JP2948618B2 - Current supply method - Google Patents

Description

The present invention relates to a current supply system of a multiplex transmission system in which transmission of an AC signal such as a video signal and supply of a DC current are performed by a pair of transmission lines. For example, it is used in the field of two-wire television intercoms.

[Prior Art] FIG. 9 shows a schematic configuration of a conventional intercom system with a television. This system is configured by combining a master unit J having a monitor TV 1 installed in a dwelling unit and a slave unit G having a TV camera 21 installed at the entrance, both of which are dedicated to coaxial cable or the like. Are connected by a transmission line l. A DC current is supplied to the slave unit G from the master unit J as an operation power source, and a video signal is transmitted from the slave unit G to the master unit J. The audio signal is transmitted bidirectionally.

FIG. 10 shows a frequency division state of a signal transmitted through the transmission line 1 in the present system. As shown in the figure, FM-modulated wave of voice signal sent from the slave unit G to the main unit J is transmitted in the first carrier frequency f _1, the master unit J slave unit G
FM modulated wave of the audio signal sent to the second carrier frequency f ₂
Is transmitted. The carrier frequencies f ₁ and f ₂ of the audio signal are set to be higher than the video signal frequency band of the television camera transmitted in the baseband, thereby preventing interference. Further, a DC current is superimposed as an operation power supply of the slave unit G, and these are multiplex-transmitted through a dedicated transmission line l.

The more specific configuration of the intercom system is described in Section 11.
This will be described with reference to the drawings. Base unit J includes a power supply superimposing circuit 8 for supplying power to handset G, and a call detection circuit for detecting a call signal transmitted in response to operation of call switch 24 of handset G.
19. A ringing tone generation circuit 20 for generating a ringing tone from the calling speaker 3 when a calling signal is detected, a voice modulation circuit 17 for FM-modulating a voice signal, and demodulating an FM-modulated signal sent from the slave unit G to generate a voice signal. Handset 2 with voice demodulation circuit 13 to be taken out, microphone and speaker for call, Handset 2
The audio amplifiers 14 and 15 and the side tone prevention circuit 16 which constitute the communication circuit including the video signal output circuit 11 which extracts the video signal transmitted from the slave unit G and outputs the video signal to the monitor television 1 and the audio modulation circuit 17 Input through the band-pass filter 18 and the FM-modulated signal transmitted from the slave G is output to the audio demodulation circuit 13 through the band-pass filter 12 and transmitted from the slave G. The video signal is output to the video signal output circuit 11 via the video filter 10,
Further, a balance input / output circuit 9 for transmitting the supply voltage of the power supply superimposing circuit 8 to the slave unit G is provided. The voice modulation circuit 17 is configured to FM-modulate the transmission voice signal from the handset 2 and send the result to the transmission line 1 through the balanced input / output circuit 9.
The audio demodulation circuit 13 is configured to demodulate the FM modulation signal from the balanced input / output circuit 9 and output the audio of the slave G from the handset 2. The video signal transmitted from the slave unit G is amplified by the video signal output circuit 11 from the balanced input / output circuit 9 through the video filter 10, and then output to the monitor television 1. The power supply superposition circuit 8 is provided with a short circuit protection circuit 6 and an open circuit detection circuit 7 for the transmission line. When the monitor switch 4 is operated, the control circuit 5 operates to activate the power supply superimposing circuit 8 and supply the operating power (for example, 24 VDC) to the slave unit G.

