JPH0320959B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a voltage polarity reversal system for telephone lines in telephone exchange subscriber circuits.

(Prior Art) FIG. 1 is a connection diagram of a subscriber circuit and a terminal device for explaining a conventional polarity reversal system. In the same figure, TEL is a telephone, NCU is a network control device,
DATA is data equipment, LA, LB are subscriber lines,
SLC indicates subscriber circuit. Also subscriber circuit SLC
VB is the call power supply, AA is the current supply relay,
E is ground, r ₁ and r ₂ are polarity reversal switches, fr is
NCU call signal, ca ₁ and ca ₂ are NCU call switches, and C is a DC cutoff capacitor.

Here, the subscriber circuit SLC is a circuit at the boundary between a telephone exchange (not shown) and a terminal, and transmits/receives voice signals, supplies power, sends out calling signals, etc. via a pair of lines between the terminal and the telephone exchange. It has testing, call monitoring, and other signal sending and receiving functions. Furthermore, the terminal consists of a network control unit NCU, etc. that connects the telephone TEL or the data device DATA and the subscriber lines LA and LB.

A call on a TEL telephone is made by ringing a bell, and a low frequency, high voltage signal is used as the signal for this purpose. Responses and calls are made by operating the TEL switch HS of the telephone by the subscriber's off-hook, thereby forming a DC closed circuit within the telephone. On the other hand, there is a silent calling method in which a call to the network control unit NCU connected in parallel to the telephone TEL is performed by a combination of inversion of the feeding polarity and a low-level AC signal within the voice band. In the silent ring system, the feeding polarity is reversed when the subscriber is not talking and is in an on-hook state, that is, when the series circuit of the Vencoil LLB and the capacitor CB is connected via the hook switch HS. It is necessary to take measures to prevent the bell from ringing.

The conventional polarity reversal method will be explained below. The data device DATA conducts a call via the network control unit NCU and the subscriber lines LA and LB when the telephone TEL is on-hook, that is, the subscriber lines LA and LB are not in use. The communication method of this data device DATA is as follows. First, when the data device DATA receives an incoming call request, the subscriber circuit SLC operates the polarity reversing switches r ₁ and r ₂ , and then operates the NCU call switches ca ₁ and ca ₂ . The negative terminal of the telephone power supply VB is normally connected to the network control unit NCU via the subscriber line LA.
Negative pole of telephone power supply VB - Current supply relay AA - Polarity reversal switch r ₁ - Connected through the path of subscriber line LA,
Also, the positive terminal of the telephone power supply VB is connected to the positive terminal of the telephone power supply VB through the subscriber line LB - ground E - current supply relay.
When the polarity reversal switches r ₁ and r ₂ connected through the path AA - polarity reversal switch r ₂ - subscriber line LB are operated, the connection polarity between the subscriber lines LA, LB and the communication power supply VB is reversed. Next, NCU call switch ca ₁ ,
When ca ₂ is activated, the NCU ringing signal fr is sent to the subscriber line.
Appears between LA and LB. The network control unit NCU constantly monitors the subscriber lines LA and LB, and when it detects the polarity reversal and the NCU call signal fr, it determines that there is an incoming call request to the data device DATA, and sends the subscriber lines LA and LB to the data device DATA. Connect. The data device DATA then communicates. by the way,
During the above operation, the telephone TEL bell circuit is connected to the subscriber line.
It is connected to LA, LB, but the subscriber line LA, LB
The bell circuit does not operate because the NCU ringing signal fr sent out is at a sufficiently lower voltage than the telephone ringing signal and at a different frequency from the telephone ringing signal. However, the telephone TEL bell may ring immediately after the polarity reversal switches r ₁ and r ₂ are activated. This means that the voltage on subscriber lines LA and LB is switched to polarity reversal.
This is because, due to the operations of r ₁ and r ₂ , the charge in the capacitor CB of the bell circuit is rapidly discharged and charged to a reverse voltage when the signal is inverted, and a large current sufficient to ring the bell flows through the bell coil LLB. At this time, the line voltage switches instantaneously to the voltage VA ₁ shown in Figure 3, but the line current at this time is
It can be seen that a current with a large peak current value is flowing with a waveform like the current i ₁ shown in the figure.

