JP3167379B2 - Local line connection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal device such as a telephone device which connects to a telephone network and opens and closes a line, and more particularly to a line closing circuit for preventing electric shocks during incoming calls and standbys. It is provided.

[0002]

2. Description of the Related Art As a conventional telephone device, a circuit provided with an electric shock prevention circuit as shown in FIG. 2 is known as a circuit for preventing electric shock during an incoming call.

This circuit includes a diode bridge 1 for polarity matching connected to the office lines L1 and L2, a relay 61 for separating the ground of the telephone network from the ground of the telephone device, and a diode bridge.
An incoming call detection circuit 4 connected to the bridge 1;
And a control unit 5 for controlling the local line closing circuit 20 and the relay driving circuit 6 based on the output of the incoming call detection circuit 4.

When a call signal arrives from the telephone network, the incoming call detection circuit 4 detects that there is an incoming call, and the control unit 5
Output that information to At this time, the control unit 5 does not operate the relay drive circuit 6 and keeps the ground of the network and the ground of the telephone device separated.

Next, when shifting to the call state, the control unit 5 activates the relay drive circuit 6 to close the contact of the relay 61 to make the ground of the network and the ground of the telephone device common.

As described above, in a conventional telephone device which is designed to prevent an electric shock during an incoming call, when a user touches a metal part such as a charging terminal connected to the ground in the telephone device during the incoming call, the contact goes through the ground. To prevent hazard voltages from being applied to the human body,
Relay 61 on the negative side of diode bridge 1 for polarity matching
To separate the ground from the telephone network.

[0007]

However, in such a conventional telephone device, an expensive relay is required in addition to the local line closing circuit due to ground separation, and it is difficult to construct the telephone device at low cost. there were.

The present invention has been conceived in order to solve such problems of the conventional telephone apparatus, and can be manufactured at a low cost, and furthermore, has an open line circuit. In some cases, it is an object of the present invention to provide an excellent local line closing circuit that can separate the telephone network from the ground.

[0009]

Means for Solving the Problems A diode for polarity matching
A collector is connected between the negative side of the bridge and the ground of the terminal.
Comprising a transistor whose emitter path is connected, performs閉結or open DC circuit by switching the transistor via a photo-coupler, the straight
By separating the ground of the ground and the terminal device of the telephone network by opening the flow circuit, which is constituted so as to prevent electric shock during and waiting call.

[0010]

According to the present invention, by applying a forward current to the light emitting diode of the photocoupler by the control unit, the transistor can be turned on and the DC circuit can be closed, and no forward current flows to the light emitting diode of the photocoupler. Sometimes, the DC circuit can be opened by turning off the transistor.

Further, according to the present invention, the collector of the transistor is connected to the negative side of the polarity matching diode bridge.
Since the emitter electric circuit is formed, the ground of the telephone network and the ground of the terminal device can be separated when the transistor is in the cut-off state, and the electric shock during the incoming call and the standby can be prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a polarity matching diode bridge 1 connected to central office lines L1 and L2, an incoming call detection circuit 4 connected to the diode bridge 1, and a communication circuit 3 are shown. The system includes a line closing circuit 2 for opening and closing a line, and a control unit 5 for controlling the line closing circuit 2 based on the output of the incoming call detection circuit 4.

The local line closing circuit 2 has a collector circuit between the negative side of the diode bridge 1 for polarity matching and the communication circuit 3.
A transistor 21 having an emitter circuit connected thereto and a photo
The photocoupler 22 includes a transistor 23 and a light emitting diode 24.The phototransistor 23 of the photocoupler 22 is connected to the base electrode of the transistor 21 via a current limiting resistor 25. Are connected to the control unit 5.

[0014] During an incoming call and waiting, a photo coupler is used.
When the phototransistor 23 is turned off and the transistor 21 is turned off at the same time without turning on the light-emitting diode 24 of the transistor 22, the collector-emitter electric circuit of the transistor 21 is in a high resistance state. Can be separated.

When the incoming call is detected by the incoming call detection circuit 4 and the operation is shifted to the talking state and the DC circuit is closed, a forward current is passed from the control unit 5 to the light emitting diode 24 of the photocoupler 22,
The photo transistor 23 is turned on, and the transistor 21 is turned on.
Of the collector-emitter circuit of the transistor. Transistor
The collector-emitter path when 21 conducts has a low resistance and the forward voltage is a few hundred mV so that the DC circuit can be closed.

[0016]

As is apparent from the above description of the embodiment, the grounding of the telephone network and the grounding of the telephone equipment can be separated by the local line closing circuit 2 during the incoming call and the waiting, so that the electric shock is prevented. Can be prevented.

Further, since the transistor 21 is connected to the negative electrode side of the diode bridge 1 for polarity matching and the line is closed by utilizing the switching characteristic, an expensive relay is not required and the telephone can be constructed inexpensively. There is an effect that the ground of the network and the ground of the telephone device can be separated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a telephone device provided with a local line closing circuit according to the present invention, and a circuit diagram partially shown by blocks;

FIG. 2 is a block diagram showing an example of a telephone device provided with a conventional electric shock prevention circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diode bridge for polarity matching 2 Local line closing circuit 3 Talking circuit 4 Incoming detection circuit 5 Control part 22 Photocoupler

──────────────────────────────────────────────────続 き Continuing from the front page (72) Katsuhiko Tanto 3-1, Tsunashimahigashi, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Within Matsushita Communication Industrial Co., Ltd. Matsushita Communication Industrial Co., Ltd. (3-1) Matsushita Communication Industrial Co., Ltd. (72) Inventor Emori Omoto 4-3-1 Tsunashima Higashi, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Matsushita Communication Industrial Co., Ltd. 20791 (JP, A) JP-A-63-285061 (JP, A) JP-A-61-15864 (JP, U) JP-B-57-37267 (JP, B2) JP-B 3-42756 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04M 1/00

Claims (1)

(57) [Claims] A transistor having a collector-emitter circuit connected between a negative electrode of a polarity matching diode bridge and a ground of a terminal device, and closing or opening a DC circuit by switching the transistor. And by opening the DC circuit, the grounding of the telephone network and the grounding of the terminal device are separated , and the
A local line closing circuit characterized by preventing electricity .