JP2714145B2 - Satellite broadcast receiver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite broadcast receiving apparatus that protects a DC power supply circuit for a BS converter from an output short-circuit accident.

[Prior Art] A satellite broadcast receiving apparatus 1 shown in FIG. 2 converts the frequency of a satellite broadcast radio wave captured by a satellite broadcast receiving antenna 2 called a BS antenna by a BS converter 3 connected to a waveguide, and converts the frequency of the BS broadcast. A configuration for sending the signal to the tuner 4 is adopted. That is, a broadcast wave transmitted from a broadcast satellite launched into a geosynchronous orbit at 35800 km above the equator is captured by the satellite broadcast receiving antenna 2 and sent into the BS converter 3 as a 12 GHz band signal. In the BS converter 3, the signal is first converted into a TEM mode signal having no electromagnetic field in the propagation direction in the waveguide / coaxial converter 5, and then supplied to the mixing circuit 7 via the high frequency amplifier circuit 6 having a low noise figure. . The mixing circuit 7 performs lower heterodyne detection based on the local oscillation signal of 10.678 GHz sent from the local oscillation circuit 8, and outputs 11.71 to 12.01 GHz.
The high frequency signal of z is converted to a first intermediate frequency of 1.035 to 1.335 GHz. The signal down-converted by the mixing circuit 7 is amplified by the subsequent first intermediate frequency amplifier circuit 9 and the signal attenuation due to the expected transmission loss is compensated in advance.
It is sent to the BS tuner 4 side.

Since the BS converter 3 handles a weak signal in the 12 GHz band, it is necessary to avoid the influence of the power supply hum as much as possible.
It is desired to configure without using a power transformer or a rectifier circuit. For this reason, a method of supplying a 15V DC power supply from the BS tuner 4 side is generally used. In the case of this example, a 15V DC power supply sent through the connection cable 10 is received through the AC cut-off coil Lo. DC power supply circuit
11 is built in. For this type of stabilized DC power supply circuit 11, a three-terminal regulator or the like that can easily compensate for a voltage drop due to the connection cable 10 is used. And the first intermediate frequency amplifying circuit 9.

On the other hand, the first intermediate frequency sent into the BS tuner via the connection cable 10 is obtained by selecting the signal of the desired channel by the channel selection demodulation circuit 12 and then performing FM demodulation on the signal converted to the second intermediate frequency. By doing so, the video signal and the audio PCM signal are separated and extracted. The extracted video signal is subjected to processing such as cancellation of high-frequency emphasis and removal of an energy diffusion signal in the video signal processing circuit 13 to be the same video signal as that on the transmission side. The audio PGM signal is subjected to four-phase DPSK demodulation in the audio PCM signal processing circuit 14, is subjected to various digital signal processings, and is finally converted into an analog signal and output.

Reference numeral 15 denotes a DC power supply circuit for the BS converter, which sends out a 15 V DC power supply to a power supply line connected to the connection cable 10 via a diode D for preventing backflow and a coil Li for preventing AC.

[Problems to be Solved by the Invention] The conventional satellite broadcast receiving apparatus 1 includes a BS tuner 4 and a BS
The connection cable 10 connecting the converter 3 serves as both a 1 GHz band signal line and a feed line for the BS converter 3.
Generally, as shown in FIG.
A coaxial cable, such as TVEFCX, in which an insulator 17, an outer conductor 18, and a jacket 19 are coaxially coated around 16, is used. In addition, for the terminal processing of the connection cable 10, a C15 type connector 20 newly developed for a satellite broadcast receiving system is used, and there are differences in applications such as indoor or outdoor use, or a pin contact type and a core wire. Although there is a difference in structure such as a contact type, the user can connect the connector 20 to the connection cable 10 with a little knowledge.