In this way, when the bell rings when calling the data device DATA as described above, the user calls the telephone.
I misunderstood it as a call to TEL and mistakenly went off-hook to the intended data device DATA.
There is a problem in that a bell rings every time a connection is made to the network control unit NCU and noise is generated even if connection to the network control unit NCU is established and even if the connection does not go off-hook.

In order to solve this problem, the conventional device uses a circuit configuration as shown in FIG. 2 to prevent the bell from ringing when the polarity is reversed.

Figure 2 shows a conventional polarity reversal circuit, in which the communication power supply VB in Figure 1 is replaced with a power supply POW, and the polarity reversal switches r ₁ and r ₂ are removed, and the other circuit symbols are It is equivalent to the one with the same symbol in Figure 1. The power supply POW receives the polarity reversal control signal REV as an input, and outputs a voltage that changes slowly like the voltage VA ₂ shown in FIG. 3 when the polarity is reversed. By the way, capacitor CB is connected to bell coil LLB, subscriber line LA,
Power POW via LB and current supply relay AA
The output voltage of the power supply POW is charged to the capacitor CB. When the output voltage of the power supply POW changes, the voltage of the capacitor CB changes from the power supply
Current flows through capacitor CB in the direction equal to the voltage of POW. This current increases as the potential difference between the voltage of the capacitor CB and the power supply POW increases. The voltage applied to the capacitor BC, and the capacitance as C, the voltage as V, the current as i, and the time as t, C・V=
There is an i·t relationship, and the product of the flowing current value and time is proportional. Therefore, the voltage VA ₂ shown in FIG.
If you charge and discharge with a voltage with a small potential difference with respect to the voltage of the capacitor CB over time using a voltage that changes slowly, the charging and discharging current value will be a small value, preventing the bell ringing that occurs when the polarity is reversed. can do.

Power supply POW of the conventional polarity inversion circuit shown in Figure 2
As mentioned above, it is necessary to have the function of inputting the polarity inversion signal REV and outputting the voltage VA ₂ shown in FIG. However, the hardware that outputs this slowly changing polarity inversion voltage has disadvantages that make it uneconomical, such as requiring a transistor-controlled power source.

(Object and Structure of the Invention) The present invention has been made to solve the above-mentioned drawbacks, and by performing polarity reversal via a constant current power supply mode or a high resistance power supply mode, This prevents the bell from ringing.

Embodiments of the present invention will be described in detail below with reference to the drawings.

(Embodiment) FIG. 4 shows a polarity inverting circuit according to a first embodiment of the present invention. This figure shows the conventional polarity inversion circuit shown in Fig. 1 with a charging switch CG and constant current circuit CC added, and the other circuit configurations of the subscriber circuit SLC and the terminal device configuration are those with the same symbols in Fig. 1. is equivalent to The constant current circuit CC is a circuit that allows a small constant current to flow regardless of the applied voltage. Charging switch CG is connected to polarity reversal switch _R2 , the ground side of current supply relay AA, and one end of constant current circuit CC, and when not in operation, polarity reversal switch _R2 is connected to current supply relay AA.
Connected to the ground side of AA. The other end of the constant current circuit CC is connected to earth E. Next, the operation of the circuit shown in FIG. 4 will be explained. When the telephone TEL is on-hook and before the data device DATA is called, that is, before the polarity is reversed, the polarity reversal switches r ₁ and r ₂ and the charging switch CG are in the recovery state, and the voltage of the power supply VB is being charged. When reversing the polarity, use the polarity reversal switch r ₁ ,
Operate r ₂ and charging switch CG. As a result, the constant current circuit CC becomes connected to the capacitor CB, and current flows through the following path. That is, constant current circuit CC - charging switch CG (make state) - polarity reversal switch r ₂ (make state) - subscriber line LA - bell coil LLB - capacitor CB - subscriber line LB - polarity reversal switch r ₁ (make state) - Current supply relay AA - Positive pole of DC power supply VB - Earth E - Path of constant current circuit CC. This current is
The constant current circuit CC limits the value to a sufficiently low value so that the bell does not ring. Therefore, when discharging and charging capacitor CB with this circuit, there is no ringing of the bell. When a certain period of time elapses with charge switch CG operating, capacitor CB becomes a constant current circuit.
DC power supply with almost opposite polarity before reversal due to current from CC
Charged to the voltage value of VB. Then turn on the charging switch
When cg is restored, the DC power supply VB is connected to the capacitor
Although it is connected to CB without going through the constant current circuit CC, the voltage of the DC power supply VB and the voltage charged in the capacitor CB have the same polarity and almost the same value, so almost no current flows. When the polarity reversing switches r ₁ and r ₂ change from operating to restoring, the charging switch CG is operated at the time of switching, and charging is performed for a certain period of time or more with a minute current to the polarity opposite to that before switching.

