JPS6258599B2 - - Google Patents

Description

Detailed Description of the Invention The present invention transmits a high frequency signal such as a television signal through a coaxial cable while being amplified by a plurality of amplifiers provided along the way, This relates to a CATV transmission circuit that sends power supply current from a power supply device to operate the cable. This invention relates to a CATV transmission circuit that cuts off the supply of power supply current when an accident such as a short circuit occurs in an amplifier.

In conventional CATV transmission circuits of this kind, when a short circuit occurs, the power supply current is cut off, and the cutoff state is connected again after the cause of the short circuit has been removed. There is the hassle of having to deactivate the circuit breaker each time, and even after the cause of the accident has been removed, power supply current is not supplied to the amplifier until the circuit breaker is deactivated, and during that time, high-frequency signals are not transmitted. There was a drawback that the transmission remained interrupted.

Therefore, the present invention is designed to eliminate the above-mentioned drawbacks.In addition, when a short-circuit accident occurs, the power supply current can be cut off.Furthermore, after the cause of the accident is removed, the power supply current can be cut off automatically and immediately. The purpose of this project is to provide a CATV transmission circuit that can restore the supply of cables.

The drawings showing the embodiments of the present application will be described below. Reference numerals 1 to 6 indicate each element constituting a well-known CATV transmission circuit, where 1 is an antenna, 2 is a coaxial cable, 3 is a CATV amplifier, 4 is a power supply inserter, 5 is a brancher, and 6 is a television. The receivers are shown respectively. Next, 7 is a power supply device, and 8 is an input plug thereof. Next, 10 indicates a disconnection device, in which 11 indicates an input terminal, and 12 indicates an output terminal, which are connected to the power supply inserter 4 via a connecting wire 13 (a coaxial cable is used). 15 is the first
The switch element is a mechanical switch such as a relay or a semiconductor switch such as a triax. Reference numeral 16 indicates a power supply current detection section, 17 indicates a search power supply circuit, 18 indicates a search current detection section, and 19 indicates a second switch element, which is the same as the first switch element. Next, 20 indicates a control section, in which 21 indicates a control circuit, and 22 indicates a discrimination circuit.

Next, in FIG. 2 showing a specific circuit of the above-described structure, a power transformer 25 is used as the power supply device 7. The capacity of this power transformer is, for example, 30V3A. 26 indicates a commercial power source to which the plug 8 is connected. In place of this commercial power source 26, a battery, a DC-Ac inverter, or the like may be used that is configured to send out enough voltage to operate the CATV equipment. Next, relay contacts are used as the first switch element 15 and the second switch element 19, respectively. A current transformer 27 is used as the power supply current detection section 16, and its primary side is connected to the input terminal 11 and the output terminal 1 via the switch element 15.
It is connected between 2. A transformer 28 is used as the search power supply circuit 17. This transformer 28 is designed to supply a search current that does not exceed the permissible current value of the transmission line including the coaxial cable 2 and the amplifier 3, and its output voltage is, for example, about 5V. is used. A resistor 29 is used as the search current detection section 18. This resistor 29 also acts as a current limiting resistor, and even if the total load for the power supply current on the transmission line including the coaxial cable 2 and amplifier 3 is close to 0Ω in the event of a short circuit accident as described later, the above-mentioned resistance will be applied to the transmission line. It is designed to prevent a current exceeding the permissible current from flowing. For example, the resistance value is
A 10Ω one is used. Next, in the control circuit 21, D ₁ is a rectifier diode, Tr ₁ is a transistor, D ₂ is a diode, 30 is a time constant circuit, smoothing capacitor C ₁ , bias resistors R ₁ , R ₂
are connected and configured as shown in the figure. _R3
indicates the bias resistance. Reference numeral 31 denotes a relay coil which, when excited, opens the first switch element 15 and closes the second switch element 19. Next, the discrimination circuit 22 includes transistors Tr ₂ to _{Tr 4} , a rectifying diode D ₃ , a smoothing capacitor C ₂ , bias resistors R ₄ , R ₅ , current limiting resistors R ₆ to _{R 9} , a feedback resistor R ₁₀ , and a bias resistor A Schmidt circuit composed of resistors _R11 and the like is used. This discrimination circuit 22 does not output anything when the input signal from the search current detection section 18 is less than a predetermined constant value (voltage value generated in the resistor 29 when the search current is at a limit value described later). It is designed to send out an output signal when the input signal exceeds a certain value, and other circuits that function in a similar manner can also be used in place of the Schmitt circuit. Reference numeral 32 denotes a power supply circuit for circuit operation, which is a circuit for supplying power (DC power) for operating the control circuit 21 and the discrimination circuit 22.