However, when a user who does not have specialized knowledge performs terminal processing, the braided wire of the outer conductor 18 often comes into contact with the inner conductor 16 or the inner and outer conductors may not easily contact due to external vibration or the like. It is easy to make a connection error prohibited by the precautionary statement of the manual, such as connecting the connector 20 in an unstable state, and such a connection error seems to be the DC power supply circuit 15 for the BS converter in the BS tuner 4. It will have no calamity. In other words, it is good if the connection error is improved by poor reception, but if not, when the terrestrial broadcast other than the satellite broadcast is selected and received while the power switch of the BS tuner 4 is turned on, The problem that the DC power supply circuit 15 for the BS converter continues to flow a large current to the output side in a short-circuit state without any notice from the outside, which may lead to the worst situation such as abnormal heat generation and thermal destruction of circuit components. I was having.

In addition, besides the connection error between the connection cable 10 and the connector 20, as a connection error that cannot be considered with common sense, for example, the connection cable 10 is connected to the 75Ω unbalanced terminal side of the 75Ω / 300Ω Always short-circuited
A connection cable with a 75Ω unbalanced terminal that could cause a simple short circuit accident, or a notch such as a cutter
There have been reports of accidents such as the use of 10 outdoors without knowing it, and the intrusion of rainwater from the cuts causing a short circuit between the inner conductor 16 and the outer conductor 18. The broadcast receiving device 1 was completely defenseless.

Further, Japanese Utility Model Application Laid-Open No. 1-13 published after the filing of the present application.
No. 7641 `` Satellite receiver '' monitors the DC current supplied from the BS converter power supply circuit to the BS converter, and the DC current that is usually 200 to 300 mA is a large current of 500 mA or more, or 100 mA A satellite broadcast receiver having a configuration in which the following small current is determined to be in an abnormal state and current supply from a power supply circuit for a BS converter to a BS converter is cut off by a current cutoff circuit is disclosed. This one is
For example, when the output short circuit causes the BS converter power supply circuit to
When an abnormal current is supplied to the converter, the current interruption circuit cuts off the current supply to the BS converter, thereby avoiding the dripping state of the abnormal current, but notifying the user of the current interruption state. Since the key operation is not restricted and the key operation is not restricted, it is easy for the user to take a correct action, and it takes a long time to recover from a short circuit accident or an open accident. The current cutoff circuit is configured to detect the current supplied to the BS converter by comparing two threshold currents, an upper limit current and a lower limit current. It has to rely on a circuit configuration that leads the voltage drop across the resistor with a known value to the inverting input terminal of the comparator via a voltage-dividing resistor, etc., and has problems such as the inevitable complication of the circuit configuration. Met.

[Means for Solving the Problems] The present invention solves the above problems, and provides power supply and signal transmission to a BS converter that converts radio waves captured by a satellite broadcast receiving antenna into an intermediate frequency in a predetermined band. A BS tuner connected via a dual-purpose connection cable
A satellite broadcast receiver for supplying DC power from a built-in DC power supply circuit for a BS converter, and selecting and demodulating a signal of a desired channel, connected to a power supply line of the DC power supply circuit for a BS converter, and detecting an output short circuit. A power supply control circuit for interrupting the power supply output of the DC power supply circuit for the BS converter in response to the supply of a signal, and monitoring the output voltage of the power supply control circuit, and when the output voltage drops below an abnormal voltage indicating an output short circuit. An output short-circuit detection circuit for supplying the output short-circuit detection signal to the power supply control circuit; connected to the output short-circuit detection circuit;
Key lock means for locking operation keys attached to the tuner inoperable except for a power switch is provided.

[Operation] According to the present invention, an output short-circuit detection circuit connected to a DC power supply circuit for a BS converter detects an abnormal decrease in output voltage due to an output short-circuit, and operates upon receiving an output short-circuit detection signal from the output short-circuit detection circuit. A power supply control circuit cuts off power supply from the DC power supply circuit for the BS converter to the BS converter, and key lock means connected to the output short-circuit detection circuit receives the output short-circuit detection signal and receives an operation key attached to the BS tuner. By locking the power supply switches so that they cannot be operated except for the power switch, the DC power supply circuit for the BS converter in the BS tuner is protected from output short-circuit accidents, and the key operation is disabled to promptly take corrective action. Can be.

