JPH06121076A - Speech current supply circuit - Google Patents

Abstract

PURPOSE:To provide the speech current supply circuit with less heat in which the mount area for speech current supply to a telephone set connecting to an exchange is small. CONSTITUTION:A constant current circuit 11 is disposed between a power supply circuit 34 and a telephone set 40 in a speech current supply circuit 1 to prevent an aural signal from being fed to the power supply circuit 34, a transformer having been used in a conventional circuit is replaced with a DC block capacitor 10 and then the transformer is not required for this circuit. The DC block capacitor 10 prevents a speech current fed to the telephone set 40 from being given to a channel switch 30. The constant current circuit 11 is made up of a 3-terminal regulator 12 and a resistor (R) 13 and supplies a prescribed speech current to the telephone set 40. The constant current circuit 11 has a property that its output impedance is equivalently very high and the aural signal is not given to the power supply circuit 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a call current supply circuit for a telephone such as a telephone exchange.

[0002]

2. Description of the Related Art In an exchange, a call current supply circuit for a telephone connected to the exchange has been conventionally constructed as shown below. FIG. 2 shows the subscriber circuit of the exchange.
It is a figure which shows the structure of the conventional call current supply circuit 2 which extracted the part regarding the call current supply. The conventional call current supply circuit 2 divides the winding on the telephone 34 (secondary) side of the transformer 20 into (n / 2: n / 2) windings 22 and 23, and is shown by (a) in the figure. It is a circuit that supplies a telephone call current (station power supply) necessary for the operation of the telephone 40 from the middle point to the telephone 34.

In FIG. 2, the transformer 20 includes a core 24.
And winding ratio of (m: n / 2: n / 2), respectively, the communication path switch 30 (primary) side winding 21 and secondary side winding 2
This is a transformer that has 2, 23 and performs impedance matching and transmission between a voice signal exchange and a telephone line.
At the midpoint (a) of the windings 22 and 23 on the secondary side, an AC signal passing capacitor 33 for the purpose of AC short-circuiting the midpoint is provided. From this point, the power supply circuit 34 is provided. As a result, the call current is supplied to the telephone 40.

The call path switch 30 sets the call path of the exchange. The resistors 31 and 32 normally have the same resistance value, and are connected to the power supply circuit 34 and the ground and the transformer 20.
And limits the output current of the power supply circuit 34.
The AC signal passing capacitor 33 is a capacitor for passing an AC signal as described above. The AC signal passing capacitor 33 has a large capacity that does not prevent passage of an audio signal, which is a signal in the audible frequency band.

The power supply circuit 34 normally has an output voltage of 24V to
It is a power supply circuit of the exchange of about 48 V, which supplies the power used in the exchange and also supplies the telephone call current to the telephone 40. Each part described above is a part built in the exchange. The telephone 40 is a telephone connected to the exchange through the telephone lines (L1, L2), for example, a 601-A type telephone or the like. The electric power required for the operation of the telephone 34 is usually supplied as a call current from the exchange through the telephone line in a manner superimposed on the voice signal.

The operation of the conventional call current supply circuit 2 will be described below. Voice signals between the exchange and the telephone 40 are transmitted via the transformer 20. Here, the potential of the middle point (a) of the secondary side of the transformer 20 does not change. Therefore, even if this point is grounded by DC or connected to a power supply, the audio signal does not flow to the ground or the power supply, and the transmission of the audio signal is not adversely affected.

Utilizing this property, the conventional call current supply circuit 2 superimposes a DC call current on an AC voice signal on the telephone line and supplies the call current to the telephone 40. The call current output from the power supply circuit 34 is supplied to the telephone 40 via the resistor 31, the winding 22, and the telephone line L1. This call current returns to the ground of the power supply circuit 34 again via the telephone line L2, the winding wire 23, and the resistor 32. On the other hand, the voice signal is the call path switch 30 and the telephone 4
Between 0, the transformer 20 and the AC signal passing capacitor 3
3, and over the telephone line. Here, the AC signal passing capacitor 33 does not hinder the transmission of the voice signal and blocks only the call current.

[0008]

Since the conventional speech current supply circuit is constructed as described above, it has the following problems. Since the transformer is used for supplying the call current and transmitting the voice signal, the mounting area is large and the cost is high. In addition, the power supply circuit is relatively high voltage (usually 24V
Since it operates at about 48 V), there is a problem that the transformer and the resistor generate heat.

The present invention has been made in view of the above-mentioned problems of the prior art, and it is not necessary to use a transformer for supplying call power to a telephone connected to an exchange, so that the mounting area is small. It is an object of the present invention to provide a speech current supply circuit which operates at a low voltage and generates a small amount of heat.

[0010]

To achieve the above object, a speech current supply circuit of the present invention is arranged between a power source and a telephone line, has a high output impedance, and is connected from the power source to an exchange. The telephone has a current supply means for supplying a call current to the telephone and a capacitor for blocking a DC current flowing from the current supply means to the talk path switch side of the exchange.

