This application claims the benefit of Korean Patent Application No.10-2006-0109924 filed on Nov. 8, 2006, which is hereby incorporated by reference as if fully set forth herein.
1. Field of the Invention
The present invention relates to a driving circuit of a surface light source which is suitable for decreasing the luminance-stabilization period of time and improving the low-temperature starting properties by optimizing a starting voltage and current, and a method of driving the same.
2. Discussion of the Related Art
With the recent development in many kinds of light source, the wide application of the light sources has been accelerated in various fields, for example, illuminating fields, information industrial fields, and image-displaying industrial fields.
The light source is largely classified into a one-dimensional light source including an optical distribution formed in shape of a dot; a two-dimensional light source including an optical distribution formed in shape of a line; and a three-dimensional light source including an optical distribution formed in shape of a surface.
A typical example of the one-dimensional light source corresponds to a light-emitting diode (LED). Also, typical examples of the two-dimensional light source correspond to a cold cathode fluorescent lamp (CCFL) and an external electrode fluorescent lamp (EEFL), and a typical example of the three-dimensional light source corresponds to a flat fluorescent lamp (FFL).
A liquid crystal display (LCD) device necessarily requires an additional backlight since the LCD device is not a self-emission device. For a light source included in the backlight of the LCD device, it is necessary to emit the uniform light in a large-sized area thereof, and to lower the power consumption.
In order to apply the one-dimensional and two-dimensional light sources to the backlight of the LCD device, the light source additionally needs a light-guiding plate (LGP), and optical members including a diffusion member and a prism sheet. Thus, the LCD device using the backlight of the one-dimensional or two-dimensional light source, for example, CCFL or LED, has increased in its volume and weight due to the optical members.
To overcome these problems, a three-dimensional surface light source having a flat type has been newly developed for the backlight of the LCD device. The surface light source may be fabricated with a plurality of discharge sections by forming a glass substrate through the use of a mold or by providing a plurality of glass or ceramic walls between two glass substrates.
The former heats the moldable glass substrate at a predetermined temperature, and then processes the moldable glass substrate by the mold, to thereby form the plurality of discharge sections which are separated from one another by the walls, and are also connected to one another. The processed glass substrate is bonded to another glass substrate by a sealing frit, thereby forming the plurality of discharge sections between the two glass substrates.
The latter forms the plurality of walls using the glass or ceramic material on the glass substrate, and then bonds the glass substrate including the plurality of walls to another glass substrate, thereby forming the plurality of discharge sections between the two glass substrates.
Typically, the FFL of the surface light source uses Hg gas. In comparison to the linear type lamp such as the CCFL or EEFL, the FFL has the larger lamp area and the more channels. Thus, if using the normal driving current and voltage after turning on the FFL, it has the increased time period to stabilize the luminance as compared with that of the related art lamp.
Hereinafter, a related art light source will be explained with the focus on the luminance properties and the low-temperature starting properties.
In
Referring to
If the FFL using Hg gas is operated in the low-temperature surroundings, it spends a long time to activate Hg gas. Also, since the flat fluorescent lamp has a large-sized cross section and also includes a plurality of channels, there is high possibility of ununiform discharge.
If the proper voltage and current are not applied to the driving circuit on the low-temperature starting and driving, the incomplete light may occur as shown in
If the voltage and current are increased to stabilize the initial luminance of driving circuit, it is possible to stabilize the luminance of driving circuit. In this case, unless the voltage and current are slowly decreased by preset periods of time, the flickering and the rapid decrease of luminance may occur.
Accordingly, the present invention is directed to a driving circuit of a surface light source and a method of driving the same that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a driving circuit of a surface light source which is suitable for decreasing the luminance-stabilization period of time and improving the low-temperature starting properties by optimizing a starting voltage and current, and a method of driving the same.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a driving circuit of a surface light source comprises an inverter controller which feedbacks a current supplied to the surface light source, and compares the feedback current to a preset reference value, to control the current supplied to the surface light source; a temperature sensor which senses an operation temperature of the surface light source; and a driving-condition determining controller which determines operation modes of the surface light source on the basis of the temperature sensed in the temperature sensor, and varies the feedback current inputted to the inverter controller according to the operation modes of the surface light source.
In another aspect, a driving circuit of a surface light source comprises an inverter controller which feedbacks a current supplied to the surface light source, and compares the feedback current to a preset reference value, to control the current supplied to the surface light source; a temperature sensor which senses an operation temperature of the surface light source; and a driving-condition determining controller which determines operation modes of the surface light source on the basis of the temperature sensed in the temperature sensor, varies the feedback current inputted to the inverter controller according to the operation modes of the surface light source, and outputs on/off signals to control an operation time period of the inverter controller by varying a duty ratio depending on the varied feedback current.
