Lamp driving device and driving method thereof and liquid crystal display device using the same

The present invention relates to a lamp drive device and a drive method and a liquid crystal display device using the same, and more particularly to a lamp drive device and a drive method having a protection circuit capable of complying with safety standards and a liquid crystal display device using the same.

In general, liquid crystal displays (hereinafter referred to as "LCDs") have a wider range of applications due to their features such as light weight, thinness, and low power consumption drive, and are used in office automation equipment, audio / video equipment, and the like. .. On the other hand, in the LCD, the transmission amount of the light beam is adjusted by the video signals applied to a plurality of control switches arranged in a matrix, and a desired image is displayed on the screen.

Since such an LCD is not a self-luminous display device, a light source such as a backlight is required. Such LCD backlights include a direct type type and an edge type type depending on the arrangement of the lamps, and there are a cold cathode tube lamp and an external electrode type lamp depending on the form of the lamp.

In the classification method based on the arrangement of the lamps, the edge type method is a method in which a lamp is provided around a flat plate, and light is incident on the entire surface of the liquid crystal panel from the lamp using a transparent light guide plate. In the direct type, a plurality of lamps are arranged on a flat surface. Then, a diffuser plate is provided between the lamp and the liquid crystal panel to maintain a constant distance between the liquid crystal panel and the lamp.

Further, in the classification method according to the form of the lamp, in the cold cathode tube lamp (Cold Cathode Fluerescent Lamp) method, electrodes are inserted inside the glass tube at both ends of the glass tube of the lamp to supply power. On the other hand, in the external electrode fluorescent lamp (External Electrode Fluerescent Lighting) method, power is supplied to the electrode portion in which both ends of the glass tube of the lamp are covered with a metal material.

FIG. 1 is a drawing showing a related lamp drive device 60. Referring to FIG. 1, the lamp drive device 60 is connected to a plurality of lamps 36, and an inverter 46 that receives a DC power supply (Vin) from an external power source and converts it into an AC signal, and an AC signal generated from the inverter 46. The transformer 48 that boosts the voltage and supplies the boosted AC signal to the lamp 36, the feedback circuit 42 for detecting the current supplied from the inverter 46 to the lamp 36, and the inverter 46 by the feedback signal generated from the feedback circuit 42. A control unit 44 for controlling is provided.

Here, the transformer 48 has a primary winding 51 connected to the inverter 46, a secondary winding 53 connected to the lamp 36 side, and an auxiliary winding 52 arranged between the primary and secondary windings 51 and 53. And.

The lamp drive device 60 having such a structure must satisfy the safety standard in consideration of the safety of the user. This safety standard states that when the user comes into contact with the lamp drive device 60, the current flowing through the user must be limited to a current (mA) of 0.7 times or less the system operating frequency. In order to satisfy such a standard, a single lamp is manufactured in consideration of this safety standard when it is manufactured.

Specifically, the contact of the user's lamp drive device 60 is set to non-load 2KΩ, the equivalent resistance component of the lamp 36 is set to the normal value of about 200KΩ, the operating frequency is set to 65KHz, and the lamp 36 is operating normally. If the voltage of the secondary winding 53 is made to correspond to 1500V at a certain time, the resonance characteristic of the secondary winding 53 will change abruptly when 2KΩ comes into contact with the secondary winding 53.

Generally, the secondary winding 53 resonates in parallel, and in parallel resonance, the voltage gain of the input and the output changes in proportion to the resistance component of the load. That is, the equivalent resistance component 200KΩ of the lamp 53 and the 2KΩ of the user's no-load resistance 59 are connected in parallel, and the equivalent resistance seen from the secondary winding 53 side is about 2KΩ (200KΩ // 2KΩ). Therefore, when a load change of about 1/100 occurs, a gain change of about 1/100 also occurs in the voltage of the secondary winding 53, which satisfies the safety standard.

Quantitatively calculated, the lamp safety standard limit current for 65KHz frequency is 46mA (0.7 × 65). Also, since the gain of the secondary winding 53 is 1/100, it is about 15V (1500 x 1/100), and the current through 2KΩ is 7mA according to Ohm's law, so it is 46mA or less of the safety standard. It will meet the standard.

However, when driving a plurality of lamps 36, for example, when driving a plurality of 10 lamps 36, the equivalent resistance of the lamps 36 becomes 20 KΩ, and at this time, the user in the system When connecting, that is, when 2KΩ of the no-load resistor 59 is connected, the gain of the output voltage becomes 1/10, so that the voltage of the secondary winding 53 becomes about 150V and flows to the no-load resistor 59. The current will be 70mA and the safety standard cannot be satisfied.