On the other hand, the slave unit G includes an audio demodulation circuit 38 for demodulating the FM modulated signal transmitted from the master unit J and extracting an audio signal, and a microphone.
A voice modulation circuit 40 for modulating a voice signal from 23; a call signal generation circuit 43 for generating a call signal in response to the operation of a call switch 24; An operation state determination circuit 42, an FM modulation signal output from the audio modulation circuit 40 via the band pass filter 41, a call signal output from the call signal generation circuit 43, and a video filter 30 from the television camera 21. And a video signal output through a video signal output circuit 31 to output a multiplexed transmission signal to a transmission line l and output an FM modulation signal to a voice demodulation circuit 38 via a band pass filter 37. A depolarizing circuit 33 composed of a diode bridge for depolarizing the connection between the transmission line l and the slave unit G; and a balanced input / output circuit based on the modulated signal sent from the master unit J via the transmission line l. 32 And a power separation circuit 34 for separating the power supply of the slave unit G through. The power supply separation circuit 34 allows only a DC current to pass therethrough and has a high impedance with respect to an AC signal. The power supply voltage separated by the power supply separation circuit 34 is used as a camera power supply and a circuit power supply via a power supply switch circuit 35 and a shunt regulator 36. In the audio modulation circuit 40, the audio signal input from the microphone 23 and amplified by the audio amplifier 26 is FM-modulated and transmitted to the master unit J via the balanced input / output circuit 32.
The FM modulation signal from the balanced input / output circuit 32 is demodulated, amplified by the audio amplifier 39, and output from the speaker 22.

With the above configuration, the master unit J can monitor the situation on the slave unit G side by video and can communicate with the slave unit G side.

FIG. 8 shows a current supply method used in this conventional example. The master unit J is provided with a power supply superimposing circuit 8 for mixing a direct current into the transmission line l, and sends out a direct current at a constant current. As a result, the terminal voltage on the slave unit G side is always kept constant, and the terminal voltage on the master unit J side fluctuates due to the variation of the voltage drop due to the length of the transmission line l. On the slave unit G side, a power supply separation circuit 34 for separating a DC current from the transmission line 1 is provided, and an excess current of the separated DC current is consumed by the shunt regulator 36 to reduce a predetermined power supply voltage. It has gained. With this configuration, the potential difference between the current input / output terminals in the power supply separation circuit 34 on the slave unit G side can be made constant, and the heat generation on the slave unit G side can be minimized.

[Problems to be Solved by the Invention] As described above, by adopting a current supply method that absorbs a variation in the voltage drop due to the length of the transmission line on the master unit side, it is possible to prevent heat generation on the slave unit side. Space is reduced, and downsizing of the slave unit can be realized. However, in the conventional current supply method, in order for the shunt regulator to function normally and to supply a constant voltage to the slave unit circuit, the current consumption of the slave unit is the same as the constant current sent from the master unit. Or slightly less. For this reason, there is a problem that the combination of the child device and the parent device is fixed, and a child device of a different model cannot be connected. Also, considering the variation of the current consumption of the slave unit, the constant current supplied from the master unit is set to a value that is expected to be the maximum as the current consumption of the slave unit, and the difference from the current actually consumed is: There is a problem that the heat is consumed by the shunt regulator, and the heat generated by the shunt regulator cannot be ignored.

The present invention has been made in view of such a point,
The purpose is to diversify the combinations of the current supply side and the current consumption side by always controlling the supply current from the current supply side to the current consumption side current consumption to the optimum value. It is another object of the present invention to provide a current supply system capable of reducing heat generation on the current consuming side.

[Means for Solving the Problems] In the current supply system according to the present invention, in order to solve the above problems, as shown in FIG. In the multiplex transmission system using the transmission line l, the direct current supply side 50 includes a direct current mixing circuit 51 for mixing the direct current into the transmission line l, and the direct current consumption side 70 includes the transmission line and a shunt regulator for consuming a surplus of the DC current separated by the DC separation circuit 71 to obtain a constant voltage.
72, a detection circuit 73 for detecting the amount of current consumed by the shunt regulator 72, and a control circuit for controlling the magnitude of the DC current separated by the DC separation circuit 71 according to the amount of current detected by the detection circuit 73 74 is provided.

[Operation] Hereinafter, the operation of the basic configuration shown in FIG. 1 will be described. An AC signal such as a video signal is transmitted to the transmission line l, and a DC current is mixed by a DC mixing circuit 51 from a power supply terminal 52 on the current supply side 50. The DC separation circuit 71 on the current consuming side 70 separates the DC current from the transmission line l. And
An extra current of the separated DC current is consumed by the shunt regulator 72 to obtain a constant voltage at the power supply terminal 76. The amount of current consumed by the shunt regulator 72 is detected by the detection circuit 73.
The magnitude of the DC current separated by the DC separation circuit 71 is controlled by the control circuit 74 according to the detected current amount. In this way, the shunt regulator 72
Is controlled so that the amount of current consumed by the control unit becomes constant.

