JP2899428B2 - Telephone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephone equipped with a power supply circuit for outputting a constant current by receiving power from an office power supply.

[0002]

2. Description of the Related Art In general, telephones include a microcomputer for system control, a transfer circuit, and a DTMF (dial toe).
The control circuit usually includes an integrated circuit including a signal and a generator. A battery is provided as one of the power supplies for driving such a control circuit, and its main purpose is to back up a memory in the control circuit and to activate the CPU during standby. Further, a constant current source circuit driven by a station power supply obtained through a telephone line is provided, and is mainly responsible for supplying power to the control circuit at the time of talking and calling.

[0003] In a telephone set of a type capable of connecting a plurality of branches, a branch detection circuit for detecting a drop in line voltage caused by the branch-connected telephone capturing the line (branch state), It has an LED for displaying the branch status. When the branch detection circuit detects the branch state, the control circuit receives the output and causes the LED to blink, or controls the communication circuit to be in a secret state. In this branch state, the current consumption is increased compared to the normal standby time for turning on the LED. Therefore, the lighting of the LED is usually performed by battery power supply, and power supply to the control circuit is usually performed by a constant current source circuit driven by a local power supply.

The amount of current consumed by the control circuit at the time of this branch detection is, for example, about 1 mA. In this case, if the constant current source circuit supplies a current larger than this consumption current, the current taken from the telephone line by the constant current source circuit becomes a large value, and as a result, a problem such as a line length not sufficiently extending occurs. . Therefore, the amount of current supplied by the constant current source circuit is suppressed to a value appropriate for the amount of current consumed by the control circuit.
Should not be larger than necessary. However, when the telephone makes a call in the DTMF mode, D.P.
Since the TMF generator is driven, its current consumption increases to about twice the above. Therefore, at the time of transmission, the supply current of the constant current source circuit must be large.

[0005]

As described above, since the amount of current consumed by the control circuit in the telephone differs depending on the operation mode, the amount of output current of the constant current source circuit for supplying a drive current thereto is also changed. Must-have. One possible means for this is to provide two constant current source circuits, for example, but this is not desirable in terms of cost increase.

Accordingly, an object of the present invention is to make it possible to realize different supply current amounts with one constant current source circuit.

[0007]

According to the present invention, there is provided a communication circuit which is supplied with power from an office power supply and enables a call by a handset or a call to an office line. A control circuit that outputs a low-level control signal; a control circuit in which the level of the control signal is high when the dial control section outputs a selection signal; A power supply circuit provided between the power supply circuit and receiving a power supply from the office power supply, and outputs a constant current to the control circuit, the power supply circuit, a control signal from the dial control unit input, When the level of the control signal is high, a larger constant current is output to the control circuit than when the level is low.

[0008]

When the dial control section outputs a selection signal, the current consumption of the control section becomes large, but the power supply circuit inputs a high-level control signal from the dial control section at this time. Then, the power supply circuit outputs a larger constant current to the control circuit than when a low-level control signal is input from the dial control unit.

[0009]

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

A single telephone 3 to which the present invention is applied and another single telephone 5 are branch-connected to a public telephone line (office line) 1. Yet another telephone may be branch connected to the office line 1. These other telephones may have the same configuration as the telephone 3 of the present invention or may have a different configuration.

In the telephone 3, a diode bridge 7 is connected to the central office line 1, and an output terminal of the diode bridge 7 is connected to a branch detection circuit 9 for detecting a branch state. The internal communication line 18 of the telephone 3 is connected to the output terminal of the diode bridge 7 via a line transistor 17 for capturing an office line and generating a dial pulse (DP). This internal call line 18
Is connected to a communication circuit 47, to which a handset 61 having a transmitter and a receiver is connected. When the handset 61 is set to the off-hook state, the hook switch 15 is closed and the transistor 21 is turned on, whereby the line transistor 17 is turned on to electrically connect the office line 1 and the communication circuit 47 (the office line 1).
Capture). As a result, the communication circuit 47 operates by receiving power supply from the office power supply, and the communication by the handset 61 and the office line 1 are performed.
Enables transmission to

The internal communication line 18 also has a diode 23
Is connected to the input terminal 28 of the power supply circuit 27 according to the present invention. Therefore, when the line transistor 17 is capturing the office line 1, that is, at the time of a call or a call, the power supply circuit 27 operates by receiving the supply of the DC voltage from the office power supply. Further, the input terminal 28 of this power supply circuit is also connected to the output terminal of the diode bridge 7 via the transistor 13. Here, the transistor 13 is placed under the control of the branch detection circuit 9 via the transistor 11, and is turned on when the branch state is detected. Therefore, even when the branch state is detected, the power supply circuit 27 operates by receiving power supply from the station power supply. This power supply circuit 2
7 operates as a constant current source, and its output current amount can be switched in two stages as described later. The switch is
This is performed by a control signal 86 provided from the control circuit 77.