Embodiment An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a circuit diagram showing an embodiment of a satellite broadcast receiving apparatus according to the present invention.

The satellite broadcast receiver 21 shown in FIG. 1 connects an output short-circuit detection circuit 22 for detecting an abnormal drop in output voltage due to an output short-circuit to a DC power supply circuit 15 for a BS converter. In response to the output short-circuit detection signal, BS
A power supply control circuit 23 for stopping power supply by the DC power supply circuit 15 for the converter is provided, and a warning maintenance circuit 26 is provided between the output short-circuit detection circuit 22 and the operation keys 24 and the indicator lamp 25 for when an output short-circuit occurs. Is provided.

The output short-circuit detection circuit 22 is a circuit in which a series connection circuit of a constant voltage diode Dz having a breakdown voltage (Zener voltage) of about 10 V and a resistor R is shunt-connected to a power supply line connecting the power supply control circuit 23 and the diode D. It detects that the output voltage of the power supply control circuit 23 has dropped below the breakdown voltage of the constant voltage diode Dz corresponding to the abnormal voltage indicating an output short circuit.

The power supply control circuit 23 arranges a transistor Q as a switching element for power supply control on a power supply line connecting the DC power supply circuit 15 for the BS converter and the connection cable, and operates upon receiving an output short-circuit detection signal of the output short-circuit detection circuit 22. The switching circuit 27 controls the switching of the transistor Q. The switching circuit 27 switches the transistor Q1 for controlling the switching of the transistor Q, the transistor Q2 that is turned off when the output short-circuit detection signal of the output short-circuit detection circuit 22 is received as a base, and that the transistor Q2 is turned off. It has three transistors, that is, a transistor Q3, which conducts later after receiving and switches the transistor Q1 to a cutoff state.

The transistor Q1 has a collector connected to the base of the transistor Q and an emitter grounded. The output voltage of the DC power supply circuit 15 for the BS converter divided by the base bias resistors R1 and R2 is applied to the base. The transistor Q2 has a base connected to the output short-circuit detection circuit 22 via the resistor R3, an emitter grounded, and a collector connected to the base of the transistor Q3. Transistor Q3
Is connected in parallel to a base bias resistor R2, and a capacitor C is connected in parallel with R5 of its own base bias resistors R4 and R5. This capacitor C is a BS tuner
When the power of the power supply 28 is turned on, the output of the output short-circuit detection circuit 22 is simulated to be in an output short-circuit detection state, and the power supply control circuit 23 is driven to stop power supply. Plays a role of a delay element for preventing the transistor Q3 from conducting until the transistor becomes conductive.

Q4 is a transistor provided to protect the transistor Q from overcurrent, and is connected in parallel to a resistor R6 connecting the base and the emitter of the transistor Q,
When the voltage drop in the overcurrent detection resistor R7 connected between the base and the emitter exceeds the voltage between the base and the emitter, the transistor becomes conductive, and functions to shunt a part of the excess current to a part other than the transistor Q.

The warning maintenance circuit 26 connected to the output short-circuit detection circuit 22
Has a built-in microcomputer whose operation is specified through software, and a level detection circuit that detects that the output level of the output short-circuit detection circuit 22 has dropped abnormally.
26a, a display drive circuit 26b operating in response to the output of the level detection circuit 26a, a key scan circuit 26c, and the like. The display drive circuit 26b drives the display lamp 25 to blink when the output short circuit occurs, and the key scan circuit 26c
Locks the keys other than the power switch in an inoperable state in response to the occurrence of an output short circuit.

