JP4902872B2 - Driving device and display device - Google Patents

Description

  The present invention relates to a driving device that applies a driving voltage such as a sine wave having a predetermined frequency to a light source that irradiates light to a display panel, that is, a fluorescent tube that forms a so-called backlight, and a display device using the driving device.

  Conventionally, a liquid crystal display device that displays an image on a liquid crystal panel has been widely used. A liquid crystal display device displays video by driving a liquid crystal panel in accordance with a video signal supplied from an external device such as a PC (personal computer) or a playback device, or a video signal received by a built-in tuner. I have to do it. However, since the liquid crystal panel itself does not have a light emitting function, the liquid crystal display device has a fluorescent tube such as a CCFL (Cold Cathode Fluorescent Lamp) as a backlight that emits light from the back of the liquid crystal panel, It is necessary to mount a driving circuit for applying a driving voltage to the fluorescent tube. A fluorescent tube used as a backlight needs to be driven by a sinusoidal AC voltage, and various drive circuits have been proposed.

  FIG. 9 is a circuit diagram showing an example of a conventional drive circuit. In the figure, reference numeral 100 denotes a fluorescent tube for irradiating light to a liquid crystal panel (not shown). A drive circuit for applying a sinusoidal drive voltage to the fluorescent tube 100 includes a step-up transformer T100, a resonance coil L101 and a capacitor C101, switching NPN transistors Q101 and Q102, resistors R101 and R102, and a power source. E101 and the like. A capacitor C101 is connected in parallel to both ends of the primary side winding T111 of the transformer T100, and a midpoint of the primary side winding T111 is connected to the positive side terminal of the power source E101 via the coil L101. .

  One side of the capacitor C101 is connected to the collector of the transistor Q101, the other side is connected to the collector of the transistor Q102, and the emitters of the transistors Q101 and Q102 are both connected to the ground potential. The base of the transistor Q101 is connected to the positive terminal of the power source E101 via the resistor R101, and is connected to one end of the other primary winding T112 of the transformer T100. Similarly, the base of the transistor Q102 is connected to the positive side terminal of the power source E101 via the resistor R102, and is connected to the other end of the primary side winding T112 of the transformer T100. Also, one end of the secondary winding T120 of the transformer T100 is connected to one end of the fluorescent tube 100, and the other end of the secondary winding T120 and the other end of the fluorescent tube 100 are connected to the ground potential. is there.

  In the drive circuit configured as described above, the two transistors Q101 and Q102 are alternately turned on and off to switch the direction of the current flowing through the primary winding T111 of the transformer T100, and the primary winding T111 and the coil L101. A driving voltage for driving the fluorescent tube 100 is generated by generating a sine wave by a resonance circuit using the inductance and the capacitance of the capacitor C101 and boosting the voltage by the transformer T100. This drive circuit is a self-excited inverter circuit, which has a problem that drive efficiency is poor, and also has a problem that frequency control cannot be performed because the frequency of the drive voltage is determined by the resonance circuit on the primary side.

  FIG. 10 is a circuit diagram showing another example of a conventional drive circuit. In the figure, reference numeral 200 denotes a fluorescent tube, and a drive circuit for driving the fluorescent tube 200 includes a step-up transformer T200, a resonance capacitor C201, a switch SW, a power supply E201, and the like. One end of the primary winding T201 of the transformer T200 is connected to the positive terminal of the power source E201 via the switch SW, and the other end of the primary winding T201 is connected to the ground potential. A capacitor C201 and a fluorescent tube 200 are connected in parallel to the secondary winding T202 of the transformer T200.

  In the drive circuit having the above configuration, the voltage generated in the primary winding T201 is repeatedly boosted by the transformer T201 by repeatedly turning on and off the switch SW, and the leakage inductance L202 of the secondary winding T202, the capacitor C201, A sine wave is generated by the resonance circuit and applied to the fluorescent tube 200. This drive circuit is a separately-excited inverter circuit, and has better drive efficiency than the self-excited inverter circuit shown in FIG.

  In Patent Document 1, a pulse width modulation signal is generated from a level difference between a triangular wave generated by a control IC (Integrated Circuit) and a sine wave generated by a sine wave generation circuit. High voltage generation with a configuration in which the switching transistor connected to the primary winding is driven by PWM (Pulse Width Modulation), and the voltage obtained from the secondary winding of the transformer is demodulated by the pulse width demodulation filter and output. A device has been proposed. This high voltage generation circuit has the advantage that the characteristics of the output voltage can be variably controlled by varying the characteristics of the sine wave generated by the sine wave generation circuit. The high voltage generator is suitable for an electronic device that requires a high voltage such as a copying machine or a laser beam printer.

In Patent Document 2, a transformer, a primary circuit having a switch means in a bridge or push-pull configuration, and a secondary circuit having a combination of one or two pairs of switch means that are complementarily driven are provided. Primary side driving first signal, second signal obtained by two-state modulation of the signal to be amplified, and secondary side driving obtained by passing the first signal and the second signal through a logic circuit The output signal and the voltage source can be isolated by controlling the switch means and the switch means pair with the third signal, and amplifying the power of the two-state modulated second signal and passing through the low-pass filter. An isolated class D amplifier that can set the maximum output appropriately has been proposed. This insulated class D amplifier can be suitably used as an amplifier for acoustic signals, and can also be used for motor drive or uninterruptible power supply.
JP 7-244103 A JP-A-9-46144

  Since the above-described separately excited inverter circuit (see FIG. 10) can drive the fluorescent tube 200 with power efficiency, it is the most widely used drive circuit in current liquid crystal display devices. However, in recent years, there has been a tendency for the fluorescent tubes to increase in size as the liquid crystal display device increases in size. When the fluorescent tube is enlarged, the area where the casing of the liquid crystal display device that forms the ground potential and the fluorescent tube are close to each other increases, and the stray capacitance between the fluorescent tube and the casing increases. There was a problem that the drive efficiency of the system deteriorated.

