JPH06311256A - Polarity inversion detecting circuit and terminal equipment using the same - Google Patents

Abstract

PURPOSE:To provide a polarity inversion detecting means which improves the impedance and facilitates integration. CONSTITUTION:When a potential at an L1 gets higher in comparison with a potential at an L2, a transient current flows in the direction of L2 through a second rectifying means 2 so as to charge a capacitor C1 of a first CR rectifying means 3. This is detected by a first detecting means 7, and a first detection signal is outputted to a point A. On the contrary, when the potential at the L2 gets higher in comparison with the potential at the L1, the transient current flows in the direction of L1 through the first rectifying means 1 so as to charge a capacitor C2 of a second CR rectifying means 4, this is detected by a second detecting means 8, and a second detection signal is outputted to a point B. A discharging path is composed of 3rd and 4th rectifying means 5 and 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal device connected to a telephone line, and more particularly to a means for detecting the power supply polarity of the telephone line.

[0002]

2. Description of the Related Art Telephones and data terminals are connected by telephone lines (two connecting lines, a first line L1 and a second line L2). Hereinafter, they will be referred to as L1 and L2.

Power is supplied from the exchange to the telephone and the data terminal via L1 and L2, and the voltage between L1 and L2 is about 48 V DC when released. The off-hook operation of lifting the handset of the telephone means terminating L1 and L2 with a DC resistance of 50Ω to 300Ω. On the contrary, in the on-hook state, there is a DC resistance of 1M between L1 and L2.
Ω or more is secured. Normally, a telephone detects a ringing signal from the exchange and rings a bell to notify that an incoming call has been received. The telephone is in an on-hook state when the bell rings, and the ringing signal received from the exchange is a DC voltage of 48V superposed as an AC signal with an effective value of 75V and a frequency of 16Hz.

Now, there is a no ringing (NR) communication service in which an exchange calls a terminal device without ringing a bell of the telephone when the telephone and the terminal device are connected to the same telephone line.

When calling a data terminal, the exchange does not send a calling signal but uses calling means dedicated to NR. First, the exchange reverses the polarity of power to the data terminal. Then, the NRS signal in which the same two types of AC signals as the push button (PB) signal of the telephone are superimposed is transmitted. Therefore, the data terminal needs to be provided with a polarity reversal detection means for detecting reversal of the power supply polarity of the telephone line.

When connecting a data terminal to a telephone line, the data terminal is equipped with a polarity reversing means that enables connection work without paying attention to the polarity of the telephone line.

A conventional technique of such polarity inversion detecting means will be described. The first example is shown in FIG. L1, the capacitor C3, the resistor R9, the diode of the phototransistor PTR1, and L2 are connected in series.

The phototransistor PTR1 has a current of L
It is turned on when flowing in both directions from 1 to L2 and from L2 to L1.

When the phototransistor PTR1 is on,
A DC circuit of the DC power supply VDD and the resistor R10 is formed, and the current I flows through the resistor R10.

When -48V is applied to L2 with respect to L1, the charging current to the capacitor C3 is changed to the phototransistor P.
It flows from L1 to the direction of L2 through the diode of TR1. Eventually, the voltage across the capacitor C3 becomes equal to the voltage supplied from the exchange and the current stops. Only so-called transient current flows. The time during which the current flows is determined by the size of the resistor R9 and the capacitance of the capacitor C3. The phototransistor PTR1 is turned on only during the period when this transient current flows in the diode of the phototransistor PTR1, and a pulsed voltage is output to the point D.

Now, suppose that the polarity of the voltage fed through L1 and L2 is inverted and L1 changes to -48V with respect to L2. Since the charging direction of the capacitor C3 is reversed, the capacitor C3 is discharged and the charging current is supplied in the opposite direction again to the phototransistor PTR1.
Flows in the direction from L2 to L1 via the diode of. Eventually, the voltage across the capacitor C3 again becomes equal to the voltage supplied from the exchange, and the current stops. Then, the phototransistor PTR1 is turned on only while the transient current is flowing to the diode of the phototransistor PTR1.
A pulsed voltage is output to the point.

After that, even when the polarity of the voltage supplied through L1 and L2 is restored and L2 changes to -48V with respect to L1, the transient current in the capacitor C3 causes the phototransistor PTR1 to turn on and pulse to the point D. Voltage is output.

