JP2005064781A - Television receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a television receiver in which the occurrence of light emission when the power supply is turned off, so called "remaining spot", can be prevented and in which a circuit arrangement and control procedures of a microcomputer are not made complicated. <P>SOLUTION: The television receiver 10 includes a cthode ray tube 5, flyback transformer 3 for supplying high voltage to the cathode-ray tube 5, and a chroma IC 2 for processing a video signal. A Zener diode ZD 1 is provided between a circuit for connecting the ACL input terminal 2a of the chroma IC2 and the ACL output terminal 3a of the flyback transformer 3 and a power line 7 for supplying operating voltage to the chroma IC2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a television receiver including a cathode ray tube.

  The television receiver includes a cathode ray tube for displaying an image, a chroma IC for processing an image signal, and a flyback transformer for outputting a voltage for operating the cathode ray tube. Then, a video signal (color signal) processed by the chroma IC is input to the cathode ray tube while a predetermined high voltage is applied to the cathode ray tube by the flyback transformer, so that an image based on the image signal is displayed on the cathode ray tube. Is done.

  By the way, when the television receiver is turned off to stop the operation, lightning-like light emission called so-called spot residue may appear on the screen of the cathode ray tube.

That is, since a high voltage is applied to the cathode ray tube, the screen may emit light after the power is turned off due to the influence of the remaining charge or the like. Such light emission on the screen after the power is turned off is visually unpleasant and gives the viewer an unpleasant impression. Therefore, some conventional television receivers are provided with means for preventing this spot remaining (see, for example, Patent Documents 1 and 2).
Japanese Utility Model Publication No.4-2169 Utility Model Registration No. 3088321

  Here, in the television receiver disclosed in Japanese Utility Model Laid-Open No. 4-2169, a circuit for preventing a spot remaining is constituted by a number of circuit elements, which is a complicated configuration.

  Further, in the television receiver disclosed in Japanese Utility Model Registration No. 3088321, the microcomputer performs processing for preventing spot remaining, and the microcomputer performs complicated control.

  Therefore, an object of the present invention is to provide a television receiver capable of preventing spot remaining without complicating a circuit configuration and a microcomputer control procedure.

In order to solve the above-described problems, the present invention provides a cathode ray tube for displaying an image, and an auto contrast limiter (ACL) for processing a video signal to display an image on the cathode ray tube and adjusting the luminance of the display of the cathode ray tube. And a flyback transformer for applying a predetermined high voltage for operating the cathode ray tube to the cathode ray tube,
The flyback transformer outputs a control voltage signal indicating the intensity of the beam current flowing along with the display of the cathode ray tube from the ACL output terminal,
The ACL input terminal of the chroma IC is connected to the ACL output terminal of the flyback transformer,
A television receiver in which brightness of an image displayed on the cathode ray tube is adjusted by inputting the control voltage signal to an ACL input terminal of the chroma IC;
A Zener diode is connected between a power supply line for supplying a voltage for operating the chroma IC, and an ACL input terminal of the chroma IC and an ACL output terminal of the flyback transformer,
The Zener diode has a cathode connected to the power supply line side, an anode side connected to the ACL input terminal side of the chroma IC,
When the television receiver is turned off, the Zener diode is conducted in the direction from the cathode to the anode, and the voltage of the power line is applied to the ACL input terminal side of the chroma IC. is there.

  According to the television receiver of the present invention, when the television receiver is turned off, the potential on the anode side of the Zener diode is lowered. As a result, the potential applied in the reverse direction between the cathode and the anode of the Zener diode increases, and the Zener diode conducts in the reverse direction.

  When the Zener diode conducts in the reverse direction, a voltage based on the voltage of the power supply line is applied to the anode side of the Zener diode, and further applied to the ACL input terminal of the chroma IC. Thereby, the fall of the voltage applied to the ACL input terminal of chroma IC stops.

