JPS584866B2 - current supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a direct current supply system that reduces the size and cost of electromagnetic elements by replacing the electromagnetic circuit with a semiconductor circuit for supplying direct current to communication terminals such as telephones. It concerns the supply circuit.

2. Description of the Related Art In telephone exchanges and the like, it is necessary to supply a direct current as a communication current to a telephone, which is a communication terminal, when making a call.

However, this direct current is not only unnecessary in the exchange connection operation, but also extremely harmful when the connection process is implemented using a semiconductor circuit.

Therefore, many current supply circuits have been proposed for cutting off this direct current to the exchange side and supplying it only to the telephone side, and some of them have reached the stage of practical use.

Figure 1 shows a typical example of a conventionally used current supply circuit.

In a, the communication current flows through the resistor Ra, the primary winding N1 of the transformer T, the subscriber line and the telephone (not shown in the figure), the primary winding N1' of the transformer T, and the resistor Rb. For short (0 km) subscribers, a current exceeding 100 mA flows as shown at point P in Figure 2, and resistors Ra and Rb
The rated power of the transformer T was large, and the transformer T was extremely large and uneconomical because it passed 100 mA of direct current and required sufficient inductance.

b is a modification of this, in which the communication current passes through a choke coil CH, and the transformer T is made smaller, but a larger choke coil CH is used.
This not only hinders downsizing but is also uneconomical.

Generally, the primary inductance of a 600Ω to 900 series audio band transformer T that handles audio signals of +10 dBm (10 mW) or less needs to be 1 to 2 Henrys.

For example, if a DC superimposed current of 100 mA flows through the primary winding of this, an equivalent transformer (50 Hz
Conversion) Capacity is 1/2ωLIdc2=(1/2)×100π×(1~2
)H×0. IX=1.57~3.14Watt(at
50Hz), the audio transformer capacity of 10mW is negligibly small, and the size of the transformer T is determined almost by the primary winding capacity.

Therefore, since reducing the DC superimposed current is related to making the transformer T more compact and economical, some attempts have been made to counteract the apparent DC ampere turns to prevent saturation of the iron core and to make the shape of the iron core more compact.

Figures 1C and d are examples. However, in example C, the electrical characteristics such as the unbalance to the ground and the frequency characteristics of the A and B lines deteriorated significantly, and the unbalance to the ground in particular greatly exceeded the standard value of the switch, and the switch for the public communication network The drawback was that it could not be used.

In addition, in the example of d, there is a maximum of 100 m on the primary winding side of the transformer T.
Since the N1'' winding, which is equivalent to the winding over A, is wound, the amount of copper in the coil is almost doubled, and not only is it insufficient to make the transformer T smaller and more economical, but also requires a +V auxiliary power supply. It has drawbacks such as: 1.C, and its electrical characteristics such as ground unbalance are also poor, although not as good as C, making it difficult to meet the standards.

Figure 2 shows the relationship between the line current of each circuit shown in Figure 1 a, b, c, and d and the subscriber line loop resistance including the local resistance.The subscriber line distance is 0 and the local resistance is 440Ω only. When the telephone station battery voltage is -48V, the maximum line current is 109mA.
However, when the line resistance is 2 kΩ, approximately 20 mA flows.

Figure 1 a, b, and d show this tendency, and c is a constant current supply, so even if the line length is 0, the communication current does not exceed 20 mA, so the amount of copper in the primary winding is not as large as d. This is the smallest of the four plans, but as mentioned above, it has the worst ground unbalance and cannot be used as a public communication network switch.

In the present invention, a semiconductor type current supply circuit is inserted symmetrically between the A line and the ground, and between the B line and the negative battery, and the primary winding of the transformer T, which is divided into two, is By connecting a capacitor and connecting both ends of this capacitor to the base of the transistor of the current supply circuit using resistors of the same value, ground unbalance is eliminated and the transformer T
In addition to reducing the DC superimposed current in the primary winding of the device to several tens or hundreds of times that of the previous one, it also provides power supply characteristics that allow line current and subscriber loop resistance characteristics to be freely selected within a predetermined range. This provides a DC current supply circuit that is free from the above-mentioned drawbacks.

The details will be described below according to the drawings.

FIG. 3 shows a circuit diagram for explaining the basic principle of the present invention.
Figure 4 shows the line current vs. subscriber loop resistance characteristics.

In Figure 3, the transistor Ta between the A line and the earth G,
Resistors Re1, Rb1, diode Da, transistor Tb between the B line and negative polarity battery 1B, resistor Re2,
Rb2 and diode Db each constitute a semiconductor current supply circuit.

