KR101202031B1 - Device for driving light source of liquid crystal - Google Patents

Abstract

The present invention relates to a drive device for a light source for a liquid crystal display device, the light source emitting light; An inverter providing a driving voltage for driving the light source; A transformer for boosting a driving voltage provided from the inverter to provide the light source; A pulse width modulation controller configured to control switching of the inverter to adjust an amount of current provided to the light source; And a feedback current providing unit dividing the tube current output from the light source into a detection current and a feedback current to provide the feedback current to the pulse width modulation controller. The feedback current providing unit provides more of the feedback current in inverse proportion to the temperature below the reference temperature. The feedback current providing unit further includes a current limiting circuit for limiting the amount of the feedback current.

Liquid crystal display, light source, thermistor

Description

Device for driving light source for liquid crystal display device

1 is a circuit diagram illustrating a driving device of a light source for a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 2 is a graph illustrating temperature characteristics of a thermistor used in the feedback current providing unit of FIG. 1.

3 is a circuit diagram illustrating a modified embodiment of the feedback current providing unit of FIG. 1.

4A to 4D are circuit diagrams for simulating the feedback current providing unit of FIG. 3.

DESCRIPTION OF THE REFERENCE NUMERALS (S)

20: inverter 40: transformer

60: pulse width modulation control unit 80: feedback current providing unit

100: light source

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device of a light source for a liquid crystal display device and a driving method thereof, and more particularly, to reduce the luminance of the light source for a liquid crystal display device at low temperature (for example, room temperature or less). A drive device for a light source for a liquid crystal display device.

In today's information society, the role of electronic displays has become very important, and various electronic displays have been widely used in various industrial fields. In the electronic display device field, electronic display devices having new functions suitable for the demands of the information society, which have been continuously developed and diversified, are continuously being developed. In general, an electronic display device refers to a device that transmits various pieces of information to a human through vision. That is, an electronic display device refers to an electronic device that converts an electronic information signal output from various electronic devices into an optical information signal that can be recognized by a human eye, and is a device that plays a role of a bridge between humans and electronic devices. It can be said.

In such an electronic display device, when an optical information signal is displayed by a light emitting phenomenon, it is referred to as a light emitting display device, and when it is displayed by light modulation due to reflection, scattering, or interference phenomenon, it is called a light receiving display device. Light emitting displays, also called active display devices, include cathode ray tubes (CRTs), plasma display panels (PDPs), organic electroluminescent displays (OELDs), light emitting diodes ( Light Emitting Diode (LED) etc. can be mentioned. The light receiving display device, which is called a passive display device, may include a liquid crystal display (LCD), an electrophoretic image display (EPID), and the like.

Cathode ray tube display device, which is used for television and computer monitor, and has the longest history, has the highest market share in terms of economy, but has many disadvantages such as heavy weight, large volume and high power consumption. .

Recently, due to the rapid progress of semiconductor technology, there is a demand for a flat panel display device as an electronic display device suitable for a new environment in accordance with the trend of lowering and lowering power of various electronic devices and miniaturization, thinning, and lightening of electronic devices. It is rapidly increasing. Accordingly, flat panel display devices such as a liquid crystal display (LCD), a plasma display device (PDP), an organic EL display device (OELD), and the like have been developed, and among these flat panel display devices, it is easy to miniaturize, light weight, and thinner. In particular, liquid crystal display devices having low power consumption and low driving voltage are drawing attention.

Since the liquid crystal display is not a light emitting display as described above, a light source such as a backlight is required. There are two types of backlight for liquid crystal display devices, a direct type type and a light guide plate type. The direct type places several lamps in the plane. A diffuser plate is provided between the lamp and the liquid crystal panel to keep the liquid crystal panel and the lamp constant. In the light guide plate system, a lamp is installed outside the flat plate, and light is incident from the lamp onto the entire surface of the liquid crystal panel using a transparent light guide plate. The brightness of the backlight for the liquid crystal display device is adjusted according to the magnitude of the tube current provided.

Conventional backlights for liquid crystal displays have been provided with a constant tube current regardless of temperature. However, when a constant tube current is provided to the backlight for the liquid crystal display regardless of temperature, the backlight for the liquid crystal display exhibits a property of decreasing heat generation at room temperature (about 25 ° C. or less) and thus decreasing luminance. The liquid crystal display device including the backlight for the conventional liquid crystal display device has a problem that the brightness of the light source is reduced at room temperature or less, thereby failing to express desired image data and causing screen abnormality.