Next, the operation of the above configuration will be explained.

(1) Normal state In this case, the commercial power supply 26 is connected to the power transformer 2.
5, low voltage AC (e.g. 30V)
The power supply current that has become
1, first switch element 15, current transformer 2
The current is sent to the coaxial cable 2 via the output terminal 12 on the primary side of the power source 7, the connecting line 13, and the power supply inserter 4, and the current is sent from the coaxial cable 2 to each amplifier 3, 3. As a result, each amplifier 3 performs an amplification operation.

When amplifier 3 performs amplification operation, antenna 1
A high frequency signal such as a television signal received by the receiver is transmitted through the coaxial cable 2 while being amplified by the amplifiers 3, 3. Also, a part of the high frequency signal is sent to the splitter 5.
The signal is sent to the television receiver 6 of each home (CATV subscriber's home) via.

In this state, the value of the power supply current is detected by the current transformer 27, further rectified by the rectifying diode _D1 , and applied to the base of the transistor _Tr1 via the time constant circuit 30. However, in this normal state, the power supply current is below a predetermined value, that is, the permissible current value for the transmission line including the coaxial cable 2 and the amplifier 3, so the transistor _Tr1 does not conduct. This keeps the first switch element 15 closed and the second switch element 19 open.

(2) In the event of an accident such as a short circuit or equipment failure In this case, a large amount of power supply current flows through the current transformer 27, and a larger current appears on the secondary side of the transformer 27 than in the normal state. When this current is rectified by the rectifier diode D ₁ and then applied to the time constant circuit 30, the smoothing capacitor C ₁
is charged instantaneously, transistor Tr ₁ becomes conductive, and current flows through relay coil 31 .
The first switch element 15 then becomes open and the second switch element 19 becomes closed. This blocks the flow of the large current (short circuit current). Further, the switch element 15,
19, at the same time, the search power supply circuit 17
A search current is sent out from the output terminal 12 via the second switch element 19, which search current is sent via the connecting line 13, the power supply inserter 4 to the coaxial cable 2. At this time, the total load on the power supply current of the transmission line including the coaxial cable 2 and the amplifier 3 is reduced due to the short circuit accident, so the current value of the search current is a value corresponding to the permissible passing current value, that is, the limit value. will be a larger value. (The above-mentioned limit value means that when the value of the power supply current sent from the power supply device 7 to the coaxial cable 2 is the above-mentioned allowable passing current value, the search current is caused to flow from the above-mentioned search power supply circuit toward the above-mentioned total load. (This limit value is naturally selected to be extremely smaller than the above-mentioned allowable passing current value.) The search current with a large value is determined by the resistance of the search current detection unit 18. 2
9, and a high voltage is generated across the resistor. The voltage is applied to the base of the transistor Tr ₂ in the discrimination circuit 22 via the diode D ₃ and the bias resistor R ₄ . Then transistor Tr ₂ turns ON and transistor Tr ₃ turns OFF.
Therefore, transistor Tr ₄ is turned on, and the control circuit 2 is connected from the emitter of transistor Tr ₄ .
1 is given an output signal. This signal is applied to the time constant circuit 30 via the diode _D2 in the control circuit 21, and further applied to the base of the transistor _Tr1 . This causes transistor Tr ₁
remains in the ON state, and the switch elements 15 and 19 controlled by the relay coil 31 each maintain the above-mentioned state. In the above case, even if the signal from the current transformer 27 or the discrimination circuit 22 to the control circuit 21 disappears for a short time (for example, 3 to 5 seconds), the transistor Tr ₁ is kept in the ON state due to the presence of the time constant circuit 30. drooping Therefore, even if the switching characteristics of the first and second switch elements 15, 19 are such that the second switch element 19 closes after the first switch element 15 opens, their oscillating motion is prevented. Ru.

