JPS59193633A - Current control circuit in wire transmission line - Google Patents

Abstract

PURPOSE:To prevent crosstalk from being generated in other transmission lines by making a coupling transistor (TR) nonconductive when the TR is electrically conducted by a switching control circuit and a large current flows to a cable. CONSTITUTION:When a photocoupler 2 and a TR3 are turned on, terminals C, D are electrically conducted, a large current flows to the cable by a voltage induced transiently, a voltage is produced across a resistor R4 and a TR5 is turned on. Thus, a current (i) flowing from the coupler 2 is by-passed and flows directly to the terminal D, and no current flows to the base of the TR3. Thus, the TR3 is turned off, the terminals C, D are made nonconductive and no large current flows. Since no current flows to the resistor R4 owing to the turning-off of the TR3, a base-emitter voltage of the TR5 becomes zero again, the TR5 is turned off and the TR3 is turned on conversely. A large current more than a prescribed value does not flow by repeating such operations.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Technical Field of the Invention The present invention relates to a wired transmission line, and particularly relates to a current control circuit for a wired transmission line that takes measures against transient large currents generated in conjunction with switching operations. be.

(B) Technical Background As host computers become larger, various peripheral devices are connected to them in order to maximize their functions. and,
These peripheral devices are used even in locations far away from the post-computer, so information is transmitted over long distances, and interfaces for this purpose are becoming increasingly important.

(C) Prior Art and Problems A current control circuit in a conventional wired transmission line has a circuit configuration as shown in FIG. In the figure, 1 is an open collector type ITI gate (hereinafter referred to as G), and 2 is a switching control means.

3 is a transistor, and 4 is a current detection circuit (hereinafter referred to as DET). Also, R, , R2, and J are each resistance elements, and β is the length! represents the cable. In the figure, a voltage V including resistors Rz and R3 is applied to terminals A and B.
CC and VEE power supplies are connected. Below terminal C-D
will be explained assuming that terminal A is the transmitting side and terminals A and B are the receiving side. When the input of G' (cable start signal) becomes high (1), the gate opens and a current flows from the power source of voltage Vc C7 to the output terminal of G, switching control means (photocoupler) 2
becomes conductive (ON), and I-run transistor 3 also becomes conductive. Therefore, since conduction occurs between the terminals CD, a current flows through DET4. Also, when the G input is LOW (0), the FO1-
coupler 2. Since the transistor 3 is non-conductive (OFF), there is no conduction between the terminals CD. Therefore DET4
If there is no current, it will not flow. In this way, a signal is transmitted from terminal A-B to CD depending on whether current flows through DET4 or not.

In such a circuit, transistor 3 is OFF→○
Considering the case where the voltage is N, when the transistor 3 is OFF, a large voltage of Vcc-VEfE is applied between the collector and emitter of the transistor 3 (between the terminals CD). Furthermore, when the transistor 3 is ON, the voltage between the collector and emitter of the transistor 3 is approximately IV (the voltage between the collector and emitter of the transistor of the photocoupler 2 and l.
voltage between the base and emitter of transistor 3).

Therefore, when transistor 3 changes to 0FF-ON, the amount of voltage change becomes Vcc-VEE-1 (V),
This is generally a large amount of voltage change. Therefore, if the length of the cable β is long, a transient phenomenon will occur 1, for example, at terminal C.
The current flowing through changes as shown in FIG. Since the cable is generally bundled with several lines, it induces a large loss loaf with respect to other transmission lines, causing malfunction.

(D) Object of the Invention In view of the above-mentioned conventional drawbacks, an object of the present invention is to provide a current control circuit in a wired transmission line that can prevent transient phenomena from occurring.

(E) Structure of the invention and the object of the invention is to provide a transistor for switching a cable connecting a transmitting side and a receiving side, and a switching control means for keeping the transistor in a conductive state while a cable activation signal is input. The wired transmission line is characterized by being provided with a current limiting circuit that makes the transistor non-conductive if a current of a predetermined value or more flows through the cable when the transistor is made conductive by the switching control means. This is achieved by providing a current control circuit in the wired transmission line.