FIG. 6 shows the state of the line current at the time of this polarity reversal. In the figure, i ₁ is the line current when no additional equipment such as a polarity reversal power supply is provided as in the conventional example shown in Fig. 1, and i ₂ is the line current as in the first embodiment of the present invention shown in Fig. 4. This is the line current when discharging and charging by a constant current circuit, and it can be seen that the current value is limited to the current value of the constant current source, as illustrated as waveform _i2 .

Next, FIG. 5 shows a polarity reversing circuit according to a second embodiment of the present invention, and a specific example of the case where the present invention is applied to a subscriber circuit SLC using an electronic circuit will be described.
The current-driven thyristors SCR ₁ to _{SCR 4} in FIG. 5 are the polarity reversing switches in FIG. 4, which are the first embodiment.
Corresponds to r ₁ and r ₂ and reverses the voltage polarity of the power supply to the terminal. Here, thyristors SCR ₁ and SCR ₂ are a first pair, and thyristors SCR ₃ and SCR ₄ are a second pair.
The second pair of thyristors SCR ₃ , SCR ₄ is driven by transistors QP ₂ , QP ₃ via diodes D ₁ , D ₂ . The first pair of thyristors SCR ₁ and SCR ₂ are also driven by a similar circuit, but illustration and description thereof are omitted here. Transistor QN ₁ , QP ₁ , resistor
R ₁ to R ₄ correspond to the current supply relay AA in Fig. 4,
This is a current supply circuit that supplies direct current to the terminal. In addition, the switch BF is a switch that switches the power supply resistance between low resistance (when bf is off) and high resistance (when bf is on), such as when talking, and is connected to the DC current supply circuit on the same power supply polarity side as the thyristor switch drive circuit. . In the state before polarity reversal, where the presence or absence of off-hook of the telephone TEL is monitored, switch BF has recovered and is in the break state, and transistor QN ₁ ,
A circuit consisting of resistors R ₁ , R ₂ , and R ₇ exhibits characteristics similar to the resistors R ₁ /R ₂ (R ₂ +R ₇ ) (R ₂ +R ₇ ) when each resistance value is expressed by the same symbol. Similarly, the transistor QN ₁ ,
The circuit made up of resistors R ₃ , R ₄ , and R ₈ exhibits similar characteristics to the resistance made up of R ₃ /R ₄ (R ₄ +R ₈ ) (R ₄ +R ₈ ). Here, parallel resistance is shown.

Furthermore, in this state before polarity inversion, the first pair of thyristors SCR ₁ and SCR ₂ are driven and are in a conductive state. Therefore, the subscriber line VA is at the negative potential of the communication power supply, and the subscriber line LB is at the ground potential.
If the polarity is then reversed, the first pair of thyristors
Stop driving SCR ₁ and SCR ₂ and operate switch bf to cut off thyristors SCR ₁ and SCR ₂ . That is, when switch bf is in operation, the base and emitter of transistor QN ₁ are short-circuited, and the resistance value of the circuit becomes a high resistance of R ₈ , reducing the current flowing through the thyristor below the holding current value and cutting off the thyristor. It is something to do. Next, switch
Make nor work. The switch nor operates the drive circuit of the second pair of thyristors _SCR4 .

When the switch nor operates, the transistor QP ₂ ,
The base of QP ₃ is connected to earth E via a switch nor, the emitters of transistors QP ₂ and QP ₃ are connected to the positive pole of the power supply VD through resistors R ₅ and R ₆ , respectively, and the negative pole of the power supply VD is Transistors QP 2 and QP 3 are connected to ground E, so transistors QP ₂ and QP ₃ are connected to the power supply.
It operates as a common base amplifier that flows an emitter current determined by VD and resistors _R5 and _R6 . When the collector sides of transistors QP ₂ and QP ₃ have a negative potential, a collector current approximately equal to the emitter current flows.