  In addition, beat noise is a factor that deteriorates the display quality of the liquid crystal display device. Beat noise is noise generated in a striped pattern in an image, and is generated by interference of a liquid crystal panel with an electric field generated by a fluorescent tube. In order to eliminate the beat noise, it is necessary to set the frequency of the sine wave voltage for driving the fluorescent tube in consideration of the vertical synchronization frequency related to the display of the liquid crystal panel. In the drive circuit shown in FIG. 10, the frequency of the sine wave voltage applied to the fluorescent tube 200 is a resonant circuit formed by a leakage inductance L202 of the secondary winding T202 of the transformer T200, a capacitor C201, and a stray capacitance (not shown). Determined by the resonance frequency. However, the drive circuit of FIG. 10 is difficult to eliminate beat noise because it is difficult to accurately set the resonance frequency of the resonance circuit when the uncertain stray capacitance increases due to an increase in the size of the fluorescent tube. There is a problem.

  As a countermeasure against beat noise, there is a method of canceling out the electric field generated by the fluorescent tubes by driving the two fluorescent tubes in opposite phases. However, in this method, the stray capacitance between the two fluorescent tubes is apparently doubled, and the resonance frequency of the resonance circuit must be set low in order to improve the driving efficiency. As a result, a large-capacity resonance capacitor C201 is used on the secondary side of the transformer T200 in the drive circuit, leading to deterioration in the efficiency of the drive circuit and an increase in cost, and the cost of the liquid crystal display device is reduced. There is a problem of inviting an increase. Further, when the resonance frequency is lowered, there is a possibility that the operation limit of the fluorescent tube is reached.

  The high-voltage generator described in Patent Document 1 is mainly intended to generate a high voltage to be applied to a photosensitive drum such as a copying machine or a laser beam printer. Therefore, even if this high voltage generator is used for driving a fluorescent tube of a liquid crystal display device, generation of beat noise cannot be suppressed, and the above-described problem cannot be solved. Similarly, the insulated class D amplifier described in Patent Document 2 is mainly intended to be used as an amplifier for acoustic signals, and even when used for driving a fluorescent tube of a liquid crystal display device, beat noise is generated. Cannot be suppressed, and the above-mentioned problem cannot be solved.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an inverter circuit that connects a fluorescent tube to a secondary winding of a transformer and applies an alternating voltage of a predetermined frequency. A filter means connected to the primary side winding and transmitting a voltage of a predetermined frequency is provided to output a pulse width modulated control signal in synchronism with a vertical synchronizing signal related to display on the display panel, and an inverter circuit By adopting a control configuration, it is possible to drive the fluorescent tube by generating a drive voltage without using a resonance circuit, and drive that can suppress beat noise by driving the fluorescent tube according to the display of the display panel To provide an apparatus.

  Another object of the present invention is to connect a fluorescent tube to the secondary side winding of the transformer, and connect switching means for switching the direction of application of a DC voltage from the power source to the primary side winding. By providing a filter means that transmits the voltage of the frequency, and by controlling the switching of the switching means by outputting a pulse width modulated control signal in synchronization with the vertical synchronization signal related to the display of the display panel, An object of the present invention is to provide a driving device that can drive a fluorescent tube by generating a driving voltage without using a resonance circuit, and can suppress beat noise by driving the fluorescent tube in accordance with the display of a display panel.

  Another object of the present invention is to store a data sequence composed of a plurality of data relating to the pulse width in advance and generate a control signal based on the data sequence, thereby generating a pulse It is an object of the present invention to provide a driving device that can easily generate a width-modulated control signal and control switching by a switching means.

  Another object of the present invention is to store a plurality of data strings in advance and read out the data string corresponding to the tube current of the fluorescent tube to generate a control signal. An object of the present invention is to provide a drive device that can easily adjust a drive voltage by feeding back a state.

  Another object of the present invention is to generate a high-frequency first reference signal in synchronization with the vertical synchronization signal of the display panel, and further generate a low-frequency second reference signal based on the first reference signal. The fluorescent tube synchronized with the vertical synchronizing signal of the display panel by reading the data row in accordance with the second reference signal and generating a control signal in accordance with the first reference signal from each data of the read data row It is an object of the present invention to provide a driving device that can reliably perform the above-described driving.

  Another object of the present invention is to generate a sine wave signal in synchronism with the vertical synchronizing signal of the display panel, and to generate the characteristics (amplitude, frequency, waveform, etc.) of the generated sine wave signal. Drive adjusted in accordance with the state of the fluorescent tube and in synchronization with the vertical signal by adjusting according to the current and generating a pulse width modulated control signal based on the adjusted sine wave signal An object of the present invention is to provide a driving device that can reliably generate voltage and drive a fluorescent tube.

  Another object of the present invention is that the above-described driving device is provided, the fluorescent tube is driven by a driving voltage output from the driving device, and an image is displayed on the display panel by the light emitted from the fluorescent tube. Accordingly, an object of the present invention is to provide a display device capable of displaying an image while suppressing beat noise without being affected by stray capacitance even in a large display panel.

According to a first aspect of the present invention, there is provided a driving device for applying a driving voltage of a predetermined frequency to a fluorescent tube forming a light source of a display panel, a transformer having a secondary winding connected to the fluorescent tube, and the transformer An inverter circuit for applying an alternating voltage of a predetermined frequency to the primary winding of the circuit, control signal output means for outputting a pulse width modulated control signal for controlling the inverter circuit, the inverter circuit and the primary winding And / or a filter means that is arranged between the secondary winding and the fluorescent tube and transmits a voltage of a predetermined frequency, and the control signal output means relates to a pulse width. A storage means in which a data string composed of a plurality of data is stored in advance, a control signal generation means for generating the control signal based on the data string stored in the storage means, and a vertical synchronization signal of the display panel Synchronously, the vertical First reference signal generating means for generating a first reference signal having a higher frequency than the first signal, and a second reference signal generating for generating a second reference signal having a lower frequency than the first reference signal based on the first reference signal. Means for reading a data string from the storage means in response to the second reference signal, the control signal generating means generating a control signal in response to the first reference signal, and displaying the data on the display panel. The control signal is outputted in synchronism with the vertical synchronizing signal.

