JPS6328549B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to subscriber telephone lines (hereinafter referred to as telephone lines), in addition to conceptually expressing equipment for signal transmission, This invention relates to an analog switch circuit that is suitable for application to a terminal device, etc., which is connected to a switch (also used as a switch) and uses the power supply of an exchange.

[Technical background of the invention and its problems]

The power supply of a switchboard is originally provided for the use of the switchboard itself and the telephones connected to the telephone line. Conventionally, there were no terminal devices that connected to the terminal side of the telephone line and used the power supply of the switchboard. . However, 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 to each telephone line in parallel with a telephone set, and data is transmitted to a central device.

In this case, various considerations must be made, such as not affecting telephone calls, which should be the primary priority, exhibiting high resistance during insulation tests, and not wasting the power supply of the switching equipment. For this reason, the power consumption of the exchange by the terminal equipment must be limited to the time it takes to collect data (which is a very short time when viewed from the perspective of an individual terminal equipment). To achieve this, the terminal device must be activated at least in a direct current manner.
This is because an AC calling signal cannot be detected when the device is not activated, that is, when power is not supplied. One way to start up a terminal device using direct current is to change the magnitude or polarity of the voltage applied to the telephone line to be different from the normal state, but changing the magnitude of the voltage would significantly change the current specifications. This is particularly undesirable and results in polarity reversal.

Incidentally, polarity reversal is also carried out when the telephone is on the calling side and during the above-mentioned insulation test. Because the former must not affect telephone calls, and the latter must exhibit high resistance, the terminal device is essentially not activated for polarity reversals other than when collecting data. However, technical measures are required on an individual basis. Regarding the former, for example, a method has been proposed in which a means for detecting the off-hook state of the telephone is provided and the terminal device is disconnected when a detection output is obtained.

[Purpose of the invention]

The present invention primarily provides an analog switch circuit that allows a terminal device to be connected to a telephone line without affecting insulation testing, stabilizes the operation of the terminal device, and has low signal conversion loss.

[Summary of the invention]

The present invention provides a high voltage converter that conducts when the polarity-reversed DC voltage is less than a first predetermined voltage _V1 , maintains the cutoff state otherwise, and enters the cutoff state when a release signal is supplied from the terminal device. A voltage analog switch is provided on the telephone line side, and the high voltage analog switch becomes conductive when the voltage appearing through this switch is equal to or higher than a second predetermined voltage V ₂ (V ₂ <V ₁ ). , a low-voltage analog switch is provided on the terminal device side that maintains the conduction state as long as the high-voltage analog switch is conductive once it becomes conductive, and each of these high-voltage and low-voltage analog switches Accordingly, the opening/closing between the telephone line and the terminal device is controlled, thereby achieving the above object.

[Embodiments of the invention]

First, we will discuss the aspects of telephone line insulation testing. Current insulation tests include automatic insulation testing equipment that tests at a high voltage of around 200V;
Tested by an automatic insulation tester that tests at a low voltage of 35V or less, 48V, which is the operation start voltage of the terminal device.
It is broadly classified into those using manual insulation testing equipment. In the case of insulation testing, even if the polarity is reversed, the test voltage and the operation start voltage are obviously different, so the insulation test condition is detected from the voltage difference between both sides, and the terminal equipment is connected to the telephone line. can be kept electrically disconnected from the

On the other hand, in the case of manual insulation testing equipment, when the polarity is reversed, the test voltage is equal to the operation start voltage, so the terminal equipment is activated by the voltage during the insulation test, and the telephone line is low impedance. It will be terminated. In other words, it is impossible to judge the terminal device based on the voltage during the insulation test using the manual insulation testing device. Therefore, in this case, the terminal device side uses a detection means other than voltage to detect whether it is an insulation test or a self-call, and when the terminal is not calling, it is immediately electrically disconnected from the telephone line (for example, by setting it to a high resistance state). )There is a need.

Hereinafter, an analog switch circuit of a terminal device that can be adapted to any of the above-mentioned insulation testing devices will be explained with reference to FIGS. 1 and 2. First, FIG. 1 is a block diagram showing the overall configuration of an analog switch circuit including a terminal device.
One terminal 1a of b is connected to the DC input end side of a high voltage analog switch 2 including a high voltage detection circuit, and the other terminal 1b is connected to a reverse current blocking diode 3.
are respectively connected to the common return terminal side of the high voltage analog switch 2 via the terminals. This high voltage analog switch 2 maintains the cut-off state when a DC voltage of a predetermined voltage V1 or _more is input, and conversely,
It has the function of passing DC and AC voltage with low loss when V is less than ₁ . Further, this high voltage analog switch 2 is connected to a terminal device 5 which will be described later.
When the release signal 6 is supplied from , it shifts to the cutoff state and maintains this state.

