JP2000036879A - Communication current supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the communication current supply circuit of simpler circuit constitution in the telephone set of a subscriber circuit system. SOLUTION: This communication current supply circuit is provided with a constant current circuit 10 provided between power source wiring 41 and a terminal L1 of the telephone set, a main resistor 11 provided between a ground wiring 42 and a terminal L2 of the telephone set and an AC impedance circuit 51 provided between the telephone set terminal L1 and the ground wiring 42. The main resistor 11 is designed, so as to achieve the role of keeping balance with the AC impedance circuit 51 and securing impedance to AC signals generated at the time of communication.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication current supply circuit for a subscriber circuit type telephone.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No. 57-202246 discloses a communication current supply circuit for supplying a constant communication current to a so-called subscriber circuit type telephone. Is disclosed.

FIG. 8 is a diagram showing the configuration of a conventional communication current supply circuit. Referring to FIG. 1 and EXT. Reference numeral 2 denotes a telephone, and L1 and L2 denote terminals for supplying a telephone current to the telephone (hereinafter referred to as terminals).

A conventional communication current supply circuit has a terminal L
Constant current circuits 101 and 102 for supplying a constant current to 1 and L2 are provided. Constant current circuit 1 corresponding to terminal L1
01 is connected between the DC power supply E having a negative potential and the terminal L1, and includes a transistor Q1, a resistor R1, and a Zener diode ZD1. On the other hand, the constant current circuit 102 corresponding to the terminal L2 is provided between the ground line and the terminal L2, and includes a PNP transistor Q2, a resistor R2, and a Zener diode ZD2.

Further, the communication current supply circuit includes a resistor R0 connected between the NPN transistor Q1 and the PNP transistor Q2. Zener diode ZD1, resistor R0, and zener diode ZD2 are connected between negative DC power supply E and a ground line. In this path, a constant standby current flows, and a voltage drop in the Zener diodes ZD1 and ZD2 is maintained at a constant value determined by element characteristics.

Due to the effect of the Zener diode, the potentials of the bases and the emitters of the transistors Q1 and Q2 are kept constant. Thereby, the transistors Q1 and Q2 are
The standby current is received as a base current, and a constant collector current determined by resistors R1 and R2 is represented by L
1 and L2.

FIG. 9 is a diagram showing an entire configuration of a communication current supply circuit obtained by adding an AC impedance circuit to the constant current circuit described in FIG.

In general, in supplying a call current to a telephone, an AC impedance circuit for securing an appropriate impedance for an AC signal generated by the call is provided together with a circuit for supplying the current.

FIG. 9 shows two terminals L1 and L2 in addition to the two constant current circuits 101 and 102 described in FIG.
2, AC impedance circuits 51 and 52 provided corresponding to each of FIG.

[0010] The audio signal input to the input terminal 54 is amplified by the amplifier 53 and then amplified by the impedance circuit 5.
The signal is transmitted to the terminals L1 and L2 via the terminals 1 and 52.

In particular, the balance between the AC impedance circuits 51 and 52 provided corresponding to the respective terminals is important, and if the impedances of the two are not balanced, the common mode generated on the line side Induced noise
There is a problem that the sound is reproduced as noise in the receiver.

Since the AC impedance of the DC current source can be regarded as ∞, the AC impedance designed for the terminals L1 and L2 of the telephone is kept constant irrespective of the supply of the speech current.

As described above, in the conventional communication current supply circuit, the constant current circuits 101 and 102 and the AC impedance circuits 51 and 52 of the same design are provided symmetrically at each of the two terminals L1 and L2 of the telephone. This achieves the supply of a constant current to the telephone and the maintenance of the balance of the AC impedance to the two terminals.

[0014]

However, in the prior art communication current supply circuit, since the same design circuit is provided for each of the two terminals of the telephone, the number of parts must be increased. No, it is disadvantageous in terms of cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a communication current supply circuit having a simpler circuit configuration, which achieves both supply of a constant current to a telephone and maintenance of the balance of AC impedance to two terminals of the telephone. .