At this time, the driving circuit further includes a divider which divides the feedback current, and outputs the divided current to the inverter controller; and at least two current breakers which limit the level of current divided by the divider and applied to the inverter controller under control of the driving-condition determining controller.
In another aspect, a method of driving a surface light source including an inverter controller to control a current applied to the surface light source, and a driving-condition determining controller to determine operation modes of the surface light source on the basis of an operation temperature, and to vary a current outputted to the inverter controller, comprises sensing the operation temperature of the surface light source; determining the operation modes of the surface light source according to the sensed operation temperature; and outputting an output current of the inverter controller based on the determined operation mode.
At this time, determining the operation modes includes a striking mode to apply a high current to the surface light source when the operation temperature of the surface light source is in a low-temperature range below a room temperature; a warm-up mode to apply a current, which is lower than that for the striking mode, to the surface light source when the operation temperature of the surface light source is in the room temperature range, for the stabilization of luminance; and a normal mode to drive the surface light source based on a feedback current of the surface light source when the operation temperature of the surface light source is above the room temperature range.
Also, a duty ratio is relatively low if the current applied to the surface light source is high, and the duty ratio is relatively high if the current applied to the surface light source is low, to lower the power consumption.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Hereinafter, a driving circuit of a surface light source according to the present invention and a driving method thereof will be described with reference to the accompanying drawings.
As shown in
The first, second and third current breakers 33, 34 and 35 are connected to a connection node of the first and second feedback resistors (R1, R2) of the divider 31 in common; and are connected to first, second and third ports (port1, port2 and port3) included in the driving-condition determining controller 42. That is, the first current breaker 33 is connected to the first port (port1) of the driving-condition determining controller 42; the second current breaker 34 is connected to the second part (port2) of the driving-condition determining controller 42; and the third current breaker 35 is connected to the third port (port3) of the driving-condition determining controller 42.
In
To sense the operation temperature of the surface light source, the temperature sensor 32 includes the temperature sensing part (thermistor, RT) and the resistor (R7) connected between a power source voltage terminal (VCC) and a grounded terminal in series. Thus, the connection node of the temperature sensing part (thermistor, RT) and the resistor (R7) is connected to the fourth port (port4) of the driving-condition determining controller 42.
At this time, the inverter controller 41 includes a differential amplifier (comparator) 41a which amplifies the difference between the feedback current inputted to an inversion terminal (−) and the reference current inputted to a non-inversion terminal (+). If a comparator or A/D converter is formed in the driving-condition determining controller 42, the temperature sensor 32 may use various sensors without providing an additional external circuit.
If using only an auxiliary starting circuit of the inverter controller 41, it is operated within the preset range of current owing to the limitation of feedback. In order to solve this problem, there is provided the driving-condition determining controller 42. The driving-condition determining controller 42 raises the current and voltage appropriately, whereby the driving-condition determining controller 42 enables the feedback depending on the voltage change in current increased by the change of input voltage.
An operation of the driving circuit of the surface light source according to the first embodiment of the present invention will be explained as follows.
As the voltage is applied to the driving circuit, the driving-condition determining controller 42 senses the operation temperature of the surface light source by the temperature sensor 32 connected to the fourth port (port4). That is, the driving-condition determining controller 42 determines the driving conditions of the striking mode for the low-temperature driving, the warm-up mode for the stabilization of luminance, and the normal mode for the normal-state driving on the basis of the sensed operation temperature of the surface light source.
As explained above, if the flat fluorescent lamp (FFL) using Hg gas is operated in the low-temperature surroundings, it spends a long time to activate Hg gas. Also, since the flat fluorescent lamp has a large-sized cross section and also includes a plurality of channels, there is high possibility of ununiform discharge. In this respect, a relatively high voltage is applied to the driving circuit when the driving circuit is operated in the low-temperature surroundings.
For the stabilization of initial luminance, the optimized current is applied for a preset period of time, thereby securing the initial stabilization time. After the preset period of time, the lamp current is slowly decreased by fixed intervals to thereby prevent the flickering and the unstable luminance.
The striking mode is operated when the operation temperature of the surface light source, which is sensed by the temperature sensor (RT) at the first sensing time after applying the voltage to the inverter, is in the low-temperature range (−10° C.˜0° C.). The warm-up mode is operated when the operation temperature of the surface light source is between 1° C. and 40° C. (and more particularly, 1° C.<the operation temperature≦40° C.). The normal mode is operated in the normal state after completing the warm-up mode.