Accordingly, an object of the present invention is to provide a driving device of a light source for a liquid crystal display device that can effectively suppress the decrease in the luminance of the light source for a liquid crystal display device at a low temperature (for example, below room temperature).

delete

Technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

In one embodiment, a driving device of a light source for a liquid crystal display device includes: a light source for emitting light; An inverter providing a driving voltage for driving the light source; A transformer for boosting a driving voltage provided from the inverter to provide the light source; A pulse width modulation controller configured to control switching of the inverter to adjust an amount of current provided to the light source; And a feedback current providing unit dividing the tube current output from the light source into a detection current and a feedback current to provide the feedback current to the pulse width modulation controller.
The feedback current providing unit provides more of the feedback current in inverse proportion to the temperature below the reference temperature.
The feedback current providing unit further includes a current limiting circuit for limiting the amount of the feedback current.

delete

delete

delete

delete

delete

delete

delete

delete

delete

delete

delete

Specific details of the invention are included in the detailed description and drawings. Advantages and features of the present invention, and methods of achieving the same will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. Like reference numerals refer to like elements throughout.

1 and 2, a driving apparatus for a liquid crystal display and a driving method thereof according to an exemplary embodiment of the present invention will be described. 1 is a circuit diagram illustrating a driving device of a light source for a liquid crystal display according to an exemplary embodiment of the present invention. FIG. 2 is a graph illustrating temperature characteristics of a thermistor used in the feedback current providing unit of FIG. 1.

As shown in FIG. 1, a driving apparatus for a liquid crystal display according to an exemplary embodiment of the present invention includes a light source 100 for emitting light and a driving voltage for driving the light source 100 by receiving a direct current voltage VCC. Inverter 20 for providing a, the transformer 40 to boost the driving voltage provided from the inverter 20 to provide to the light source 100, and to control the switching frequency of the inverter 20 provided to the light source 100 Pulse Width Modulation (Pulse Width Modulation) by dividing the pulse width modulation control unit 60 and the tube current (IL) output from the light source 100 into a detection current (IS) and a feedback current (IF); PWM) control unit 60 is provided with a feedback current providing unit 80 for providing a feedback current (IF).

Halogen Cathode Fluorescent Tubes (HCFLs) or Cold Cathode Fluorescent Tubes (CCFLs) are used as the light source 100 for the liquid crystal display device. (CCFL) is a cold cathode tube (CCFL) that emits electrons generated by applying a strong electric field to the surface of the cathode, and generates low heat, high brightness, long life, and easy to display all colors. Therefore, it is mainly used as the light source 100 for liquid crystal display devices. Therefore, a case where a cold cathode tube is used as the light source 100 for the liquid crystal display device in the driving device of the light source for the liquid crystal display device according to the exemplary embodiment of the present invention will be described.

The transformer 40 is connected to the high pressure electrode of the cold cathode tube 100, and the feedback current providing unit 80 is connected to the low pressure electrode. The cold cathode tube 100 is supplied with an AC signal boosted and supplied from the transformer 40. When the AC signal is applied to the cold cathode tube 100, the electrons are emitted and collides with the inert gases in the glass tube to exponentially increase the amount of electrons. As the current flows inside the glass tube by the increased electrons, ultraviolet rays are emitted as the inert gas is excited by the electrons. These ultraviolet rays collide with the luminescent phosphor applied to the inner wall of the glass tube to emit visible light.

The inverter 20 converts the DC voltage VCC provided from the outside into an AC signal in order to drive the light source 100.

The transformer 40 is boosted by an AC signal suitable for driving the cold cathode tube 100 by the winding ratio between the primary winding and the secondary winding. To this end, an AC signal provided through the inverter 20 is applied to the primary winding of the transformer 40, and the AC signal provided to the primary winding is boosted by the turns ratio and is induced in the secondary winding. The boosted AC signal induced in the secondary winding is provided to the high voltage electrode of the cold cathode tube 100 through one end of the secondary winding. The other end of the secondary winding is connected to ground power supply (GND).