Embodiment 1 FIG. 1 shows a schematic configuration of an embodiment of the present invention.
First, between the power supply terminal 52 on the current supply side 50 and the transmission line connection terminal 53, a DC mixing circuit 51 including an inductance element or the like is provided.
Is connected. An AC signal such as a video signal is superimposed on the transmission line connection terminal 53, but since the DC mixing circuit 51 has a high impedance to the AC signal, the AC signal does not leak between the power supply terminals 52. . A DC voltage + V is applied to the power supply terminal 52, and a DC current is supplied from the power supply terminal 52 to the transmission line 1 via the DC mixing circuit 51.

Next, on the current consuming side 70, a DC separation circuit 71 is connected between the transmission line connection terminal 75 and the power supply terminal 76. Power terminal
76 is grounded via a shunt regulator 72.
The amount of current flowing through the shunt regulator 72 is determined by the detection circuit 73
And is input to the control circuit 74 as a control signal. The control circuit 74 controls the magnitude of the DC current separated from the transmission line 1 by the DC separation circuit 71 in accordance with the amount of current flowing through the shunt regulator 72. An AC signal such as a video signal is superimposed on the transmission line connection terminal 75, but since the DC separation circuit 71 has a high impedance with respect to the AC signal, the AC signal leaks to the power supply terminal 76 side. There is no.

FIG. 2 shows an example in which the DC mixing circuit 51 is realized by an electronic circuit. To the power supply terminal 52, the emitter of the control transistor Q ₁ is being connected, the collector of the transistor Q ₁ is connected to a transmission line connecting terminal 53 through a resistor r _1. In addition, the base of the transistor Q _1, the transistor Q ₂
And the collector-base PN junction is connected to the collector of the transistor Q ₁ via the resistor r _2. Transistor Q ₂
The emitter is connected to the collector of the transistor Q ₁ via the resistor r _3. The series circuit of the resistors r _1, r _2, the capacitor C ₀ is connected in parallel. Further, between the base of the emitter and the transistor Q ₂ of the transistor Q ₁ is the resistance r ₄ is connected. With the above circuit configuration, the potential difference between the power supply terminal 52 and the transmission line connection terminal 53 becomes constant, and the current sending terminal potential becomes constant regardless of the amount of current sent from the transmission line connection terminal 53 to the transmission line l. The DC mixing circuit 51
Has a function of sending a DC current from the power supply terminal 52 to the transmission line 1 via the transmission line connection terminal 53 and a function of preventing an AC signal of the transmission line connection terminal 53 from leaking to the power supply terminal 52 side. The circuit configuration is not limited to the circuit shown in FIG.

FIG. 3 is a specific circuit diagram of the current consuming side 70. Hereinafter, the configuration of each unit will be described. First, the DC separation circuit 71
A transistor Tr ₁ for controlling the magnitude of the DC current to separate from the transmission line connecting terminal 75, a resistor R ₁ in order to provide a bias current to the transistor Tr _1, the transistor Tr
A resistor R ₂ connected in series to _one of the emitter, the transistor T
capacitor for fixing the base potential of the r ₁ to a high frequency
Consisting of C ₁ Metropolitan. The base current of the transistor Tr ₁ is supplied via the resistor R ₁ from the transmission line connecting terminal 75, since the base current is shunted by a control circuit 74 which will be described later, by controlling the amount flow, DC it is capable of controlling the magnitude of the DC current flowing through the transistor Tr ₁ in the separation circuit 71. The variation in the voltage drop due to the length of the transmission line 1 is absorbed by the DC separation circuit 71.
For this reason, in the present embodiment, the potential of the transmission line connection terminal 75 varies depending on the length of the transmission line l.