Now, when the switches Sa and sb are in the open state and the resistor R0 is connected between the base terminals 5 and 6 of the transistors Ta and Tb, the voltage from the earth G to Rb1-Da
A direct current flows through the negative polarity battery 1B through the path -Ro-Db-Rb2.

If transistors Ta and Tb with a sufficiently large current amplification factor β are used, the voltage across the base circuit resistors Rb1 and Rb2 will be equal to the voltage of the negative battery 1B and the resistors Rb1 and R0.
The voltage drop across the resistors Rb1 and Rb2 remains constant regardless of external factors such as variations in the length of the subscriber line.

Here, since the transistors Ta and Tb have β sufficiently large and α approximately equal to 1 as described above, their emitter current is approximately equal to the collector current.
Therefore, the following relationship holds true.

Here, vRb1, vRb2 are base resistances Rb1, Rb2
, VD is the voltage drop across diodes Da and Db,
IRO is a current flowing through resistor R0.

However, it is assumed that Rb1=Rb2 and Re1=Re2.

That is, the emitter currents of the transistors Ta and Tb maintain a constant current value determined by the resistance values of Rb1, Rb2, R0, Re1 and Re2 regardless of the length of the line, and the transistors Ta and Tb operate as constant current sources.

For example, current IR0 is 2mA, transistors Ta and Tb
Assuming that the collector current (:emitter current) of is 20mA,
If the current amplification factor of the transistors Ta and Tb is selected to be about β≧500 and the current flowing into the bases of the transistors Ta and Tb is ignored, then the following equation is obtained.

Here, a transistor with β≧500 or so can be easily obtained by a composite connection transistor such as a Darlington connection or a complementary connection.

Therefore, by selecting the resistors Rb1=Rb2 to be 10 times Re1=Re2, a 20 mA constant current supply circuit as shown in FIG. 4 C3 can be obtained, and moreover, compared to the constant current supply circuit shown in FIG. (1) Direct current is not superimposed on the primary winding of the transformer.

(2) The unbalanced impedance of the A and B lines to the ground does not decrease.

Benefits such as:

However, in this case, since each current supply circuit operates as a constant current source,
The potential between the wire and battery 1B becomes unstable.

Here, from the viewpoint of potential equilibrium, the potential VGA of the A line that drops from the ground G in any subscriber line usage state, and the potential VGA of the battery -
It is usually desirable that the voltage is equal to the potential VB-B of the B line rising from B.

In order to satisfy this condition, for example, the switch S shown in FIG.
When transistors a and Sb are closed, the resistor R1 (or R1
') increases, and the current in transistor Ta (or T
The collector-base voltage difference in b) is automatically controlled in the direction of lowering it.

Therefore, by inserting the resistors R1 and R1', the potential difference between the potentials VGA and VB-B is balanced, and the above-mentioned potential instability condition is eliminated.

However, when the resistors R1 and R1' are inserted in this way, the equivalent output resistance R of each current supply circuit for the A line, for example, becomes Rb1<<R1, β≧500.

Here, if we insert the aforementioned 1/10 as Re1/Rb1, for example, even if the resistors R1 and R1' are selected to be around 500kΩ, both wires A and B will each have approximately 4.5kΩ.
This is equivalent to connecting a resistance of

To prevent this, one possible method to lower the impedance of resistor Rb1 within the audio band is to insert bypass capacitors into each of resistors Rb1 and Rb2.
A problem arises in waveform distortion when reproducing and relaying dial pulses.

In order to solve this problem, it is desirable that the resistor R1 has a high impedance for the audio band, while operating as a resistor for the DC component that determines the DC potential of the A and B lines. .

Therefore, for example, if the position of the A line side terminal 1 of the resistor R1 is set to a DC potential, the position of the primary winding terminal 2 of the transformer T is approximately the same, and the position of the B line side terminal 8 of the resistor R1' is similarly set to the DC potential. 1
Move to the next winding terminal 3 position.

The embodiment of the present invention shown in FIG. 5 is constructed in this manner.

With this configuration, the direct current potential of both lines A and B is automatically controlled by the transistors Ta and Tb, which is the same as the state in which the switches Sa and Sb are closed in FIG. Terminal 2 to which resistors R1 and R1' are connected
The potentials of and 3 remain unchanged due to capacitor C, and transistors Ta and Tb maintain high impedance.

Therefore, within the audio band, the current supply circuit exhibits the extremely important feature of having no insertion loss.

Moreover, at this time, the current flowing through the primary winding of the transformer T is sufficiently small compared to the current flowing through the subscriber line, so the transformer T
Achieving significant miniaturization and economy.

Next, another important feature of the present invention will be described.