The output current 45 of the power supply circuit 27 is supplied to a control circuit 77 through a diode 75. Further, power can be supplied from the battery 63 to the control circuit 77 through the battery protection circuit 65 and the diode 73. Normally, since the output voltage of the power supply circuit 27 is higher than the output voltage of the battery 63, power is preferentially supplied from the power supply circuit 27 during operation of the power supply circuit 27, and battery power is supplied when the power supply circuit 27 is not operating such as during standby. Power supply from 63 is performed. Power supply circuit 27
During the operation of the battery, even if the output voltage is slightly lower than the output voltage of the battery, the battery protection circuit 65
3 is continued, the power supply circuit 2
7 is continued to prevent the battery 63 from being consumed. When the output voltage of the power supply circuit 27 further decreases, the FET of the battery protection circuit 65 conducts, and the control circuit 77 is energized by the battery 63.

The control circuit 77 includes an LED driver 79, a secret control unit 81, a dial control unit 85, and a DTMF (dial
Tone signal) generator 87 and the like. They are,
This is combined with or incorporated in a system control microcomputer (not shown) in the control circuit 77. LED driver 79 is for display LE
D71, for example, the branch detection circuit 9
Causes the LED 71 to blink while the branch state is detected. The secrecy controller 81 performs a secrecy function while the branch state is detected. That is, by turning on the transistor 19 during branch detection, the secret talk control unit 81 keeps the line transistor 17 in the off state regardless of the hook state, and makes it impossible to observe calls of other telephones. The dial control unit 85 detects ON / OFF of the dial switch 89 and controls generation of a corresponding selection signal. Outgoing selection of whether to perform a DTMF mode or carried out in DP mode performed by calling the mode selection switch 91.

When the dial switch 89 is operated in the off-hook state, the dial control unit 85 generates a corresponding DP by driving the line transistor 17 on / off via the transistors 19 and 21 in the DP mode. In the case of the DTMF mode, the DTMF generator 87 is driven to generate a corresponding DTMF. The generated DTMF is sent to the changeover switch 59 of the communication circuit 47. Further, the dial control unit 85 controls the control signal 86
Is output. This signal 86 is made high when the selection signal is generated, and is made low at other times. The control signal 86 controls the changeover switch 59 so that the DTMF input to the changeover switch 59 is input to the line driver amplifier 55 and transmitted to the office line 1.

As described above, the control signal 86 is also applied to the power supply circuit 27, and is used to switch the output current amount in two stages. The power supply circuit 27 operates in each of the detection of a branch state, a call, and a call to supply a drive current to the control circuit 77. The amount of current to be supplied differs depending on the case. In other words, the current consumption of the control circuit is relatively small, for example, 1 mA during branch detection and talking. On the other hand, when a DTMF occurs during transmission,
In order to drive the DTMF generator 87, the current consumption increases to about twice. In order to extend the line length sufficiently, the amount of output current of the power supply circuit 27 at the time of branch detection or a call is suppressed to a small value corresponding to the small current consumption of the control circuit 77, and only when the DTMF in which the current consumption increases is generated. It is desirable to increase the amount of output current. Therefore, the power supply circuit 27 controls the control signal 8 from the control circuit 77.
Only when 6 goes high when the select signal is generated,
It is configured to increase the amount of the output current 45.

The power supply circuit 27 includes a constant current circuit 27a and a dynamic range improvement circuit 27b. The constant current circuit 27a includes a transistor 41 as a current source circuit that generates an output current 45 as a collector current, and a drive stage circuit for driving and controlling the current source transistor 41. The dynamic range improvement circuit 27b detects the saturation of the current source transistor 41 that may be caused by the audio signal when the voltage from the station power supply decreases,
Is turned on to prevent distortion of the audio signal due to saturation.