As described above, the pulsed voltage is output to the point D each time the power supply polarity is reversed and restored.

The control unit such as a microcomputer detects this output and knows that there is polarity inversion and restoration, and starts the NR communication process.

A second conventional example for detecting polarity reversal to which this principle is applied is Japanese Patent Publication No. 2-278957. In this example, the potential of L2 is +4 from the state of -48V with respect to L1.
This is devised so that the polarity inversion is determined only when the voltage changes to 8V or when the voltage changes from + 48V to -48V. The electrical conditions for the NR communication service are: (1) 1 MΩ or more when the DC circuit is open. (2) The AC impedance is 100 KΩ or more except when performing no ringing communication. Is defined, and it is preferable that both the DC impedance and the AC impedance are infinite. The conventional technique shown in the second example realizes both high impedances. Furthermore, (3) Do not apply a DC voltage to the telephone line. In order to satisfy this requirement, a control unit driven by an AC power supply, a battery power supply, etc. and a line are insulated from each other by a photo coupler.

Now, as semiconductor technology has advanced, circuits on a communication path connected to a telephone line such as a telephone have been integrated. Next, the prior art of the polarity reversal detection means that is easy to integrate will be described for the third and fourth examples.

The integration condition that can be directly coupled to the input / output port of the microcomputer, which is the main element constituting the control section, is that the control signal (eg 0 to 5V) having a positive voltage with reference to the ground of the microcomputer is used. It can be handled. Both the third and fourth examples are devised to handle only control signals having a positive voltage with reference to the ground of the control section.

A third example is Japanese Patent Publication No. 3-148943.
Then, by connecting L1 and L2 with high resistance and making the midpoint of the potential at both ends of the high resistance common to the ground of the control unit, the potential between ground and L1 and the potential between ground and L2 are controlled. This is a means for detecting polarity reversal by observing the part.

The fourth example is Japanese Patent Laid-Open No. 2-92062 and Japanese Patent Laid-Open No. 4-119051, in which the potential difference between the DC side ground of full-wave rectification and L1 of the AC side, and the DC side ground of full-wave rectification. Is a means for detecting the polarity by detecting the potential difference between L2 on the AC side and the AC side. In this example, a comparator is used to detect the potential difference, and the comparator must always be powered on to detect the start of NR communication.

Both the third and fourth examples have means for detecting the polarity by drawing a minute current from the telephone line.
The DC impedance and the AC impedance are smaller than those in the first and second examples.

[0021]

However, such a conventional technique has the following problems.

(1) Since the conventional polarity reversal detection means which is easy to integrate is terminated with a high resistance between L1 and L2, the DC / AC impedance before and after the polarity reversal cannot be made sufficiently large.

(2) The conventional polarity reversing means for isolating the control section (microcomputer or the like) from the telephone line with the photocoupler can sufficiently increase the DC / AC impedance before and after the start of the polarity reversal, but at a cost. Since an expensive photo coupler must be used, the cost of the terminal device using this means becomes high.

Therefore, it is a first object of the present invention to provide a polarity reversal detection circuit which is easy to integrate and can have a sufficiently large DC / AC impedance.

A second object is to provide a polarity reversal detection circuit capable of easily discriminating the polarity at an arbitrary point of time, and reversing and recovering the polarity.

A third object is to provide means for mounting the terminal device at a lower cost.

[0027]

In order to achieve the above first object, the polarity reversal detection circuit of the present invention comprises a first rectifying means for supplying a current only from the ground to the L1 direction and a ground to the L2 direction. Second rectifying means for flowing current only to L
The first CR rectifying means for flowing a current only in the ground direction from 1 to the first capacitor and the first resistance, and the current only in the ground direction from L2 to the second capacitor and the second resistor. The second CR rectifying means for flowing the current and the first from the ground
The current to flow only in the L1 direction via the third capacitor
Rectifying means, a fourth rectifying means for flowing a current from the ground only through the second capacitor in the L2 direction, and the fact that the current has flowed through the first resistor, and outputs a first detection signal. And a second detecting means for detecting a current flowing through the second resistor and outputting a second detection signal.

In order to achieve the second object, the first
Signal conversion means for alternately changing the logic output of 1 and 0 only when the detection signal of 1 and the second detection signal are alternately input,
And a determination unit that detects the polarity based on the logical value of the logical output of the signal conversion unit.