Now, in Fig. 5, if the resistors R1 and R1' are set to (1), a constant current characteristic as shown by C3 in Fig. 4 can be obtained as described in Fig. 3, but as shown in Fig. 6. Conversely, resistance R0
∽, resistors R1, Rl', Re1, Re2, Rb
1 and Rb2 are the equivalent output resistance R obtained from equation (6).
can also be chosen to be 220Ω, which is used in common telephone exchanges.

For example, in the example of equation (6) above, the resistance ratio Re1/Rb1
An example is to set R1 to 1/10 and resistor R1 to 2.42 kΩ, but there are various values for the three types of resistance (6)
It can be taken within the range of expression.

The relationship between line current and subscriber line loop resistance (including that within the station) at this time is shown by curve C1 in FIG.

This characteristic curve corresponds to the characteristics shown in FIGS. 1a, b, and d of the conventional method, except that the current in the primary winding of the transformer T and the semiconductor current supply circuit side, that is, the transistor Ta, This means that current flows to the collector side of Tb.

For example, when the resistance ratio Re1/Rb1 is 1/10, the sixth
The currents of the transistors Ta and Tb flow through the primary winding of the transformer T shown in the figure.

In other words, the DC current in the primary winding of transformer T has a resistance ratio R
Since e1/Rb1=1/10, it is 1/11 as described above, and if this resistance ratio Re1/Rb1 is selected to be even smaller, it is not impossible to further reduce it to about 1/100.

Next, with the resistance ratio Re1/Rb1 = 1/10, resistor R
1, R2 is twice the above 2.42kΩ, or 4.84k
If Ω25kΩ is selected, the subscriber line current that can flow through resistors R1 and Rl' will always be 1 on the curve shown by C1 in Fig. 4.
/2, that is, the characteristic shown by the dotted line C2 in the figure.

Next, if the resistor R0 is selected to be approximately twice that of the one shown in Figure 3 so that a constant current characteristic of 10 mA, which is 1/2 of the 20 mA constant current shown by C3, is obtained, the current supply circuit Because of the constant current of 10 mA added to the curve C4, the composite characteristic in FIG. 5 becomes a curve C4.

That is, in FIG. 5, the resistances R0, R1, R1' and the resistance ratio R
By arbitrarily selecting e1/Rb1, etc., the current supply circuit of the present invention can operate within the range of curves C1 to C3 in FIG. The conditions can be freely selected, and the ratio of the communication current (maximum value) of the subscriber closest to the station to the communication current (minimum value) of the farthest subscriber is selected, and the value of the resistors R0, R1 = R1' is selected. This allows for free selection and design.

This is extremely effective in reducing power consumption, heat dissipation design, and miniaturization of the switchboard.

Next, as shown in FIG. 1, voltage limiting elements Za, such as low voltage diodes, are connected across the resistors Rb1 and Rb2.
When a voltage limit circuit consisting of Zb and resistors R2 and R2' is connected, when the subscriber line current reaches point P in FIG. 8, constant current diodes Za and Zb conduct and the voltage vRb increases.
1, vRb2 is controlled, and the transistors Ta and Tb shift to near constant current operation.

If the resistances R2 and R2' are 0 and the dynamic impedance of the constant voltage diodes Za and Zb is 0, the characteristics will be as shown by the curve C5 in FIG. 8, but in reality, the constant voltage diodes Za,
Since Zb itself has a finite dynamic impedance and the resistance R2 also has a finite value, it is possible to obtain line resistance and line current characteristics as shown by curve C6, for example.

That is, in the circuit example shown in Fig. 1, point P (
The communication current limit can be applied only to the subscribers in the range up to (Fig. 8).

Here, the voltage limit element can be obtained by, for example, a combination of a battery and a diode, in addition to the above-mentioned constant voltage diode.

Fig. 9 shows that from a practical standpoint, an optical coupling switch element is added to control the operation and stop of the semiconductor current supply circuit so that the current supply circuit operates only when necessary, and measures against external surges are added. This study included the following.

In the figure, photocouplers PC and PC', which are a one-to-one combination of a light emitting diode and a phototransistor, are used as optical coupling switch elements.

That is, the drive input terminals X, Y of the photocouplers PC, PC'
Only when a drive signal is applied to the transistors Ta,
A signal is applied to the base of Tb.

Therefore, the operation and stopping of the current supply circuit can be controlled by the drive signals of the drive input terminals X and Y, and the control becomes extremely simple when, for example, high and dry processing is performed on a subscriber.

It is also effective for eliminating constant power loss when the subscriber is not talking.

Additionally, the following countermeasures have been taken against external surges that are applied to the A and B lines.