<p> The present invention has been made in view of the above points, and an object of the present invention is to provide a lamp drive device and a drive method capable of complying with safety standards regardless of the number of lamps, and a liquid crystal display device using the same. To do.</p>

<p> In order to achieve the above object of the present invention, the lamp driving device according to the present invention uses at least one lamp, an inverter for supplying an AC signal, and a first voltage and a second voltage for signals from the inverter. The transformer that supplies the first and second voltages boosted to the first and second ends of the lamp, and the first voltage and the second voltage that are supplied to the lamp are detected, respectively. The DC level is the sum of the first and second detection units that output the first detection signal and the second detection signal, and the first and second voltages detected by the first detection unit and the second detection unit. The rectifying unit that integrates into the voltage, the comparing unit that compares the signal integrated by the rectifying unit with a predetermined threshold value, and the inverter in either the shut down state or the operating state according to the comparison result from the comparison unit. The polarities of the first voltage and the second voltage are different from each other, including the transistor for switching to one of the states, and the signals integrated by the rectifying unit are the first voltage and the second voltage.<u style="single">If they have the same magnitude, they cancel each other out and become a zero level signal, and if the first voltage and the second voltage have different magnitudes and do not cancel each other out, they become a constant level signal.</u>It is characterized by that.</p><p> Further, the lamp driving method according to the present invention is a driving method for driving at least one lamp coupled to a transformer that boosts an AC signal from an inverter to a first voltage and a second voltage, respectively, and supplies the boosted signal to the lamp. In the step of detecting the first voltage and the second voltage supplied to the first end and the second end of the lamp and outputting the first detection signal and the second detection signal, respectively, and the first detection signal and The first step includes a step of combining the second detection signals and integrating them into a DC level, a step of comparing the integrated signals with a predetermined threshold voltage, and a step of shutting down the transformer based on the comparison result. The polarities of the 1 voltage and the 2nd voltage are different from each other, and the integrated signal is the 1st voltage and the 2nd voltage.<u style="single">If they have the same magnitude, they cancel each other out and become a zero level signal, and if the first voltage and the second voltage have different magnitudes and do not cancel each other out, they become a constant level signal.</u>It is characterized by that.</p><p> Further, the liquid crystal display device according to the present invention is further provided with a liquid crystal panel for displaying an image with respect to the lamp driving device having the above configuration, and the lamp irradiates the liquid crystal panel with light. ..</p>

<p> As described above, the lamp drive device and the drive method according to the present invention and the liquid crystal display device using the same can comply with the safety standard of the lamp drive device regardless of the number of lamps. Further, in the lamp drive device according to the present invention, when a plurality of lamps are applied in groups, only the reference voltage can be changed and satisfied in order to comply with the safety standard, so that various types and numbers of lamps can be satisfied. Will be applicable to.</p>

FIG. 2 is a drawing showing a liquid crystal display device including a lamp driving device according to an embodiment of the present invention. Referring to FIG. 2, the liquid crystal display device adopting the direct type backlight according to the embodiment of the present invention includes a liquid crystal panel 102 for displaying an image and a tube for irradiating the liquid crystal panel 102 with uniform light. It comprises a backlight assembly that includes a lamp 136 that keeps the current constant, and a lamp drive 160 that drives the backlight assembly.

In the liquid crystal panel 102, liquid crystal cells are arranged in an active matrix between the upper and lower substrates, and a pixel electrode and a common electrode for applying an electric field to each of the liquid crystal cells are provided. Each of such pixel electrodes will be connected to a thin film transistor used as a switch element. The pixel electrode drives the liquid crystal cell together with the common electrode by the data signal supplied through the thin film transistor, and displays the image corresponding to the video signal.

The backlight assembly includes a lamp housing 134, a reflective sheet 114 laminated on the front surface of the lamp housing 134, a plurality of lamps 136 located above the reflective sheet 114, a diffuser plate 112, and an optical sheet 110.

The lamp housing 134 prevents light leakage of visible light emitted from each of the plurality of lamps 136, and reflects visible light traveling to the side surfaces and the back surface of the plurality of lamps 136 toward the front surface, that is, the diffuser plate 112 side. This improves the efficiency of the light generated from the lamp 136.

The reflective sheet 114 is arranged between the upper surface of the lamp housing 134 and the plurality of lamps 136, reflects the light generated from the lamps 136, and irradiates the light in the direction of the liquid crystal display panel 102, thereby achieving light efficiency. To improve.

The diffuser plate 112 allows the light emitted from the plurality of lamps 136 to travel toward the liquid crystal panel 102 so that the light can be incident on a wide range of angles. As such a diffuser plate 112, a film made of a transparent resin coated on both sides with a light diffusing member is used.