[0016]

A speech current supply circuit according to claim 1 is a speech current supply circuit for supplying a constant speech current to a telephone, wherein a first power supply for supplying a first reference potential. Wiring, a second power supply wiring for supplying a second reference potential, one of two terminals receiving a telephone call current, and a first power supply wiring or a second power supply wiring. A constant current circuit provided between the first power supply line and the other of the first power supply line or the second power supply line and the other of the two terminals receiving the communication current of the telephone. And a main resistor provided in the main body.

According to a second aspect of the present invention, there is provided the communication current supply circuit according to the first aspect, wherein one terminal is provided with an AC impedance circuit, and the resistance value of the main resistor is: Balances with the impedance value of the AC impedance circuit.

According to a third aspect of the present invention, there is provided a communication current supply circuit according to the second aspect, wherein the constant current circuit comprises:
A first transistor having a first electrode connected to one of the terminals; a first transistor connected between a second electrode of the first transistor and one of a first power supply wiring and a second power supply wiring; A first auxiliary resistor, a second auxiliary resistor connected between the input electrode of the first transistor and the other of the first power supply line and the second power supply line, and a first power supply line. Alternatively, it includes a Zener diode connected between one of the second power supply wires and the input electrode of the first transistor.

A communication current supply circuit according to a fourth aspect is the communication current supply circuit according to the second aspect, wherein the constant current circuit comprises:
A first transistor having a first electrode connected to one of the terminals; a first transistor connected between a second electrode of the first transistor and one of a first power supply wiring and a second power supply wiring; A first auxiliary resistor, a second auxiliary resistor connected between the input electrode of the first transistor and the other of the first power supply wiring and the second power supply wiring, and a first auxiliary resistance of the first transistor. A diode connected between the input electrode and one of the first power supply wiring and the second power supply wiring.

The communication current supply circuit according to claim 5 is the communication current supply circuit according to claim 2, wherein the constant current circuit is:
A first transistor having a first electrode connected to one of the terminals; a first transistor connected between a second electrode of the first transistor and one of a first power supply wiring and a second power supply wiring; A first auxiliary resistor, a second auxiliary resistor connected between the input electrode of the first transistor and the other of the first power supply wiring and the second power supply wiring, and a first auxiliary resistance of the first transistor. A diode connected between the input electrode and one of the first power supply wiring and the second power supply wiring and a third auxiliary resistance are included.

According to a sixth aspect of the present invention, there is provided the communication current supply circuit according to the third aspect, wherein the constant current circuit comprises:
A second transistor, the second transistor being Darlington connected with the first transistor,
And the cathode of the Zener diode are connected to the input electrode of the second transistor.

The communication current supply circuit according to claim 7 is the communication current supply circuit according to claim 4, wherein the constant current circuit is
A second transistor, the second transistor being Darlington connected with the first transistor,
Are connected to the input electrode of the second transistor.

The communication current supply circuit according to claim 8 is the communication current supply circuit according to claim 5, wherein the constant current circuit comprises:
A second transistor, the second transistor being Darlington connected with the first transistor,
Are connected to the input electrode of the second transistor.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a diagram showing a configuration of a call current supply circuit 2 according to a first embodiment of the present invention. The call current supply circuit 2 supplies a constant current to two terminals L1 and L2 of the telephone 1.

Referring to FIG. 1, call current supply circuit 2 includes:
A power supply wiring 41 for supplying a negative DC potential (-Vdd);
It includes a ground wiring 42, a constant current circuit 10 provided between the terminal L1 and the power supply wiring 41, and a main resistor 11 provided between the terminal L2 and the ground wiring 42.

The audio signal input to the input terminal 54 is amplified by the amplifier 53,
2, and is transmitted to the terminal L1.

The constant current circuit 10 supplies a constant current to the telephone. The AC impedance circuit 51 has a terminal L
1 to ensure the AC impedance.