In the present invention, a fluorescent tube is connected to the secondary side winding of the transformer, an inverter circuit for applying an AC voltage of a predetermined frequency is connected to the primary side winding, and the inverter circuit is controlled by a pulse width modulated control signal. Is controlled to generate a drive voltage and apply it to the fluorescent tube. There is no need to provide a resonant circuit on the primary or secondary side of the transformer. For this reason, the frequency of the drive signal can be accurately controlled even when the stray capacitance is increased due to the enlargement of the display panel and the fluorescent tube. In addition, a control signal for controlling the inverter circuit is generated and output in synchronization with a vertical synchronizing signal related to display on the display panel. Accordingly, since the fluorescent tube can be driven in accordance with the display on the display panel, the fluorescent tube can be driven by controlling the frequency so as to suppress the occurrence of beat noise. Further, filter means that transmits a voltage of a predetermined frequency is disposed between the inverter circuit and the primary winding and / or between the secondary winding and the fluorescent tube. Thereby, a high frequency component can be removed from the AC voltage output from the inverter circuit, and a sine wave voltage having a desired frequency can be applied to the fluorescent tube. In addition, according to the present invention, for example, a plurality of data such as a duty ratio of one pulse of the control signal is collected for one period or half period to form a data string, and this data string is stored in a memory or the like in advance. When generating the control signal, the stored data string may be read to form a waveform. For this reason, it is possible to generate a control signal without mounting a generation circuit such as a sine wave signal and a triangular wave signal necessary for pulse width modulation in the driving device. Also, the frequency and amplitude of the drive voltage can be easily changed by changing the data string stored in the memory. Furthermore, in the present invention, a first reference signal having a frequency higher than that of the vertical synchronization signal is generated in synchronization with the vertical synchronization signal of the display panel, and the first reference signal having a frequency lower than that of the first reference signal is generated based on the first reference signal. Two reference signals are generated. The stored data string is read out by the second reference signal, and the control signal based on the data string is generated by the first reference signal. For example, when data for one cycle of the control signal is stored as a data string, data for one cycle is read according to the second reference signal, and one pulse is read from each data according to the first reference signal. The waveform can be configured to be generated. By setting the frequency of the first reference signal to an integer multiple of the frequency of the vertical synchronization signal and the frequency of the second reference signal being an integer fraction of the first reference signal, a control signal whose frequency is an integer multiple of the vertical synchronization signal is obtained. The fluorescent tube can be driven in synchronization with the vertical synchronizing signal.

The drive device according to a second aspect of the present invention further comprises detection means for detecting a tube current of the fluorescent tube, the storage means stores a plurality of types of data strings, and the control signal output means A data sequence corresponding to the detection result of the detection unit is read from the storage unit, and the control signal generation unit generates the control signal based on the data sequence.

  In the present invention, for example, a plurality of data strings such as different frequency patterns or different amplitude patterns are stored in a memory or the like in advance. Thus, the frequency or amplitude of the drive voltage can be easily changed by changing the data string to be read. Further, the tube current of the fluorescent tube is detected, and the data string to be read is changed according to the detection result. As a result, the driving voltage can be adjusted by feeding back the operating state of the fluorescent tube.

Further, a display device according to a third aspect of the present invention is any one of the above driving devices, a fluorescent tube to which a driving voltage of a predetermined frequency is applied by the driving device, and light emitted from the fluorescent tube is irradiated to display an image. And a display panel for displaying.

  In the present invention, the above-described driving device is mounted on a display device to drive the fluorescent tube and display an image on the display panel. Since the drive device does not use a resonant circuit, even a display device having a large display panel can reliably drive the fluorescent tube without being affected by stray capacitance. Further, since the driving device drives the fluorescent tube according to the vertical synchronization signal of the display panel, it is possible to suppress the occurrence of beat noise in the display of the display panel.

According to the first aspect of the present invention, a fluorescent tube is connected to the secondary winding of the transformer, an inverter circuit that applies an alternating voltage of a predetermined frequency is connected to the primary winding, and a filter that transmits the voltage of the predetermined frequency By providing the means and controlling the inverter circuit with the pulse width modulated control signal, it is not necessary to provide a resonance circuit on the primary side or the secondary side of the transformer. The fluorescent tube can be driven without being affected. Therefore, the fluorescent tube can be easily increased in size, and a display device having a large display panel can be easily realized. Further, by adopting a configuration in which a control signal for controlling the inverter circuit is generated in synchronization with a vertical synchronization signal related to display on the display panel, a driving voltage synchronized with the vertical synchronization signal can be generated. Since the fluorescent tube can be driven in accordance with the display, the generation of beat noise can be suppressed, and the display quality of the display panel can be improved. In addition, a data string composed of a plurality of data relating to the pulse width is stored in advance in a memory or the like, and this data string is read to generate a control signal, thereby enabling a sine wave necessary for pulse width modulation. Since it is possible to generate a control signal without mounting a generation circuit such as a signal and a triangular wave signal, it is possible to reduce the size and cost of the driving device. Further, since the frequency and amplitude of the drive voltage can be easily changed by changing the data string stored in the memory, even various display devices having different sizes or the number of mounted fluorescent tubes can be used. Since the same drive device can be used only by changing the data string, the versatility of the drive device can be improved. Further, a high-frequency first reference signal is generated in synchronization with the vertical synchronization signal of the display panel, a low-frequency second reference signal is generated based on the first reference signal, and a data string is generated according to the second reference signal. And a control signal is generated from each data of the read data string according to the first reference signal, for example, the frequency of the first reference signal is an integer multiple of the frequency of the vertical synchronization signal, and the second reference By setting the frequency of the signal to 1 / integer of the first reference signal, it is possible to generate a control signal whose frequency is an integral multiple of the vertical synchronization signal. Therefore, the fluorescent tube can be driven in synchronization with the vertical synchronization signal, and the generation of beat noise can be suppressed, so that the display quality of the display panel can be improved more reliably.