The optical sheet 110 can improve the front luminance of the liquid crystal display device and reduce the power consumption by narrowing the viewing angle of the light emitted from the diffuser plate 112.

As shown in FIG. 3, the lamp drive device 160 is connected to a plurality of lamps 136, and is supplied with a DC power supply (Vin) from an external power source to convert it into an AC signal, and an AC generated from the inverter 146. The transformer 148 that boosts the signal and supplies the boosted AC signal to the lamp 136, the feedback circuit 142 for detecting the current supplied from the inverter 146 to the lamp 136, and the inverter 146 by the feedback signal generated from the feedback circuit 142. It is provided with a control unit 144 that controls the above, and a safety circuit 170 that detects the current supplied from the inverter 146 to the lamp 136 and cuts off and maintains the current supplied to the lamp 136.

Each of the plurality of lamps 136 includes a glass tube, an inert gas inside the glass tube, and a negative electrode and a positive electrode provided at both end portions of the glass tube. The inside of the glass tube is filled with an inert gas, and the inner wall of the glass tube is coated with a phosphor. Further, the negative electrode portion and the positive electrode portion of each lamp 136 are integrated into the same polarity.

The inverter 146 receives a DC power supply from an external power supply and switches the built-in switch element to convert the DC power supply into an AC signal.

The transformer 148 is induced in the AC voltage generated in the primary winding 151 by connecting to the inverter 146 to generate an AC signal, the auxiliary winding 152, and the switching of the switch element included in the inverter 146. It includes a secondary winding 153 that generates a high voltage of alternating current that has been amplified and amplified, and an auxiliary winding 152 that is arranged between the primary winding 151 and the secondary winding 153. Such a transformer 148 boosts an AC signal generated from the inverter 146 and supplies it to a plurality of lamps 136.

The feedback circuit 142 detects a high AC voltage generated from the inverter 146 and is supplied to the lamp 136, and generates a feedback voltage. Such a feedback circuit 142 can be located at the output end of the lamp 136, and when located at the output end, detects the output value output from the lamp 136.

The control unit 144 receives the input of the feedback voltage (F / B) generated from the feedback circuit 142 and controls the switch element included in the inverter 146.

The safety circuit 170 detects the high AC voltage generated by the inverter 146 and is supplied to the lamp 136, inspects whether it conforms to safety standards, and cuts off and maintains the current and voltage supplied to the lamp 136. Let me.

A safety circuit 170 connected to the lamp 136 of the liquid crystal display device according to the embodiment of the present invention having such a structure will be discussed in detail with reference to FIG. Referring to FIG. 4, in the safety circuit 170 according to the embodiment of the present invention, the detection unit 171 that detects the voltage supplied to both ends of the plurality of lamps 136 and the signal detected from the detection unit 171 are combined. The rectifying unit 173 that integrates into the DC level, the comparing unit 175 that compares the rectified signal with the reference signal, and the output end of the comparing unit 175 are connected to shut up and shut down the inverter 146. It is equipped with a switching unit 179 that determines (-down).

The detection unit 171 is connected to the secondary winding 153 connected to the lamp 136 to detect the voltage supplied to the secondary winding 153. For example, when the polarities of both ends of the lamp 136 are different and a high voltage of the same magnitude is applied, the detection unit 171 detects high voltages having different polarities at both ends of the lamp 136. That is, detection units 171 are arranged at both ends of the lamp 136.

The rectifier unit 173 adjusts the high voltage detected from each detection unit 171 to one signal, and then half-wave rectifies the signal using a half-wave rectifier 172 in which diodes are arranged in parallel to perform half-wave rectification. The signal is further integrated into a DC level using a low pass filter 174.

The comparison unit 175 compares the signal integrated to the DC level with the threshold voltage or the reference voltage (Vref) by passing through the rectifier unit 173 using the comparator 176, and outputs the signal when it is larger than the reference voltage (Vref). The voltage is turned on, and if it is small, the output voltage is turned off. Here, the reference voltage (Vref) is measured experimentally in consideration of the characteristics of each lamp 136, the operating frequency, the voltage applied to the lamp 136, and the like, and then a voltage conforming to the safety standard is used.

