JP2011003439A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device having reduced cost for suppressing the number of input ports for detection signals to be used for determining whether the magnitudes of one of a tube current in a lamp and tube voltage or both of them lie within adequate ranges.SOLUTION: The display device 1 includes a lighting control circuit 3 for lighting the discharge lamp 6a, and an image signal processing part 5 for displaying an image relating to an input image signal on a display 6. A detection circuit 4 outputs the detection signal, showing whether the magnitude of the tube current of the discharge lamp 6a lies between a lower limit value and an upper limit value, and a main control part 2 monitors the state of the detection signal input from the detecting circuit 4. When the state of the detection signal shows that the magnitude of the tube current in the discharge lamp 6a does not lie between the lower limit value and the upper limit value, the main control part 2 instructs the lighting control circuit 3 and the image signal processing part 5 to stop their operations.

Description

  The present invention relates to a display device that displays an image using a discharge lamp such as a cold cathode tube as a backlight.

  Conventionally, there has been a liquid crystal display device that displays an image using a discharge lamp such as a cold cathode tube as a backlight. Liquid crystal display devices are used for television receivers and are used as monitors for personal computers.

  In addition, when an abnormality is detected in the discharge lamp, the liquid crystal display device is provided with a protection circuit for stopping peripheral circuits including a lighting control circuit for controlling the lighting of the discharge lamp and preventing damage to these peripheral circuits. (See Patent Document 1, etc.). For example, in Patent Document 1, the first comparison result comparing the tube current of the discharge lamp with a predetermined minimum current, and the first comparison result of the tube current of the discharge lamp with a predetermined maximum current. 2 is input to the microcomputer. The microcomputer determines whether the tube current of the discharge lamp is within an appropriate range (between the minimum current and the maximum current) based on the input first comparison result and second comparison result. . When the microcomputer determines that the tube current of the discharge lamp is not within the proper range, the microcomputer stops the peripheral circuits including the lighting control circuit that controls the lighting of the discharge lamp and prevents the peripheral circuits from being damaged. ing.

JP 2004-87374 A

  However, in the conventional configuration disclosed in Patent Document 1 and the like, the first comparison result obtained by comparing the discharge lamp tube current with a predetermined minimum current and the discharge lamp tube current are compared with the microcomputer. And a second comparison result obtained by comparing a predetermined maximum current with each other. That is, a microcomputer that can secure two input ports for inputting the first comparison result and the second comparison result has to be used.

  The object of the present invention is to reduce the number of detection signal input ports used for determining whether the magnitude of one or both of the lamp tube current and / or the tube voltage is within an appropriate range, thereby reducing costs. Another object is to provide a display device.

  In order to achieve the above object, the display device of the present invention is configured as follows.

  This display device is a liquid crystal display device or the like that displays an image using a backlight.

  The lighting control circuit controls the lighting state of the lamp that functions as a backlight. This lighting control circuit has a known inverter, for example, and controls the on / off frequency of the switching transistor on the primary side by using the DC voltage connected to the primary winding of the inverter to control the secondary side winding. Transmits the voltage necessary for lamp operation to the wire. The lamp is connected to this secondary winding.

  The detection unit sets at least one of a tube current and a tube voltage in the lamp as a detection target, and outputs a detection signal indicating whether the size of the detection target is between a predetermined lower limit value and an upper limit value. The main control unit, when the detection signal input from the detection unit is in a state indicating that the size of the detection target is not between the predetermined lower limit value and the upper limit value, with respect to the lighting control unit Instructs the lamp to turn off. The lighting control circuit stops the inverter (on / off control of the switching transistor on the primary side) in response to an instruction to turn off the lamp from the main control unit.

  As described above, since the detection signal indicating whether the size of the detection target is between the predetermined lower limit value and the upper limit value is input to the main control unit, the microcomputer provided in the main control unit Can have one input port for signals used for lamp abnormality detection. Therefore, an inexpensive microcomputer with a small number of input ports can be used, and the cost of the main body can be reduced.

  In addition, the detection unit is configured to include, for example, a first comparator and a second comparator. The first comparator receives a measurement signal indicating the size of the detection target, compares the size of the detection target with a lower limit value, and outputs a low level when it is smaller than the lower limit value. The second comparator receives a measurement signal indicating the size of the detection target, compares the size of the detection target with an upper limit value, and outputs a low level when it is greater than the upper limit value.