A method of controlling the current amount on the respective conditions (except the normal mode) by switching the first, second and third ports (port1, port2 and port3) on the basis of the determination conditions of the driving-condition determining controller 42 will be explained as follows.
Referring to
This will be explained in detail.
First, if the low signal is outputted to the first, second and third ports of the driving-condition determining controller 42, the respective diodes (D1, D2, D3) of the first, second and third current breakers 33, 34 and 35 are operated in the forward direction, whereby the current path is formed in the respective current breakers 33, 34 and 35. Accordingly, the feedback current applied to the inversion terminal (−) of the differential amplifier 41a provided in the inverter controller 41 is decreased to the minimum. In this case, the differential amplifier 41a amplifies and outputs the highest current, as shown in (step#1) of
As the high signal is outputted to the first port of the driving-condition determining controller 42, and the low signal is outputted to the second and third ports, the current path is formed not in the first current breaker 33 but in the second and third current breakers 34 and 35. Thus, the feedback current applied to the inversion terminal (−) of the differential amplifier 41a provided in the inverter controller 41 is increased more than the feedback current applied when the low signal is outputted to the first, second and third ports of the driving-condition determining controller 42. In this case, the differential amplifier 41a amplifies and outputs the current having the level shown in (step#2) of
If the high signal is outputted to the first and second ports of the driving-condition determining controller 42, and the low signal is outputted to the third port, the current path is formed not in the first and second current breakers 33 and 34 but in the third current breaker 35. Thus, the feedback current applied to the inversion terminal (−) of the differential amplifier 41a provided in the inverter controller 41 is increased more than the feedback current applied when the high signal is outputted to the first port and the low signal is outputted to the second and third ports. In this case, the differential amplifier 41a amplifies and outputs the current having the level shown in (step#3) of
If the high signal is outputted to the first, second and third ports of the driving-condition determining controller 42, the first, second and third current breakers 33, 34 and 35 have no current path formed therein. Thus, the feedback current applied to the inversion terminal (−) of the differential amplifier 41a provided in the inverter controller 41 becomes the maximum without regard to the control of the driving-condition determining controller 42. In this case, the differential amplifier 41a amplifies and outputs the current having the level shown in (step#4) of
At this time, the potential of feedback current inputted to the inverter controller 41 is controlled smoothly without the rapid change thereof by the third current breaker 35.
This will be explained with reference to
Referring to (C) of
That is, the striking mode is operated by (step#1) and (step#2) of
The feedback current applied to the inversion terminal of the differential amplifier 41a of the inverter controller 41 is controlled by the driving-condition determining controller 42; and the current applied to the surface light source is controlled depending on the output signal of the differential amplifier 41a. As shown in
A driving method of the surface light source according to the first embodiment of the present invention will be explained with reference to
If the surface light source is powered-on (S901), the driving-condition determining controller 42 senses the temperature of the surface light source by the temperature sensor 32, to thereby select the operation mode. Thus, it is determined whether the operation temperature of the surface light source is in the room temperature (S903). For the first embodiment of the present invention, the room temperature is determined at the range from 1° C. to 40° C.
If the sensed temperature is in the room temperature, the warm-up mode is operated to stabilize the luminance (S904). By the subdivision of the operation temperature, the warm-up mode is maintained for 5 minutes in case of 15° C.<the operation temperature≦40° C., and the warm-up mode is maintained for 6 minutes in case of 1° C.≦the operation temperature≦15° C. That is, the driving-condition determining controller 42 outputs the high signal to the first and second ports, and outputs the low signal to the third port, whereby the current having the level corresponding to (step#3) of
In another method, if 1° C.≦the operation temperature≦15° C., the driving-condition determining controller 42 outputs the high signal to the first port, and outputs the low signal to the second and third ports, whereby the current having the level corresponding to (step#2) of
After stabilizing the luminance by the warm-up mode, the normal mode having the level corresponding (step#4) of
The normal mode is maintained until the power switch is turned-off (S911).
In the step (S903), if the sensed operation temperature of surface light source is not in the range of room temperature, it is determined whether the driving circuit is in the striking mode for the low-temperature starting and driving (S906).
If the sensed temperature is in the range between −10° C. and 0° C. (−10° C.<the operation temperature≦0° C.), the striking mode for the low-temperature starting is carried out (S907). The striking mode is operated by the level corresponding to (step#1) and (step#2) of
As the maximum current is applied to the surface light source, the surface light source is started. Then, the driving-condition determining controller 42 outputs the high signal to the first port, and outputs the low signal to the second and third ports, whereby the current having the level corresponding to (step#2) of
If the operation temperature of the surface light source is not in the room temperature or the low-temperature range but in the high-temperature range, for example, above 40° C. (S909), the warm-up pulse (level corresponding to step#3 of
The normal mode is carried out until the switch is turned-off.
