JPH0787237A - Dc loop circuit - Google Patents

Abstract

PURPOSE:To keep a current fetched from a line constant as supplying a bias voltage stabilized by a constant voltage source by fetching a constant current from a telephone line by a constant current means, outputting a constant voltage by a constant voltage means setting the current as input, and setting the voltage as the base bias voltage of a transistor. CONSTITUTION:A constant current source 2 is connected with the telephone line, and outputs the constant current II by inputting a line voltage VL. The constant voltage source 3 outputs the contant voltage VBB by inputting the current II. When the voltage VBB is inputted to the transistor 4 as the base bias voltage, the emitter current IE of the transistor 4 goes to (VBB-VBE)/RE. Since the base bias voltage VBB is always kept constant, the emitter current IE can be also kept constant as far as the VBE is kept stably. Consequently, the current fetched from the telephone line can go to the sum of the current II and the emitter current IE, which always enables the constant current to be fetched even when the line voltage VL changes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC loop circuit using a transistor used in a line terminal device connected to a telephone line to perform no ringing communication.

[0002]

2. Description of the Related Art A circuit using a transistor is used in a telephone or the like as a DC loop circuit which is connected to a telecommunication line facility and forms a DC loop by using a current from the line to terminate the line. An example of the configuration of a DC circuit of a conventional electronic telephone using this DC loop circuit is shown in FIG.

In FIG. 3, when the current amplification factor of the transistor 4 is sufficiently high, the line voltage VL can be approximated by the following equation.

[0004]

[Equation 1]

Here, VBE is the base of the transistor 4.
It is the voltage between the emitters. From the above equation, it can be seen that the line voltage VL has a slope R3 and is proportional to the line current IL. At this time, the DC resistance value ZDC of the DC circuit seen from the line side is

[0006]

[Equation 2]

The minimum value R3 is obtained, and the value is inversely proportional to IL. It is stipulated that the direct current resistance at the time of actual telephone communication is set within 50 to 300Ω when the line current is 20 to 100 mA. If VBE is kept constant at 0.7V, R1, R2, and R3 are 20kΩ and 10k, respectively.
When the line current is 20 to 100 mA, the resistance value is 51 Ω to 135 Ω, which satisfies the specified value. In addition, the signal VIN from the base of this transistor 4
You can send a signal to the line by inputting.

For example, a configuration diagram of a line terminal device for performing no-ringing communication used in an automatic meter-reading system or the like for measuring the usage amount of gas, water, electricity, etc. and transmitting this data to a center device via a general telephone network is shown. As shown in FIG. In FIG. 4, reference numeral 41 is a teleconverter terminal device for measuring the amount of gas, water, electricity, etc. used, 42 is a line terminal device having a line control function such as a DC circuit and a signal transmission / reception circuit, and 43 is a home terminal It is a telephone.

In the no-ringing communication, when an incoming call is received from the center device via a telephone line, the direct-current resistance of the DC circuit of the line terminal device 42 remains 4 kΩ or more to enter the no-ringing incoming call state, and between the teleconverter terminal device 41 and the center device. Exchange data. This is because the communication is performed with the DC resistance kept relatively large, so that the line terminal device 42
This is so that the bell of the telephone set 43 connected in parallel with does not ring. Also, when trying to output the output signal up to 0 dBm, the output load is set to 300Ω and AC ±
It requires a line current of 3.65 mA. Therefore, when the signal is transmitted from the circuit of FIG. 3, the emitter current needs to be 3.65 mA or more in order not to clip the output signal.

Since the conventional no-ringing communication equipment is designed so that the DC resistance ZDC at the line voltage VL60V is 10 kΩ or more and operates up to VL30 V, the circuit of FIG. If you try to do that, you cannot achieve it.

Therefore, it can be considered to set the bias voltage of the transistor to a constant value. Emitter resistance RE is 30
If Ω is set, the emitter voltage VE becomes 0.12 V when the emitter current is constant at 4 mA, and 0.82 V, which is a potential increased by VBE, may be added as the base voltage. If this base voltage is to be taken from the line like a normal telephone, a voltage is applied to the base from the line using a constant voltage source as shown in FIG.

[0012]

However, the above-mentioned FIG.
In such a configuration, the line voltage VL differs depending on communication conditions such as the distance from the exchange, and the input voltage to the constant voltage source changes, so the current consumed by the constant voltage source itself changes. Therefore, although the base voltage to the transistor is made constant by the constant voltage source, the current consumed in the entire DC loop circuit depends on the line voltage VL.

Further, since the base-emitter voltage VBE of the transistor is affected by the variations due to the constituent elements and the temperature change, there is a problem that even if the same base voltage is applied, the emitter current also varies. .

The present invention is intended to solve the above-mentioned problems.
It is an object of the present invention to provide a DC loop circuit which can supply a constant bias voltage by a constant voltage source and make the current taken in from the line constant.

A second object of the present invention is to provide a DC loop circuit which can flow a constant DC current without depending on the variation in the base-emitter voltage of the transistor.

[0016]

In order to achieve the first object, the DC loop circuit of the present invention comprises a constant current means for taking in a constant current from a telephone line and a constant voltage depending on the output current of the constant current means. And constant current means for generating and a current amplification means that operates using the output voltage of the constant voltage means as a bias voltage.

For the second purpose, the present invention is provided with a current amplifying means composed of a P-type transistor and an N-type transistor which operates by using the emitter voltage of the P-type transistor as a base bias voltage.

[0018]

According to the first aspect of the present invention, the constant current II is taken in from the telephone line by the constant current means, and this current is input to the constant voltage means to output the constant voltage.
This constant voltage is the base bias voltage V of the transistor
Since it is B, the current consumed by the DC loop circuit is the sum of the current I1 output by the constant current means and the emitter current IE of the transistor.