According to the second aspect of the invention, a plurality of data strings are stored in advance, and the frequency or amplitude of the drive voltage is changed by changing the read data string to change the frequency or amplitude of the drive voltage. Therefore, for example, it is possible to generate a driving voltage according to a change in display brightness or a change in the characteristics of the fluorescent tube due to a temperature change. Furthermore, by adopting a configuration in which the tube current of the fluorescent tube is detected and the data string to be read is changed according to the detection result, the driving voltage can be easily adjusted by feeding back the state of the fluorescent tube. Therefore, the fluorescent tube can be driven with an appropriate driving voltage even when the fluorescent tube has a variation in characteristics or a change in temperature due to a temperature change. Can be improved.

Further, in the case of the third invention, the above-described driving device is mounted on the display device to drive the fluorescent tube and display the image on the display panel, so that the fluorescent light is not affected by the stray capacitance. Since the tube can be reliably driven, a large display device having a large display panel can be easily realized. In addition, since the fluorescent tube can be driven according to the vertical synchronization signal of the display panel, it is possible to suppress the occurrence of beat noise in the display of the display panel, and the display device displays a high-quality image. be able to.

(Embodiment 1)
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. FIG. 1 is a block diagram showing a configuration of a display device according to the present invention. In the figure, reference numeral 1 denotes a display device that displays a video on the display panel 2 in accordance with a video signal or video data input from an external device such as a PC (personal computer) 99. In addition to the display panel 2, the display device 1 includes a fluorescent tube 3, a video display processing unit 4, an operation unit 5, an input unit 6, a drive circuit 10, and the like.

  The display panel 2 is, for example, a liquid crystal panel using a light transmission type liquid crystal device using the birefringence of a liquid crystal layer having a thickness of several μm that can be controlled by an external electric field, and the display panel 2 itself has a light emitting function. Absent. For this reason, one or a plurality of fluorescent tubes 3 are disposed as a backlight on the back surface of the display panel 2, and the display panel 2 displays an image by light emitted from the fluorescent tubes 3. The display panel 2 controls the transmissivity of each pixel by liquid crystal based on various video signals such as RGB signals, vertical synchronization signals, and horizontal synchronization signals given from the video display processing unit 4, thereby Display is done.

  The fluorescent tube 3 is, for example, a CCFL or the like, and is lit by a driving voltage supplied from the driving circuit 10 and irradiates light to the back surface of the display panel 2. The drive circuit 10 turns on the fluorescent tube 3 in accordance with the lighting command given from the video display processing unit 4 and the brightness of the fluorescent tube 3 according to the brightness setting given from the video display processing unit 4. Is adjusted. Further, the drive circuit 10 of the present invention is supplied with a vertical synchronization signal from the video display processing unit 4 to the display panel 2, and lights the fluorescent tube 3 in synchronization with the vertical synchronization signal.

  The operation unit 5 includes a plurality of buttons or switches provided on the front surface or the side surface of the housing of the display device 1. When the display device 1 includes a remote controller, the operation unit 5 may include the remote controller and an infrared signal receiving circuit. The user can change display settings such as the brightness and color of the video displayed on the display panel 2 by operating the buttons or switches of the operation unit 5. The operation content is notified to the video display processing unit 4.

  The input unit 6 has an input terminal connected to an external device such as a PC 99 or a hard disk recorder via a cable, and supplies a video signal or video data supplied from the external device to the video display processing unit 4. It is. Further, the display device 1 may be configured to include a television tuner or the like that receives radio waves related to public television broadcasting instead of the input unit 6, and in this case, a video signal or video data received by the television tuner. May be provided to the video display processing unit 4. Of course, the display device 1 may be configured to include both the input unit 6 and the TV tuner.

  The video display processing unit 4 performs signal processing for converting the video signal or video data given from the input unit 6 into a signal suitable for display on the display panel 2, control of hardware related to display of the display device 1, and the like. Is. For example, the video display processing unit 4 converts the video signal or video data given from the input unit 6 into various video signals necessary for display on the display panel 2 such as RGB signals, vertical synchronization signals, and horizontal synchronization signals, This is applied to the display panel 2. Further, when the operation unit 5 is operated by the user, the video display processing unit 4 notifies the display panel 2 and the drive circuit 10 of the display settings changed by this operation, and according to the changed display settings. Video display is performed. For example, when the setting such as the hue is changed, the video display processing unit 4 notifies the changed setting to the display panel 2 to change the hue, and when the setting such as the brightness is changed. Is configured to change the light emission amount of the fluorescent tube 3 through the changed setting to the drive circuit 10.

  Further, in the display device according to the present invention, when the video display processing unit 4 gives the vertical synchronizing signal to the display panel 2, the same vertical synchronizing signal is also given to the drive circuit 10 of the fluorescent tube 3. The drive circuit 10 outputs a sinusoidal drive voltage synchronized with the vertical synchronization signal supplied from the video display processing unit 4 to the fluorescent tube 3 to drive the fluorescent tube 3 and light the fluorescent tube 3.

  FIG. 2 is a circuit diagram showing a configuration of drive circuit 10 according to Embodiment 1 of the present invention. FIG. 3 is a schematic diagram for explaining the operation of the drive circuit 10 according to the first embodiment of the present invention, and shows output signals of the respective circuits constituting the drive circuit 10. A drive circuit 10 that outputs a drive voltage to the fluorescent tube 3 includes a PLL (Phase Locked Loop) circuit 12, a counter 13, a data string readout circuit 14, a control signal generation circuit 15, a driver 16, a switching circuit 17, a transformer T1, A coil L1 and a capacitor C1 that form a filter, a detection circuit 18 that detects the tube current of the fluorescent tube 3, and a drive control unit 11 that controls each of these circuits are provided.

