JPS6214149B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention refers to a subscriber telephone line (hereinafter referred to as a telephone line, which is used not only to conceptually represent equipment for signal transmission, but also to mean a two-line line). This invention relates to an analog switch circuit that is suitable for application to end-of-line equipment that is connected to a switch () and uses the power supply of an exchange.

The power supply of a switchboard is originally intended to be used by the switchboard itself and the telephones connected to the telephone line. Conventionally, there has been no end-of-line equipment that connects to the end of the telephone line and utilizes the power of the switchboard. Ta. However, in recent years, an automatic meter reading system has been planned in which a terminal device that operates only from the power supply of the exchange is connected in parallel with a telephone to each telephone line, and automatically reads usage data of electricity, gas, water, etc. from a remote location. ing.

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 consumption of the power supply of the exchange by the end devices must be substantially limited to the time of data collection (which is a very short time from the point of view of the individual end devices). To achieve this, at least the start-up of the end device must be performed using direct current.
This is because an AC calling signal cannot be detected when the device is not activated, that is, when power is not supplied. As a direct current method, it is conceivable 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 is preferable because it would significantly change the current specifications. In the end, it is due to 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 end device is essentially activated for polarity reversals other than when collecting data. should not be used, and require technical measures on an individual basis. Regarding the former, for example, a method has been proposed in which means is provided to detect the off-hook state of the telephone, and when a detection output is obtained, the off-hook device is disconnected.

The present invention has been made in view of the above circumstances, and its main purpose is to enable connection of unconnected equipment to a telephone line without affecting the insulation test, and to stabilize the operation of unconnected equipment at the same end. The present invention provides an analog switch circuit with low signal conversion loss.

Below, in describing an embodiment of the present invention, first, aspects of insulation testing of telephone lines will be described. In other words, current insulation tests include tests using an automatic insulation tester that tests at a high voltage of about 200V, tests using an automatic insulation tester that tests at a low voltage of 35V or less, and tests using 48V, which is the operating voltage of the endless equipment. It is broadly divided 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 state is detected from the difference between the two voltages, and the end device is called. It can be kept electrically disconnected from the line.

On the other hand, in the case of manual insulation test equipment, when the polarity is reversed, the test voltage and the operation start voltage are equal, so the voltage at the time of the insulation test activates the terminal equipment, and the telephone line becomes a low-impedance It will be terminated with. In other words, when using a manual insulation tester, it is impossible to make a judgment based on voltage during an insulation test. Therefore, in this case, the end device side uses a detection means other than voltage to detect whether it is an insulation test or a self-call, and when the call is not made, it is immediately electrically disconnected from the telephone line (for example, if the device is in a high resistance state) setting) is necessary.

Hereinafter, an analog switch circuit suitable for any of the above-mentioned insulation test apparatuses 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 terminal equipment, and includes telephone line connection terminals 1a and 1.
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 the DC and AC voltage with low loss when V is less than ₁ . The DC voltage appearing through this high voltage analog switch 2 is input to the subsequent low voltage analog switch 4.
Here, the relationship between the same voltage and the operation start voltage of the terminal device is determined.

In other words, this low voltage analog switch 4 is
It has a switch main body and a low voltage detection section that are inserted in series with the subscriber telephone line, and the DC voltage supplied via the high voltage analog switch 2 is a predetermined voltage V ₂
(V ₂ < V ₁ ) or more, the switch body changes from a cut-off state to a conduction state, and once it is in a conduction state, the high voltage analog switch 2 is in a conduction state and the bistable circuit described later is in a short-circuit state. It has a switch function that maintains the conduction state of the switch body as long as the switch body is in a conductive state.