  Thereby, when the beam current accompanying the display of the cathode ray tube is adjusted by the ACL of the chroma IC, the beam current can be prevented from being lowered. As a result, the charge remaining in the cathode ray tube after the power is turned off can be quickly discharged.

  As a result, according to the television receiver of the present invention, it is possible to prevent the spot remaining by a simple circuit having a Zener diode as a main circuit element. Thereby, according to the television receiver of the present invention, it is possible to prevent the remaining spot without complicating the circuit configuration and the microcomputer control procedure.

The present invention is implemented in the form as described above, and has the following effects.
According to the television receiver of the present invention, the remaining spot can be prevented by a simple circuit. Thereby, it is possible to prevent spot remaining without causing the control microcomputer to execute a complicated control procedure or to provide a complicated circuit.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a television receiver 10 according to an embodiment of the present invention. FIG. 1 shows a part of the circuit of the television receiver 10. The television receiver 10 includes a chroma IC 2, a flyback transformer 3, a cathode ray tube 5, and a spot remaining prevention circuit 1.

  The chroma IC 2 performs processing for forming a video signal composed of color signals (R, G, B) to be input to the cathode ray tube 5. The chroma IC 2 extracts the carrier color signal from the composite video signal and performs a process of generating an original color signal by a predetermined color demodulation process.

  A video signal is input to the chroma IC 2 from a video signal source not particularly shown in FIG. As a video signal source, there is a tuner for selecting and receiving a broadcast channel to be received. As another video signal source, there is a reproducing means for reproducing a recording medium on which video is recorded.

  Then, the chroma IC 2 outputs the processed video signal from a video signal output terminal (not shown). The video signal (color signal) output from the chroma IC 2 is input to the cathode ray tube 5 through a signal transmission path (not shown).

  Further, the chroma IC 2 includes an auto contrast limiter (ACL). The ACL is a circuit for adjusting the contrast (brightness) of the video signal. The chroma IC 2 performs processing for adjusting the contrast of the input video signal by the ACL.

  The ACL of the chroma IC 2 performs a process of adjusting the brightness of the video signal based on the control voltage signal input to the ACL input terminal 2a. This control voltage signal is output from the ACL output terminal 3a of the flyback transformer 3 described later.

  This control voltage signal is a signal whose voltage value changes in accordance with the intensity of the beam current input to the cathode ray tube 5 as the screen of the cathode ray tube 5 is displayed. Thereby, the ACL of the chroma IC 2 detects the luminance of the image displayed on the cathode ray tube 5 based on the voltage value of the input control voltage signal.

  When the ACL of the chroma IC 2 detects that the luminance of the video output to the cathode ray tube 5 is high, it performs a process of reducing the contrast of the video signal. On the other hand, when the ACL of the chroma IC 2 detects that the luminance of the video output to the cathode ray tube 5 is low, it does not perform processing for reducing the contrast of the video signal.

  The chroma IC 2 is applied with an operating voltage from the chroma IC power line 7. The chroma IC power line 7 is connected to a power circuit in the television receiver 10 and is supplied with a predetermined positive potential voltage Vcc for operating the chroma IC 2.

  The ACL input terminal 2a of the chroma IC 2 is connected to the chroma IC power line 7 via the resistor R2. The ACL input terminal 2a of the chroma IC 2 is connected to the ground via a resistor R3.

  The ACL input terminal 2a of the chroma IC 2 is connected to one terminal of the resistor R4. The other terminal of the resistor R4 is connected to a chroma IC side connection end 1E of a spot remaining prevention circuit 1 described later. The other terminal of the resistor R4 is connected to the anode side of a diode D1 described later.

  A capacitor C1 is connected between the other terminal of the resistor R4 and the ground. The capacitor C1 is provided to stabilize the control voltage signal input to the ACL input terminal 2a of the chroma IC2.