Further, in order to achieve the third object, a communication means for controlling and communicating a direct current loop of the telephone line and a full-wave rectification of the telephone lines L1 and L2 by a diode bridge are connected to the communication means. Full-wave rectification means, first CR rectification means for flowing a current only in the ground direction from L1 via the first capacitor and the first resistance, and from L2 via the second capacitor and the second resistance. Via a second CR rectifying means for flowing a current only in the direction of the earth, a third rectifying means for flowing a current only in the direction of L1 from the ground through the first capacitor, and a second capacitor from the ground A fourth rectifying means for flowing a current only in the L2 direction, and a first rectifying means for detecting a current flowing through the first resistor and outputting a first detection signal.
And a second detecting means for detecting a current flowing through the second resistor and outputting a second detection signal.

[0030]

In the polarity inversion detection circuit of the present invention, the potential of L1 is L
When the electric potential becomes higher than the electric potential of 2, the first condenser of the first CR rectifying means is charged with L through the second rectifying means.
Transient current flows in two directions. The first detection means detects that this transient current flows through the first resistor and outputs a first detection signal. On the contrary, when the potential of L2 becomes higher than the potential of L1, a transient current flows in the L1 direction through the first rectifying means so as to charge the second capacitor of the second CR rectifying means. The second detection means detects that this transient current flows through the second resistor and outputs a second detection signal. In addition, since the current flows through the first rectifying means, the ground and the L1 are connected.
Since the potential between them becomes small, a current flows so that the electric charge charged in the first capacitor is discharged in the L1 direction by using the third rectifying means. Again, when the potential of L1 becomes higher than the potential of L2, the first capacitor has already been discharged, so that the first capacitor of the first CR rectifying means is charged through the second rectifying means. As a result, a transient current flows in the L2 direction, and the first detection signal is output. At this time, since the current flows through the second rectifying means, the potential between the ground and the second line becomes smaller. Therefore, the charge charged in the second capacitor by using the fourth rectifying means is directed in the L2 direction. A current flows so as to discharge.

The conversion means alternately changes the logic outputs of 1 and 0 when the first detection signal and the second detection signal are alternately input. The judging means judges the polarity based on the logical output value.

Further, the first object for achieving the first object
Instead of the rectifying means and the second rectifying means, it functions as a full-wave rectifying means for controlling the DC loop of the communication means and for keeping the polarity of the telephone line constant for communication.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.
I will explain based on.

FIG. 1 is a circuit diagram of the polarity inversion detection circuit of the present invention. The polarity reversal detection circuit of the present invention is
The first rectifying means 1 of the diode D4 which allows the current to flow only in one direction, the second rectifying means of the diode D2 which allows the current to flow only in the direction of L2 from the ground, the first capacitor C1 and the first resistor (from L1 to R2 and R3), and a first CR rectifying means 3 in which a diode D1 for flowing a current only in the ground direction is connected in series, and L2 to a second capacitor C.
Second CR rectifying means 4 in which a diode D3 for flowing a current only in the earth direction via the second and second resistors (R5 and R6) is connected in series, and the first capacitor C from the earth.
Diode D5 that allows current to flow only in the L1 direction via 1
Second rectifying means 5 and ground to a second capacitor C
Diode D6 that allows current to flow only in the L2 direction via 2
When a current flows through the fourth rectifying means 6 and the first resistors (R2 and R3), the voltage appearing across the first resistor R3 becomes a bias voltage, the transistor TR1 turns on, and the first detection is made at point A. A first detection means 7 for outputting a signal, and a second
The second resistor R when current flows through the resistors (R5 and R6)
The voltage appearing at both ends of 6 becomes a bias voltage, the transistor TR2 is turned on, and the second detection means 8 which outputs the second detection signal to the point B is constituted.

The Zener diode ZD1 in the first CR rectifying means 3 and the Zener diode ZD2 in the second CR rectifying means 4 have a Zener voltage of about 36V. The transistor TR1 has an emitter connected to the ground and a collector to which a direct current voltage VDD (5V) is applied via a resistor R7.
When 1 is off, H level is output at point A. The transistor TR2 is also the same as the transistor TR1.