For example, a terminal device 5 for data collection is connected to the DC output side of the low voltage analog switch 4. The end device 5 is a low voltage analog switch 4.
The supply of operating power is started when the switch becomes conductive, and when collecting data, a call is made from the central equipment depending on whether or not reception of a specific calling signal is detected, which should be sent from the central equipment (not shown) after polarity reversal by the exchange. It has a function of determining whether or not a call has been made, and if it is not a call, supplying a release signal 7 to the bistable circuit 6 after a certain period of time has elapsed.

The bistable circuit 6 is a low voltage analog switch 4.
and the common return line of the subscriber telephone line, and input the voltage of the subscriber telephone line supplied via the high voltage analog switch and the release signal generated from the terminal device 5, respectively. When this detecting section detects that the high voltage analog switch 4 is conductive, the switch section becomes short-circuited, thereby causing the low voltage detecting section of the low voltage analog switch 4 to be connected to the common low voltage detecting section. When connected to the return line and detecting that a release signal is generated from the terminal device 5, the switch section becomes open, thereby setting the low voltage analog switch to the cutoff state.

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.

The high voltage analog switch 2 includes an opening/closing transistor Q21 as a switch body, an opening/closing control transistor Q22 constituting a high voltage detection section,
A constant voltage diode ZD21 for voltage detection and resistors R21, R22, and R23 are connected as shown in the figure. If a voltage higher than the predetermined voltage V ₁ (an arbitrary value between the operation start voltage of the device and the voltage during the above-mentioned test) is applied between points A and C in the figure, the voltage regulator diode ZD ₂₁ has
Through the resistor R ₂₁ and the constant voltage diode ZD ₂₁ ,
Additionally, resistor R ₂₂ and the base of transistor Q ₂₂
A Zener current flows between the emitters and the transistor _Q22 is turned on.
When transistor Q ₂₂ is on, no base current flows through transistor Q ₂₁ and the transistor
Q ₂₁ is in the off state. In this state, point A, C
The DC resistance value between the points is greater than or equal to the parallel resistance value of resistors R ₂₁ and R ₂₃ . The voltage between points A and C is the specified voltage
When V ₁ or lower, no current flows through the voltage regulator diode ZD ₂₁ and the transistor Q ₂₂ is in an off state. Therefore, transistor _Q21 is in an on state.

The bistable circuit 6 includes a transistor Q61 as a switch section and a transistor Q as a detection section.
62, diodes D61, D62, resistor R61,
R62, R63 and capacitor C61 are connected as shown. B in the diagram now
If a voltage appears between point C and point C through the high voltage analog switch 2, a base current flows through resistor _R62 to transistor _Q62 , turning transistor _Q62 on. On the other hand, the current through the low resistor R ₆₁ and the diode D ₆₁ becomes a charging current for the capacitor C ₆₁ , which cannot supply the base current necessary for the transistor Q ₆₁ to turn on, and the transistor Q ₆₂ is turned on. Tanochi wa Resistance R ₆₁
Since current flows from the capacitor _C61 through the diode D62 and the transistor _Q62 , no charging current flows to the capacitor _C61 , and as a result, the transistor _Q61 does not turn on. In other words, when a voltage appears through the high-voltage analog switch, only the transistors Q ₆₁ , Q ₆₂ and Q ₆₂ , which had been off until then, turn on, and the potential at the output terminal 60 becomes almost the same as the potential at point C. become. In this state, from the terminal device 5,
When a release signal with a voltage sufficiently higher than the potential at point C is supplied, a charging current flows to capacitor C ₆₁ through resistor R ₆₃ , and transistor Q ₆₁ is soon turned on. When transistor Q ₆₁ turns on, the transistor Q ₆₂ that was on until then turns on.
The base current no longer flows through the transistor Q ₆₂
changes to the off state. Even if the above release signal is no longer supplied after such a change occurs, the resistance remains
Since the base current flows to the transistor Q ₆₁ through R ₆₁ and the diode D ₆₁ , the transistor Q ₆₁ is kept on and the transistor Q ₆₂ is kept off. That is, the bistable circuit 6 changes its state by being supplied with a release signal from the terminal device, and the output terminal 60 becomes an open state. In this case, the DC resistance value between point A and point C is the resistance R ₆₁ and R ₆₂
is greater than or equal to the parallel resistance value of Note that when the high voltage analog switch 2 is cut off and no voltage is applied between points B and C, the transistor Q ₆₁ is also turned off and the internal operation is restored to its original state. The low voltage analog switch 4 has a main opening/closing transistor Q41 as the switch body.
and the transistor Q that constitutes the low voltage detection section.
41 transistor Q42 for maintaining ON operation, constant voltage diode ZD41 for voltage detection, diode D41 and resistors R41, R42, R43, R
44 are connected as shown in the figure. When the voltage between point B in the figure and the output terminal 60 of the bistable circuit 6 exceeds a predetermined value V ₂ (an arbitrary value between the operation start voltage of the terminal device and the voltage at the time of the above-mentioned test) , Zener current flows through the constant voltage diode ZD ₄₁ through a parallel current path between the resistor R ₄₂ , the emitter-base of the transistor Q ₄₁ , and the resistor R ₄₁ . Transistor _Q41 is therefore turned on. When transistor _Q41 is in the on state, the resistor
A current flows through R ₄₃ , diode D ₄₁ , resistor R ₄₄ , and between the base and emitter of transistor Q ₄₂ to turn on the transistor Q ₄₂ . Therefore, the base current of transistor Q ₄₁ can flow through R ₄₁ and transistor Q ₄₂ , so
Even if the voltage between point B and the output terminal 60 decreases thereafter,
The on state of transistor _Q41 is maintained. However, when the output terminal 60 of the bistable circuit 6 is opened, the transistor _Q42 is turned off, and therefore the transistor _Q41 is also turned off.