  The flyback transformer 3 outputs a predetermined high voltage for operating the cathode ray tube 5 to the cathode ray tube 5. The flyback transformer 3 applies a predetermined high voltage between an anode and a cathode (not shown) of the cathode ray tube 5. The flyback transformer 3 outputs a high voltage to the cathode ray tube 5 so that the anode side of the cathode ray tube 5 has a relatively positive voltage and the cathode side of the cathode ray tube 5 has a relatively negative voltage.

  The flyback transformer 3 detects the intensity of the beam current that flows along with the display of the cathode ray tube 5.

  The flyback transformer 3 then outputs a control voltage signal corresponding to the detected beam current from the ACL output terminal 3a. The control voltage signal output from the ACL output terminal 3a of the flyback transformer 3 is input to the ACL input terminal 2a of the chroma IC2.

  The ACL output terminal 3a of the flyback transformer 3 is connected to the cathode side of the diode D1. The ACL output terminal 3a of the flyback transformer 3 is connected to the ACL input terminal 2a of the chroma IC 2 via the diode D1 and the resistor R4.

  The diode D1 is connected so that the direction from the flyback transformer 3 toward the chroma IC 2 is reversed. A circuit unit (not shown) is provided between the diode D 1 and the ACL output terminal 3 a of the flyback transformer 3. The application of the current output from the circuit unit to the chroma IC 2 is prevented by the diode D1.

  The cathode ray tube 5 displays an image based on an image signal (color signals (R, G, B)) input from the chroma IC 2. In the cathode ray tube 5, the electron beam is accelerated by the high voltage output from the flyback transformer 3, the electron beam is scanned in the horizontal direction and the vertical direction based on the input video signal, and an image is displayed on the screen.

  A cathode ray tube grounding line 6 is connected to the cathode ray tube 5. The cathode ray tube grounding line 6 gives the cathode ray tube 5 a ground potential level. The cathode ray tube grounding line 6 is connected to a common grounding line 8. The common ground line 8 is a part of a common ground line that is commonly used for the entire television receiver 10.

  Then, when the television receiver 10 is powered off and the electric charge remaining in the cathode ray tube 5 is discharged, the current accompanying the discharge of the electric charge is guided to the common ground line 8 through the cathode ray tube grounding line 6.

  The television receiver 10 is provided with a spot remaining prevention circuit 1. The spot remaining prevention circuit 1 has the power line side end 1F as one end and the chroma IC side end 1E as the other end. The power line side end 1 </ b> F is connected to the power line 7. The chroma IC side end 1E is connected to the other terminal of the resistor R4, the anode of the diode D1, and the capacitor C1. In the spot remaining prevention circuit 1, a Zener diode ZD1 and a resistor R1 are connected in series.

  The Zener diode ZD1 is connected such that the anode side is the 1E side and the cathode side is the 1F side. The cathode of the Zener diode ZD1 is connected to the power supply line 7 via the resistor R1. The anode of the Zener diode ZD1 is connected to the other terminal of the resistor R4, the anode of the diode D1, and the capacitor C1.

The Zener diode ZD1 becomes conductive (ON) in the direction from the cathode to the anode (reverse direction) when the voltage of the cathode with respect to the anode becomes equal to or higher than the withstand voltage V _{ZD1 in the} reverse direction.

  When the Zener diode ZD1 becomes conductive in the reverse direction, the Zener diode ZD1 becomes electrically conductive from one end 1F of the spot remaining prevention circuit 1 to the other end 1E. As a result, a constant voltage is output from the power supply line 7 to the other end 1E of the spot remaining prevention circuit 1.

  This Zener diode ZD1 is selected based on the following circumstances. When the television receiver 10 is turned off, along with the discharge of the electric charge, the cathode ray tube 5 passes through the cathode ray tube grounding line 6 through the common ground line 8, and passes through R3, R4 and the diode D1 to flyback transformer. A current I3 that passes through 3 and flows toward the cathode ray tube 5 is formed as described later.

  When the current I3 is conducted, the voltage at the other end 1E of the spot remaining prevention circuit 1 is lowered. As a result, the potential difference between one end 1F and the other end 1E of the spot remaining prevention circuit 1 is increased.