Next, the shunt regulator 72 is made from the constant voltage circuit of a general parallel-controlled, resistors R ₃ and the Zener diode ZD
To generate a constant voltage V _ZD to a connection point of the series circuit of, and applies the constant voltage to the base of the control transistor Tr _2.
The emitter potential of the transistor Tr _2, when a forward voltage drop of the base-emitter PN junction and V _BE, V _ZD + V _BE, and the which is the output voltage of the power supply terminal 76. Since the collector current of the transistor Tr ₂ flows through the resistor R _4, the magnitude of the current to the control transistor Tr ₂ is shunted can be detected as a voltage across the resistor R _4. This voltage is averaged by the capacitor C ₂ of the detection circuit 73, it is applied to the non-inverting input terminal of the operational amplifier OP _1. Operational amplifier OP ₁
Are applied with a reference voltage Vref. Therefore, the output terminal of the operational amplifier OP _1, averaged voltage and the reference voltage Vref and the voltage across the resistor R ₄ in the capacitor C ₂
Is obtained by amplifying the difference between This voltage control circuit 74 are applied via a resistor R ₅ to the base of the transistor Tr ₃ constituting the base current of the transistor Tr ₁ is shunted by a current flowing through the transistor Tr _3. When the amount of current consumed by the shunt regulator 72 increases, the output voltage of the detection circuit 73 increases.
The increased current flowing through the transistor Tr ₃ is the DC current flowing through the transistor Tr ₁ in the DC separator 71 is decreased.
Thus, the amount of current consumed by the shunt regulator 72 can be controlled to a preferable constant value.

Although only a small heat generation to make the current amount is small to be consumed by the shunt regulator 72, in order to stabilize the output voltage V ₂ of the shunt regulator 72, it is necessary to consume a certain amount of current to the shunt regulator 72 Therefore, the minimum current must be within the range that can guarantee the constant voltage operation of the shunt regulator 72 stably.
The DC current flowing through the DC separation circuit 71 may be controlled so as to flow through the DC separation circuit 72.

FIG. 4 is a circuit diagram of a modification of the present embodiment. In the circuit of FIG. 3, as a transistor Tr ₁ in the current control of the DC separator 71, the use of the NPN-type transistor,
In the circuit of FIG. 4, a PNP transistor is used. Therefore, in the circuit shown in FIG.
The arrangement of the emitter side circuit and the collector side circuit of Tr ₁ is reversed from the circuit shown in FIG. Further, the current flowing through the transistor Tr ₃ of the control circuit 74 increases, the current flowing through the transistor Tr ₁ in the DC separator 71, in the circuit of FIG. 3 decreases, the circuit of FIG. 4 increases conversely. Thus, in the circuit shown in FIG. 4, the polarity of the input terminal of the operational amplifier OP ₁ is opposite to the circuit shown in Figure 3. Therefore, in the circuit shown in FIG.
If the amount of current flowing through the resistor R ₄ in 72 decreases, the output voltage of the detection circuit 73 rises, the current flowing through the transistor Tr ₃ of the control circuit 74 increases, the current flowing through the transistor Tr ₁ in the DC separator 71 To increase. This makes it possible to control the current flowing through the resistor R ₄ of the shunt regulator 72 in certain preferred value.

FIG. 5 is a circuit diagram of another modification of the present embodiment. In this circuit, resistors R ₆ and R ₇ , capacitor C ₃ and diode D ₁
Includes a bottom hold circuit become more, the amount of current flowing through the resistor R ₄ is lowered to a level that can not guarantee a stable operation of the shunt regulator 72, the diode D ₁ is conducting, the voltage of the capacitor C ₃ is reduced. Thus, the operational amplifier OP ₁ of the output voltage is changed, under control of the control circuit 74, the DC current increases, which is separated by the DC separator 71. Therefore, a current of a level that can guarantee a stable operation can always flow through the shunt regulator 72.