The communication current supply circuit 2 is the same as that shown in FIG.
Compared with the conventional speech current supply circuit of the related art, the main resistor 11 is provided in place of the constant current circuit 102 connected to the terminal L2 and the AC impedance 52.

The resistance value of the main resistor 11 is designed in accordance with the impedance value of the AC impedance circuit 51 so that the balance between them is maintained. As a result, the call current supply circuit 2 supplies the call current required for the telephone by the constant current circuit 10, while the main resistor 11 and the AC impedance circuit 51 connect each terminal to the AC signal generated during the call. Keep the impedance balanced.

That is, the call current supply circuit 2 realizes the effect obtained by the conventional call current supply circuit with a simpler circuit configuration.

FIG. 2 is a circuit diagram showing the configuration of the constant current circuit 10 in more detail. Referring to FIG. 2, constant current circuit 10
Includes a transistor 21, a Zener diode 23, and auxiliary resistors 31 and 32.

The Zener diode 23 is connected to the power supply wiring 41
And a cathode connected to the base of transistor 21. Zener diode 2
3 is a power supply wiring 41 and a ground wiring 4 together with an auxiliary resistor 32.
3 are connected in series.

In this path, a constant standby current determined by the value of the auxiliary resistor 32 flows, and the voltage drop (hereinafter referred to as VF) at the Zener diode is:
It has a constant value determined by the element characteristics.

Due to the effect of the Zener diode, the potentials of the base and the emitter of the transistor 21 are kept constant, and the standby current is used as the base current as the transistor 21.
Supplied to

As a result, the collector current of the transistor 21 is maintained at a constant value, and the ground wiring 42 to the main resistors 11 to
The communication current supplied to the telephone through the path from the terminal L2 to the telephone 1 to the terminal L1 to the transistor 21 to the auxiliary resistor 31 to the power supply wiring 41 can be made constant.

Further, as described above, the main resistor 11
Secures an impedance to an AC signal generated during a call while maintaining balance with the AC impedance circuit 51.

Since the values of the auxiliary resistors 31, 32 and VF determine the base current and the emitter current of the transistor 21, they are designed according to the set value of the communication current and the element characteristics of the transistor.

FIG. 3 shows a modification of the first embodiment.
FIG. 3 is a circuit diagram showing a configuration of a constant current circuit 12 using, for example, two diodes instead of the Zener diode 23 in the constant current circuit 10 shown in FIG. 2. Referring to FIG. 3, in constant current circuit 12, diodes 24 and 25 are provided between DC power supply wiring 41 and the base of transistor 21 in place of zener diode 23 in FIG. Connection is made with the direction toward 41 as the forward direction.

The diodes 24 and 25 are connected to the ground wiring 4
3 and the DC power supply wiring 41 are forward-biased and conductive. Accordingly, the forward voltage drop of diodes 24 and 25 is fixed as a constant value determined by the element characteristics, so that the base and emitter potentials of transistor 21 are kept constant.

As a result, the collector current of the transistor 21 has a constant value, and the talk current supplied to the telephone can also be constant.

By using diodes 24 and 25 instead of zener diode 23, constant current circuit 12
Is a more advantageous circuit configuration in terms of cost.

FIG. 4 shows a modification of the first embodiment.
FIG. 3 is a circuit diagram showing a configuration of a constant current circuit 13 that connects a diode and a resistor instead of the Zener diode in the constant current circuit 10 of FIG. 2. Referring to FIG. 4, in constant current circuit 13, a single diode 26 and an auxiliary resistor 33 are connected instead of zener diode 23. Also in the constant current circuit 13, the diode 26 is forward-biased and conducts, thereby forming a current path between the power supply wiring 12 and the ground wiring 14 together with the auxiliary resistors 32 and 33. As in the case of the constant current circuit 12, the transistor 21
Of the base and the emitter and the current supplied to the base are maintained at constant values, so that the current supplied to the telephone 1 through the terminals L1 and L2 is constant.

[Second Embodiment] In the second embodiment, the transistors included in the constant current circuit have a so-called Darlington configuration.