  That is, one end 1F of the spot remaining prevention circuit 1 is applied with a constant potential by the power supply line 7, and the potential of the other end 1E of the spot remaining prevention circuit 1 is lowered.

  The Zener diode ZD1 is selected to be in the conductive state in the reverse direction of the Zener diode ZD1 when the potential of the other end 1E of the circuit 1 when the TV receiver 10 is turned off.

Moreover, when selecting a Zener diode, it can select as follows. For example, when the voltage of the power supply line 7 is 8V (volt), the Zener diode ZD1 having a reverse breakdown voltage of V _ZD1 = 12V can be used.

  In general, the control voltage signal output from the ACL output terminal 3a of the flyback transformer 3 is not less than −4 V for a video signal by general broadcasting. However, when the current I3 is conducted along with the discharge of the charge stored in the cathode ray tube 5 when the power is turned off, the voltage at the other end 1E of the spot remaining prevention circuit 1 can be less than −4V. As a result, the potential difference applied in the reverse direction to the Zener diode ZD1 exceeds the reverse breakdown voltage, and the Zener diode ZD1 conducts in the reverse direction.

  The television receiver 10 described above is provided with a power switch (not shown in FIG. 1). When the power switch is turned on, the television receiver 10 is supplied with power and operates.

  The television receiver 10 is provided with a power button and a power key as power switches. The power button is provided on the main body of the television receiver 10. The power button is turned on and off by an operation of a user who uses the television receiver 10.

  The power key is provided on an operation remote controller for operating the television receiver 10 and is provided as a part of the operation key. The power key is turned on and off by a user operation.

  The television receiver 10 is turned on when the power button is turned on and starts operating. The television receiver 10 is turned off when the power key is turned off while the power button is turned on. The television receiver 10 is turned on again when the power key is turned on again with the power button turned on.

  Further, the television receiver 10 is turned off when the power button is turned off. In the state where the power button is turned off, the television receiver 10 cannot be turned on even if the power key is turned on.

  The television receiver 10 described above includes a control microcomputer (not shown) (hereinafter abbreviated as “control microcomputer”), and the operation is controlled by the control microcomputer.

  The user's operation on the operation remote controller is detected by the control microcomputer, and the operation of the television receiver 10 is controlled according to the user's operation. Further, when an operation for turning on or off the power of the television receiver 10 is performed, the control microcomputer detects this power on or power off.

  Even when the television receiver 10 is turned off by a user operation, power is supplied to the chroma IC power line 7, and the chroma IC power line 7 maintains a predetermined voltage for operating the chroma IC 2. ing.

  The chroma IC power line 7 stops the supply of voltage when the power outlet for powering the television receiver 10 with a commercial power source (for example, AC 100V AC power source) is removed from the commercial power source.

  An example of the operation of the television receiver 10 described above will be described with reference to FIG. FIG. 2 is a diagram showing a current loop that is conducted immediately after the television receiver 10 is powered off.

  The television receiver 10 is turned on and operated to display an image on the screen of the cathode ray tube 5. Then, when the user operates the operation remote controller, the television receiver 10 is turned off. A current that is conducted after the television receiver 10 is turned off will be described with reference to FIG.

  When the television receiver 10 is turned off, the electric charge remaining in the cathode ray tube 5 is discharged along with the formation of the image. Then, due to the discharge of the charge remaining in the cathode ray tube 5, a current I4 flowing from the cathode ray tube 5 to the ground through the cathode ray tube grounding line 6 is conducted.

  The current I3 is conducted along with the conduction of the current I4. As shown in FIG. 2, the current I3 passes from the cathode ray tube 5 through the cathode ray tube grounding line 6 through the ground line 8, through R3, R4 and the diode D1, through the flyback transformer 3, and into the cathode ray tube 5 Conduction along the loop returning to

  When the current I3 is conducted, the potential input to the ACL input terminal 2a of the chroma IC 2 is lowered. As a result, the chroma IC 2 determines that the display brightness of the screen of the cathode ray tube 5 has increased, and performs control to reduce the display brightness of the cathode ray tube 5. That is, the chroma IC 2 performs control so as to decrease the intensity of the beam current that conducts the cathode of the cathode ray tube 5 in order to reduce the display brightness of the cathode ray tube 5.