The pulse width modulation control unit 60 generates a pulse width modulation (PWM) signal for adjusting the switching of the switching elements disposed in the inverter 20 according to the feedback current IF to output the amount of current output from the inverter 20. Adjust. That is, when the amount of feedback current IF increases, the pulse width modulation controller 60 adjusts the duty ratio of the PWM signal to increase so that the amount of current output from the inverter 20 increases, and the amount of feedback current IF increases. When the size is reduced, the duty ratio of the PWM signal is reduced to adjust the amount of current output from the inverter 20 to be small.

The feedback current providing unit 80 divides the tube current IL output from the cold cathode tube 100 into the detection current IS and the feedback current IF, and divides the feedback current IF into the pulse width modulation control unit 60. And below the reference temperature, more feedback current IF is inversely proportional to temperature. As a result, the pulse width modulation controller 60 adjusts the amount of current output from the inverter 20 to be inversely proportional to the temperature at or below the reference temperature, thereby providing more current to the cold cathode tube 100.

Therefore, the driving device of the light source for the liquid crystal display device according to the exemplary embodiment of the present invention is different from the conventional driving device of the light source for the liquid crystal display device. Since the light source 100 is provided for the light source 100, the heat generation characteristics of the light source 100 for the liquid crystal display device may be reduced at a low temperature, thereby effectively suppressing the decrease in the luminance. Here, the reference temperature is 10 ℃ ~ 40 ℃, it can be adjusted according to the temperature of the place where the liquid crystal display device is placed. That is, when the temperature of the place where the liquid crystal display is placed is low, the reference temperature is adjusted to around 10 ° C., and when the temperature of the place where the liquid crystal display is placed is high, the reference temperature may be determined to be about 40 ° C.

In detail, the feedback current providing unit 80 includes a first diode D1, a second diode D2, a thermistor Tm, and a resistor Rs. The first diode D1 rectifies the tube current IL input from the low voltage electrode of the cold cathode tube 100 to provide the detection current IS to the thermistor Tm and the resistor Rs, and the second diode D2. Blocks the reverse current flowing from the ground power supply (GND). The detection current IS flows to the ground power supply GND through the thermistor Tm and the resistor Rs, and the feedback current IF, which is the current other than the detection current IS in the tube current IL, is pulse width modulated. It is transmitted to the control unit 60.

As shown in FIG. 2, the thermistor Tm has a characteristic that the resistance value increases when the temperature decreases. In the thermistor Tm, since the resistance value hardly changes at a temperature of 40 ° C or higher, the amount of detection current IS hardly changes at a temperature of 40 ° C or higher. However, at a temperature of 40 ° C. or lower, since the resistance value increases as the temperature decreases, the amount of detection current IS decreases as the temperature decreases. Therefore, the amount of feedback current IF increases as the amount of detection current IS decreases. On the other hand, the resistor (Rs) is not necessarily to be composed of only one, it may be composed of a plurality.

3 and 4A to 4D, a modified embodiment of the feedback current providing unit 80 will be described. 3 is a circuit diagram illustrating a modified embodiment of the feedback current providing unit 80 of FIG. 1. 4A to 4D are circuit diagrams for simulating the feedback current providing unit 80 of FIG. 3.

The feedback current providing unit 80 further includes a current limiting circuit 81 for limiting the amount of the feedback current IF. Thus, when the resistance value of the thermistor Tm becomes very large so that the amount of feedback current IF becomes very large, the current limiting circuit 81 determines the amount of feedback current IF transmitted to the pulse width control section 60. You can limit it.

Specifically, as shown in FIG. 3, the current limiting circuit 81 is activated by the detection current IS flowing through the thermistor Tm to transfer a part IF1 of the feedback current IF to the ground power source GND. The pulse width modulation controller 60 controls the feedback current IF2 excluding the feedback current IF activated by the first current transmitting element Q1 and the tube current IL flowing through the first current transmitting element Q1. And a second current transfer element Q2 to be delivered. The first current transfer element Q1 and the second current transfer element Q2 may be configured as a bipolar junction transistor (BJT).

A resistor R7 is connected between the collector of the first current transfer element Q1 and the ground power supply GND, a resistor R6 is connected to the emitter, and a thermistor Tm between the base and the resistor R6. Is connected. On the other hand, the resistors R3 and R4 constitute the Rs resistor of FIG. 3. A resistor R10 is connected between the base of the second current transmitting element Q2 and the ground power supply GND, a resistor R1 is connected to the emitter, and a resistor R5 is connected between the base and the resistor R1. It is connected, the collector is connected to the pulse width modulation control unit 60. Meanwhile, the first diode D1 and the second diode D2 of FIG. 1 are omitted.