FIG. 5 is a circuit diagram showing a configuration of constant current circuit 14 according to the second embodiment. Referring to FIG. 5, constant current circuit 14 further includes a transistor 22 in addition to the configuration of constant current circuit 10 shown in FIG.

The transistor 22 has a collector connected to the collector and the terminal L 1 of the transistor 21, an emitter connected to the base of the transistor 21, and a base connected to the cathode of the Zener diode 23.

The base of transistor 21 is connected to the emitter of transistor 22 and receives current from transistor 22.

Transistor 21 connected in Darlington
And 22 can increase the overall current gain. That is, an emitter current of the transistor 21 having a higher amplification factor than the base current supplied to the transistor 22 can be obtained. Therefore, when supplying a predetermined call current, the base current supplied to the transistor 22 can be designed to be a small value.

That is, the standby current that always flows through the path of the power supply wiring 41, the zener diode 23, the auxiliary resistor 32, and the ground wiring 43 can be reduced, and the power consumption of the communication current supply circuit can be reduced.

FIG. 6 shows a modification of the second embodiment.
FIG. 3 is a circuit diagram showing a configuration of a constant current circuit 15 in which a Zener diode 23 included in the constant current circuit 14 is, for example, two ordinary diodes 24 and 25.

The operation of diodes 24 and 25 is the same as in FIG. That is, with the configuration of the constant current circuit 15, the effect provided by the constant current circuit 14 can be obtained at lower cost.

FIG. 7 is a circuit diagram showing a configuration of a constant current circuit 16 which is another modification of the second embodiment. FIG.
, In the constant current circuit 16, the diode 2
6 and an auxiliary resistor 33 are provided instead of the Zener diode 23 of the constant current circuit 14.

The operations of the diode 26 and the auxiliary resistor 33 are the same as those in FIG. 4, and the effect of the constant current circuit 14 can be obtained more advantageously in terms of cost.

As described above, in the first and second embodiments, FIG.
In the configuration of the communication current supply circuits of Nos. 1 to 7, the ground wiring 43 included in the constant current circuits 10, 12 to 16 and the ground wiring 42 connected to the terminal via the main resistor are electrically independent. However, the present invention is not particularly limited to a configuration in which both are independent, and they can be connected to the same wiring.

In Embodiments 1 and 2,
Although the case where the constant current circuit is connected to the power supply line for supplying the negative DC potential (-Vdd) and the main resistor is connected to the ground line has been exemplified, the configuration of the talk current supply circuit of the present invention is It is not limited to such a case.

That is, when the main resistor has a negative DC potential (-V
dd), the constant current circuit is connected to the main resistor to the ground wiring, and the same configuration and the same structure can be obtained by changing the polarity of the transistors shown in the first and second embodiments. It is possible to The same applies to the case where the power supply wiring supplies a positive DC potential (+ Vdd).

It should be noted that the embodiment disclosed this time is an example in all aspects and is not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0057]

According to the first, second and third aspects of the present invention, the communication current supply circuit more efficiently supplies a constant communication current to the telephone and maintains the balance of the AC impedance between each terminal and the ground wiring. With a simple circuit configuration.

According to a fourth aspect of the present invention, the communication current supply circuit comprises:
The same effect as that of the communication current supply circuit according to the first aspect can be obtained by a more cost-effective configuration.

According to the communication current supply circuit of claim 6, in addition to the effect of the communication current supply circuit of claim 3, the power consumption can be further reduced.

According to a seventh or eighth aspect of the present invention,
The same effect as that of the communication current supply circuit according to the first aspect can be obtained by a more cost-effective configuration.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a configuration of a call current supply circuit 2 according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a constant current circuit 10 according to the first embodiment of the present invention.

FIG. 3 is a constant current circuit 1 according to a modification of the first embodiment of the present invention.
2 is a circuit diagram showing a configuration of FIG.

FIG. 4 is a constant current circuit 1 according to a modification of the first embodiment of the present invention.
3 is a circuit diagram illustrating a configuration of FIG.

