JPH04260262A - Telephone set power supply circuit - Google Patents

Abstract

PURPOSE:To realize a different load drive current through the use of one constant current source circuit provided to a telephone set, driven by a station power supply and supplying a load drive current to a prescribed load circuit in the telephone set. CONSTITUTION:The power supply circuit is provided with a current source circuit 41 generating a load drive current 45 and drive stage circuits 33,35,31,37,39 coupled with the current source circuit 41 in a relation of current mirror and each drive stage circuit includes an activating circuit 39 generating a current of the drive stage circuit in response to the state of a load circuit 77.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a constant current source circuit built into a telephone set and driven by a central office power supply for supplying drive power to a control circuit within the telephone set, and in particular to a constant current source circuit built into a telephone set and driven by a central office power supply. It is suitable as a power supply circuit for a telephone that can be connected to a branch.

0002

2. Description of the Related Art Generally, a telephone has a built-in control circuit, usually an IC, including a microcomputer for system control, a transfer circuit, a DTMF (dial tone MF signal) generator, and the like. A battery is provided as a power source for driving such a control circuit, and its main purpose is to back up the memory in the control circuit and energize the CPU during standby. Furthermore, a constant current source circuit driven by the local power source obtained through the telephone line is also provided, and this is primarily responsible for supplying power to the control circuit during calls and outgoing calls.

[0003] A type of telephone that allows multiple branch connections is equipped with a branch detection circuit for detecting a drop in line voltage that occurs when a branch-connected telephone seizes the line (branch state), and It has an LED to indicate the branch status. When the branch detection circuit detects the branch state, the control circuit receives its output and causes the LED to blink or controls the communication circuit to be in the confidential state. In this branch state, current consumption increases compared to a normal standby state in order to light up the LED. Therefore, the LEDs are usually lit using battery power, and the control circuit is powered from a constant current source circuit driven by a local power source.

The amount of current consumed by the control circuit during 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 in from the telephone line by the constant current source circuit will be a large value, resulting in problems such as the line length not being extended sufficiently. . Therefore, the amount of current supplied by the constant current source circuit is suppressed to a value commensurate with the amount of current consumed by the control circuit.
It should not be made larger than necessary. However, when this phone makes a call in DTMF mode, the control circuit
Since the TMF generator is driven, its current consumption increases to about twice the above amount. Therefore, during transmission, the current supplied by the constant current source circuit must be large.

[0005]

[Problem to be Solved by the Invention] As described above, since the amount of current consumed by the control circuit in the telephone varies depending on its operating mode, the amount of output current of the constant current source circuit that supplies the drive current to the control circuit varies depending on its operating mode. Must-have. One possible means for this purpose is to provide, for example, two constant current source circuits, but this is undesirable in terms of increased costs.

[0006] Accordingly, an object of the present invention is to enable different amounts of supplied current to be realized with one constant current source circuit.

[0007]

[Means for Solving the Problems] The power supply circuit of the present invention is a constant current power supply circuit provided in a telephone set and driven by a local power supply for supplying a load driving current to a predetermined load circuit within the telephone set. The drive stage circuit has a current source circuit that generates a load drive current, and a drive stage circuit coupled to the current source circuit in a current mirror relationship, and this drive stage circuit changes depending on the state of the load circuit. The circuit includes an active circuit that actively generates a current, and a passive circuit.

[0008]

[Operation] The active circuit of the drive stage circuit controls the current of the drive stage circuit according to the state of the load circuit. Corresponding to the current of this drive stage circuit, the load drive current generated in the current source circuit is controlled by a current mirror relationship. In other words, it is possible to supply current commensurate with the current consumption of the load circuit.