Further, according to the second structure, by inputting a constant voltage as the base bias voltage VB1 to the P-type transistor, the emitter voltage VE1 becomes a potential higher than VB1 by VBE1, and this VE1 is applied to the N-type transistor as a base. By inputting as the bias voltage VB2, the emitter voltage VE2 becomes a potential which is lower than VB2 by VBE2. At this time, in the integrated circuit, VBE of the two transistors has substantially the same variation, and since the influence of the temperature change is the same, VE2 = VB1. Therefore, the emitter current IE of the N-type transistor is proportional to only the emitter voltage VB1 of the P-type transistor, that is, the output voltage of the constant voltage source.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, 1 is a DC loop circuit connected to a telephone line having a line voltage VL, 2 is a constant current source for taking in a fixed amount of line current, 3 is a constant voltage source for outputting a constant voltage, and 4 is a constant voltage source. It is an N-type transistor that operates using the output voltage of the voltage source 3 as a base bias voltage.

In the above structure, the constant current source 2 is connected to the telephone line and inputs the line voltage VL to output the constant current II. The constant voltage source 3 inputs the current II and outputs a constant voltage VBB. When this voltage VBB is input to the transistor 4 as a base bias voltage, the emitter current IE of the transistor 4 becomes (VBB-VBE) / RE. Since the base bias voltage VBB is always constant, the emitter current IE of the transistor 4 is also constant as long as VBE is stable. As a result, the current taken in from the telephone line is the sum of the current I1 by the constant current source 2 and the emitter current IE of the transistor 4, and a constant current is always taken in even if the line voltage VL changes. In other words, the telephone line can be terminated by a DC loop that allows a constant current to flow.

According to the configuration of the first embodiment, there is an effect that a constant current can always be taken from the telephone line regardless of the voltage change of the telephone line.

FIG. 2 shows a second embodiment. Instead of one transistor of the first embodiment, the voltage generated by the resistance voltage division of the output voltage from the constant voltage source 3 operates as the base bias voltage. It comprises a P-type transistor 5, a constant current source 6 for supplying a collector bias current of the P-type transistor 5, and an N-type transistor 4 which operates by using the emitter voltage of the P-type transistor 5 as a base bias voltage. There is.

In the above structure, the output of the voltage VBB from the constant voltage source 3 is the same as in the first embodiment. With this voltage VBB as the base bias voltage, the P-type transistor 5
When it is input to, the emitter voltage becomes a potential which is higher than VB1 by VBE1. The emitter voltage of the P-type transistor 5 is the base bias voltage V of the N-type transistor 4.
By inputting as B2, the emitter voltage VE2 becomes a potential lower than VB2 by VBE2. At this time, in the integrated circuit, VBE of the two transistors has almost the same variation, and the influence of temperature change is the same, so VE2 = V
It becomes B1. Therefore, the emitter current IE of the N-type transistor 4 can be approximated to VB1 / RE, so that the emitter voltage V of the P-type transistor 5 is not affected by the variation of VBE.
B1 is proportional to only the output voltage of the constant voltage source.

According to the structure of the second embodiment, there is an effect that a constant DC current can be passed through the N-type transistor 4 without depending on the variation in the base-emitter voltage of the transistor.

[0027]

As described above, the DC loop circuit of the present invention has the first configuration, which takes in the constant current II from the telephone line by the constant current means, and inputs this current to output the constant voltage by the constant voltage means. However, since this constant voltage is used as the base bias voltage VB of the transistor, the current consumed by the DC loop circuit is the sum of the current I _I output by the constant current means and the emitter current IE of the transistor, and stabilized by the constant voltage source. This has the effect that the current taken from the line can be made constant while supplying the base current.

According to the second configuration, by inputting a constant voltage to the P-type transistor as the base bias voltage VB1, the emitter voltage VE1 becomes a potential higher than VB1 by VBE1, and this VE1 is applied to the N-type transistor as a base. By inputting as the bias voltage VB2, the emitter voltage VE2 becomes a potential VBE2 lower than VB2.
At this time, VBE of two transistors in the integrated circuit
Has almost the same variation, and the influence of the temperature change is the same, so that VE2 = VB1. Therefore, since the emitter current IE of the N-type transistor is proportional to only the emitter voltage VB1 of the P-type transistor, that is, the output voltage of the constant voltage source, a constant DC current is supplied to the transistor without depending on the variation of the base-emitter voltage of the transistor. By flowing the current, it is possible to make the current consumption from the line constant.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a DC loop circuit according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a DC loop circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a DC circuit of a conventional electronic telephone using a DC loop circuit.

FIG. 4 is a block diagram of a no ringing communication system.

FIG. 5 is a configuration diagram of a DC loop circuit with a constant bias voltage.

[Explanation of symbols]

 1 DC loop circuit 2 Constant current source 3 Constant voltage source 4 N-type transistor 5 P-type transistor

Claims (3)

[Claims] 1. A first constant current means for taking a constant current from a telephone line, a constant voltage means for generating a constant voltage by an output current of the first constant current means, and an output voltage of the constant voltage means. A direct current loop circuit comprising a second constant current means for supplying a constant current from a telephone line. 2. A constant current means for taking in a constant current from a telephone line, a constant voltage means for generating a constant voltage by an output current of the constant current means, and a current which operates by using an output voltage of the constant voltage means as a bias voltage. A DC loop circuit having an amplifying means. 3. A P-type transistor as current amplification means,
3. The DC loop circuit according to claim 2, further comprising current amplifying means constituted by an N-type transistor which operates by using an emitter voltage of the P-type transistor as a base bias voltage.