This collector current takes a substantially constant value regardless of the collector voltage, and transistors QP ₂ and QP ₃ operate as constant current sources. Since the transistor QN ₁ side shows a low resistance value corresponding to the power supply resistance, current flows from the collector of transistor QP ₃ to the negative terminal of the communication power supply in the following path, but since transistor QP ₃ operates at a constant current, The current that flows is a limited value. The path of this current is from the collector of transistor QP ₃ to the diode D ₂ to the thyristor.
Gate of SCR ₄ - Cathode of thyristor SCR ₄ - Subscriber line LA - Bell coil LLB - Capacitor CB -
Subscriber line LB - Anode of thyristor SCR ₃ - Cathode of thyristor SCR ₃ - Transistor QN ₁ - Resistor R ₁ - Negative pole of telephone power supply VB - Positive pole of telephone power supply VB - Earth E - Power supply VD - Resistor R ₆ - Transistor
The order is emitter of QP ₃ - collector of transistor QP ₃ . Due to this operation during polarity reversal, capacitor CB is charged with a constant current, but this current value is a value that can conduct the thyristor SCR ₄ , for example, 1 mA, and a low current value that does not cause the bell to ring. It is possible to set it to .

After the capacitor CB is charged after a certain period of time by the circuit operation described above, when the switch BF is restored and the transistor QP ₁ is activated, the earth E is connected to the subscriber line LA via the transistor QP ₁ and the thyristor SCR ₄ . The polarity reversal operation is completed. To return to the original polarity, use thyristor SCR ₃ ,
Stop driving SCR ₄ , and turn off thyristors SCR ₁ and SCR ₂ .
By driving , and operating switch BF in the same way, the drive circuit of thyristor SCR ₂ is discharged and charged, and the polarity can be reversed without the bell ringing again.

(Effects of the Invention) As explained in detail above, the present invention can prevent the bell from ringing when the polarity is reversed by using a constant current circuit with a simple circuit configuration, and the constant current circuit also If the inversion switch is constructed from a current-driven thyristor, its drive circuit can be used for polarity inversion.

Furthermore, the current supplied by the current supply circuit as a constant current circuit can be reduced to reverse polarity, for example, resistor R ₃ - resistor R ₈ - anode of thyristor SCR ₄ -
Current can also flow through the path of the cathode of thyristor SCR ₄ , so the resistance R ₃ .R ₄ in Figure 5
The present invention can also be realized by setting .

As described above, according to the present invention, there is no need for an expensive transistor control source, etc., and there is an advantage that polarity reversal during a silent call can be easily and economically realized compared to the conventional polarity reversal method.

[Brief explanation of the drawing]

Figures 1 and 2 are connection diagrams of the subscriber circuit and terminal equipment to explain the conventional polarity reversal system, and Figure 3 shows the state of the line voltage at the time of polarity reversal in Figures 1 and 2. FIG. 4 is a polarity inversion circuit diagram of the first embodiment of the present invention, FIG. 5 is a polarity inversion circuit diagram of the second embodiment of the invention, and FIG. 6 is a diagram of FIGS. 1 and 4. FIG. 3 is a diagram showing the state of the line current when the polarity is reversed. TEL...Telephone, NCU...Network control device,
DATA...Data equipment, LA, LB...Subscriber line,
SLC...Subscriber circuit, VB...Telephone power supply, AA...
...Current supply relay, E...Earth, _r1 , _r2 ...Polarity reversal switch, fr...NCU call signal, _ca1 ,
ca ₂ ...NCU call switch, HS...Hook switch, LLB...Bell coil, C, CB...Capacitor, POW, VD...Power supply, REV...Polarity reversal control signal, CC...Constant current circuit, cg... Charging switch, i ₁ , i ₂ ... Line current, VA ₁ , VA ₂ ... Line voltage, SCR ₁ ~ SCR ₄ ... Thyristor, QP ₁ ~
QP ₃ , QN ₁ ... transistor, D ₁ , D ₂ ... diode, R ₁ to _{R 6} ... resistance, nor, bf ... switch.

Claims (1)

[Claims] 1. It has a DC current supply circuit and two pairs of current-driven thyristor switches, first and second, and reverses the polarity of the power supply voltage to the terminal by switching and driving the two pairs of thyristor switches. In the subscriber circuit of a telephone exchange that has the function of Power is supplied with a constant current, the other DC current supply circuit continues in a low resistance state, and after a certain period of time when the polarity starts to be reversed, the DC current supply circuit on the same power supply polarity side as the thyristor switch drive circuit is returned to a low resistance state. A polarity reversal method that is characterized by reversing the polarity.