  Further, a line connecting the first comparator output terminal and the output terminal of the second comparator is pulled up to a predetermined voltage, and this line is output as a detection signal. The connection point between the first comparator output terminal and the output terminal of the second comparator becomes high level when the size of the detection target is between the lower limit value and the upper limit value. When the value is smaller than the lower limit value or larger than the upper limit value, it becomes a low level. The main control unit can determine whether or not the detection target is in an appropriate state between the lower limit value and the upper limit value depending on whether the detection signal is at a high level or a low level.

  In addition, if the measurement signal indicating the size of the detection target is input to the first comparator and the second comparator via a low-pass filter, the size of the detection target is previously set due to noise or the like. It is possible to prevent erroneous determination that it is not between the set lower limit value and upper limit value, and to improve the reliability of the apparatus main body.

  According to the present invention, the number of signal input ports used for determining whether the magnitude of one or both of the lamp tube current and the tube voltage is within an appropriate range can be reduced, and Cost can be reduced.

It is a block diagram which shows the structure of the principal part of the display apparatus which is embodiment of this invention. It is a figure which shows a detection circuit. It is a figure which shows the circuit which detects the voltage according to the tube current of a discharge lamp. It is a figure which shows the circuit which detects the voltage according to the tube voltage of a discharge lamp. It is a figure which shows the detection circuit concerning another embodiment.

  Hereinafter, a display device according to an embodiment of the present invention will be described.

  FIG. 1 is a block diagram showing a configuration of a main part of a display device according to an embodiment of the present invention. The display device 1 includes a main control unit 2, a lighting control circuit 3, a detection circuit 4, a video signal processing unit 5, and a display 6. The main control unit 2 controls the operation of each part of the main body. The display 6 is a liquid crystal display that displays an image using a discharge lamp 6a such as a cold cathode tube as a backlight light source. The lighting control circuit 3 controls the lighting state of the discharge lamp 6a. This lighting control circuit 3 has an inverter, controls the on / off frequency of the switching transistor on the primary side with the DC voltage connected to the primary side winding of the inverter, and discharges the discharge voltage on the secondary side winding. The voltage necessary for lighting 6a is transmitted. A discharge lamp 6a is connected to the secondary winding. In addition, a driver for controlling the on / off frequency of the switching transistor on the primary side is provided. Since this type of lighting control circuit 3 is publicly known, detailed description thereof is omitted here.

  The detection circuit 4 inputs a detection signal indicating whether or not the magnitude of the tube current in the discharge lamp 6a is between a predetermined lower limit value and an upper limit value to the main control unit 2. The lower limit value and the upper limit value are values set according to the discharge lamp 6a, and define a range when the lighting state of the discharge lamp 6a is appropriate. That is, when the magnitude of the tube current in the discharge lamp 6a is outside the range between the lower limit value and the upper limit value, the lighting state of the discharge lamp 6a is not appropriate.

  Details of the detection circuit 4 will be described later.

  The video signal processing unit 5 processes a video signal input from an external device (not shown), a tuner, or the like, and causes the display 6 to display a video based on the video signal.

  In this display device 1, the lighting control circuit 3 lights the discharge lamp 6 a, and the video signal processing unit 5 displays the video relating to the input video signal on the display 6. The detection circuit 4 outputs a detection signal indicating whether or not the magnitude of the tube current of the discharge lamp 6a is between the lower limit value and the upper limit value. The main control unit 2 monitors the state of the detection signal input from the detection circuit 4. When the state of the detection signal indicates that the magnitude of the tube current of the discharge lamp 6a is not between the lower limit value and the upper limit value, the main control unit 2 performs the lighting control circuit 3 and the video signal. An instruction to stop the operation is given to the processing unit 5 and the like. That is, the main control unit 2 controls the lighting when the magnitude of the tube current of the discharge lamp 6a becomes lower than the lower limit value or when the magnitude of the tube current of the discharge lamp 6a becomes larger than the upper limit value. The circuit 3 and the video signal processing unit 5 are instructed to stop the operation. The lighting control circuit 3, the video signal processing unit 5, and the like stop their operations in accordance with instructions from the main control unit 2 regarding the operation stop.

  As a result, when the display device 1 detects an abnormality in the discharge lamp 6a, the peripheral circuit including the lighting control circuit 3 that controls the lighting of the discharge lamp 6a and the video signal processing unit 5 is stopped. Can be prevented from being damaged. Further, the main control unit 2 has one signal input port number for determining whether or not the magnitude of the tube current of the discharge lamp 6a is between the lower limit value and the upper limit value (within an appropriate range). The cost of the main body can be reduced.