To give an example of the various values at the time of the above short circuit, the total load for the power supply current of the transmission line including the coaxial cable 2 and the amplifier 3 in the normal state was 10Ω, but in the case of a short circuit, for example,
Assuming that the current value is 6.7Ω, the current value of the search current is 0.3A, and the voltage generated across the resistor 29 of the search current detection section 18 is 3V.

(3) After the cause of the accident has been removed In this case, the total load on the power supply current of the transmission line including the coaxial cable 2 and the amplifier 3 will be the same value as in the normal case, so the current value of the search current becomes below the limit value, and the voltage generated across the resistor 29 of the search current detection section 18 also decreases. As a result, each transistor of the discrimination circuit 22 is inverted from the above-mentioned state, and the control circuit 21
There will be no output to. Then, in the time constant circuit 30, a predetermined short time (for example, 3~
After 5 seconds), the transistor Tr ₁ becomes OFF, and under the control of the relay coil 31, the first switch element 15 becomes closed, while the second switch element 19 becomes open. As a result, the same power supply current as in the normal state is supplied.

As described above, in the present invention, a high frequency signal can be transmitted via the coaxial cable 2 while being amplified by a plurality of amplifiers 3 interposed in the coaxial cable 2, and the high frequency signal can be transmitted via the coaxial cable 2 while being amplified by the It has the advantage of being able to supply power supply current to multiple amplifiers.

Moreover, if a short circuit occurs in the amplifier 3 or the coaxial cable 2 during the supply of the power supply current, the cutoff device 10 interposed between the power supply device 7 and the coaxial cable 2 is activated, and the power supply It is possible to cut off the supply of current, and there is a safety feature that can prevent the short-circuit accident from spreading to a major accident such as damage to the coaxial cable 2 or amplifier 3 or a fire.

Furthermore, even if the circuit is cut off as described above, it is convenient because the supply of power supply current can be automatically restored when the cause of the accident is removed.

Moreover, when the supply is restored in this way, a search current is continuously passed through the coaxial cable 2 from the time the accident occurs until the cause of the accident is removed to continue monitoring whether or not the cause of the accident has been removed. Therefore, when the cause of the accident is removed, normal supply of power current can be immediately restored.

Furthermore, even if the search current is continuously passed as described above, the current is a weak current, so the connector used to connect the coaxial cable and the amplifier or the amplifier circuit may be subject to large currents. Even if the material is vulnerable to damage, it is safe enough to prevent damage.

[Brief explanation of the drawing]

The drawings show an embodiment of the present application, and FIG.
A block diagram of a CATV facility, FIG. 2 is a diagram showing an example of a circuit of a cutoff device. 2... Coaxial cable, 3... Amplifier, 7... Power supply device, 10... Cutoff device, 15... First switch element, 16... Power supply current detection unit, 17...
... Search power supply circuit, 18... Search current detection section, 1
9...Second switch element, 20...Control unit.

Claims (1)

[Claims] 1 A plurality of CATV amplifiers each designed to amplify the high frequency signal are interposed in tandem in the coaxial cable designed to transmit high frequency signals, and the above coaxial cable is further connected to the plural CATV amplifiers via the coaxial cable. In a CATV transmission circuit that connects a power supply device capable of supplying power current to a CATV amplifier, a power supply current interrupting device is interposed between the coaxial cable and the power supply device, and The cutoff device includes a switch element and a power supply current detector interposed in series between the coaxial cable and the power supply device, and the cutoff device has a current value higher than the permissible current value of the coaxial cable and the amplifier. A search power supply circuit is provided which is connected to the coaxial cable via a search current detection section so as to supply a search current of a weak value to the coaxial cable, and the cutoff device further includes a search power supply circuit connected to the coaxial cable via a search current detection section. The current value and the detected current value of the search current detection section are input, and if the detected current value of the power supply current is larger than the above allowable current value, the switch element is opened, while the detected current value of the search current is A CATV transmission circuit characterized in that it also includes a control unit configured to close the switch element when the current falls below a value corresponding to the allowable current value.