JPS607428B2 - Telephone power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit for subscribers of an exchange, primarily a telephone exchange.

Conventionally, electromagnetic devices such as Tatsuji relays have been widely used in switching equipment, and power to subscribers' telephones has often been supplied through the contacts of the relays in the switching circuit. However, I don't understand the electronic exchange. In the switching circuit, the switching operation is performed only on signals, for example, call signals, and power supply to the subscriber's telephone is performed by providing power supply capability to the subscriber's circuit, sending DC power from this circuit to the telephone, and converting the DC power into the DC power. A method is used in which the signal components that come are separated using a transformer or the like and then supplied to a switching circuit. One example is the circuit shown in FIG. Figure 1 is an example of a power supply circuit (sometimes called a subscriber circuit) using a transformer, where the subscriber's telephone is connected to terminal 101.
The power supply for the subscriber telephone is connected to the transformer 10
7 primary windings 105, 106, current limiting resistors 103,
It is supplied from a current limited power source 110 at 104 . In this case, the windings 105 and 106 are connected to each other by the capacitor 102.
The connection is made with a sufficiently low impedance at the communication signal frequency used. In this way, the terminal 101 is supplied with direct current in equilibrium with the earth, and the speech signal component is passed through the secondary winding 108 of the transformer 107 to the secondary terminal 101.
Appears at 9 and is sent to the exchange circuit. In such cases, all-electronic switching circuits are used, such as PCM time-division switching, PNFN diodes, and PNP switching circuits.
Various new techniques are used, such as an electronic contact space division method using an N triode (for example, a controlled rectifier), a time division exchange method using a pulse oscillation modulation method, and so on. If a transformer is used in the power supply circuit for such subscribers, it is possible to construct a circuit that is easy to take care of, such as line balance and insulation resistance. When this is done, the core of the transformer 107 is excited by direct current, so in order to prevent distortion etc. caused by this, it is necessary to take measures such as increasing the cross-sectional area of the core of the transformer, introducing an air gap, and increasing the number of windings. This results in larger transformers, increased call loss, etc.
This is a factor that prevents equipment from becoming smaller and becoming more economical. The object of the present invention is to reduce the adverse effects of direct current excitation of the iron core in such cases. In the present invention, in order to reduce the above-mentioned drawbacks, a first constant current circuit is connected to one end of the primary winding having a midpoint, and current is supplied from this circuit to the subscriber. By using a constant current circuit, a part of this current is passed from one end of the primary winding connected to the first constant current circuit to the middle point, and by passing the current through it, the DC excitation generated by the primary winding is reduced or canceled. The purpose is to The present invention considers two methods for this purpose. One method is to connect a second constant current circuit between the first constant current circuit and the primary winding, connect it in parallel with the second constant current circuit, and provide a sufficiently small impedance for communication signals. The other one is to divide the primary winding into two at the midpoint, connect a capacitor with a sufficiently small impedance between the two, and connect the first constant current circuit to the other winding. Insert a second constant current circuit on the midpoint side,
This method cancels out the DC magnetic field generated by the current flowing through the other winding. In either method, unless the first constant current circuit has good constant current characteristics, loss will occur in the call signal component, but the second constant current circuit will cause loss even if it is not very strict. Therefore, for the latter, a constant current diode using the constant current property of a field effect transistor or a simple constant current circuit can be used. In addition, in this invention, even when the subscriber is not operating, that is, when the hook-on state and no current is flowing, current is flowing between the first constant current circuit and the second constant current circuit, so there is no problem. It's the economy. Therefore, when there is no need to supply current to subscriber telephones, it is better to configure the circuit by adding a circuit that shuts off both or one of these two constant current circuits without operating them. In some cases, it may be a good idea. However, in this case, if both are turned off, there is a risk that subscriber hook-off detection may not be possible, and a hook-off detection circuit will need to be provided separately, so it is necessary to make a decision from the economic point of view of the entire device. The present invention will be explained in detail below with reference to Examples.

FIG. 2 shows an embodiment of the present invention, in which a first constant current circuit and a second constant current circuit are located between the primary winding of a transformer and a line connected to a subscriber. . In FIG. 2, the subscriber is connected to terminal 201. A constant current circuit 203 is connected to one end of the line connected to this subscriber. The capacity of this constant current circuit is usually selected to be twice the current flowing through the subscriber's telephone, and for example, about 1 hA is used. On the other hand, this first constant current circuit 203 is
A second constant current circuit 204 is inserted between the circuit and the circuit 5. This second constant current circuit has a capacitor 202 in parallel,
The alternating current signal of the speech signal component is bypassed through this capacitor.

The value of this capacitor used is about 2 F to 4 F. The capacity of the second constant current circuit is selected to be approximately half that of the first constant current circuit, and its polarity is selected to reduce the current flowing to the subscriber. When such a value is used, the DC current flowing through the winding 205 cancels out the current flowing through the subscriber into the winding 206 in terms of the DC magnetic field, and the influence of DC excitation on the core of the transformer 207 is reduced. do. On the other hand, the AC signal, which is a call signal component, is directly passed through the secondary winding 2.
08, appears at the terminal 209 connected to the exchange circuit, and is exchanged. The circuit of FIG. 2 has the advantage of directly grounding the midpoint, but has the disadvantage that the second constant current circuit floats above the ground.

The embodiment shown in FIG. 3 is an example in which one end of the second constant current circuit is connected to the ground.