(F) Examples of the invention EMBODIMENT OF THE INVENTION Below, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a circuit diagram showing one embodiment of the present invention.

In this figure, the same numbers as in FIG. 1 represent the same parts. In this embodiment, resistance elements R, , I-transistors 5 are added as current limiting means 7. The operation of this circuit will be explained with reference to the figure. In this embodiment, a photocoupler 2 is used as the switching control means 2. First, the photocoupler 2 and the transistor 3 are turned on, which makes the terminal CD conductive. When a large current flows due to the transiently induced voltage Vcc-VEE-1, a voltage is generated across R, and the transistor 5 is turned on. becomes. Therefore, the current i flowing out from the photocoupler 2 flows to the transistor 5 and does not flow to the transistor 3. That is, the current i is bypassed by the transistor 5 and flows directly to the terminal, and no current flows to the base side of the transistor 3. Therefore, transistor 3 is OFF
Therefore, there is no conduction between terminals CD, and no large current flows. In this case, since the voltage between the base and emitter of the transistor 5 can be adjusted by the resistance value of R4, the transistor 5 can be turned on when a current of an arbitrary predetermined value or more flows.

Then, transistor 3 is turned off, so that Rq
Since no current flows through , the voltage between the base and emitter of transistor 5 becomes 0 again, turning transistor 5 off, and conversely transistor 3 turns on.

By repeating the above operations, it is possible to prevent a large current exceeding a predetermined value from flowing.

Another embodiment is shown in FIG. Similar to FIG. 3, the same parts as in FIG. 2 are represented by the same numbers. In this embodiment, Rq and a photocoupler 6 are used as current limiting means to limit the current. The operation of this circuit will be explained below with reference to the figure.

Photocoupler 2 and transistor 3 are turned on, and a large current flows between terminals CD. At this time, the current flowing through RLA turns on the photocoupler 6 and the cable activation signal is bypassed and grounded through the photocoupler 6. Therefore, the cable activation signal from the current Vcc7 does not flow to the photocoupler 2, and the photocoupler 2 is turned OFF, and the transistor 3 is turned OFF, so that there is no conduction between the terminals CD, and a large current can be prevented from flowing. Here, if the Rq2 photocoupler 6 is appropriately selected, when a current of an arbitrary predetermined value or more flows through Rq, the terminal CD can be turned off. When transistor 3 is turned off, no current flows through R<=, so photocoupler 6 is turned off, and transistor 3
is turned on, and the terminal CD becomes conductive. By repeating the above steps, it is possible to prevent a large current exceeding a predetermined value from flowing.

(G) Effect of invention As described above in detail, there are two aspects of the present invention.

If an attempt is made to flow a large current exceeding a predetermined value, the cable driving transistor is turned off, and no large current flows through the cable, so crosstalk with other transmission paths does not occur.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a current control circuit in a conventional wired transmission line; Fig. 2 is a diagram for explaining transiently flowing current;
3 and 4 are circuit diagrams of the current control circuit according to the present invention. In the drawing, 1 is the TTL game 1- of the oven collector.
．． 2.6 is a photocoupler, 3.5 is a transistor 14 is a current detection circuit, and 7 is a current detection circuit. Rt, R2, R2, and Rq are resistance elements.

Claims (1)

[Claims] 1) A transistor that switches a cable connecting a transmitting side and a receiving side, and switching control means that maintains the transistor in a conductive state while a cable activation signal is input. In the wired transmission line 〃l;A, (), when the transistor is made conductive by the switching control means, current limiting means is provided which makes the transistor non-conductive if a current of a predetermined value or more flows through the cable. A current control circuit in a wired transmission line, characterized by the following. 2) The current control circuit in a wired transmission line according to claim 1, wherein the current limiting means bypasses the base current of the transistor to make the transistor non-conductive. 3) Current control in a wired transmission line according to claim 1, wherein the current limiting means bypasses a cable activation signal input to the switching control means to make the transistor non-conductive. circuit.