The switching unit 179 maintains the switch 178 in a turn-off state when there is no output voltage of the comparison unit 175, that is, when the voltage from the comparison unit 175 is lower than the reference voltage (Vref). As a result, the switching unit 179 keeps the inverter 146 of the lamp drive device 160 connected to the emitter in a high state, so that the lamp drive device 160 keeps the shut-up state. On the other hand, when the output voltage of the comparison unit 175 is turned on, that is, when the voltage from the comparison unit 175 is higher than the reference voltage (Vref), the switching unit 179 turns on the switch 178 to the lamp drive device 160. Ground the powering inverter 146 so that the lamp drive 160 is shut down. The switch 178 is a transistor, the base terminal is connected to the output terminal of the comparison unit 176, the emitter terminal is grounded, and the collector terminal is connected to the inverter 146.

A method of driving a lamp driving device of a liquid crystal display device according to an embodiment of the present invention having such a structure will be considered. First, in the case of normal operation, that is, when the contact between the user and the lamp driving device 160 does not occur, when the polarities of both ends of the lamp 136 are different from each other and signals of the same magnitude are applied, the detection unit After combining the two signals detected from 171, the two signals that have passed through the rectifying unit 173 cancel each other out and become a zero-level signal. As a result, the output voltage of the comparison unit 175 is always in the turn-off output state, the switch 178 of the switching unit 179 is turned off, and the lamp drive device 160 is maintained in the shut-up state.

Next, when the user contacts the lamp drive 160, that is, when the 2KΩ no-load resistor 159 contacts one side of the secondary winding 153, it is substantially one side of the secondary winding 153. The output voltage will be reduced to about 1/10, and the voltage will rise on the other side. As a result, the signal outputs of the detection unit 171 are left with signals that do not cancel each other out, and this signal is output at a constant level voltage by passing through the rectifying unit 173. When such a constant level voltage is compared with the reference voltage and the constant level voltage is large, the comparison unit 175 is turned on and the output becomes high, and this output turns on the switch 178. .. As a result, the inverter 146 of the lamp drive device 160 connected to the emitter of the switch 178 is grounded and goes into a low state, so that the lamp drive device 160 is shut down.

Here, the user has described the no-load resistor 159 as 2 KΩ, the equivalent resistance of the lamp 136 as 200 KΩ, and the plurality of lamps 136 as 10 lamps, respectively, but the present invention is not limited to this. .. Further, in the safety circuit 170 according to the embodiment of the present invention, as shown in FIG. 5, instead of detecting the voltage supplied to both ends of the lamp 136, the same by connecting a resistor and detecting the current. Can have various effects. Furthermore, the lamp driving device according to the embodiment of the present invention can be applied regardless of the form of the lamp, that is, the cold cathode tube type and the external electrode type. More specifically, the signal supplied to both ends of the lamp corrects the reference voltage (Vref) of comparison unit 175 without being related to the fact that one side is grounded and one side is supplied with a high voltage signal. Thereby, the voltage and current changes of the lamp drive device 160 can be detected, and such changes can be compared with the reference value to shut down and shut up the lamp drive device 160.

The lamp drive device according to the embodiment of the present invention is utilized in various industrial fields such as portable information equipment, general information equipment, office information equipment, etc., as shown in the notebook illustrated in FIG. be able to.

As described above, the lamp drive device and the drive method according to the embodiment of the present invention and the liquid crystal display device using the lamp drive device can comply with the safety standard of the lamp drive device regardless of the number of lamps. Further, the lamp drive device according to the embodiment of the present invention can be satisfied by changing only the reference voltage in order to comply with the safety standard when applying a plurality of lamps in a group unit, and thus various types. And it can be applied to the number of lamps.

As described above, it can be understood that those skilled in the art can make various changes and modifications without departing from the technical idea of the present invention. Therefore, the technical scope of the present invention is not limited to the contents described in the detailed description of the specification, but must be defined by the scope of claims.

<figref num="1">It is a drawing which shows the related lamp drive device.</figref><figref num="2">It is a drawing which shows the liquid crystal display device which concerns on embodiment of this invention.</figref><figref num="3">It is a drawing which shows the lamp drive device of FIG.</figref><figref num="4">It is a drawing which shows the safety circuit of FIG. 3 in detail.</figref><figref num="5">It is a figure which shows the other form of the safety circuit of FIG.</figref><figref num="6">It is a drawing which shows the notebook in which the lamp drive device which concerns on embodiment of this invention is built.</figref>

Code description

36, 136 Lamp 42, 142 Feedback circuit 44, 144 Control unit 46, 146 Inverter 48, 148 Transformer 51, 151 Primary winding 52, 152 Auxiliary winding 53, 153 Secondary winding 60, 160 Lamp drive 102 LCD panel 110 Optical sheet 112 Diffusing plate 114 Reflecting sheet 134 Lamp housing 170 Safety circuit 171 Detection unit 173 Rectifier unit 175 Comparison unit