First, to deal with surges of normal polarity, use transistors Ta and Tb that have a high counter-voltage of the elements themselves, and to deal with surges of opposite polarity, insert diodes D5 and D6 in their collectors. I avoid it by doing this.

Furthermore, for the photocouplers PC and PC', by connecting the control terminal side to the ground air G and the negative polarity battery -B with a diode bridge composed of diodes D1 to D4, external surges can be connected to the ground air G and the negative polarity battery -B. It is clamped between the voltage of battery-B.

Here, it goes without saying that the present invention is not limited only to the above embodiments.

FIG. 10 shows an example in which the method of the present invention is installed on the primary and secondary sides of a transformer to configure an intra-office trunk of a telephone exchange, where the primary side of the transformer is installed on the calling subscriber's side, side indicates the called subscriber side.

Although circuit constants are not shown, it goes without saying that each of the methods described above can be used as needed.

Further, the present invention is not limited to the example of trunks within the own office, but can be generally applied to power supply methods for telecommunication equipment in addition to current supply for general trunks.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional current supply circuit, FIG. 2 is a diagram for explaining its characteristics, FIG. 3 is a circuit diagram for explaining the principle of the present invention, and FIG. ~ Figures 7, 9, and 10 are circuit diagrams showing embodiments of the present invention;
FIG. 8 and FIG. 8 are diagrams showing the characteristics. T: Transformer, N1, N1'; Primary winding, C: Capacitor, R0, R1, R1', R2, R2', Rb1, Rb
2, Re1, Re2; Resistor, Ta, Tb; Transistor, Da, Db, D1-D6; Diode, Za1, Z
b; Constant voltage diode, PC, PC'; Photocoupler,
G: earth, -B: negative polarity battery.

Claims (1)

[Claims] 1. A transformer is used to transfer communication information between communication paths connected to the primary and secondary windings of the transformer, and to transfer communication information between both sides of these communication paths or to a desired location. In a current supply circuit for supplying DC current to one side, the winding to which the communication path that needs to supply the DC current of the transformer is connected is divided into two, and these are connected via a capacitor. Semiconductor current supply circuits each including a transistor are connected symmetrically between the earth and the A line of this communication path, and between the B line and the battery, and between the bases of both transistors. are connected with a resistor R0, and the resistor R0
A current supply circuit characterized in that both ends of the capacitor are connected to both ends of the capacitor via a resistor R1 and a resistor R1', respectively. 2 As two semiconductor type current supply circuits, one circuit has a resistor between the ground terminal and the emitter of the transistor, and the other circuit has a resistor between the battery terminal and the emitter of the transistor, and a resistor between the base and the base. A series circuit of a resistor and a diode is connected respectively, and the collector of the transistor of the former circuit is connected to the line A of the communication path, and the collector of the transistor of the latter circuit is connected to the line B of the communication path, and each of the transistors is connected to the line B of the communication path. 2. The current supply circuit according to claim 1, wherein both semiconductor type current supply circuits are complementary. 3 As two semiconductor type current supply circuits, one circuit has a resistor between the earth terminal and the emitter of the transistor, and the other circuit has a resistor between the battery terminal and the emitter of the transistor, and a resistor between the base and the base. A circuit in which a diode is connected in series is connected to a voltage limit circuit consisting of each resistor and a voltage limit element, and a parallel circuit of resistors, and the collector of the transistor in the former circuit is connected to line A of the communication path, and the collector of the transistor in the latter circuit is connected to the A line of the communication path. and connect it to line B of the communication path,
2. The current supply circuit according to claim 1, wherein each of said transistors is complementary in both said semiconductor type current supply circuits. 4. The current supply circuit according to claim 2 or 3, characterized in that a composite connection transistor is used as the transistor. 5 Using a transformer, transfer communication information between communication paths connected to the primary and secondary windings of this transformer, and supply direct current to both sides or desired one side of these communication paths. In the current supply circuit for supplying direct current to the transformer, the winding to which the communication path that needs to be supplied is connected is divided into two, and these are connected via a capacitor, and the winding is connected to the ground air and this communication path. A semiconductor current supply circuit including a transistor is connected symmetrically between the A line and the B line and the battery, and the bases of both transistors are connected with a resistor R0. Both ends of the resistor R0 are connected to both ends of the capacitor via a resistor R1 and a resistor R1', respectively, and a switch element operated by a drive signal is provided between the resistor R0 and the base of the transistor of each of the semiconductor current supply circuits. A current supply circuit characterized in that the current supply circuit is provided and operates only when necessary. 6. The current supply circuit according to claim 5, characterized in that an optically coupled switch element is used as the switch element operated by a drive signal.