JP3036785B2 - 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. 5 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. 6 shows a frequency division state of a signal transmitted via 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.

A more specific configuration of the intercom system is described in the seventh section.
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 input a multiplexed transmission signal to the transmission line l, and output an FM modulation signal to a voice demodulation circuit 38 via a band pass filter 37. A circuit 32, a depolarization 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 from the modulation signal transmitted from the master unit J via the transmission line l. Output circuit 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.

Here, as a method of supplying a DC current from the master unit J to the slave unit G, by sending a DC current at a constant current, the terminal voltage on the slave unit G side is always kept constant, and the length of the transmission line l is maintained. The terminal voltage on the master unit J side fluctuates due to the variation in the voltage drop amount due to the above. With this configuration, the potential difference between the current input / output terminals in the power supply separation circuit 34 on the slave unit side can be kept 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 constantly controlling the constant current from the current supply side to the current consumption on the current consumption side 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 a current supply system according to the present invention, in order to solve the above problems, a system in which a plurality of AC signals can be transmitted over a pair of transmission lines by frequency division is used. In a multiplex transmission system in which a DC current is supplied from one side of the transmission line to the other side, as shown in FIG. 1, a DC current supply side 50 receives a control signal from the transmission line l. Control signal receiving circuit 51 and the control signal receiving circuit 51
A constant current circuit 52 for controlling the amount of current sent out to the transmission line l in response to the control signal received at the, a DC separation circuit for separating the DC current from the transmission line l 71, a shunt regulator 72 for obtaining a constant voltage V ₂ consumes additional current out of the separated DC current, transmits a control signal corresponding to the amount of current consumed by the shunt regulator 72 to the transmission line l And a control signal transmission circuit 73 that performs the control.

The control signal transmitted from the control signal transmitting circuit 73 to the control signal receiving circuit 51 via the transmission line 1 is a PCM-modulated or PWM-modulated pulse signal which is transmitted by performing ASK modulation or FSK modulation on the carrier signal. Is preferred.

[Operation] Hereinafter, the operation of the basic configuration shown in FIG. 1 will be described. A constant current is supplied from the constant current circuit 50 on the current supply side 50,
Only the DC current is passed by the DC separation circuit 71 on the current consuming side 70. Then, obtain a voltage V ₂ to a constant voltage by the shunt regulator 72. The surplus current is consumed by the shunt regulator 72. The amount of current consumed by the shunt regulator 72 is detected, and the information is transmitted from the control signal transmission circuit 73 to the current supply side 50 via the transmission line l. On the current supply side 50, the information transmitted from the control signal transmitting circuit 73 is received by the control signal receiving circuit 51, and the amount of current sent out by the constant current circuit 52 is changed according to the received information. In this way, the transmission current of the constant current circuit 52 is controlled so that the amount of current consumed by the shunt regulator 72 becomes constant.

Note that an AC signal such as a video signal is superimposed on the terminal 53 of the current supply side 50, and the current consumption side 70 is connected via the transmission line l.
This AC signal is interrupted by a DC separation circuit 71 composed of an inductance element or the like, and does not affect the supply of DC current.

Embodiment 1 FIG. 2 is a block circuit diagram of one embodiment of the present invention.
In the figure, 73a is a pulse width modulation circuit, 73b is an ASK modulation circuit, and these constitute a control signal transmission circuit. Also, 51a is a demodulation circuit, 51b is a rectifying and smoothing circuit, 51c
Is a DC amplifier circuit, and these constitute a control signal receiving circuit.

Hereinafter, the operation of the present embodiment will be described. First, the shunt regulator 72 in the current consumer 70 is a general parallel-controlled constant voltage circuit generates a constant voltage V _ZD to a connection point of the series circuit of a resistor R ₂ and the Zener diode ZD, controls the constant voltage It is applied to the base of the use transistor Q _1. Assuming that the forward voltage drop of the PN junction between the base and the emitter is V _BE , the emitter potential of the transistor Q ₁ is V _ZD + V _BE
Next, which is the output voltage V _2. Since the collector current of the transistor Q ₁ is flowing through the resistor R _1, the magnitude of the current shunted to the control transistor Q ₁ is, it can be detected as a voltage across the resistor R _1. This voltage is converted into a pulse signal by the pulse width modulation circuit 73a. The pulse signal with a period is constant, the pulse width of which changes in accordance with the voltage across the resistor R _1. This pulse signal is converted by the ASK modulation circuit 73b into an ASK modulation signal having a carrier frequency fc, and transmitted to the current supply side 50 via the transmission line l. In this ASK modulation signal, the amplitude of the carrier frequency fc is “1” of the pulse signal.
Alternatively, it is a signal that changes according to “0”, and switches the presence or absence of the carrier frequency fc according to, for example, “1” or “0” of the pulse signal.