The DC voltage of the telephone lines 1a, 1b that appears on the output side when the high-voltage analog switch 2 is turned on is input to the subsequent low-voltage analog switch 4, and this switch 4 sets it as the operation start voltage of the terminal device 5. The relationship between is determined. In other words, this low voltage analog switch 4 has an input DC voltage of a predetermined voltage.
When the voltage is less than V ₂ (V ₂ <V ₁ ), the cut-off state is maintained, and when the voltage is equal to or higher than the predetermined voltage V ₂ , it becomes conductive. Once this conductive state is established, the conductive state is maintained even if the input DC voltage becomes less than the predetermined voltage _V2 .

A terminal device 5 for data collection, for example, is connected to the DC output side of the low voltage analog switch 4. This terminal device 5 starts operating with power supplied from the telephone lines 1a and 1b when the low voltage analog switch 4 is turned on. Then, it is determined whether reception of a specific calling signal superimposed on the inverted DC voltage and sent from a central device (not shown) has been detected, and if the above-mentioned calling signal cannot be detected within a certain period of time, the high voltage analog switch 2 is It has a function of generating a release signal 6.

FIG. 2 is a circuit diagram embodying the analog switch circuit of FIG. 1. First, the configuration and operation of each block will be explained.

High voltage analog switch 2 is a transistor
Main switching section 21 consisting of Q ₂₁ and transistor Q ₂₂
an opening/closing control section 22 consisting of a transistor Q ₂₃ ;
and a voltage detection section 23 consisting of a constant voltage diode ZD ₂₃ , and these sections are connected to resistors R ₂₁ , R ₂₂ ,
The connection is made using _R23 as shown in the figure.
Therefore, in a state where a voltage higher than a predetermined voltage V ₁ (an arbitrary value between the operation start voltage of the terminal device and the voltage at the time of the above-mentioned test) is applied between points A and C in the figure, Constant voltage diode of voltage detection section 23
The transistor Q 22 of the switching control section 22 is turned on via ZD ₂₁ and the resistor R ₂₁ , and thereby the transistor Q ₂₁ of the main switching section ₂₁ is turned off. Furthermore, at this time, the transistor Q ₂₃ of the voltage detection unit 23 is turned on by the current flowing through the resistor R ₂₂ , so even if the voltage between points A and C drops below the predetermined voltage V ₁ , the transistor Q 23 can be opened/closed. The on state of the transistor _Q22 of the control section 22 is maintained. The DC resistance value between points A and C when the transistor Q ₂₁ of the main switching section 21 is in the off state is greater than or equal to the parallel resistance value of the resistor R ₂₁ and the resistor R ₂₂ .

On the other hand, when the voltage between point A and point C is lower than the predetermined voltage _V1 , no current flows through the voltage regulator diode _ZD1 of the voltage detection section 23, so the transistor Q22 of the switching control section ₂₂ is turned off. As a result, the transistor _Q21 of the main switching section 21 is in an on state.

By the way, when a release signal 6 having a voltage sufficiently higher than the potential at point C is supplied from the terminal device 5 in this state, the transistor Q ₂₂ of the opening/closing control section 22 is turned on via the resistor 23. this transistor
When Q ₂₂ is turned on, transistor Q ₂₁ of the main switching section 21 is turned off. In addition, the opening/closing control section 22
Due to the transition of transistor Q ₂₂ to the on state,
Since the transistor Q ₂₃ of the voltage detection unit 23 is turned on, even if the release signal 6 is cut off from now on, the opening/closing control unit 2
The on state of the transistor Q ₂₂ of the main switching section 21 and the off state of the transistor Q ₂₁ of the main switching section 21 are maintained as they are. In other words, the release signal 6 is sent from the terminal device 5.
As a result of this supply, the high voltage analog switch 2 shifts to the cutoff state. In this case, the DC resistance value between points A and C is the resistance as described above.
It is equal to or greater than the parallel resistance value of R ₂₁ and resistor R ₂₂ .