The structure and operation of each block has been explained above, and next, the operation of the whole block will be explained.

(1) 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.

(2) If the switching equipment reverses the polarity of the voltage 48V applied to the telephone line in order to start up the terminal device 5 and collect data, then a specific AC calling signal is sent out superimposed on it. , the high-voltage analog switch 2 becomes conductive, the potential at the output terminal 60 of the bistable circuit 6 becomes approximately the same as the potential at point C, and the low-voltage analog switch 4 becomes conductive.
As a result, a current flows through the terminal device 5 through the route of terminal 1a - high voltage analog switch 2 - low voltage analog switch 4 - terminal terminal device 5 - diode 3 - terminal 1b. In other words, operating power is supplied, and the end device starts operating.
First, the presence or absence of reception detection of a specific calling signal is monitored. Since this is now detected, the end device knows that its call has been made and can perform the desired data transmission.

(3) If the insulation test described above is performed at 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 ₂₃ . It is easy to select the values of the resistors R _{21 and} R 23 so that the parallel resistance value is equal to or higher than the insulation resistance value of the telephone line and so as not to affect the operation of the transistors Q ₂₁ and Q ₂₂ .

(4) 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 becomes conductive, thereby turning on the transistor Q ₆₂ of the bistable circuit 6. As a result, the potential at the output terminal 60 becomes approximately the same potential as the potential at point C, but the low voltage analog switch 4 cannot conduct. Terminals 1a and 1b at this time
The DC resistance between them is greater than the parallel resistance value of the resistors R ₆₁ and R ₆₂ in the bistable circuit 6 described above. In order to make this value higher than the insulation resistance value of the telephone line,
It is easy to select the values of R ₆₁ and R ₆₂ .

(5) If the insulation test described above was performed with a voltage (48V) with the terminal 1a side being positive, this
This corresponds to the case (2) in which no calling signal is sent, and a current flows through the terminal device 5. However, even if the termination device 5 starts operating, it does not detect a specific calling signal, so it sends a release signal to the bistable circuit 6 after a predetermined period of time has elapsed. As a result, the output terminal 60 of the bistable circuit 6 is opened, so that the low voltage analog switch 4 returns to its cut-off state. In this state, the bistable circuit 6
The transistor Q ₆₁ inside is in the on state, and the DC resistance value between the terminals 1a and 1b at this time is also greater than the parallel resistance value of the resistors R ₆₁ and R ₆₂ . Note that during this insulation test, the DC resistance value between the terminals 1a and 1b decreases significantly for the predetermined time, but this time can be made extremely short and there is no problem at all.