  The PLL circuit 12 is a circuit that generates an output signal having a frequency that is an integral multiple of the input signal in synchronization with the input signal. The PLL circuit 12 of the drive circuit 10 is supplied with a vertical synchronizing signal (see FIG. 3A) from the video display processing unit 4 of the display device 1, and is an integer multiple (for example, several tens to several hundreds) of the vertical synchronizing signal. The first clock signal (see FIG. 3B) is generated and supplied to the counter 13 and the control signal generation circuit 15.

  The counter 13 counts up in accordance with the first clock signal supplied from the PLL circuit 12 and notifies the data string reading circuit 14 when the count value reaches a predetermined value or determines the logic of the output signal. Circuit. That is, the counter 13 generates a second clock signal (see FIG. 3C) in which the frequency of the first clock signal output from the PLL circuit 12 is an integer, and the second clock signal is read from the data string. Can be applied to the circuit 14.

  The data string reading circuit 14 has a memory such as a mask ROM (Read Only Memory) or an EEPROM (Electrically Erasable Programmable ROM) (not shown), and a pulse signal (hereinafter referred to as “pulse signal”) obtained when the sine wave signal is subjected to pulse width modulation. A plurality of duty ratios of each pulse (PWM (Pulse Width Modulation) signal) are stored in advance as a data string in the memory. In the example shown in FIG. 3 (d), one cycle of the sine wave signal is represented by eight pulses of the PWM signal (however, in practice, several tens to several hundreds of pulses are necessary, but simplified) In the memory of the data string reading circuit 14, a plurality of data of one cycle (eight in the example of FIG. 3) such as 60%, 80%, 70%,. A data string is stored. The data string reading circuit 14 reads one data string from a plurality of data strings stored in the memory in accordance with an instruction given from the drive control unit 11, and controls the data string in synchronization with, for example, the rising edge of the second clock signal. The signal generation circuit 15 is provided.

  The control signal generation circuit 15 is supplied with the first clock signal from the PLL circuit 12 and the data string from the data string reading circuit 14. The control signal generation circuit 15 sequentially generates a pulse with a specified duty ratio according to each data of a given data string, and controls a PWM signal (see FIG. 3E) composed of the generated plurality of pulses. The signal is output to the driver 16 as a signal.

  The switching circuit 17 is a bridge circuit composed of two P-type transistors Q1 and Q3 and two N-type transistors Q2 and Q4. Specifically, the sources of the transistors Q1 and Q3 are connected to the positive terminal of the power supply E1, the drain of the transistor Q1 is connected to the drain of the transistor Q2, and the drain of the transistor Q3 is connected to the drain of the transistor Q4. The source of Q4 is connected to the ground potential. One end of the primary side winding T11 of the transformer T1 is connected to the drains of the transistors Q1 and Q2, and the other end of the primary side winding T11 of the transformer T1 is connected to the drains of the transistors Q3 and Q4 via the coil L1. Is connected. The gates of the transistors Q1 to Q4 are connected to the driver 16, respectively.

  When the transistors Q1 and Q4 are turned on and the transistors Q2 and Q3 are turned off in the switching circuit 17, a current flows from the power source E1 through the transistor Q1 to the primary side winding T11 of the transformer T1. A current flows from T11 to the ground potential through the transistor Q4. When the transistors Q1 and Q4 are turned off and the transistors Q2 and Q3 are turned on, a current flows from the power source E1 through the transistor Q3 to the primary winding T11 of the transformer T1, and the transistor Q2 from the primary winding T11. Current flows through to ground potential. That is, the application direction of the voltage applied to the primary winding T11 of the transformer T1 is reversed between when the transistors Q1 and Q4 are turned on and when the transistors Q2 and Q3 are turned on. In other words, the switching circuit 17 is an inverter circuit that converts a DC voltage from the power supply E1 into an AC voltage.

  The driver 16 is a circuit that performs switching by the switching circuit 17 in accordance with the control signal given from the control signal generation circuit 15. For example, the driver 16 turns on the transistors Q1 and Q4 of the switching circuit 17 and turns off the transistors Q2 and Q3 when the supplied control signal is “H”, and turns off the transistors Q2 and Q3. The transistors Q2 and Q3 of the switching circuit 17 are turned on and the transistors Q1 and Q4 are turned off.

  One end of the fluorescent tube 3 is connected to one end of the secondary winding T12 of the transformer T1, and the other end is connected to the ground potential. A capacitor C1 is connected between both ends of the secondary winding T12. The AC voltage applied to the primary side winding T11 of the transformer T1 is boosted to a voltage value corresponding to the number of turns of the primary side winding T11 and the secondary side winding T12 and applied to the fluorescent tube 3 as a driving voltage. Applied. At this time, the coil L1 and the capacitor C1 form a filter, transmit the frequency of the desired sine wave signal, and the inductance and the capacitance value are determined in advance so as to cut the higher frequency. Thereby, the sine wave signal set by the drive control unit 11 is restored, and a drive voltage having a desired frequency is applied to the fluorescent tube 3.

  The other end of the fluorescent tube 3 is connected to the ground potential via the detection circuit 18. The detection circuit 18 includes two diodes D1 and D2 and a resistor R1. The anode of the diode D1 is connected to the other end of the fluorescent tube 3, and the cathode is connected to the ground potential via the resistor R1. The anode of the diode D2 is connected to the ground potential, and the cathode is connected to the other end of the fluorescent tube 3. The fluorescent tube 3 to which the driving voltage is applied emits light, and a tube current flows to the detection circuit 18 along with this. This tube current flows from the diode D1 of the detection circuit 18 to the ground potential through the resistor R1. The diode D2 is a protective diode. The detection circuit 18 outputs a voltage between the diode D1 and the resistor R1, that is, a voltage applied to the resistor R1 by the tube current to the drive control unit 11 as a tube current detection result.