The first current transfer element Q1 is activated when the voltage applied by the current flowing through the thermistor Tm becomes more than a predetermined voltage (for example, 0.7V), and is activated to the current path to the ground power source GND. Since a path is formed, a part IF1 of the feedback current IF can flow to the ground power supply GND, and the second current transfer element Q2 has a voltage applied by the current flowing through the resistor R5. When the predetermined voltage (for example, 0.7V) or more, it is activated to form a current path to the pulse width modulation controller 60, so that the feedback current IF1 flowing through the first current transfer element Q1. The remaining feedback current IF2 except for) may be transmitted to the pulse width modulation controller 60.

4A to 4D, the amount of current IF2 transmitted from the feedback current providing unit 80 to the pulse width modulation control unit 60 when the resistance value of the thermistor Tm changes from 1 kΩ to 20 kΩ is determined. Take a look.

4A is a circuit diagram of a feedback current providing unit 80 for simulating a case where the resistance value of the thermistor Tm is 1 k 1. Tube current (IL) is 7mA, R1 resistance is 100kΩ, R3 resistance is 1kΩ, R4 resistance is 10kΩ, R5 resistance is 50kΩ, R6 resistance is 10kΩ, R7 resistance is 100kΩ, R10 resistance is 100kΩ, R8 resistance is pulse width modulation The controller 60 is equivalently represented, and the first diode D1 and the second diode D2 of FIG. 1 are omitted. In this case, since the resistance value of the thermistor Tm is very small compared to the resistance of R6, the applied voltage is very small, and since the first current transfer element Q1 is not activated, the ground power supply is provided through the first current transfer element Q1. The amount of current IF1 flowing to (GND) is 1.899 pA. In addition, since the resistance value of the R5 resistor is very large compared to the resistance value of the R1 resistor, the second current transfer element Q2 is always activated when the tube current IL is applied. The amount of current IF2 delivered to the pulse width modulation control unit 60 through the two current transfer elements Q2 is 6.772 mA.

FIG. 4B is a circuit diagram of the feedback current providing unit 80 for simulating a case where the resistance value of the thermistor Tm is 5 kΩ. Tube current (IL) is 7mA, R1 resistance is 100kΩ, R3 resistance is 1kΩ, R4 resistance is 10kΩ, R5 resistance is 50kΩ, R6 resistance is 10kΩ, R7 resistance is 100kΩ, R10 resistance is 100kΩ, R8 resistance is pulse width modulation The controller 60 is equivalently represented, and the first diode D1 and the second diode D2 of FIG. 1 are omitted. In this case, since the resistance value of the thermistor Tm is smaller than the resistance of R6, the applied voltage is insignificant, and since the first current transfer element Q1 is not activated, the ground power supply GND through the first current transfer element Q1. The amount of current IF1 flowing in) is 35.50nA. In addition, since the resistance value of the R5 resistor is very large compared to the resistance value of the R1 resistor, the second current transfer element Q2 is always activated when the tube current IL is applied. The amount of current IF2 delivered to the pulse width modulation control unit 60 through the two current transfer elements Q2 is 6.808 mA. As compared with the case where the resistance value of the thermistor Tm is 1 kΩ, the increase in the amount of current IF2 delivered to the pulse width modulation control unit 60 increases the resistance value of the thermistor Tm, through the thermistor Tm. This is because the amount of current IS transferred decreases.

4C is a circuit diagram of a feedback current providing unit 80 for simulating a case where the resistance value of the thermistor Tm is 10 kΩ. Tube current (IL) is 7mA, R1 resistance is 100kΩ, R3 resistance is 1kΩ, R4 resistance is 10kΩ, R5 resistance is 50kΩ, R6 resistance is 10kΩ, R7 resistance is 100kΩ, R10 resistance is 100kΩ, R8 resistance is pulse width modulation The controller 60 is equivalently represented, and the first diode D1 and the second diode D2 of FIG. 1 are omitted. In this case, since the resistance value of the thermistor Tm is equal to the resistance of R6, the applied voltage is increased, so that the first current transfer element Q1 is activated and the ground power supply GND through the first current transfer element Q1. The amount of current IF1 flowing in) is 9.65 uA. In addition, since the resistance value of the R5 resistor is very large compared to the resistance value of the R1 resistor, the second current transfer element Q2 is always activated when the tube current IL is applied. The amount IF2 of the current delivered to the pulse width modulation control unit 60 through the two current transfer elements Q2 is 6.819 mA. As compared with the case where the resistance value of the thermistor Tm is 5 kΩ, the increase in the amount of current IF2 delivered to the pulse width modulation control unit 60 increases the resistance value of the thermistor Tm and through the thermistor Tm. This is because the amount of current IS transferred decreases.