According to the above analog switch circuit,
Not only is it suitable for high-voltage and low-voltage automatic insulation test equipment, but also for manual insulation tests performed at a voltage equal to the operating start voltage of unused equipment, the arrival time of the call signal from the central equipment can be detected to determine if it is a call. When it is determined that it is an insulation test, the end device is electrically disconnected from the telephone line, so the end device that uses the power supply of the exchange is connected to all telephone line insulation test equipment. can be adapted to In addition, when collecting data, only the turned-on transistors Q ₂₁ and Q ₄₁ are inserted between the telephone line connection terminal 1a and the terminal device 5, so signal loss is very small, and the terminal device 5 is not connected. 5 can also be stably supplied.

It goes without saying that the present invention is not limited to the above embodiments. For example, as shown in Figure 3 a and b, transistors Q ₂₁₁ and Q ₂₁₂ are connected in a Darlington manner.
If Q ₂₁ is used, and transistors Q ₄₁₁ and Q ₄₁₂ are connected in Darlington to form Q ₄₁ , the insertion loss can be lowered. Especially on the Q ₂₁ side, in addition to this, the value of resistor R ₂₃ can be made lower. It has the advantage of being able to be selected at a higher price. In addition, the present invention can be modified in various ways without departing from the spirit thereof.

Therefore, since the present invention is configured as described above,
It is possible to make the terminal device that connects to the telephone line and uses the power supply of the switchboard compatible with various insulation test equipment, and to stably supply current to the terminal device with little signal loss when operating the terminal device. We can provide you with an analog switch circuit that can be used.

[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...
... Endless device, 6... Bistable circuit, 7... Release signal.

Claims (1)

[Claims] 1. The operating voltage is supplied from the power supply of the exchange, and the polarity of the DC voltage applied by the exchange to the subscriber telephone line is reversed from the normal state as a necessary condition for receiving the operating power supply. Used with a terminal device that generates a release signal when a specific call signal is not received within a predetermined time after the start of receiving power supply, and controls opening/closing between the subscriber telephone line and the terminal device in direct current and alternating current. The analog switch circuit has a high voltage detection section that is disposed on the subscriber telephone line side and connected between the switch body inserted in series into the subscriber telephone line and the subscriber telephone line end, and the high voltage detector causes the above-mentioned A high-voltage analog switch whose switch body becomes conductive when it is determined that the polarity-inverted voltage of the subscriber telephone line is equal to or lower than a first predetermined voltage _V1 , and otherwise maintains a cut-off state; It has a detection section that inputs the voltage of the subscriber telephone line supplied via the analog switch and a release signal generated from the terminal device, and a switch section that is opened and closed by the detection section. a bistable circuit in which a switch part changes to a short-circuit state when conduction is detected, and a switch part changes to an open state when it is detected that a release signal is supplied from the terminal device, and the terminal device side and a low voltage detection section connected between the terminals of the subscriber telephone line through the switch body inserted in series into the subscriber telephone line and the switch section of the bistable circuit in series, the low voltage detector As a result, the voltage of the subscriber telephone line supplied via the high voltage analog switch is a second predetermined voltage V ₂
(V ₂ < V ₁ ) or more is detected, the switch body changes from the cut-off state to the conduction state, and once it is in the conduction state, the low voltage detection section changes the high voltage analog switch to the conduction state. and a low-voltage analog switch that maintains the conduction state of the switch body as long as it is detected that the switch section of the bistable circuit is in a short-circuit state.