  The drive control unit 11 includes an A / D conversion circuit (not shown) that converts the voltage detected by the detection circuit 18 into a digital value. The drive control unit 11 is given setting information such as brightness setting from the video display processing unit 4 of the display device 1, and according to the given setting information and the tube current detected by the detection circuit 18. The data string read circuit 14 is instructed to read which data string from the memory.

  FIG. 4 is a schematic diagram showing an example of a data string stored in the memory of the data string reading circuit 14. In the memory of the data string reading circuit 14, a plurality of data strings are stored with one cycle of the sine wave signal of the data relating to the duty ratio of each pulse of the PWM signal as one set of data strings. FIG. 4 shows three data strings in which the amplitude of the sine wave signal increases in order from the data string (a) to (c). In the memory of the data string reading circuit 14, the data string is stored in order so that the amplitude gradually increases (or decreases), and the data string reading circuit 14 responds to an instruction given from the drive control unit 11. One data string is read out and output.

  FIG. 5 is a flowchart showing the procedure of the driving process of the fluorescent tube 3 performed by the drive circuit 10 according to the first embodiment of the present invention, which is the process performed by the drive control unit 11 of the drive circuit 10. First, the drive control unit 11 performs various starting processes such as starting the PLL circuit 12 (step S1). After the start-up process is completed, the drive control unit 11 acquires setting information given from the video processing control unit 4 (step S2) so that a drive voltage for lighting the fluorescent tube 3 can be applied with brightness according to the setting. The data string to be read is determined by the data string reading circuit 14 (step S3), and an instruction is given to the data string reading circuit 14 to turn on the fluorescent tube 3 with a desired brightness.

  Next, the drive control unit 11 checks whether an instruction to stop driving the fluorescent tube 3 is given from the video processing control unit 4 (step S4). When the stop instruction is not given (S4: NO), the drive controller 11 determines the current value of the tube current detected by the detection circuit 18 (in practice, the voltage between the diode D1 and the resistor R1 is A / D converted value) is obtained (step S5), and the target value of the tube current corresponding to the desired brightness is compared with the detected tube current value to determine whether the tube current of the fluorescent tube 3 is the target value. Whether or not is checked (step S6). If the detected tube current is the target value (S6: YES), the drive control unit 11 returns to step S4.

  If the detected tube current is not the target value (S6: NO), the drive control unit 11 further checks whether the tube current is less than the target value (step S7). When the tube current is less than the target value (S7: YES), the drive control unit 11 changes the data string read by the data string reading circuit 14 to a data string that increases the amplitude of the drive voltage by one step (step S8). Return to step S4. When the tube current is larger than the target value (S7: NO), the drive control unit 11 changes the data string read by the data string reading circuit 14 to a data string that decreases the amplitude of the drive voltage by one step (step S9). Return to step S4.

  Thereafter, the drive control unit 11 repeatedly performs the processing from step S4 to S9, and when an instruction to stop driving the fluorescent tube 3 is given from the video processing control unit 4 in step S4 (S4: YES), the PLL circuit Various stop processes such as 12 stop are performed (step S10), and the drive process is terminated.

  In the display device 1 having the above configuration, the fluorescent tube 3 is connected to the secondary winding T12 of the transformer T1 of the drive circuit 10, the switching circuit 17 is connected to the primary winding T11 of the transformer T1, The driver 16 is switched by the switching circuit 17 based on the control signal (PWM signal) generated by the control signal generation circuit 15 to generate a sinusoidal drive voltage, so that the primary side of the transformer T1 and Since a sinusoidal drive voltage can be generated without providing a resonance circuit on the secondary side, the drive circuit 10 can drive the fluorescent tube 3 without being affected by the stray capacitance of the fluorescent tube 3. Therefore, the fluorescent tube 3 can be easily enlarged and the display panel 2 of the display device 1 can be easily enlarged.

  In addition, the vertical synchronization signal given to the display panel 2 by the video display processing unit 4 of the display device 1 is also given to the drive circuit 10, and the drive circuit 10 generates a control signal (PWM signal) synchronized with the vertical synchronization signal. As a result, the drive circuit 10 can generate a drive voltage according to the vertical synchronization signal, and can drive the fluorescent tube 3 according to the display on the display panel 2, thereby suppressing the occurrence of beat noise. The display quality of the display panel 2 can be improved.

  In addition, a plurality of data relating to the duty ratio of the PWM signal is stored in advance as a data string in a memory included in the data string reading circuit 14, and the control signal generation circuit 15 generates a control signal for the PWM signal based on the data string. Since the drive circuit 10 does not need to have a generation circuit for generating a sine wave signal and a triangular wave signal or the like, which is normally necessary for generating a PWM signal, the PWM signal can be generated easily by adopting the generation configuration. The circuit 10 can be reduced in size and cost. In addition, since the characteristics of the drive circuit 10 can be changed simply by rewriting the data in the memory of the data string readout circuit 14, the versatility of the drive circuit 10 can be improved.

  The data string reading circuit 14 stores a plurality of data strings in advance, and the data reading circuit 14 reads one data string and gives it to the control signal generation circuit 15 in accordance with an instruction from the drive control unit 11. Thus, the amplitude of the drive voltage applied to the fluorescent tube 3 can be changed dynamically and easily. Further, the tube current of the fluorescent tube 3 is detected by the detection circuit 18, and the drive control unit 11 changes the data string to be read by giving an instruction to the data string reading circuit 14 according to the detection result. Since the driving voltage can be adjusted by feeding back the lighting state of the tube 3, the fluorescent tube 3 can be lighted with a desired brightness with high accuracy. Therefore, even if the characteristics of the fluorescent tube 3 vary or the characteristics of the fluorescent tube 3 change due to temperature changes, the fluorescent tube 3 can be driven with an appropriate driving voltage. Quality can be improved more reliably.