The driving voltage for the control of operation is determined depending on the level of
For the first embodiment of the present invention, the range of operation temperature may vary on the properties of the surface light source. The present invention is not limited to the above-explained preferred embodiment. For example, one inverter structure may be individually set by each surface light source; the low-temperature range is set between −20° C. and 0° C.; the room temperature range is set between 1° C. and 10° C., between 11° C. and 38° C., or between 11° C. and 39° C.
In the first embodiment of the present invention, the driving-condition determining controller 42 forcibly increases the driving current of the surface light source, to thereby improve the low-temperature properties and to decrease the time period of stabilizing the luminance.
That is, the surface light source is normally driven by about 130 mA. However, the surface light source using the driving-condition determining controller 42 to decrease the luminance-stabilization time period and to improve the low-temperature starting properties is operated by about 200 mA.
However, manufactures using the surface light source, for example, a liquid crystal display (LCD) device has the limitation on power consumption (W). Accordingly, if driving the surface light source according to the first embodiment of the present invention, the surface light source can not be applied to the LCD device.
To overcome the problem in relation with the limitation on power consumption (W), a driving circuit of a surface light source according to the second embodiment of the present invention and a driving method thereof are proposed. That is, the driving circuit of the surface light source according to the second embodiment of the present invention maintains the instantaneous current and decreases the time period of supplying the current, thereby decreasing the power consumption.
As shown in
Except the driving-condition determining controller 42, the above-mentioned elements provided in the surface light source according to the second embodiment of the present invention are identical in structure and function to those provided in the surface light source according to the first embodiment of the present invention.
When driving the striking mode or the warm-up mode to decrease the time period of stabilizing the luminance and to improve the low-temperature starting properties, the high current is forcibly applied to the surface light source, whereby the power consumption (W) is increased. In case of the driving-condition determining controller 42 according to the second embodiment of the present invention, even though it is supplied with the high current on the striking mode or the warm-up mode, the time period of applying the current is decreased to lower the power consumption (W). Accordingly, the driving-condition determining controller 42 according to the second embodiment of the present invention includes a fifth port which outputs on/off signals to control the operation time period (duty ratio) of the inverter controller 41.
A driving method of the surface light source according to the second embodiment of the present invention is explained as follows.
The driving method relating the striking mode, the warm-up mode and the normal mode in the surface light source according to the second embodiment of the present invention is the same as that of the first embodiment of the present invention shown in
In order to lower the power consumption (W) on the striking or warm-up mode, the inverter controller 41 is turned-on/off, to thereby control the ratio of operation time.
If the sensed temperature is in the range between −10° C. and 0° C. (−10° C.< the operation temperature≦0° C.), the driving mode for the low-temperature starting of the level corresponding to (step#1) of
As starting the surface light source, the driving-condition determining controller 42 outputs the high signal to the first port, and outputs the low signal to the second and third ports, whereby the current having the level corresponding to (step#2) of
When operating the warm-up mode to stabilize the luminance by the level corresponding to (step#3) of
In the same method, when operating the normal mode based on (step#4) of
For (A) to (D) of
As mentioned above, the driving circuit of the surface light source according to the present invention and the method of driving the same have the following advantages.
To stabilize the luminance on the initial driving of the surface light source, the current and voltage are increased to the predetermined level, thereby shortening the time period for the stabilization of luminance.
Also, the inverter controller outputs the different ranges in relation to the operation current based on the determination of the temperature and operation conditions by outputting the various driving pulses in addition to the current range for the normal operation, to thereby improve the operation properties of the surface light source.
The operation current range of the surface light source is not fixed but varied depending on the operation modes, whereby the driving circuit of the surface light source improves in the low-temperature starting and driving properties.
Furthermore, the voltage applied to the input port of the comparator is regularly changed within the fixed range, so that it is possible to prevent the unstable luminance caused by the rapid current change in the lamp. To stably maintain the luminance after raising the current, the pulse having the shape similar to PWM waveform of the predetermined frequency is applied for the preset period of time, whereby the current and voltage are linearly decreased to improve the luminance-stabilization properties.
Even though the high current is forcibly applied to the surface light source to decrease the time period for the stabilization of luminance and to improve the low-temperature starting properties, the power consumption (W) can be decreased by shortening the time period of supplying the high current. In this respect, the surface light source according to the present invention may be applied to the various manufactures.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
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