FIG. 5 is a circuit diagram showing a configuration of a constant current circuit 14 according to a second embodiment of the present invention.

FIG. 6 is a constant current circuit 1 according to a modification of the second embodiment of the present invention.
5 is a circuit diagram showing a configuration of FIG.

FIG. 7 is a constant current circuit 1 according to a modification of the second embodiment of the present invention.
6 is a circuit diagram showing the configuration of FIG.

FIG. 8 is a circuit diagram of a communication current supply circuit according to a conventional invention.

FIG. 9 is a schematic diagram illustrating a configuration of a conventional call current supply circuit.

[Explanation of symbols]

 Reference Signs List 1 telephone 2 call current supply circuit L1, L2 telephone terminal 10, 12-16, 101, 102 constant current circuit 11 main resistor 21, 22 transistor 23 zener diode 24, 25, 26 diode 31-33 auxiliary resistor 41 DC power supply wiring 42 , 43 Ground wiring 51, 52 AC impedance circuit 53 Amplifier 54 Input terminal

Claims (8)

[Claims] 1. A communication current supply circuit for supplying a constant communication current to a telephone, comprising: a first power supply line for supplying a first reference potential; and a second power supply for supplying a second reference potential. A constant current circuit provided between a wiring, one of two terminals receiving a call current of the telephone, and one of the first power supply wiring and the second power supply wiring; And a main resistor provided between the other of the two terminals receiving the call current of the telephone and the other of the first power supply wiring or the second power supply wiring. A communication current supply circuit. 2. The communication current supply circuit according to claim 1, wherein an AC impedance circuit is provided at the one terminal, and a resistance value of the main resistor is balanced with an impedance value of the AC impedance circuit. . 3. The constant current circuit, comprising: a first transistor having a first electrode connected to the one terminal; a second electrode of the first transistor and the first power supply wiring or A first auxiliary resistor connected between one of the second power supply lines, an input electrode of the first transistor, and one of the first power supply line and the other of the second power supply line; And a Zener diode connected between one of the first power supply wiring or the second power supply wiring and an input electrode of the first transistor. The communication current supply circuit according to claim 2, comprising: 4. The constant current circuit, comprising: a first transistor having a first electrode connected to the one terminal; a second electrode of the first transistor and the first power supply line or A first auxiliary resistor connected between one of the second power supply lines, an input electrode of the first transistor, and one of the first power supply line and the other of the second power supply line; And a diode connected between an input electrode of the first transistor and one of the first power supply wiring or the second power supply wiring. A communication current supply circuit according to claim 2. 5. The constant current circuit, comprising: a first transistor having a first electrode connected to the one terminal; a second electrode of the first transistor and the first power supply line or A first auxiliary resistor connected between one of the second power supply lines, an input electrode of the first transistor, and one of the first power supply line and the other of the second power supply line; And a diode connected between an input electrode of the first transistor and one of the first power supply wiring or the second power supply wiring, and a third auxiliary resistance connected between the second auxiliary resistance and the third power supply wiring. 3. The communication current supply circuit according to claim 2, further comprising an auxiliary resistor. 6. The constant current circuit further includes a second transistor, wherein the second transistor is Darlington connected to the first transistor, and wherein the second auxiliary resistor and a cathode of the Zener diode are connected to each other. , Connected to the input electrode of the second transistor,
The call current supply circuit according to claim 3. 7. The constant current circuit further includes a second transistor, wherein the second transistor is Darlington connected to the first transistor, and wherein the second auxiliary resistor and an anode of the diode are: 5. The semiconductor device according to claim 4, which is connected to an input electrode of said second transistor.
A call current supply circuit as described. 8. The constant current circuit further includes a second transistor, wherein the second transistor is Darlington-connected to the first transistor, and wherein the second auxiliary resistor and an anode of the diode are 6. The semiconductor device according to claim 5, which is connected to an input electrode of the second transistor.
A call current supply circuit as described.