JPH0683308B2 - Telephone line connection circuit - Google Patents

Description

The present invention relates to a telephone line connection circuit suitable for use when amplifying and outputting a received signal from a telephone line through a speaker or the like.

[Outline of Invention]

In the present invention, the magnitude of the power supply current supplied to the amplifier circuit that amplifies and outputs the reception signal from the telephone line is switched according to the mode.

[Background technology]

Recent telephones have been provided with various functions in addition to the function of transmitting and receiving a transmission signal and a reception signal by the handset. As one of such functions, there is a function of dialing with the handset set in the main body (on-hook dial) or outputting a reception signal through a speaker (loud reception). A telephone having this function is provided with a speaker and an amplification (power amplification) circuit for driving the speaker.

[Problems to be solved by the invention]

Conventionally, the gain of such an amplifier circuit is controlled in accordance with the line current of the telephone line, but the power supply current is fixed. Therefore, if the value of the power supply current is set large, power is consumed more than necessary, and if it is set small, the dynamic range becomes small.

Therefore, the present invention makes it possible to secure a sufficient dynamic range while sufficiently reducing the power consumption.

[Means for solving problems]

The present invention relates to a telephone line connection circuit, which is connected to a telephone line and has a first constant current or a second constant value larger than the first constant current.
Current circuit for generating a constant current, an amplifier circuit for amplifying a received signal from a telephone line, a supply circuit for supplying the first or second constant current as a current to the amplifier circuit, a first constant current and a first constant current And a logic circuit for switching the constant current of 2 according to the mode.

[Action]

A current circuit connected to the telephone line produces a first constant current or a second constant current of a greater value. The first or second constant current is supplied to the amplifier circuit that amplifies the received signal as its power supply through the supply circuit. The logic circuit switches between the first constant current and the second constant current according to the mode.

〔Example〕

FIG. 1 is a block diagram of a telephone line connection circuit of the present invention. Terminals 1 and 2 are connected to a telephone line (not shown). However, a positive DC voltage is supplied to the terminal 1 and a negative DC voltage is supplied to the terminal 2, respectively, which are connected via a predetermined circuit (for example, a diode ring circuit) as necessary. A smoothing circuit 71 is composed of the resistors 11 and 12 and the capacitor 31. The smoothing circuit 71 smoothes the line current (voltage) of the telephone line flowing between the terminals 1 and 2. The output voltage of the smoothing circuit 71 (capacitor 31) changes according to the line current, and increases when the line current is large and decreases when the line current is small.
However, when the output voltage exceeds a predetermined reference value,
Since the diode 21 as a limiter circuit which is normally off is turned on, the output voltage thereof does not exceed the reference value. As a result, the maximum value of the power supply current supplied to the amplifier circuit 73 described later is regulated.

The emitter of the NPN transistor 53 is connected to the current circuit 74 including the resistors 13 and 14 and the NPN transistors 51 and 52.
The logic circuit 64 outputs a predetermined constant voltage signal from the terminals 5 and 6 in response to the control signal input from the terminals 9 and 10 to turn on one of the transistors 51 and 52. Transistor
The value of the resistor 13 connected to 51 is set smaller than the value of the resistor 14 connected to the transistor 52. Therefore, when the transistor 51 is turned on, a predetermined constant current larger than that when the transistor 52 is turned on flows. The volume of the speaker 63 during on-hook dialing is preferably lower than that during loud voice reception. Therefore, the transistor 52 is turned on during the on-hook dial and the transistor 51 is turned on during the loud voice reception. Since the amplifier circuit 73 is not required during a normal call, both the transistors 51 and 52 are turned off.

The output voltage of the smoothing circuit 71 is a transistor as a control circuit.
Supplied to 52 bases. The operating resistance of the transistor 53 decreases when the output voltage of the smoothing circuit 71 is high, and increases when it is low. That is, as the line current increases, the current flowing through the transistor 53 also increases. The collector of the transistor 53 has resistors 19, 20, 27 and PNP transistors 41, 4
Current mirror circuit consisting of 2, 49 and NPN transistor 59
72 is connected. Therefore, the constant current flowing through the transistor 53 selected by the logic circuit 64 is transferred from the transistor 41 forming the current mirror circuit 72 to the transistor 59. The current output from the transistor 59 is the backflow prevention NPN transistor 58 that functions as a supply circuit.
Is supplied as a power supply current to the amplifier circuit 73 via. When the line current thus increases, the power supply current also increases, and the dynamic range of the amplifier circuit 73 increases.