  Also, a first clock signal having a frequency that is an integral multiple of the vertical synchronizing signal provided from the video display processing unit 4 is generated by the PLL circuit 12, and a second clock having a frequency that is 1 / integer of the first clock signal. The signal is generated by the counter 13, and the data string reading circuit 14 reads the data string in response to the second clock signal and gives it to the control signal generating circuit 15, and the control signal generating circuit 15 receives the data string in accordance with the first clock signal. Since the fluorescent tube 3 can be driven with a sinusoidal driving voltage synchronized with the vertical synchronizing signal by generating the control signal of the PWM signal from the beat signal, beat noise is generated in the video display of the display panel 2. This can be suppressed, and the display quality of the display device 1 can be improved.

  In addition, a coil L1 is provided on the primary side of the transformer T1 of the drive circuit 10 and a capacitor C1 is provided on the secondary side to serve as a filter so that only a voltage having a predetermined frequency is transmitted. The sine wave voltage having a desired frequency can be applied to the fluorescent tube 3.

  In the present embodiment, the fluorescent tube 3 is driven with a sinusoidal drive voltage. However, the present invention is not limited to this, and the fluorescent tube 3 may be driven with a drive voltage having another waveform. . In this case, drive voltages having various waveforms can be generated and applied to the fluorescent tube 3 only by appropriately changing the data in the memory included in the data string readout circuit 14. Further, the memory of the data string readout circuit 14 is configured to store the duty ratio of each pulse of the PWM signal as data, but the present invention is not limited to this, and a pulse of the PWM signal can be generated. Other data may be stored. For example, it is possible to store a series of “0” or “1” data corresponding to each pulse of the PWM signal.

  FIG. 6 is a schematic diagram illustrating a waveform example of a drive voltage that can be generated in the drive circuit 10. In the drive circuit 10 of the present invention, the control signal can be changed according to the data stored in the memory of the data string readout circuit 14, and drive voltages having various waveforms can be generated and applied to the fluorescent tube 3. . For example, with respect to the basic sine wave shown in FIG. 6A, the amplitude of the sine wave can be increased or decreased by changing the duty ratio of the control signal (see FIG. 6B).

  Further, the cycle of the sine wave can be changed by changing the cycle of the repetitive pattern of the control signal (see FIG. 6C). Depending on the pattern of the control signal, a drive voltage having a waveform other than a sine wave can be generated (see FIG. 6D). Further, by adjusting the output period of the control signal, adjustment of the generation timing of the sine wave (see FIG. 6E), adjustment of the generation period of the sine wave (see FIG. 6F), etc. It can also be done (these are so-called PWM dimming or burst dimming). The data stored in the memory of the data string readout circuit 14 is not limited to the pattern that generates the drive voltage having the waveform shown in FIG. 6, but may be the one that generates the drive voltage having another waveform.

  The switching circuit 17 shown in FIG. 2 has a full-bridge circuit configuration using four transistors Q1 to Q4, but is not limited to this, and may have other configurations. Further, the control method of the switching circuit 17 by the driver 16 is not limited to that of the present embodiment. Similarly, the configuration of the detection circuit for detecting the tube current of the fluorescent tube 3 is not limited to the circuit configuration shown in FIG. Further, in order to apply only a sinusoidal driving voltage of a predetermined frequency to the fluorescent tube 3, the coil L1 is provided on the primary side of the transformer T1 as a filter, and the capacitor C1 is provided on the secondary side. However, the present invention is not limited to this, and a configuration in which filters having other configurations are provided on the primary side and / or the secondary side of the transformer T1 may be employed. For example, in the circuit shown in FIG. 2, the coil L1 is not provided on the primary side of the transformer T11, and the degree of coupling between the primary side winding T11 and the secondary side winding T12 of the transformer T1 (primary side winding T11). 2 is determined by the ratio of the magnetic flux induced to the secondary winding T12 and the structure of the winding, etc., to obtain the same filter effect as the circuit of FIG. it can.

(Embodiment 2)
FIG. 7 is a circuit diagram showing a configuration of drive circuit 310 according to Embodiment 2 of the present invention. The drive circuit 10 according to the first embodiment is configured to generate a PWM signal (control signal) by the PLL circuit 12, the counter 13, the data string readout circuit 14, and the control signal generation circuit 15, but according to the second embodiment. Instead of these, the drive circuit 310 is configured to generate a PWM signal (control signal) by the sine wave generation circuit 312, the amplitude adjustment circuit 313, the triangular wave generation circuit 314, and the control signal generation circuit 315.

  The sine wave generation circuit 312 is supplied with a vertical synchronization signal from the video display processing unit 4 of the display device 1. The sine wave generation circuit 312 generates a sine wave having a frequency that is an integral multiple of the frequency of the vertical synchronization signal in synchronization with a given vertical synchronization signal and outputs the sine wave to the amplitude adjustment circuit 313. The amplitude adjustment circuit 313 amplifies and adjusts the amplitude of the sine wave given from the sine wave generation circuit 312 according to an instruction from the drive control unit 311, and outputs it to the control signal generation circuit 315. The triangular wave generation circuit 314 generates a triangular wave having a frequency higher than that of the sine wave output from the sine wave generation circuit 312 and outputs the triangular wave to the control signal generation circuit 315.

  The control signal generation circuit 315 has a comparator that compares the sine wave supplied from the amplitude adjustment circuit 313 with the triangular wave supplied from the triangular wave generation circuit 314, and the comparison result between the sine wave and the triangular wave is a control signal. Is output to the driver 16 as follows. FIG. 8 is a schematic diagram for explaining a control signal generation method by the control signal generation circuit 315 of the drive circuit 310 according to the second embodiment of the present invention. In FIG. 8, the sine wave (a) from the amplitude adjustment circuit 313 and the triangular wave (b) from the triangular wave generation circuit 314 are overlapped. The control signal generation circuit 3 compares the voltage values of the sine wave (a) and the triangular wave (b) with a comparator, and outputs “H” as a control signal when the voltage value of the sine wave (a) is large. When the voltage value of the triangular wave (b) is large, “L” is output as the control signal (see FIG. 8C). The control signal generated in this way is given to the driver 16, and the driver 16 switches on / off of the transistors Q1 to Q4 of the switching circuit 17, so that a sine wave is generated in the primary winding T11 of the transformer T1. It is generated and boosted by the transformer T1, and the boosted sine wave is applied to the fluorescent tube 3 as a drive voltage. Since the configuration and operation of each circuit after the driver 16 are the same as those of the drive circuit 10 of the first embodiment, detailed description thereof is omitted.