Embodiment 2 FIG. 6 shows a schematic configuration of another embodiment of the present invention. The present embodiment is an intercom system with a television used in an apartment house or the like, in which one slave G and a plurality of masters are provided.
J ₁ , J ₂ , J ₃ , J ₄ are connected in a star shape via a switch K. A plurality of call switches C ₁ , C ₂ , C ₃ , and C ₄ are provided in the child device G in accordance with the number of master devices J ₁ , J ₂ , J ₃ , and J ₄ . The slave unit G and each of the master units J ₁ , J ₂ , J ₃ , J ₄ are connected to the current consuming side 7 shown in FIG.
It has the same configuration as that of 0 and consumes the DC current supplied from the switch K.

FIG. 7 shows the configuration of the switch K. 90 is a slave unit connection terminal,
Reference numerals 91 to 94 denote master unit connection terminals, 95 and 96 denote DC mixing circuits for mixing DC currents supplied to the slave unit and the master unit, respectively, and 97 denotes a bidirectional signal amplifier circuit. The supply current to the slave G is supplied by the DC mixing circuit 95 so as to match the current consumption in the slave G. The master unit by the call switch C ₁ -C ₄ handset G
When any one of J _{1 to} J ₄ is selected, the changeover switch S ₁
Corresponding one of ON of the to S _4, the other is turned OFF, the slave unit -
The master units are connected one-to-one. The bidirectional signal amplifying circuit 97 bidirectionally transmits a video signal and an audio signal between the child device and the parent device. Further, the current supplied to the selected master unit is supplied by the DC mixing circuit 96 so as to match the current consumption of the master unit. Therefore, in this system, the master units J ₁ , J ₂ ,
Even if J ₃ and J ₄ are different models and have different current consumptions, it is possible to send out an optimal amount of current from the DC mixing circuit 96 of the switch K, for the selected parent machine model.
Similarly, even when the model of the slave unit G is changed, a DC current suitable for the model after the change is supplied.

[Effect of the Invention] In the present invention, as described above, a DC current corresponding to the amount of current consumed by the shunt regulator on the current consuming side is separated from the transmission line by the DC separating circuit on the current consuming side. As a result, a current suitable for the current consuming side can always be sent out from the current supplying side, so that the combination of the current supplying side and the current consuming side can be diversified. Is not sent out, so that the heat generation on the current consuming side can be reduced, which contributes to the downsizing of the device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of a DC mixing circuit used in the above embodiment, and FIG. 3 is a circuit diagram showing a specific example of a current consuming side used in the embodiment. FIG. 4, FIG. 4 is a circuit diagram showing another circuit example on the current consuming side used in the embodiment, FIG. 5 is a circuit diagram showing still another circuit example on the current consuming side used in the embodiment, and FIG. FIG. 7 is a circuit diagram of a switching device used in the above embodiment, FIG. 8 is a diagram showing a schematic configuration of a conventional current supply system, and FIG. 9 is a schematic diagram of a conventional intercom system with a television. FIG. 10 is a diagram showing the configuration, FIG.
FIG. 11 is a block diagram showing a specific configuration of the above. 50 is a current supply side, 51 is a DC mixing circuit, 70 is a current consumption side,
71 is a DC separation circuit, 72 is a shunt regulator, 73 is a detection circuit, 74 is a control circuit, and 1 is a transmission line.

Continuation of the front page (56) References JP-A-1-272360 (JP, A) JP-A-2-140049 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 7 / 18 H04M 9/00 G05F 1/10

Claims (1)

(57) [Claims] 1. A multiplex transmission system for transmitting an AC signal and supplying a DC current through a pair of transmission lines, comprising a DC mixing circuit on the DC current supply side for mixing the DC current into the transmission line. On the DC current consuming side, a DC separation circuit in which the magnitude of the DC current separated from the transmission line is variable, and a constant voltage by consuming extra current among the DC currents separated by the DC separation circuit. Shunt regulator to obtain the current, a detection circuit for detecting the amount of current consumed by the shunt regulator, and control for controlling the magnitude of the DC current separated by the DC separation circuit according to the amount of current detected by the detection circuit A current supply system comprising: a circuit;