  Next, details of the detection circuit 4 will be described. FIG. 2 is a diagram illustrating a detection circuit. The detection circuit 4 has two comparators CP1 and CP2. The comparator CP1 corresponds to the first comparator in the present invention, and compares a predetermined lower limit value (for example, 3 mA) of the tube current with the tube current of the discharge lamp 6a. The comparator CP2 corresponds to the second comparator in the present invention, and compares a predetermined upper limit value (for example, 8 mA) of the tube current with the tube current of the discharge lamp 6a.

  As shown in FIG. 2, a voltage (measurement signal) corresponding to the tube current of the discharge lamp 6a is constituted by a resistor Ra and a capacitor Ca at the + input terminal of the comparator CP1 and the − input terminal of the comparator CP2. Is entered through. Specifically, as shown in FIG. 3, the voltage of the resistor R11 connected to one end of the discharge lamp 6a is used as a tube current measurement signal, and the + input terminal of the comparator CP1 and the comparator CP2 are connected via the low-pass filter 11. -The signal is input to the input terminal. The diode D11 connected in parallel to the resistor R11 is provided for measuring the tube current flowing in one direction of the discharge lamp 6a. That is, the current flowing in the forward direction of the diode D11 is cut, the voltage corresponding to the tube current flowing in the reverse direction of the diode D11 is measured, and input to the + input terminal of the comparator CP1 and the −input terminal of the comparator CP2.

  A voltage corresponding to the lower limit value (for example, 3 mA) of the tube current of the discharge lamp 6a is input to the negative input terminal of the comparator CP1. Specifically, a voltage obtained by dividing the power supply voltage Vcc with resistors R1 and R2 is input. The resistance values of the resistors R1 and R2 are determined so that a voltage corresponding to the lower limit value of the tube current of the discharge lamp 6a can be drawn. Further, a voltage corresponding to the upper limit value (for example, 8 mA) of the tube current of the discharge lamp 6a is input to the + input terminal of the comparator CP2. Specifically, a voltage obtained by dividing the power supply voltage Vcc by resistors R3 and R4 is input. The resistance values of the resistors R3 and R4 are determined so that a voltage corresponding to the upper limit value of the tube current of the discharge lamp 6a can be drawn.

  Further, diodes D1 and D2 are connected in the opposite directions to the output terminals of the comparators CP1 and CP2, respectively (connected to the cathode side of the diodes D1 and D2). The anodes of the diodes D1 and D2 are connected at point A. The point A is pulled up to an appropriate voltage Vi through a resistor R5.

  Further, a resistor R6 and a resistor R7 are provided between the point A and the ground, and a diode D3 is connected to a connection point between the resistor R6 and the resistor R7. The diode D3 has a cathode connected to a connection point between the resistor R6 and the resistor R7. The anode of the diode D3 is connected to the input port of the main controller 2 as a detection signal.

  Next, the operation of the detection circuit 4 will be described.

  First, the case where the tube current of the discharge lamp 6a input to the detection circuit 4 is between the lower limit value and the upper limit value will be described. In this case, the output terminals of the comparators CP1 and CP2 are held at a high level. Therefore, the point A is held at a high level. At this time, the resistors R5, R6, and R7 have their resistance values set so that the voltage on the cathode side of the diode D3 is higher than the voltage on the anode side. Therefore, the detection signal input to the main control unit 2 is at a high level. When the input detection signal is at a high level, the main control unit 2 determines that the tube current of the discharge lamp 6a is between the lower limit value and the upper limit value (in an appropriate state).

  In addition, since the measurement signal of the tube current of the discharge lamp 6a is input to the comparator CP1 and the comparator CP2 via the low-pass filter 11, even if this measurement signal changes temporarily greatly due to noise or the like, the influence thereof Not receive. Therefore, the reliability of the display device 1 main body can be secured.

  Next, when the tube current of the discharge lamp 6a input to the detection circuit 4 becomes lower than the lower limit value, the output terminal of the comparator CP2 is held at a high level, but the output terminal of the comparator CP1 is at a low level. Retained. For this reason, at the point A, the voltage is drawn to the output terminal side of the comparator CP1 through the diode D1 and becomes a low level. As a result, the voltage on the cathode side of the diode D3 becomes lower than the voltage on the anode side, and the detection signal input to the main control unit 2 is also at a low level. The main control unit 2 determines that the input detection signal indicates that the tube current of the discharge lamp 6a is not between the lower limit value and the upper limit value (in an inappropriate state). At this time, the main control unit 2 instructs the lighting control circuit 3, the video signal processing unit 5 and the like to stop the operation.