In FIG. 3, a subscriber's telephone is connected to a terminal 301, and the power supply for this subscriber is provided by a first constant current circuit 30.
3 is selected to be twice the current flowing through the subscriber, as in the example of FIG. On the other hand, the primary winding of the transformer 307 is divided into two, consisting of windings 305 and 306, and the middle point is connected by a capacitor 302 so as to be AC conductive. A second constant current circuit 304 is connected between the ground and the midpoint side of the winding 305 to which the first constant current circuit 303 is connected. The capacity of this constant current circuit is half that of the first constant current circuit 303 and is chosen to reduce the current flowing to the subscriber. In this way, the DC magnetic field caused by the current flowing through the subscriber's telephone in one of the primary windings 306 can be canceled out. Although the resistor 310 in FIG. 3 is a current limiting resistor, it is not necessarily necessary. Also, 30 in the figure
8 is a secondary winding, and the exchange circuit is connected to the terminal 309, as in FIG. FIG. 4 is a more specific description of FIG. 3.

In FIG. 4, the subscriber is connected to terminal 401, and the switching circuit is connected to terminal 409.
connected to. The first constant current source corresponding to 303 in FIG. 3 is a portion 403 surrounded by a dotted line, and uses a collector resistor of a transistor. Here, an NPN transistor 414 is used depending on the direction of the current. The emitter of this transistor is connected to a negative power source 416 through a resistor 415, and the base is clamped to a negative power source 411, which is more positive than the current 416, with a diode 412. A current is supplied to this base from a resistor 413. To give a numerical example actually used, power supply 41 1
is -48V, power supply 416 is -60V, resistor 41 5 is 1
200, a constant current source of about 10 hA can be constructed. In this case, the resistor 413 only needs to be able to supply a collector current to the base that is greater than the value achieved by the current increase rate of 3. The first constant current source is configured in this way, but the primary winding 4
The second constant current source 404 connected to the midpoint side of 05 is also a circuit that utilizes the collector characteristics of a transistor.
In this case, transistor 417 is PNP due to the direction of current.
A transistor is used. The base of this transistor should originally be grounded, but it is connected to the outside of the current detection transistor 421 so that no current flows when the subscriber's telephone is not hooked up. When a subscriber hooks off, current flows through one winding 406 of the primary winding.
The current flows through the current limiting resistor 420 and makes the transistor 421 conductive. As a result, current flows through resistor 418 from the emitter of transistor 417, which is at a positive potential on power supply 419. In this case, the power supply 419 is 5V, and the resistor 4 is
If 18 is 1000, it becomes a constant current circuit of about 5 mhA, and the current flowing through the winding 405 and the current flowing through the winding 406 are almost balanced, and no DC magnetic field is generated or is reduced. On the other hand, the AC component is connected to the winding 40 by the capacitor 402.
5,406 to generate a current in the secondary winding 408. In the example shown in FIG. 4, when the subscriber hooks on, no current flows through the transistor 421, so the second constant current circuit ceases to operate, and the current is cut off, eliminating unnecessary power consumption, which is economical. Although the present invention has been explained in detail using examples above, the present examples are merely examples, and the scope of the present invention is not limited by this description.

[Brief explanation of the drawing]

FIG. 1 is an example of a conventionally used power supply circuit. FIG. 2 shows an embodiment of the present invention, in which 203 is a first constant current circuit that supplies power to the subscriber, 204 is a winding 205
202 is a bypass capacitor for communication signals;
1 is a terminal connected to a subscriber, and 207 is a transformer. FIG. 3 shows another embodiment of the present invention in which the second constant current circuit can be grounded, and 301 is a terminal connected to a subscriber;
03 is a first constant current circuit that supplies power to subscribers; 30
4 is a second constant current circuit, 307 is a transformer, 305 and 306 are primary windings, 308 is a secondary winding, and 302 is a capacitor that couples the primary windings. FIG. 4 shows an embodiment in which the second constant current circuit is cut off when a subscriber hooks on, 401 is a terminal connected to the subscriber, 408 is the first constant current circuit, and 404 is the second constant current circuit. A circuit, 421, is a transistor that detects the flow of current to the subscriber, 4
05 and 406 are primary windings, and 402 is a capacitor coupling between the primary windings. Festival 'Z hair Z figure Tsutomu J figure 1st Buddha figure

Claims (1)

[Claims] 1. A telephone power supply circuit that supplies a current of value Io to a subscriber, comprising: (a) a first winding with a number of windings n_1 and a number of windings n_2;
a transformer having a primary winding consisting of a second winding (b
) constant current is (1+(n_2)/(n_1))Io
a first constant current circuit (c ) The second path has a sufficiently small impedance at the operating frequency as a side path.
a constant current circuit that supplies a current having a value of n_2Io/n_1 to the first winding in a direction that cancels the magnetic flux generated in the transformer by the current flowing from the subscriber to the second winding. a second constant current circuit; (d) means for detecting the current flowing through the subscriber and operating the second constant current circuit only when current flows through the subscriber; Power supply circuit for telephones. 2 A first constant current circuit is connected to one side of a pair of lines connected to the subscriber side, and one end of a second winding is connected to the other side of the line to control the current of the first constant current circuit. A second constant current circuit is connected between the connection point of the first constant current circuit and one end of the first winding, and a capacitor having a sufficiently small impedance at the operating frequency is connected to the return path. Second
A telephone power supply circuit according to claim 1, which is connected in parallel with a constant current circuit. 3. A capacitor having a sufficiently small impedance at the operating frequency is connected between the first winding and the second winding, and the other ends of the first and second windings are respectively connected to the subscriber line, A first constant current circuit is connected to one end of the first winding on the line side, and a second constant current circuit is connected to one end of the first winding on the midpoint side.
A telephone power supply circuit according to claim 1, which is connected to a constant current circuit.