JPS6030147B2 - telephone terminal circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a telephone termination circuit for supplying a talking current and a ringing signal current using a transformer to the A line and B line of the telephone wiring in a switching device or a button telephone device.

In a switching device, there is generally a circuit that supplies direct current to the telephone wiring as a talking current to the telephone transmitter and a direct current loop current for monitoring the start and end of a call, and an alternating current signal of about 20 Hz as a ringing signal. A telephone termination circuit consisting of circuits, etc. is provided.

The conditions required for this telephone terminal circuit include, in addition to the value of direct current supply, the transmission characteristics for voice signals and the fact that it does not deteriorate the ground plane.

FIG. 1 shows a conventional general circuit of this type. In the figure, E is a telephone, A and B are telephone wiring, T is a transformer, and L. ,−,L3 are the first, second and third windings of the transformer, C, is the first capacitor for audio frequency coupling, and S
,,S2 is a relay contact for sending out a calling signal, V
,,V2 is a DC power supply, F,,F2 is a light emitting diode circuit that detects off-hook of the telephone, W is a calling signal source, R,
, R2, R3, R4 are resistances that limit the current, Y, , Y2
is the output terminal.

In a telephone terminal circuit with such a configuration, the transformer T
Since the direct current from the DC power source V is superimposed on the , there is a problem of deterioration of the transmission characteristics of the audio frequency signal transmitted from the telephone wiring A and B to the third winding L3 of the transformer T. To prevent this deterioration, It is necessary to increase the size of the transformer T, which has the disadvantage that the device becomes extremely large and expensive.

In view of the above points, the present invention was proposed to solve these drawbacks.The purpose of the present invention is to provide a telephone termination circuit that has a simple circuit configuration, is prone to deterioration in transmission characteristics, etc., and is compact and economical. Our goal is to provide the following. FIG. 2 is a circuit diagram showing an embodiment of the telephone terminal bridge circuit according to the present invention, and the same reference numerals as in FIG. 1 indicate corresponding parts.

That is, E is a telephone, and the A line and B line of this telephone E are connected to the primary side of the transformer T.

The primary side of the transformer T is provided with a first winding L and a second winding L2, and the secondary side is provided with a third winding. It is configured such that the sum of the number of turns of the two windings L2 is equal to the number of turns of the third winding L3, and the excitation direction is opposite. Therefore, a capacitor C for audio frequency coupling is inserted between the first winding L and the second winding L, and a current limiting capacitor C is inserted at the connection point between the capacitor C and the first winding L. A DC power supply V, is connected through a resistor R,. In addition, a varistor Z is connected in parallel to the second winding L2, which exhibits high impedance for low-level audio frequency signals, and is conductive for high-level calling signals and lightning surge currents. , and the second winding L2 are grounded via a capacitor C4, and one end of the high impedance current passing circuit is connected to this connection point. This current passing circuit consists of a circuit that has high impedance for alternating current and low resistance for direct current, such as a constant current circuit using a transistor, and the other end is the third volume of transformer T. It is connected to the first output terminal Y side of the line -. The first output terminal Y of the third winding - also has a capacitor C2 for sending the audio signal to the subsequent circuit, and the second output terminal Y2 has a capacitor C3 for bypassing the audio signal to ground. is connected, and the third terminal Y3 is connected to the second terminal Y2 side of the third winding L3 in parentheses.
A DC potential detection circuit F3 having the following is followed. In addition, terminals X, , X are connected to the first output terminal Y, side of the third winding.
2, and a negative impedance circuit N, which will be described later, can be connected through these terminals X, , X2. In addition, S is the relay contact inserted into the A line,
This is for switching the line to the ringing signal source W via the current limiting resistor R3 and the line to the first winding L of the transformer T.

Further, V2 is a DC power supply supplied to the calling signal source W. Next, the operation of the present invention will be explained in detail.

According to the invention, the audio frequency signals from the telephone wires A and B are transferred to the first winding L, capacitor C, and second winding of transformer T.
Flowing through winding L2, the audio frequency appears in the third winding of transformer T and is output to output terminals Y, , Y2 by capacitors C2 and C3.