  On the other hand, due to the conduction of the current I3, the potential of the other end 1E of the spot remaining prevention circuit 1 is also lowered. As a result, the Zener diode ZD1 becomes conductive (ON) from the cathode side to the anode side.

  As a result, a voltage V2 having a predetermined voltage value is applied from the power supply line 7 to the other end 1E of the spot remaining prevention circuit 1. Thereby, the fall of the electric potential input into the ACL input terminal 2a of chroma IC2 stops.

  Thereby, when the chroma IC 2 adjusts the beam current input to the cathode of the cathode ray tube 5, it is possible to prevent the beam current from decreasing. Thereby, the electric charge remaining in the cathode ray tube 5 after the power is turned off can be quickly discharged.

  In FIG. 2, V1 indicates a voltage applied from the power supply line 7 to the ACL input terminal 2a of the chroma IC2.

  According to the television receiver 10 described above, even if the potential input to the ACL input terminal 2a of the chroma IC 2 temporarily drops due to the current I3 after the power is turned off, the ACL of the chroma IC 2 is supplied from the power line 7. A constant potential can be supplied to the input terminal 2a.

  That is, the potential of the other terminal 1E of the spot remaining prevention circuit 1 is lowered by the current I3, and the Zener diode ZD1 becomes conductive in the reverse direction. As a result, a constant potential is supplied from the power supply line 7 to the ACL input terminal 2a of the chroma IC 2 via the spot remaining prevention circuit 1.

  As a result, the chroma IC 2 controls the display luminance of the cathode ray tube 5 so as not to decrease, so that the charge remaining in the cathode ray tube 5 can be quickly discharged.

  According to the television receiver 10 described above, the remaining spot can be prevented by the spot remaining prevention circuit 1 having the Zener diode ZD1 as a main circuit element.

  Thereby, according to the television receiver 10 described above, it is possible to prevent the remaining spot without causing the control microcomputer to execute a complicated control procedure or providing a complicated circuit.

1 is a circuit diagram of a television receiver according to an embodiment of the present invention. It is a figure which shows the operation | movement immediately after power-off of the television receiver shown by FIG.

Explanation of symbols

1 Spot remaining prevention circuit 2 Chroma IC
2a ACL input terminal 3 Flyback transformer 3a ACL output terminal 5 Cathode ray tube 6 Cathode ray tube grounding line 7 Chroma IC power line 8 Common ground line 10 Television receiver

Claims (1)

A cathode ray tube for displaying an image, a chroma IC having an auto-contrast limiter (ACL) for processing a video signal to display the image on the cathode ray tube and adjusting the display brightness of the cathode ray tube, and for operating the cathode ray tube And a flyback transformer for applying a predetermined high voltage to the cathode ray tube,
The flyback transformer outputs a control voltage signal indicating the intensity of the beam current flowing along with the display of the cathode ray tube from the ACL output terminal,
The ACL input terminal of the chroma IC is connected to the ACL output terminal of the flyback transformer,
A television receiver in which brightness of an image displayed on the cathode ray tube is adjusted by inputting the control voltage signal to an ACL input terminal of the chroma IC;
A Zener diode is connected between a power supply line for supplying a voltage for operating the chroma IC, and an ACL input terminal of the chroma IC and an ACL output terminal of the flyback transformer,
The Zener diode has a cathode connected to the power supply line side, an anode side connected to the ACL input terminal side of the chroma IC,
When the power of the television receiver is turned off, the Zener diode becomes conductive from the cathode to the anode, and the voltage of the power line is applied to the ACL input terminal side of the chroma IC. .

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