The operation of the first embodiment will be described. The potential of L1 is higher than that of L2. Zener diode Z
When the Zener voltage of D1 becomes higher than 36V and becomes 48V, L1 → C1 → ZD1 → R1 → D1 → R2 → R3 → so that the first capacitor C1 of the first CR rectifying means 3 is charged.
Earth → Transient current flows in the L2 direction through the diode D2 which is the second rectifying means 2. This transient current also flows to the base of the transistor TR1 of the first detecting means 7, and the transistor TR1 is turned on while the transient current is flowing. Therefore, the first detecting means 7 has the first pulse-shaped signal at the point A. Output the detection signal. On the contrary, when the potential of L2 is higher than the potential of L1 and is higher than the Zener voltage 36V of the Zener diode ZD2 and becomes 48V, L2 → C2 → ZD2 → R4 so that the second capacitor C2 of the second CR rectifying means 4 is charged. →
A transient current flows in the direction L1 through D3 → R5 → R6 → ground → diode D4 of the first rectifying means 1. This transient current also flows to the base of the transistor TR2 of the second detecting means 8, and the transistor TR2 is supplied while the transient current is flowing.
Since 2 is turned on, the second detection means 8 outputs a pulsed second detection signal to the point B.

Further, the diode D4 of the first rectifying means 1
When a current flows through the capacitor, the potential between the ground and L1 is reduced to about 0.6V, so the charge charged in the first capacitor C1 is ground → the diode D which is the third rectifying means.
A current flows so as to discharge in the direction of 5 → R1 → ZD1 → C1 → L1. Again, when the potential of L1 is higher than the potential of L2 and the potential difference becomes 48 V, the first capacitor C1 of the first CR rectifying means 3 is charged because the first capacitor C1 has already been discharged. L1 → C1 → ZD
1 → R1 → D1 → R2 → R3 → Ground → Transient current flows in the L2 direction through the diode D2 which is the second rectifying means 2, and the first detection signal is output to the point A. At this time, since the current flows through the diode D2 which is the second rectifying means, the potential between the ground and L2 becomes as small as 0.6V.
The electric charge charged in the second capacitor C2 is ground →
Fourth rectifying means 6, diode D6 → R4 → ZD2
A current flows so as to discharge in the direction of → C2 → L2.

As described above, when L1 has a power supply polarity having a higher potential than L2, the first detection signal is output to point A, and when L2 has a power supply polarity having a higher potential than L1, a second detection signal is output to point B. The operation is repeated to output. The DC impedance before and after the polarity reversal becomes a very large value due to the first capacitor C1 and the second capacitor C2. The AC impedance also becomes a very large impedance as long as there is no change above the Zener voltage of the Zener diodes ZD1 and ZD2.

It is also possible to adjust the voltage level between L1 and L2 at which polarity inversion can be detected by the Zener diodes ZD1 and ZD2.

Next, a second embodiment will be described with reference to FIGS. In FIG. 2, the signal conversion means 9 and the determination means 10 are added to the polarity inversion detection circuit of the first embodiment. The first rectifying means 1, the second rectifying means 2, the first CR rectifying means 3, the second CR rectifying means 4, the third rectifying means 5, the fourth rectifying means 6, and the first rectifying means 6 in FIG. Detection means 7, second
The detecting means 8 has the same configuration as that of the first embodiment. FIG. 3 shows an example in which a normal RS flip-flop circuit is applied as the signal converting means 9. When a pulse is input to the set terminal (S), the output terminal (Q) changes from L level to H level, and when a pulse is input to the reset terminal (R), the output terminal (Q) becomes L level again. It works like this. When Q is at H level, the output level of Q does not change even if S pulse is input. Conversely, when Q is at L level, the output level of Q does not change even if there is an R pulse input. A
The signal at the point is connected to S and the signal at the point B is connected to R. The determination means 10 is realized by, for example, a microcomputer, and the output Q of the signal conversion means 9 (C in FIG. 2) is used.
Point) and the output level of Q is H level (logical value 1)
To L level (logical value 0) or when a change from logical value 0 to logical value 1 is detected, it is determined that polarity inversion has occurred. When the point C has a logical value of 1, L1 has a higher potential than L2, and when the logical value is 0, L2 has a potential of L1.
It is determined that the potential is higher.

In this way, polarity inversion and polarity determination can be performed by detecting only one point C.