By the way, when the power of the BS tuner 28 is turned on, the 15.7 V DC output from the DC power supply circuit 15 for the BS converter is supplied to each part in the power supply control circuit 23. At this time, the transistor Q1 receives the power supply voltage divided by the base bias resistors R1 and R2 and immediately conducts, while the transistor Q3 whose base is grounded via the capacitor C has a lower base voltage. Gradually rises along the charging curve of the capacitor C, and eventually does not conduct. Therefore, when the transistor Q1 is turned on in response to the conduction of the transistor Q1, the BS
Power supply to converter 3 is started.

In addition, at the start of this power supply, the output short-circuit detection circuit 22
However, to detect a voltage of about 5 V generated across the resistor R,
The transistor Q1 in the switching circuit 27 is turned on. As a result, the anode terminal of the capacitor C and the base of the transistor Q3 are grounded.
Is prevented from conducting.

By the way, in the connector 20 used for the terminal treatment of the connection cable 10, an output short-circuit accident occurs because the inner conductor 16 and the outer conductor 18 are in direct contact with each other, or the conductors 16 and 18 are short-circuited by rainwater invading from a crack. I have invited you. In this case, the power supply control circuit 23
Output voltage drops extremely near zero. as a result,
The constant voltage diode Dz in the output short detection circuit 22 becomes non-conductive, and the terminal voltage of the resistor R becomes zero. For this reason, the transistor Q2
Turns off, and charging of the capacitor C is started at the same time. The charging of the capacitor C is performed according to a charging time constant determined by the product of the capacitance and the resistance value of the base bias resistor R4.

When the terminal voltage of the anode terminal of the capacitor C reaches the voltage between the base and the emitter of the transistor Q3, the transistor Q3 conducts, and the base of the transistor Q1 is grounded. As a result, the transistor Q1 is turned off, and the power supply control transistor Q is reverse-biased and switched to the cutoff state. Therefore, the transistor Q is turned off only momentarily after the occurrence of the output short-circuit, thereby reliably supplying a large current to the BS converter 3 despite the occurrence of the short-circuit accident. Can be eliminated.

Also, in accordance with the power supply stoppage by the power supply control circuit 23,
The warning maintenance circuit 26 connected to the output short-circuit detection circuit 22 operates. That is, the level detection circuit 26a that has detected a decrease in the output voltage of the output short-circuit detection circuit 22 acts on the display drive circuit 26b and the key scan circuit 26c, and displays an abnormality display by blinking of the display lamp 25 and operation keys 24 other than the power switch. Lock on.

As described above, the satellite broadcast receiving apparatus 21 has a worst situation in which the DC power supply circuit 15 for the BS converter continuously flows a large current to the output side in a short-circuit state, leading to abnormal heat generation and thermal destruction of components. This can be prevented beforehand and surely.

[Effects of the Invention] As described above, according to the present invention, an output short-circuit detection circuit connected to a DC power supply circuit for a BS converter detects an abnormal decrease in output voltage due to an output short-circuit, and short-circuits the output short-circuit detection circuit. A power supply control circuit that operates in response to the detection signal cuts off power supply from the DC power supply circuit for the BS converter to the BS converter, and a key lock unit connected to the output short-circuit detection circuit receives the output short-circuit detection signal and receives a BS tuner signal. The operation keys attached to the cable are locked so that they cannot be operated except for the power switch, so that the outer conductor of the connection cable can be in direct contact with the inner conductor, or the connector can be connected in such a way that it can be easily contacted. Or the connection cable is connected to the 75Ω unbalanced terminal side of the 75Ω / 300Ω matcher, and the coil is short-circuited by the 75Ω unbalanced terminal. Even if a connection cable with a notch due to a cutter or the like is used outdoors and rainwater enters from the notch and an internal conductor and an external conductor are short-circuited, an abnormality such as a short circuit may occur. DC power supply circuit automatically stops supplying power to the output side that is in a short-circuit state, so that worst-case situations such as abnormal heat generation due to dripping of a large current and thermal destruction of circuit components are prevented beforehand and reliably. In addition, when the output short circuit occurs, the operation keys attached to the BS tuner are locked so that they can not be operated except for the power switch.
This has the effect of promptly taking corrective measures and ensuring the protection of the DC power supply circuit for the BS converter and measures against accidents.