[0011]

[Function] The constant current circuit arranged between the power supply and the telephone line
The call current is supplied to the telephone, and a high impedance is exhibited for a voice signal transmitted / received between the telephone and the exchange to prevent the voice signal from flowing into the constant current circuit. The DC blocking capacitor prevents the call current from flowing into the switch path side of the exchange.

[0012]

Embodiments of the call current supply circuit of the present invention will be described below. FIG. 1 is a diagram showing a configuration of a call current supply circuit 1 of the present invention in which a portion related to a call current supply is extracted from a subscriber circuit of an exchange. Call current supply circuit 1
Is provided with a constant current circuit 11 between the power supply circuit 34 and the telephone 40 to prevent a voice signal from flowing into the power supply circuit 34, supply a telephone call current to the telephone 40, and further use a DC blocking capacitor 10 to prevent the conventional technique. The transformer 20 described above is replaced and the transformer 20 is unnecessary.

In FIG. 1, a DC blocking capacitor 10 is provided.
Prevents the call current supplied to the telephone 40 from flowing to the call path switch 30 side. Similar to the AC signal passing capacitor 33 described in the prior art, it has a large capacitance, for example, a capacitance of about 100 μF, so as not to interfere with the transmission of an audio signal which is a signal in the audio frequency band. Constant current circuit 11
Is composed of a three-terminal regulator 12 and a resistor (R) 13, and is arranged between the power supply circuit 34 and the telephone 40 to supply a telephone call current having a constant current value to the telephone 40. Here, the three-terminal regulator 12 has an output voltage of + 3V, for example.

The output current value (I _OUT ) of the constant current circuit 11 is expressed by the following equation. I _OUT = V _OUT / R + i _G (Equation 1) Here, V _OUT is the voltage of the output terminal (OUT) of the three-terminal regulator 12, R is the resistance value of the resistor 13, and i _G is 3
It is the current flowing out from the ground terminal (G) of the terminal regulator 12. This i _G is usually about several μA to several mA. R is set according to the current value supplied to the telephone 40.

The property of the constant current circuit 11 is that the value of the output current does not change even if the load changes.
In other words, this means that the impedance is equivalently very high, so that the audio signal does not flow into the power supply circuit 34 side. The constant current circuit 11 is not limited to the one using a three-terminal regulator, but may be configured with an operational amplifier, for example. The parts described above are connected as shown in FIG. Further, the respective parts not described above are the same as the respective parts having the same reference numerals described above with reference to FIG.

The operation of the call current supply circuit 1 will be described below. The current supplied from the power supply circuit 34 is input to the input terminal (IN) of the three-terminal regulator 12 and is output from the output terminal as a constant current output (I _OUT ). This constant current output is supplied as a call current to the telephone 40 via the telephone line (L1). This call current is supplied to the power supply circuit 3 through the telephone line (L2) and the exchange ground (GND).
Return to 4. Here, the constant current output is blocked by the DC blocking capacitor 10 and does not flow into the communication path switch 30 side.

On the other hand, the voice signal is a DC blocking capacitor 10 and telephone lines (L1, L2) between the exchange and the telephone 40.
Is transmitted through. Here, as described above, the constant current circuit 11 equivalently has a very high impedance, so that the audio signal does not flow into the constant current circuit 11 side.

Here, the operation will be described by giving specific numerical values. Constant current output (call current) 20mA, telephone 40
Maximum DC resistance of 300Ω, 3-terminal regulator 12
If the output voltage of is 3V and the input / output potential difference is 0.3V,
The required minimum output voltage E of the power supply circuit 34 is expressed by the following equation. E = 0.02 (A) × 300 (Ω) +3 (V) +0.3 (V) = 9.3 (V) (Equation 2)

That is, the voltage input to the constant current circuit 11 for supplying the call current to the telephone 40 is at least 9.3V.
Will be good. The call current supply circuit 1 is capable of such a low voltage operation. In addition to the configuration described above, the call current supply circuit of the present invention can have various configurations. The embodiments described above are merely examples.

[0020]

As described above, according to the present invention, it is not necessary to use a transformer for supplying call power to a telephone connected to an exchange, and therefore, the mounting area is small, and the operation is performed at a low voltage. It is possible to provide a call current supply circuit that generates a small amount of heat.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a call current supply circuit of the present invention in which a portion related to a call current supply is extracted from a subscriber circuit of an exchange.

FIG. 2 is a diagram showing a configuration of a conventional call current supply circuit in which a portion related to a call current supply is extracted from a subscriber circuit of an exchange.

[Explanation of symbols]

 1 ... Call current supply circuit 10 ... DC blocking capacitor 11 ... Constant current circuit 12 ... 3-terminal regulator 13 ... Resistor 30 ... Call path switch 40 ... Telephone

Claims (1)

[Claims] 1. A current supply means, which is arranged between a power supply and a telephone line, has a high output impedance and supplies a call current from the power supply to a telephone connected to an exchange, and the current supply means. A call current supply circuit having a capacitor that blocks a direct current flowing to the call path switch side of an exchange.