On the current supply side 50, the ASK-modulated carrier frequency fc
Is demodulated by the demodulation circuit 51a to restore a pulse signal subjected to pulse width modulation. A rectifying and smoothing circuit for this pulse signal
At 16 the DC voltage is restored according to the pulse width
DC amplification is performed at 17 and the current sent out by the constant current circuit 52 is controlled by the output voltage. The constant current circuit 52 includes a transistor Q ₂ for current control, a bias resistor R ₃ thereof, a resistor R ₄ for current detection, and a voltage between both ends of the resistor R ₄ corresponding to the output voltage of the DC amplifier circuit 17. made so that a differential amplifier a ₁ for controlling the biasing of the transistor Q _2. The current sent from the constant current circuit 52 is the resistance of the shunt regulator 72.
It is controlled so as to minimize the current consumed by R _1.

However, within the range 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, which can ensure a stable constant voltage operation of the shunt regulator 72, The current sent from the constant current circuit 52 may be controlled so that the minimum current flows through the shunt regulator 72.

Embodiment 2 FIG. 3 is a block circuit diagram 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 receive power supply from the switch K.

FIG. 4 shows the configuration of the switch K. 90 is a slave unit connection terminal,
91 to 94 are master unit connection terminals, 95 is a bidirectional signal amplifier circuit, 96, 9
7 is a constant current circuit that supplies current to the slave unit and the master unit respectively, 9
8 and 99 are control signal receiving circuits, respectively. The current supplied to the slave G is controlled by the control signal receiving circuit 98 in accordance with the control signal received from the slave G to control the constant current circuit 96 so as to adapt to the current consumption in the slave G. You. When any one of the base unit J ₁ through J ₄ is selected by the call switch C ₁ -C ₄ handsets G, corresponding one of ON of the changeover switch S ₁ to S _4, the other is turned OFF, the child A one-to-one connection is made between the machine and the parent machine. The bidirectional signal amplifying circuit 95 bidirectionally transmits a video signal and an audio signal between the slave unit and the master unit. Further, the current supplied to the selected master unit is adapted to the current consumption of the master unit by controlling the constant current circuit 97 according to the control signal received from the master unit by the control signal receiving circuit 99. Is controlled as follows. Therefore, in this system,
Even if J ₁ , J ₂ , J ₃ , and J ₄ are different models and consume different currents, the optimal amount of current for the selected base unit model is supplied from the constant current circuit 97 of the switch K. Can be sent out.

[Effect of the Invention] In the present invention, as described above, a control signal corresponding to the amount of current consumed by the shunt regulator on the current consumption side is transmitted from the control signal transmission circuit on the current consumption side via the transmission line. Since the current is transmitted to the control signal receiving circuit on the supply side and the current sent from the constant current circuit on the current supply side is controlled according to this control signal, the current suitable for the current consuming side must always be sent from the current supply side. It is possible to diversify the combination of the current supply side and the current consumption side, and it is possible to reduce the heat generation on the current consumption side because no extra current is sent out. This has the effect of contributing to downsizing.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is a block circuit diagram of one embodiment of the present invention, FIG. 3 is a schematic configuration diagram of another embodiment of the present invention, and FIG. Vessel circuit diagram, 5th
FIG. 1 is a diagram showing a schematic configuration of a conventional example, FIG. 6 is an explanatory diagram of a frequency division state in the above, and FIG. 7 is a block diagram showing a specific configuration in the same. 50 is a current supply side, 51 is a control signal reception circuit, 52 is a constant current circuit, 70 is a current consumption side, 71 is a DC separation circuit, 72 is a shunt regulator, 73 is a control signal transmission circuit, and 1 is a transmission line.

Continuation of the front page (56) References JP-A-1-272360 (JP, A) JP-A-62-196028 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 7 / 18

Claims (1)

(57) [Claims] 1. A multiplex transmission system in which a plurality of AC signals can be transmitted over a pair of transmission lines by frequency division, wherein a DC current is supplied from one side of the transmission line to the other side. On the current supply side, a control signal receiving circuit that receives a control signal from the transmission line, and a constant current circuit that controls the amount of current sent to the transmission line according to the control signal received by the control signal receiving circuit. A DC separation circuit for separating the DC current from the transmission line; a shunt regulator for consuming a surplus of the separated DC current to obtain a constant voltage; and a shunt regulator. And a control signal transmission circuit for transmitting a control signal corresponding to the amount of current consumed in the transmission line to the transmission line.