In addition, the present invention uses a constant voltage diode that detects an output short circuit when the output voltage of the DC power supply circuit for the BS converter falls below the breakdown voltage in the output short circuit detection circuit. There is no need to use a complicated circuit such as a comparator, and the constant voltage diode branch-connected to the power supply line has an effect that an output short circuit can be easily detected.

In the power supply control circuit, a power supply control switching element provided on a power supply line that connects the DC power supply circuit for the BS converter to the connection cable, and a power supply control switching element that operates upon receiving a short-circuit detection signal of the output short-circuit detection circuit. And a switching element switching means that does not respond to a transient pseudo short-circuit detection signal supplied when the DC power supply circuit for the BS converter is started, thereby switching the power supply control switching element. This makes it possible to respond only to an output short circuit, and it is possible to satisfactorily avoid the inconvenience that the power supply switching element does not become conductive when the BS tuner is turned on.

Furthermore, the present invention provides a configuration in which visual display means is connected to the output short-circuit detection circuit to visually display the occurrence of output short-circuit, so that the satellite broadcast image is not reproduced by the television receiver. However, if the power switch of the BS tuner is in the ON state, the short-circuit accident of the connection cable connecting the BS converter and the BS tuner is visually displayed on the BS tuner,
There are effects such as being able to draw the user's attention and take corrective action.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a satellite broadcast receiver according to the present invention, FIG. 2 is a circuit diagram showing an example of a conventional satellite broadcast receiver, and FIG. It is a perspective view which shows the external appearance of the connection cable and connector shown. 2 ... satellite broadcast receiving antenna 3 ... BS converter 10 ... connection cable 15 ... DC power supply circuit for BS converter 21 ... satellite broadcast receiver 22 ... output short circuit detection circuit 23 ... power supply control circuit 28 ... BS Tuner

 ──────────────────────────────────────────────────続 き Continuing from the front page Examiner Akihiro Yamamoto (56) Reference: Hikaru 1-1137641 (JP, U)

Claims (4)

(57) [Claims] 1. A BS tuner connected via a connection cable for both power supply and signal transmission to a BS converter for converting radio waves captured by a satellite broadcast receiving antenna to an intermediate frequency in a predetermined band. A satellite broadcast receiving apparatus for supplying DC power from a DC power supply circuit for a converter, and for selecting and demodulating a signal of a desired channel.
A power supply control circuit that is connected to a power supply path of the DC power supply circuit for the converter, receives a supply of an output short-circuit detection signal, and cuts off a power supply output of the DC power supply circuit for the BS converter, and monitors an output voltage of the power supply control circuit. An output short-circuit detection circuit for supplying the output short-circuit detection signal to the power supply control circuit when the output voltage drops below an abnormal voltage indicating an output short-circuit, and an output short-circuit detection signal connected to the output short-circuit detection circuit; And a key lock unit that operates in response to the input signal and locks operation keys attached to the BS tuner inoperable except for a power switch. 2. The output short-circuit detecting circuit includes a constant-voltage diode for detecting an output short-circuit when the output voltage of the DC power supply circuit for the BS converter falls below a breakdown voltage. The satellite broadcast receiving device as described in the above. 3. The power supply control circuit operates upon receiving a power supply control switching element provided on a power supply line connecting the DC power supply circuit for the BS converter and the connection cable, and an output short detection signal from the output short detection circuit. And a switching element switching unit that sets the power supply control switching element to a cutoff state and that does not respond to a transient pseudo output short-circuit detection signal supplied when the DC power supply circuit for the BS converter is started. The satellite broadcast receiving device according to claim 1, further comprising: 4. A satellite broadcast receiving apparatus according to claim 1, further comprising a visual display means connected to said output short-circuit detecting circuit for visually displaying occurrence of an output short-circuit.