The low voltage analog switch 4 is a transistor
Main switching section 41 consisting of Q ₄₁ and transistor Q ₄₂
and a voltage detecting section 42 consisting of a constant voltage diode ZD ₄₂ , and these sections are connected together with a resistor R ₄₁ as shown in the figure. Therefore, when the voltage between points B and C in the figure exceeds the predetermined voltage V ₂ (an arbitrary value between the operation start voltage of the terminal device 5 and the voltage during the test described above), the main switch A Zener current flows between the emitter and base of the transistor Q ₄₁ of No. 41 via the constant voltage diode ZD ₄₂ .
Therefore, transistor _Q41 is turned on.
When transistor Q ₄₁ is in the on state, resistor R ₄₁
Since a current flows between the base and emitter of the transistor _Q42 of the voltage detection section 42 through the transistor Q42, the transistor _Q42 is turned on. Therefore, the main opening/closing part 4
Since the emitter-base current of the transistor Q ₄₁ of the main switching section 41 flows through the transistor Q ₄₂ of the voltage detection section 42, even if the voltage between points B and C subsequently decreases, the on state of the transistor Q ₄₁ of the main switching section 41 remains unchanged. Retained.

Next, the overall operation of the analog switch 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 DC resistance value seen from 1a and 1b is extremely high due to the reverse current blocking diode 3.

(ii) If the polarity of the 48V voltage applied to the telephone line is reversed by the exchange in order to start up the terminal device 5 and collect data, and then a specific AC calling signal is sent superimposed on it, the high The voltage analog switch 2 becomes conductive, and the low voltage analog switch 4 becomes conductive. As a result, terminal 1a-
Current flows through the terminal device 5 through the route of high voltage analog switch 2 - low voltage analog switch 4 - terminal device 5 - diode 3 - terminal 1b.
That is, when operating power is supplied, the terminal device starts operating, and first monitors whether reception of a specific paging signal is detected. Since this is now detected, the terminal device 5 recognizes that its own call has been made, and thereafter performs predetermined data transmission with the central device.

(iii) If the above-mentioned insulation test is performed with a voltage (200V) with the terminal 1a side being positive, the high voltage analog switch 2 will maintain the cut-off state, and at that time the DC resistance between terminals 1a and 1b will decrease. As mentioned above, is greater than the parallel resistance value of resistors R ₂₁ and R ₂₂ .
In order to make this parallel resistance value higher than the insulation resistance value of the telephone line and not to affect the operation of the transistors Q ₂₁ , Q ₂₂ , Q ₂₃ , each resistor R ₂₁ , ~,
Choosing the value of R ₂₂ is easy.

(iv) If the insulation test described above is performed with a voltage (35V) with the terminal 1a side being positive, the high voltage analog switch 2 will be conductive, but since the above voltage (35V) is less than the predetermined voltage _V2 , The low voltage analog switch 4 cannot conduct. Therefore, the transistor Q ₄₁ is connected between the terminals 1a and 1b at this time.
The terminal will be terminated with a high resistance value due to the off state.

(v) If the above mentioned insulation test was carried out at a voltage (48V) with terminal 1a side being positive, this
Corresponding to case (ii), power is supplied to the terminal device 5 through the high-voltage and low-voltage analog switches 2 and 4, respectively, and the terminal device 5 enters the operating state. However, since the terminal device 5 cannot detect the calling signal from the central device within a predetermined period of time, the release signal 6 is generated. As a result, the transistor Q ₂₂ of the switching control section 22 of the high-voltage analog switch 2 turns on, which turns the transistor Q ₂₁ of the main switching section 21 off, and the high-voltage analog switch 2 turns off. to move to. Therefore, the power supply to the terminal device 5 is also cut off, and the terminal device 5 returns to the non-operating state. At this time, the DC resistance value as seen from the telephone lines 1a and 1b is equal to or greater than the parallel resistance value of the resistors _R21 and _R22 , and is maintained at a level that does not interfere with the telephone connection operation. Note that during this insulation test, the terminals 1a and 1 were
Although the DC resistance value between b and b decreases, this time can be made extremely short, so there is no problem.