[0009]

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

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

In the telephone set 3, a diode bridge 7 is connected to the office line 1, and a branch detection circuit 9 for detecting a branch state is connected to the output terminal of the diode bridge 7. Also connected to the output terminal of the diode bridge 7 is an internal communication line 18 of the telephone 3 via a line transistor 17 for capturing a central office line and generating a dial pulse (DP). This internal telephone line 18
A communication circuit 47 is connected to the communication circuit 47, and a handset 61 including a transmitter and a receiver is connected to the communication circuit 47. When the handset 61 is placed off-hook, the hook switch 15 closes and turns on the transistor 21, which turns on the line transistor 17 and electrically connects the central office line 1 and the communication circuit 47 (main line 1
capture). As a result, the telephone call circuit 47 receives power from the office power supply and operates to perform telephone calls using the handset 61 and the office line 1.
It is possible to send messages to

The internal communication line 18 also includes a diode 23.
An input terminal 28 of a power supply circuit 27 according to the present invention is connected through the terminal. Therefore, when the line transistor 17 is capturing the office line 1, that is, when making a call or making a call, the power supply circuit 27 operates by receiving DC voltage from the office power supply. Furthermore, 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 a branch state is detected. Therefore, even when a branch state is detected, the power supply circuit 27 receives power from the local power supply and operates. This power supply circuit 2
7 operates as a constant current source, and its output current amount can be switched in two stages as will be explained later. The switch is
This is done by a control signal 86 given from the control circuit 77.

Output current 45 of power supply circuit 27 is supplied to control circuit 77 through diode 75. Furthermore, power can also be supplied from the battery 63 to the control circuit 77 through the battery protection circuit 65 and the diode 73. Normally, the output voltage of the power supply circuit 27 is higher than the output voltage of the battery 63, so when the power supply circuit 27 is operating, power is preferentially supplied from the power supply circuit 27, and when the power supply circuit 27 is not operating, such as during standby, the battery 63 is supplied with power. Power is supplied from 63. Power supply circuit 27
During operation, even if the output voltage is slightly lower than the output voltage of the battery, the battery protection circuit 65 protects the battery 6.
By continuing the state in which 3 is disconnected, the power supply circuit 2
7 continues to supply power, thereby preventing the battery 63 from being exhausted. When the output voltage of the power supply circuit 27 further decreases, the FET of the battery protection circuit 65 becomes conductive, and the control circuit 77 is energized by the battery 63.

The control circuit 77 includes an LED driver 79, a secret control section 81, a dial control section 85, a DTMF (dial tone MF signal) generator 87, and the like. These are combined with or incorporated into a system control microcomputer (not shown) in the control circuit 77. The LED driver 79 drives the display LED 71, and for example, while the branch state is detected by the branch detection circuit 9, the LED driver 79 drives the display LED 71.
flash. The confidential message control unit 81 performs a confidential message function while the branch state is detected. That is, by turning on the transistor 19 during branch detection, the private conversation control section 81 keeps the line transistor 17 off regardless of the hook state, thereby making it impossible to overhear conversations on other telephones. The dial control unit 85 detects whether the dial switch 89 is turned on or off and controls the generation of a corresponding selection signal. A call mode selection switch 91 can be used to select whether to make a call in DP mode or DTMF mode.

When the dial switch 89 is operated in the off-hook state, the dial control unit 85 generates a corresponding DP by turning on/off the line transistor 17 via the transistors 19 and 21 in the DP mode. In addition, in 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 section 85 receives a control signal 86
Output. This signal 86 is set to a high level when a selection signal is generated, and is set to a low level at other times. This control signal 86 controls the changeover switch 59 so that the DTMF input to the changeover switch 59 is inputted to the line driver amplifier 55 and sent 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 amount of output current from the power supply circuit 27 into two stages. The power supply circuit 27 operates to supply drive current to the control circuit 77 when detecting a branch state, making a call, and making a call, but the amount of current to be supplied differs depending on the case. That is, during branch detection and communication, the current consumption of the control circuit is a relatively small value, for example, 1 mA. On the other hand, when 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 during branch detection and calls is kept low by corresponding to the low current consumption of the control circuit 77, and only when DTMF occurs, which increases current consumption. It is desirable to increase the amount of output current. For this purpose, the power supply circuit 27 receives the control signal 8 from the control circuit 77.
Only when 6 becomes high level when the selection signal is generated,
It is configured to increase the amount of its 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 suppresses the saturation of the current source transistor 41 that may be caused by the audio signal when the voltage from the local power supply decreases by reducing the saturation of the current source transistor 41 by reducing the saturation of the current source transistor 41.
This is to prevent audio signal distortion due to saturation.

