS and CS indicates a conduction state, and the "L" level indicates a cutoff state.

In this way, with the circuit of this embodiment, if a specific terminal call signal does not arrive after the voltage is reversed, the terminal device 5 issues a release signal 6, and this release signal 6 switches the high voltage analog switch 2 into the cut-off state. _16Hz calling Even if the signal is applied at the same time as the polarity is reversed, or even if it is applied after the break period, the cut-off state can be maintained almost completely and the 16Hz ringing signal will not be adversely affected. Additionally, telephone lines generally use high voltage (approximately 200 volts) and normal voltage (48 volts).
) and low voltage (approximately 35 volts) may be applied to conduct line insulation tests. However,
In the case of the circuit of this embodiment, as is clear from the above explanation of operation, the high voltage analog switch 2 maintains the insulation state for high voltage tests, and the low voltage analog switch 4 maintains the insulation state for low voltage tests. For the 48 tests, the high voltage analog switch 2 is cut off by the release signal 6 generated from the terminal device 5, so that each insulation test can be reliably performed.

Note that the switching transistors Q ₂₁ and Q ₄₁ for high voltage and low voltage may be connected in a Darlington manner, for example, as shown in FIGS. 5a and 5b. In this way, the insertion loss can be further reduced, and especially in the case of the transistor _Q21 , the value of the resistor _R22 can be selected to be higher. In addition, the configuration of each analog switch, the settings of the predetermined voltage ₁ and the predetermined time _T1 , etc. can be modified in various ways without departing from the gist of the present invention.

〔Effect of the invention〕

An analog switch that exhibits a cutoff state when the voltage supplied via a telephone line is equal to or higher than a predetermined voltage, and thereafter maintains the cutoff state for at least a predetermined time regardless of a decrease in the supply voltage; According to the present invention, which is arranged between a telephone line and a terminal device, it is possible to provide a terminal connection circuit that does not affect a calling signal to a telephone.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a terminal connection circuit in an embodiment of the present invention, FIG. 2 is a circuit configuration diagram embodying the configuration of FIG. 1, and FIGS. 3 and 4 show the operation of the terminal connection circuit described above. Signal waveform diagrams used for explanation and FIGS. 5a and 5b are main circuit configuration diagrams showing another embodiment of the present invention. 1a, 1b...Telephone line terminal, 2...High voltage analog switch, 3...Reverse current blocking diode, 4
...Low voltage analog switch, 5...Terminal device, 6
...release signal.

Claims (1)

[Scope of Claims] 1. In a terminal connection circuit that controls connection between a terminal device operated by electric power supplied from an exchange when the polarity of the subscriber telephone line is reversed and the subscriber telephone line, the electric power supplied via the subscriber telephone line is An analog switch is connected between the subscriber telephone line and the terminal device, which exhibits a cut-off state when the voltage supplied to the switch is equal to or higher than a predetermined voltage, and thereafter maintains the cut-off state for at least a predetermined period of time regardless of a drop in the supply voltage. A terminal connection circuit characterized by being placed between. 2. The analog switch maintains the cut-off state for approximately one signal period of the 16Hz ringing signal supplied via the subscriber telephone line.
Terminal connection circuit described in section.