4D is a circuit diagram of a feedback current providing unit 80 for simulating a case where the resistance value of the thermistor Tm is 20 kΩ. Tube current (IL) is 7mA, R1 resistance is 100kΩ, R3 resistance is 1kΩ, R4 resistance is 10kΩ, R5 resistance is 50kΩ, R6 resistance is 10kΩ, R7 resistance is 100kΩ, R10 resistance is 100kΩ, R8 resistance is pulse width modulation The controller 60 is equivalently represented, and the first diode D1 and the second diode D2 of FIG. 1 are omitted. In this case, since the resistance value of the thermistor Tm is greater than the resistance of R6, the applied voltage is increased, so that the first current transfer element Q1 is activated and the ground power supply GND is passed through the first current transfer element Q1. The amount of current IF1 flowing in is 31.35 uA. In addition, since the resistance value of the R5 resistor is very large compared to the resistance value of the R1 resistor, the second current transfer element Q2 is always activated when the tube current IL is applied. The amount of current IF2 delivered to the pulse width modulation control unit 60 through the two current transfer elements Q2 is 6.819 mA. Compared with the case where the resistance value of the thermistor Tm is 10 kΩ, the amount of current IF2 delivered to the pulse width modulation control unit 60 does not change. Although the resistance value of the thermistor Tm is increased so that the amount of current IS transmitted through the thermistor Tm decreases, the amount of current IF2 delivered to the pulse width modulation controller 60 does not increase, and 1 The amount of current IF1 flowing to ground power supply GND through current transfer element Q1 is increased. That is, when the resistance value of the thermistor Tm is 10 kΩ or more, when the first current transfer element Q1 is activated, even if the resistance value of the thermistor Tm is increased, the current IF2 transferred to the pulse width modulation controller 60. It can be seen that the amount of) is not increased, but the amount of current IF1 flowing to the ground power source GND through the first current transfer element Q1 is increased.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. I can understand that. Therefore, the above-described embodiments will be described in detail so that the disclosure of the present invention may be completed, and those skilled in the art may easily implement the technical idea of the present invention. It is to be understood to be illustrative and not limitative in all respects, as it is provided to fully inform the person skilled in the art the scope of the invention, and the invention is defined only by the scope of the claims. .

The driving device of the light source for the liquid crystal display device and the driving method thereof according to the embodiments of the present invention made as described above are different in inverse proportion to the temperature below the reference temperature, unlike the conventional driving device of the light source for the liquid crystal display device. Since a large amount of current is provided to the light source for the liquid crystal display device, the heat generation characteristics of the light source for the liquid crystal display device can be reduced at low temperature, thereby effectively suppressing the decrease in the luminance.

Claims (12)

A light source emitting light; An inverter providing a driving voltage for driving the light source; A transformer for boosting a driving voltage provided from the inverter to provide the light source; A pulse width modulation controller configured to control switching of the inverter to adjust an amount of current provided to the light source; And A feedback current providing unit for dividing a tube current output from the light source into a detection current and a feedback current to provide the feedback current to the pulse width modulation controller, The feedback current providing unit provides more of the feedback current in inversely proportional to the temperature below the reference temperature, And the feedback current providing unit further comprises a current limiting circuit for limiting the amount of the feedback current. The method of claim 1, The reference temperature is 10 ° C ~ 40 ° C drive device of the light source for a liquid crystal display device. The method of claim 1, And the feedback current providing unit flows the detection current through a thermistor having a characteristic of increasing resistance when the temperature decreases. delete The method of claim 3, The current limiting circuit includes a first bipolar junction transistor (BJT) that is activated by a detection current flowing through the thermistor and flows a portion of the feedback current to ground power; And And a second bipolar junction transistor (BJT) which is activated by the tube current and transfers the remaining feedback current except for the feedback current flowing through the first bipolar junction transistor (BJT) to the pulse width modulation controller. A drive device of a light source for a liquid crystal display device. delete delete delete delete delete delete delete

Images