The emitter of the current source transistor 41 is connected to the input terminal 28 of the power supply circuit 27 via the resistor 38. A series connection of two diodes 33 and 35 is connected between the input terminal 28 and the base of the current source transistor 41, and a resistor 31 is connected between the base and the ground.
Further, a series connection of a resistor 37 and a transistor 39 is connected in parallel with the resistor 31. A control signal 86 is applied to the base of the transistor 39. Further, a capacitor 29 for absorbing an AC component of the input voltage is provided in parallel with the diodes 33 and 35. The diodes 33 and 35, the resistors 31 and 37, the transistor 39, and the capacitor 29 form a drive stage circuit for driving and controlling the current source transistor 41.

In this drive stage circuit, the current flowing through the diodes 33 and 35 is increased or decreased in two stages depending on whether the control signal 86 is at a high level or a low level. That is, when the control signal 86 changes from a low level to a high level, the transistor 39 switches from off to on, and the current flowing through the diodes 33 and 35 is actively increased. Here, the diodes 33 and 35 are operated in the non-saturation region. Therefore, the current flowing through the diodes 33 and 35 and the collector current of the current source transistor 41, that is, the output current 45 have a current mirror relationship. Therefore, the collector current of the current source transistor 41, that is, the output current 45 is increased or decreased in accordance with the increase or decrease of the current flowing through the diodes 33 and 35. As described above, the control signal 86 becomes high level only when the transmission selection signal is generated in each of the branch detection, the call, and the transmission in which the power supply circuit 27 operates,
At other times, control signal 86 is low. Therefore,
The output current 45 is increased or decreased in two stages so that it increases only at the time of generation of the selection signal, and the current can be supplied in accordance with the increase or decrease of the current consumption of the control circuit 77 described above.

The above is a preferred embodiment of the present invention,
The present invention can be implemented in various other modes.

[0021]

As described above, according to the present invention,
Since the constant current output by the power supply circuit is increased or decreased according to the difference in the level of the control signal from the dial control unit,
The amount of current supplied to the control circuit of the power supply circuit can be changed in response to the increase in the amount of current consumed by the control circuit, and a telephone that can supply different amounts of current with one power supply circuit can be realized. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a telephone according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 branch line 9 branch detection circuit 17 line transistor 27 power supply circuit 27a constant current circuit 27b dynamic range improvement circuit 31, 37 resistor 33, 35 diode 39 transistor 41 current source transistor 63 battery 71 display LED 77 control IC 79 LED driver 81 Secret control unit 85 Dial control unit 87 DTMF generator

Continuation of the front page (72) Inventor Yasuji Sato 3-1-1 Asahigaoka, Hino-shi, Tokyo Inside the Hino Plant, Toshiba Corporation (72) Inventor Mamoru Shinohara 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Within Telegraph and Telephone Co., Ltd. (72) Inventor Kimitoshi Nakamura 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Ken Shimada 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Tetsuya Imahori 2-23-2 Nishigotanda 2-chome, Shinagawa-ku, Tokyo Kanda Communication Industry Co., Ltd. (72) Katsuharu Takagi 2-chome Nishigotanda, Shinagawa-ku, Tokyo No. 23-2 Inside Kanda Communication Industry Co., Ltd. (58) Fields investigated (Int. Cl. ⁶ , DB name) H04M 19/00-19/08 H04M 1/00 H04M 1/26-1/54 H04M 1/72

Claims (3)

(57) [Claims] 1. A communication circuit receiving power from an office power supply and enabling a call by a handset or transmission to an office line, and a dial control unit for outputting either a high level or a low level control signal. A control circuit in which the level of the control signal at the time of outputting the selection signal of the dial control unit is high; and a power supply provided from the office power supply provided between the communication circuit and the office line, and a constant current. A power supply circuit for outputting to the control circuit, wherein the power supply circuit inputs a control signal from the dial control unit, and when the level of the control signal is at a high level, it is lower than at a low level. A telephone set for outputting a large constant current to the control circuit. 2. The power supply circuit has a drive stage circuit including a diode for inputting a current from the station power supply, and a transistor coupled to the diode in a current mirror manner and outputting a constant current to the control circuit. The drive stage circuit receives a control signal from the dial control unit, and when the level of the control signal is high, increases the current flowing through the diode as compared to when the level is low. The telephone according to claim 1, wherein the constant current output from the transistor to the control circuit is increased by a current mirror relationship. 3. The telephone according to claim 1, wherein the dial control unit is capable of outputting either a dial tone signal or a dial pulse signal as the selection signal.