In this case, if capacitor C3 is grounded, output terminal Y
Although the audio frequency signals obtained from , , Y2 are unbalanced outputs, the DC potential detection circuit F3 does not need to have a high impedance with respect to audio frequencies, making it economical. Also, the direct current to the telephone E is from the DC power supply V, to the resistor R, to the first winding L of the transformer T, A wire, to the telephone E, B wire, to the second winding L2 of the transformer T, to the high impedance current. The power is supplied through the passage circuit, the third winding L3 of the transformer T, the DC potential detection circuit F3, and the ground. By the way, according to the present invention, as mentioned above, in the transformer T, the sum of the number of turns of the first winding L and the second winding - is the third
The number of turns of the third winding - is equal to the number of turns of the third winding -, and the winding direction of the third winding - is configured so that the excitation direction generated by the first and second windings L, L2 is opposite to the excitation direction. As a result, transformer T is not subjected to DC excitation. Therefore, although the conventional conventional method used a large transformer to prevent transmission characteristics from deteriorating, by using the circuit of the present invention, it is possible to ensure good transmission characteristics even if the transformer T is made very small. Ta. On the other hand, recently there has been a tendency to try to use ICs and small components in this type of circuit, but in conventional circuits, the gap between the printed circuit boards is unnecessarily wide due to the large transformer, and the mounting This has the drawback that the reduced density makes the device large and expensive.

Attempts have also been made to replace the transformer with a transistor circuit, but measures such as high voltage resistance of the transistor to protect against lightning surge voltage, heat dissipation measures to reduce power consumption, high balance between A and B lines, noise prevention measures, etc. There are problems and disadvantages of high prices. In order to solve the disadvantages of the transistorized transformer, the present invention utilizes the transformer as described above to take advantage of its excellent anti-surge resistance, good ground balance, and minimal power consumption, while also achieving simple construction. In combination with electronic circuits, it is characterized by the fact that the direct current is magnetically weightless and the magnetic flux of the transformer is effectively used, making it possible to make the circuit smaller and more economical, which has a great practical effect. In addition, in FIG. 2 showing the embodiment of the present invention, if the short circuit between terminals X and X2 is removed and a current control type or voltage control type negative impedance circuit N is inserted as shown by the dotted line,
Since it is possible to compensate for subscriber line loss, the output terminal Y,
, Y2 can be efficiently transmitted.

According to the present invention, in addition to the above-mentioned advantages, the transmission loss that occurs when the communication path of the switching device is computerized can be compensated for with high precision using a simple and economical circuit, and therefore has high practical value.

FIG. 3 shows an embodiment in which the capacitor C3 in FIG. 2 is removed and an audio frequency bypass circuit K and a DC potential detection circuit T4 are connected to the second output terminal side Y3 of the third winding L3 of the transformer T, respectively. shows.

The audio frequency bypass circuit K is constructed by connecting diodes D and D2 in series between the output terminal Y2 and the ground so that a direct current flows when the telephone goes off-hook. Further, the DC potential detection circuit F4 is configured to convert the potential level of the output terminal Y2 into an appropriate voltage using a transistor Q and resistors R5 and R6 and output it to the output terminal Y3. Therefore, it is possible to output an audio frequency signal unbalanced and to detect off-hook of the telephone, which has high practical value. As described above, according to the present invention, the sum of the number of turns of the first winding and the second winding on the primary side is equal to the number of turns of the third winding on the secondary side, and the excitation of the secondary side A transformer configured such that the direction is opposite to that of the primary side is used, and a direct current de-energizer is applied between the connection point between the primary side capacitor and the second winding of the transformer and the secondary side. Because the transformer is constructed by connecting a current passing circuit that acts as a current path for the ,
Moreover, the overall circuit configuration is simple and economical.

[Brief explanation of drawings]

FIG. 1 shows a conventional telephone terminal circuit, FIG. 2 shows an embodiment of the telephone terminal circuit according to the present invention, and FIG. 3 shows an audio frequency bypass circuit that makes the audio frequency output unbalanced, which is applied to an embodiment of the present invention. The circuit and the specific configuration of a DC potential detection circuit for detecting off-hook of a telephone are shown. E...Telephone, T...Transformer, L, ~L...1st to 3rd windings, C, ~C4...Capacitor, V
,,V2...DC power supply, Day...High impedance current passing circuit, F3...DC potential detection circuit, N...Negative impedance circuit, Y,,Y2
...Output terminal, S. ...Contact, W...Call signal source, Z...Varistor. O 3 figures Juice 1 figure O 2 figures

Claims (1)

[Claims] 1 Connect one end of the first winding and the second winding of the transformer to the A line and B line of the telephone wiring, respectively, and
In a telephone terminal circuit of a switching device that supplies direct current to a telephone through a winding, a first capacitor is inserted between the other ends of the first winding and the second winding of the transformer to perform audio frequency coupling; One end of a DC power source is connected to the connection point between the first winding and the first capacitor, the other end of the DC power source is grounded, and the connection point between the second winding and the first capacitor and the third winding of the transformer are connected. A high impedance current passing circuit with high impedance for AC signals and low resistance for DC signals is connected between the first terminal of the third winding and the second terminal of the third winding. 1. A telephone terminal terminal circuit, characterized in that the input section of the third winding is grounded through an input section thereof, and an audio signal is extracted from both ends of the third winding through capacitor coupling.