  When a drive voltage is applied to the fluorescent tube 3, the tube current is detected by the detection circuit 18, and the detection result is given to the drive control unit 311. In addition, setting information such as brightness is given to the drive control unit 311 from the video display processing unit 4 of the display device 1. The drive control unit 311 controls the amplification factor of the amplitude of the sine wave by the amplitude adjustment circuit 313 based on the given setting information and the tube current detection result. Further, when the instruction to turn off the fluorescent tube 3 is given from the video display processing unit 4, the operation of the sine wave generation circuit 312 is stopped, and when the instruction to turn on is given, the operation of the sine wave generation circuit 312 is started. As described above, the drive control unit 311 controls the operation of the sine wave generation circuit 312.

  The drive circuit 310 according to the second embodiment having the above configuration is fluorescent with a drive voltage synchronized with the vertical synchronization signal provided from the video display processing unit 4 of the display device 1, as with the drive circuit 10 according to the first embodiment. The tube 3 can be driven and the drive voltage can be adjusted according to the tube current of the fluorescent tube 3. Therefore, the drive circuit 310 according to the second embodiment has the same effect as the drive circuit 10 according to the first embodiment, and drives the fluorescent tube 3 without being affected by the stray capacitance of the fluorescent tube 3. It is possible to improve the display quality of the display panel 2 by suppressing the occurrence of beat noise. In the drive circuit 310 of the second embodiment, the amplitude is adjusted by the amplitude adjustment circuit 313 as the characteristic of the sine wave signal generated by the sine wave generation circuit 312. However, the present invention is not limited to this. The drive circuit 310 may further include a circuit that adjusts other characteristics such as the frequency, waveform, signal generation timing, and / or signal generation period of the sine wave signal generated by the sine wave generation circuit 312.

  Since the other configuration of the drive circuit 310 according to the second embodiment is the same as that of the drive circuit 10 according to the first embodiment, the corresponding portions are denoted by the same reference numerals and description thereof is omitted.

It is a block diagram which shows the structure of the display apparatus which concerns on this invention. 1 is a circuit diagram illustrating a configuration of a drive circuit according to a first embodiment of the present invention. It is a schematic diagram for demonstrating operation | movement of the drive circuit which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows an example of the data row memorize | stored in the memory of the data row reading circuit. It is a flowchart which shows the procedure of the drive process of the fluorescent tube which the drive circuit which concerns on Embodiment 1 of this invention performs. It is a schematic diagram which shows the example of a waveform of the drive voltage which can be generate | occur | produced in a drive circuit. It is a circuit diagram which shows the structure of the drive circuit which concerns on Embodiment 2 of this invention. It is a schematic diagram for demonstrating the generation method of the control signal by the control signal generation circuit of the drive circuit which concerns on Embodiment 2 of this invention. It is a circuit diagram which shows an example of the conventional drive circuit. It is a circuit diagram which shows the other example of the conventional drive circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Display panel 3 Fluorescent tube 4 Image display processing part 5 Operation part 6 Input part 10 Drive circuit (drive device)
11 Drive control unit (control signal output means)
12 PLL circuit (control signal output means, first reference signal generation means)
13 counter (control signal output means, second reference signal generation means)
14 Data string readout circuit (control signal output means, storage means)
15 Control signal generation circuit (control signal output means, control signal generation means)
16 Driver 17 Switching circuit (switching means, inverter circuit)
18 detection circuit 310 drive circuit (drive device)
311 Drive control unit (control signal output means)
312 Sine wave generation circuit (control signal output means, sine wave signal generation means)
313 Amplitude adjustment circuit (control signal output means, adjustment means)
314 Triangular wave generation circuit (control signal output means)
315 Control signal generation circuit (control signal output means, control signal generation means)
C1 capacitor (filter means)
D1, D2 Diode E1 Power supply L1 Coil (filter means)
Q1 to Q4 Transistor R1 Resistance T1 Transformer T11 Primary winding T12 Secondary winding

Claims (3)

In a driving device that applies a driving voltage of a predetermined frequency to a fluorescent tube that forms a light source of a display panel,
A transformer having a secondary winding connected to the fluorescent tube;
An inverter circuit for applying an alternating voltage of a predetermined frequency to the primary winding of the transformer;
Control signal output means for outputting a pulse width modulated control signal for controlling the inverter circuit;
A filter means disposed between the inverter circuit and the primary side winding and / or between the secondary side winding and the fluorescent tube and transmitting a voltage of a predetermined frequency;
The control signal output means includes a storage means in which a data string composed of a plurality of data relating to a pulse width is stored in advance, and a control signal generation that generates the control signal based on the data string stored in the storage means Means, first reference signal generating means for generating a first reference signal having a higher frequency than the vertical synchronization signal in synchronization with a vertical synchronization signal related to display on the display panel, and based on the first reference signal, Second reference signal generating means for generating a second reference signal having a frequency lower than that of the first reference signal, reading a data string from the storage means according to the second reference signal, and according to the first reference signal Generating a control signal and outputting the control signal in synchronization with a vertical synchronization signal related to display on the display panel.
It further comprises detection means for detecting the tube current of the fluorescent tube,
The storage means stores a plurality of types of data strings,
The control signal output means reads a data string corresponding to the detection result of the detection means from the storage means, and the control signal generation means generates the control signal based on the data string. The drive device according to claim 1 , wherein
The driving device according to claim 1 or 2 ,
A fluorescent tube to which a driving voltage of a predetermined frequency is applied by the driving device;
A display device, comprising: a display panel that displays an image when irradiated with light emitted from the fluorescent tube.

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