The emitter of current source transistor 41 is connected to input terminal 28 of power supply circuit 27 via resistor 38 . A series connection of two diodes 33 and 35 is connected between this input terminal 28 and the base of the current source transistor 41, and a resistor 31 is connected between the base and ground. Furthermore, a series connection body of a resistor 37 and a transistor 39 is connected in parallel with this resistor 31. A control signal 86 is applied to the base of this transistor 39. Further, a capacitor 29 is provided in parallel with the diodes 33 and 35 to absorb the alternating current component of the input voltage. These diodes 33 and 35, resistors 31 and 37, transistor 39, and capacitor 29 constitute a drive stage circuit for driving and controlling 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, actively increasing the current flowing through the diodes 33 and 35. Here, the diodes 33 and 35 are operated in the non-saturation region, so that the current flowing through the diodes 33 and 35 and the collector current of the current source transistor 41, that is, the output current 4
There is a current mirror relationship with 5. 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 in the current flowing through the diodes 33, 35. As described above, the control signal 86 is at a high level only when the selection signal for the outgoing call is generated among the branch detection, call, and outgoing operations in which the power supply circuit 27 operates, and the control signal 86 is at the low level at other times. Therefore, the output current 45 is increased or decreased in two steps such that it increases only when the selection signal is generated compared to other times, and it is possible to supply current in response to the increase or decrease in the amount of current consumed by 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 ways.

[0021]

[Effects of the Invention] As explained above, according to the present invention,
The configuration is such that the current in the drive stage circuit of the constant current source circuit is actively increased in response to an increase in the amount of current consumed by the load circuit, thereby increasing the amount of current supplied to the load circuit through a current mirror relationship. , different amounts of supplied current can be realized with one power supply circuit.

[Brief explanation of the drawing]

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

[Explanation of symbols]

1 Office line 9 Branch detection circuit 17 Line transistor 27 Power supply circuit 27a Constant current circuit 27b Dynamic range improvement circuit 31, 37
Resistors 33, 35 Diode 39 Transistor 41 Current source transistor 63 Battery 71 Display LED 77 Control IC 79 LED driver 81 Secret control section 85 Dial control section 87 DTMF generator

Claims (3)

[Claims] 1. A constant current power supply circuit provided in a telephone and driven by a local power supply for supplying a load drive current to a predetermined load circuit in the telephone, a current source circuit that generates the load drive current. and a drive stage circuit coupled to the current source circuit in a current mirror relationship, the drive stage circuit being an active circuit that actively generates a current for the drive stage circuit in accordance with the state of the load circuit. A telephone power supply circuit comprising a circuit and a passive circuit, wherein the active circuit controls the load drive current in accordance with the current of the drive stage circuit, thereby supplying current commensurate with the current consumption of the load circuit. 2. The power supply circuit according to claim 1, wherein the load circuit is a control circuit for controlling the operation of the telephone set, and the load circuit is a control circuit for controlling the operation of the telephone set, and the load circuit is a control circuit for controlling the operation of the telephone set, and a dial tone MF is used as a selection signal when making a call.
a circuit for generating a signal, the active circuit being operative in conjunction with the control circuit to increase the current in the drive stage circuit upon generation of the dial tone MF signal, thereby increasing the current in the driver stage circuit upon generation of the dial tone MF signal; A telephone power supply circuit that can increase the load drive current in response to an increase in current consumption of the control circuit when a power supply circuit occurs. 3. The power supply circuit according to claim 1, wherein the telephone has branch detection means for detecting a branch state, and when the branch detection means detects the branch state; A telephone power supply circuit electrically coupled to the office line and driven by the office power supply when the telephone acquires the office line.