Next, a third embodiment will be described with reference to FIG. FIG. 4 is a block diagram of a terminal device showing the third embodiment. A full-wave rectification means 11 by means of a diode bridge (diodes D2, D4, D7, D8) is connected between L1 and L2, and a communication means 12 for forming a communication path and communicating on the DC side of the full-wave rectification means is connected. To be done. Also, L1
The first CR rectifying means 3, the third rectifying means 5,
The second CR rectifying means 4, the fourth rectifying means 6, and the second detecting means 8 are connected to L2. The communication means 12 opens the DC loop of the telephone line,
Closed / semi-closed control, AC impedance matching, PB
Signals and modem signals are transmitted and received, and communication protocols are performed, and the configuration in which they are connected via full-wave rectification means is well known.

The communication means 12 is activated by the first detection signal from the first detection means 7 or the second detection signal from the second detection means 8.

Now, the diode D4 of the full-wave rectifying means 12
Has a configuration that also serves as the first rectifying means 1 in the first and second embodiments, and a configuration in which the diode D2 also serves as the second rectifying means. Therefore, it is possible to realize a terminal device that requires polarity inversion detection.

[0045]

As described above, according to the polarity inversion detection circuit of the present invention, the following effects can be obtained.

(1) Since it is possible to provide a polarity reversal detection circuit having a large DC impedance and a large AC impedance before and after the polarity reversal occurs and to realize a circuit operation with reference to the ground, it is integrated with the communication means of the terminal device. Since it becomes easy to integrate, it is possible to provide an inexpensive terminal device.

(2) Since the polarity inversion has occurred and the determination of the polarity at any time can be realized by using one input port such as the microcomputer, the ROM size of the microcomputer software can be reduced.

(3) Further, since the diode of the diode bridge necessary for constructing the communication path and the diode necessary for the polarity inversion detection circuit can be used in common, an inexpensive terminal device can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a polarity inversion detection circuit according to a first embodiment of the present invention.

FIG. 2 is a block configuration diagram of a polarity inversion detection circuit according to a second embodiment of the present invention.

FIG. 3 is a diagram for explaining the circuit.

FIG. 4 is a block diagram of a terminal device using a polarity reversal detection circuit according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a conventional polarity reversal detection circuit.

[Explanation of symbols]

 1 1st rectification means 2 2nd rectification means 3 1st CR rectification means 4 2nd CR rectification means 5 3rd rectification means 6 4th rectification means 7 1st detection means 8 2nd detection means 9 signal conversion means 10 determination means 11 full-wave rectification means

Claims (3)

[Claims] 1. A first rectifying means for supplying a current only from a ground to a first line direction, a second rectifying means for supplying a current only from a ground to a second line direction, and a first rectifying means from the first line. 1
From the second line to the second CR rectifying means for flowing a current only in the direction of the earth via the first capacitor and the first resistor.
Second CR rectifying means for flowing a current only in the earth direction through the second condenser and the second resistor, and the first CR earth means from the earth.
Third rectifying means for flowing a current only in the first line direction via the second capacitor, and a fourth rectifier flowing a current only from the ground through the second capacitor in the second line direction. Means and first detecting means for detecting a current flowing through the first resistor and outputting a first detection signal;
A polarity reversal detection circuit composed of a second detection means for detecting a current flowing through the second resistor and outputting a second detection signal. 2. A signal conversion means for alternately changing the logic output of 1 and 0 only when the first detection signal and the second detection signal are alternately input from the polarity inversion detection circuit, and the signal conversion means. The polarity reversal detection circuit according to claim 1, further comprising a determination unit that detects a polarity based on a logical value of a logical output. 3. A communication means for controlling and communicating with a direct current loop of a telephone line, and a full wave for full-wave rectifying the first and second lines of the telephone line with a diode bridge to connect with the communication means. Rectifying means, a first CR rectifying means for flowing a current only from the first line to the ground via the first capacitor and the first resistor, and the second line to the second
Second CR rectifying means for flowing a current only in the ground direction via the capacitor and the second resistance, and a third CR rectifying means for flowing a current only in the first line direction from the ground via the first capacitor. A rectifying means, and a fourth current which flows from the ground through the second capacitor only in the second line direction
Rectifying means, first detecting means for detecting a current flowing through the first resistor and outputting a first detection signal, and detecting that a current flowing through the second resistor. A terminal device comprising: a second detection unit that outputs a second detection signal.