As described above, the analog switch circuit of this embodiment can be used not only for adapting high-voltage and low-voltage automatic insulation test equipment, but also for manual insulation tests conducted at a voltage equal to the operating start voltage of the terminal device. Determine whether it is a call or an insulation test by determining the arrival time of the call signal from the device.
When it is determined that it is an insulation test, the terminal equipment is electrically disconnected from the telephone line, so the terminal equipment that uses the power supply of the exchange can be adapted to all telephone line insulation testing equipment. In addition, when collecting data, transistors Q ₂₁ and Q ₄₁ that are in an on state are connected between the telephone line connection terminal 1a and the terminal device 5.
Since only the terminal device 5 is inserted, there is very little signal loss, and current can be stably supplied to the terminal device 5. Furthermore, in this embodiment, not only in high-voltage insulation tests but also in 48V tests, insulation can be performed using the high-voltage analog switch 2, so the insulation resistance can be maintained high. This makes it possible to handle 48V manual insulation tests without any problems. By the way, there is also a method to cut off the low voltage analog switch, but in this case, it is necessary to use a bistable circuit in conjunction with it to maintain the cut off state of the low voltage analog switch, since operating current flows through the bistable circuit. It is difficult to set high insulation resistance. Also,
For example, add 48V to set the insulation resistance value high.
It has been considered to provide an analog switch for isolation, but this would complicate the circuit. However, if the high-voltage analog switch is cut off as in this example, a sufficiently high insulation resistance can be obtained without providing a separate analog switch for insulation, and this can be achieved with a simple circuit configuration. . This effect is extremely effective in reducing the size and cost of the circuit, since the insulating resistor needs to have high resistance and be a high withstand voltage element. As shown in Figure 3a and b, if transistors Q ₂₁₁ and Q ₂₁₂ are connected in Darlington to form Q ₂₁ , and transistors Q ₄₁₁ and Q ₄₁₂ are connected in Darlington to form Q ₄₁ , the insertion loss can be lowered. In addition to this, the Q ₂₁ side in particular has the advantage of being able to select a higher value for the resistor R ₂₂ . In addition, the present invention can be modified in various ways without departing from the spirit thereof.

〔Effect of the invention〕

The present invention provides a high voltage converter that conducts when the polarity-reversed DC voltage is less than a first predetermined voltage _V1 , maintains the cutoff state otherwise, and enters the cutoff state when a release signal is supplied from the terminal device. A voltage analog switch is provided on the telephone line side, and the DC voltage that appears on the output side when the high voltage analog switch is turned on is a second predetermined voltage.
A low-voltage analog switch is placed on the terminal device side, which becomes conductive when V ₂ (V ₂ < V ₁ ) or more, and once it becomes conductive, it remains conductive as long as the high-voltage analog switch remains conductive. These analog switches for high voltage and low voltage are used to control opening and closing between the subscriber telephone line and the terminal device.

Therefore, according to the present invention, it is possible to maintain a sufficiently high insulation resistance with a simple configuration not only for high voltage insulation tests and low voltage insulation tests, but also for manual insulation tests. To provide an analog switch circuit capable of connecting a terminal device to a subscriber telephone line without affecting any insulation test, stabilizing the operation of the terminal device, and having little signal conversion loss. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an analog switch circuit according to the present invention, FIG. 2 is a circuit configuration diagram embodying FIG. 1, and FIGS. 3a and 3b are transistors Q ₂₁ and Q of FIG. ₄₁ is a diagram showing another example. 1a, 1b...Telephone line connection terminal, 2...High voltage analog switch, 3...Reverse current blocking diode, 4...Low voltage analog switch, 5...
...Terminal device, 6... Release signal.

Claims (1)

[Claims] 1. When the polarity of the DC voltage applied from the exchange to the subscriber telephone line is reversed from the normal state, the terminal device becomes operational by the power supplied, and within a specified period of time after receiving the above power supply, In an analog switch circuit that controls opening/closing in a DC and AC manner between a terminal device that generates a release signal when a ringing signal is not received, and the subscriber telephone line, a DC voltage with reversed polarity is provided on the subscriber telephone line side. is conductive when V is less than the first predetermined voltage _V1 , maintains the cutoff state otherwise, and transitions to the cutoff state when a release signal is supplied from the terminal device in the conduction state and maintains this state thereafter. When the voltage analog switch and the high voltage analog switch disposed on the terminal device side are electrically connected, the voltage appearing through the high voltage analog switch is a second predetermined voltage V ₂ (V ₂ <
_V1 ) It is characterized by comprising a low-voltage analog switch that changes from a cut-off state to a conductive state when the above conditions are met, and once it becomes conductive, maintains the conductive state as long as the high-voltage analog switch remains conductive. Analog switch circuit.