  Further, when the tube current of the discharge lamp 6a inputted to the detection circuit 4 becomes higher than the upper limit value, the output terminal of the comparator CP1 is held at a high level, but the output terminal of the comparator CP2 is kept at a low level. Retained. For this reason, at point A, the voltage is drawn to the output terminal side of the comparator CP2 via the diode D2 and becomes low level. As a result, the voltage on the cathode side of the diode D3 becomes lower than the voltage on the anode side, and the detection signal input to the main control unit 2 is also at a low level. The main control unit 2 determines that the input detection signal indicates that the tube current of the discharge lamp 6a is not between the lower limit value and the upper limit value (in an inappropriate state). At this time, the main control unit 2 instructs the lighting control circuit 3, the video signal processing unit 5 and the like to stop the operation.

  As described above, in this display device 1, whether or not the magnitude of the tube current of the discharge lamp 6 a is within an appropriate range (between the lower limit value and the upper limit value) is determined based on one detection signal. The number of input ports in the control unit 2 can be reduced, and the cost of the main body can be reduced.

  In the above embodiment, the detection circuit 4 outputs a detection signal indicating whether or not the magnitude of the tube current of the discharge lamp 6a is between the lower limit value and the upper limit value. It is good also as a structure which outputs the detection signal which shows whether the magnitude | size of a tube voltage exists between a lower limit and an upper limit.

  In this case, a measurement signal obtained by measuring the tube voltage of the discharge lamp 6a may be input to the + input terminal of the comparator CP1 and the − input terminal of the comparator CP2 via the low-pass filter 11. Specifically, as shown in FIG. 4, the voltage at the connection point of the resistors R20 and R21 connected in parallel to the discharge lamp 6a is connected to the + input terminal of the comparator CP1 and the comparator CP2 via the low pass filter 11. -Input to the input terminal. Further, the resistance value of the resistors R1 and R2 is adjusted to the negative input terminal of the comparator CP1, and a voltage corresponding to the lower limit value of the tube voltage of the discharge lamp 6a is input to the negative input terminal of the comparator CP2. The resistance value of R4 may be adjusted and a voltage corresponding to the upper limit value of the tube voltage of the discharge lamp 6a may be input.

  In the above embodiment, the low-pass filter 11 is provided on the input side of the tube current in the comparators CP1 and C2 and the voltage corresponding to the tube voltage. However, the low-pass filter 11 may be provided on the output side of the comparators CP1 and C2.

  Furthermore, as shown in FIG. 5, the detection signal indicating whether the magnitude of the tube current of the discharge lamp 6a is between the lower limit value and the upper limit value, and the magnitude of the tube voltage of the discharge lamp 6a is the lower limit value. It is good also as a structure which inputs into the main control part 2 the synthetic | combination detection signal which synthesize | combined the detection signal which shows whether it is between upper limit values. In this way, when either the tube current or the tube voltage of the discharge lamp 6a is inappropriate, the operation of the lighting control circuit 3, the video signal processing unit 5, etc. can be stopped. Therefore, the reliability of the display device 1 main body can be further improved.

  Note that the reference numerals with “′” shown in FIG. 5 are circuit components that perform the same operation as the same reference signs without “′”.

1-display device 2-main control unit 3-lighting control circuit 4-detection circuit 5-video signal processing unit 6-display 6a-discharge lamp 11-low pass filter CP1, CP2-comparator

Claims (3)

In a display device that displays video using a backlight,
A lighting control unit that controls the lighting state of a lamp that functions as a backlight; and
A detection unit that outputs at least one of a tube current or a tube voltage in the lamp as a detection target and outputs a detection signal indicating whether the size of the detection target is between a predetermined lower limit value and an upper limit value;
When the detection signal input from the detection unit indicates that the size of the detection target is not between a predetermined lower limit value and an upper limit value, And a main control unit that instructs to turn off. The detector is
A measurement signal indicating the size of the detection target is input, the first comparator compares the size of the detection target with the lower limit value, and outputs a low level when smaller than the lower limit value;
A second comparator that receives the measurement signal, compares the size of the detection target with the upper limit value, and outputs a low level when greater than the upper limit value;
The display device according to claim 1, wherein a line connecting the output terminal of the first comparator and the output terminal of the second comparator is pulled up to a predetermined voltage, and the line is output as the detection signal. .   The display device according to claim 2, wherein the detection unit inputs a measurement signal indicating a size of the detection target to the first comparator and the second comparator through a low-pass filter.

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