A part of the current output from the transistor 59 is shunted to the NPN transistor 54 as a supply circuit connected to the PNP transistor 43 in the inverted Darlington connection.
As a result, the current flowing through the transistor 59 can be made substantially constant even if the power supply current consumed changes according to the usage state of the amplifier circuit 73.

On the other hand, the voltage circuit 75 is configured as follows. At the time of on-hook dialing and voice reception, the logic circuit 64 has terminal 7
To turn on the NPN transistor 57. Therefore, the NPN transistors 55 and 56 turn on, and the diodes 22 and 2
3, the current flows through the resistor 15. Also, the potential at the common connection point of resistors 16, 17, and 18 drops, so PNP transistors 44, 45, and 4
6 turns on and a constant current flows through its emitter and collector. When the transistor 46 turns on, the transistor
58 turns on.

The voltage drop of the diode 24 is set smaller than the breakdown voltage of the Zener diode 25. Therefore, normally, the diode 24 is turned on and the zener diode 25 is turned off, so that the differentially connected PNP transistor 48 is turned on and the PNP transistor 48 is turned on.
The transistor 47 turns off. As a result, the potential at the connection point A between the emitter of the transistor 59 and the collector of the transistor 54 is the drop voltage of the diode 24, the base-emitter voltage of the transistor 48, and the transistor 43 as a supply circuit.
It is set to the value that the base-emitter voltage of is added.

The voltage at the connection point A is supplied to the amplifier circuit 73 as a power supply voltage via the transistor 58.

The amplifier circuit 73 is composed of the BTL-connected amplifier circuits 61 and 62, and is supplied with the above-mentioned power supply current and power supply voltage. The amplifier circuits 61 and 62 power-amplify the received signals from the telephone lines, which are input in opposite phases via the terminals 1 and 8 and the capacitor 32, and output the amplified signals to the speaker 63.

In normal call mode Transistors 57, 55, 56, 44, 45,
All 46, 47, 48 and 58 are off. Therefore, the amplifier circuit 73
Power supply current and power supply voltage are not supplied to.

However, in this case, connect the power supply 65 from the outside to terminals 3 and 4,
The amplifier circuit 73 can be put into operation. At this time, the voltage and current from the power source 65 are blocked by the transistor 58 and are not supplied in the direction of the connection point A.

〔effect〕

As described above, according to the present invention, in the telephone line connection circuit, a current circuit connected to the telephone line and generating the first constant current or the second constant current having a value larger than the first constant current, and reception from the telephone line. An amplifier circuit for amplifying a signal, a supply circuit for supplying the first or second constant current as a power source to the amplifier circuit, and a first circuit
Since the constant current and the second constant current are switched according to the mode, the dynamic range corresponding to the current consumption is secured and the power consumption is prevented from increasing more than necessary. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of a telephone line connection circuit of the present invention. 1 to 10 ... Terminals 11 to 20 ... Resistors 21 to 24 ... Diodes 25 ... Zener diodes 27 ... Resistors 31,32 ... Capacitors 41 to 49 ... PNP transistors 51 to 59 ... NPN transistors 61, 62 …… Amplifier circuit 63 …… Speaker 64 …… Logic circuit 65 …… Power supply 71 …… Smoothing circuit 72 …… Current mirror circuit 73 …… Amplifier circuit 74 …… Current circuit 75 …… Voltage circuit

Claims (1)

[Claims] 1. A current circuit connected to a telephone line for generating a first constant current or a second constant current having a value larger than the first constant current, and an amplifier for amplifying a reception signal from the telephone line. A circuit, a supply circuit that supplies the first or second constant current as a power source to the amplifier circuit, and a logic circuit that switches between the first constant current and the second constant current mode. Telephone line connection circuit characterized by.