WO2009028863A2

WO2009028863A2 - Method and apparatus for thermal control of led device

Info

Publication number: WO2009028863A2
Application number: PCT/KR2008/005008
Authority: WO
Inventors: Tae Sun Jang
Original assignee: Inix Co., Ltd.
Priority date: 2007-08-27
Filing date: 2008-08-27
Publication date: 2009-03-05
Also published as: WO2009028863A3

Abstract

Thermal control method and apparatus of an LED device are provided. The thermal control method of an LED device includes: applying excess current larger by a predetermined level than normal current to at least one LED; and repeatedly switching supply and interception of the excess current to the at least one LED and controlling a supply time of the excess current to the at least one LED. Accordingly, it is possible to prevent or minimize the deterioration of the LED and the accumulation of heat, thereby enhancing the reliability of the LED.

Description

METHOD AND APPARATUS FOR THERMAL CONTROL

OF LED DEVICE

Technical Field

[1] The present invention relates to thermal control method and apparatus of an LED device, and more particularly, to thermal control method and apparatus of an LED device in which excess current greater than normal current is supplied to the LED device to control a supply time of the excess current. Background Art

[2] Examples of a lighting apparatus include an advertising board, a traffic light, and an emergency light. Such lighting apparatuses perform a lighting operation or output a signal by emitting light from a light emitting section thereof.

[3] For example, an LED (lighting Emitting Diode) is used for the light emitting section.

The light emitting section including the LED has an advantage of displaying high brightness with low power consumption. Light emitting devices outputting a variety of colors have been developed and are widely used in the lighting apparatuses such as an advertising board and a traffic light.

[4] It is determined that the lighting device such as an LED ends its lifetime when the emission efficiency thereof is lowered by 70%. The lifetime is determined by the light- emitting duration, but the lifetime remarkably varies due to thermal deterioration resulting from heat generated at the time of emitting light. That is, the lifetime is shortened due to the thermal deterioration.

[5] The problem with heat is solved by forming a board, which the LED is bonded to, of aluminum. In addition, a large-sized heat radiating plate may be attached thereto. In some cases, a heat radiating fan is used.

[6] The above ^nentioned solutions give a great burden in view of volume or cost.

[7] In the LED device, a method of continuously supplying current smaller than normal current of the LED device to emit light is used.

[8] Fig. 1 is a graph illustrating a relation between time t and current I supplied to the

LED device.

[9] As shown in Fig. 1, the LED device has a structure for continuously supplying current Il smaller than the normal current to emit light and thus has a problem that the lifetime of the LED device is shortened due to the accumulation of heat.

[10] It is intended to solve the problem with heat by increasing the size of a bonding material 10 and/or a bonding board 11 bonded to an LED 9, which is not a fundamental solution.

[11] Fig. 2 is a graph illustrating a temperature distribution in an LED bonding structure.

[12] As shown in Fig. 2, the temperature forms a peak at a position of the LED 9 and decreases as the distance from the position of the LED 9 increases. Here, for the purpose of the prevention of deterioration due to the heat radiation of the LED and the elongation of lifetime, a heat radiating plate or other heat radiating fan is used to stabilize the temperature of the LED 9 in the range of 12⁰C to 6O⁰C, which is not a fundamental solution but causes a problem with an increase in volume and cost. Disclosure of Invention Technical Problem

[13] A goal of the invention is to provide thermal control method and apparatus of an

LED device that can overcome the above^nentioned problems.

[14] Another goal of the invention is to provide thermal control method and apparatus of an LED device that can elongate the lifetime of the LED device.

[15] Another goal of the invention is to provide thermal control method and apparatus of an LED device that can prevent or minimize the deterioration of an LED and the ac- cumlation of heat.

[16] Another goal of the invention is to provide thermal control method and apparatus of an LED device that can reduce the cost and the volune. Technical Solution

[17] According to an aspect of the invention, there is provided a thermal control method of an LED device including: applying excess current larger by a predetermined level than normal current to at least one LED; and repeatedly switching supply and interception of the excess current to the at least one LED and controlling a supply time of the excess current to the at least one LED.

[18] The supply time of the excess current may be determined such that the at least one

LED is not deteriorated and destructed, and an interception time of the excess current may be determined on the basis of an amount of heat emitted from the at least one LED.

[19] The at least one LED may be bonded to a base substrate for radiating heat and dispersing heat.

[20] According to another aspect of the invention, there is provided a thermal control apparatus of an LED device including: an LED light-emitting section including at least one LED; a power source supplying excess current, which is larger by a predetermined level than normal current of the at least one LED, to the at least one LED; a control signal generator generating a control signal for controlling a supply time of the excess current by supplying and intercepting the excess current; and a switching section connected between the LED light-emitting section and a ground terminal so as to perform a switching operation in response to the control signal.

[21] The control signal may be a rectangular wave or a PWM signal.

[22] The switching section may include at least one switching element having at least one field effect transistor (FET) or at least one transistor (TR).

[23] The at least one LED may be bonded to a base substrate for radiating heat and dispersing heat.

Advantageous Effects

[24] According to the above^nentioned aspects of the invention, it is possible to elongate the lifetime by the thermal control of the LED and to reduce the manufacturing cost and the use of raw materials. It is possible to reduce the size of the apparatus, thereby finely decorating the appearance. It is also possible to prevent or minimize the deterioration of the LED and the accumulation of heat, thereby enhancing the reliability. By changing the brightness and the intensity of illunination using a variety of colors of the LEDs, it is possible to provide a variety of chromaticity. Brief Description of the Drawings

[25] Fig. 1 is a graph illustrating a relation between time t and current I supplied to a known LED device.

[26] Fig. 2 is a graph illustrating a temperature distribution in a known LED bonding structure.

[27] Fig. 3 is a circuit diagram illustrating a thermal control apparatus of an LED device according to an embodiment of the invention.

[28] Fig. 4 is a graph illustrating a relation between time and current supplied to an LED shown in Fig. 3.

[29] Fig. 5 is a graph illustrating a temperature distribution in an LED bonding structure having the structure shown in Fig. 3. Mode for the Invention

[30] Hereinafter, exemplary embodiments of the invention will be described in detail with reference to the accompanying drawings, which are intended to provide only better understanding of the invention to those skilled in the art. [31] Fig. 3 is a circuit diagram illustrating a thermal control apparatus 300 of an LED device according to an embodiment of the invention.

[32] As shown in Fig. 3, the thermal control apparatus 300 of an LED device includes an

LED light-emitting section 320, a control signal generator 310, and a switching section 330. The thermal control apparatus may further include a base substrate (indicated by reference mineral 11 of Fig. 5) mounted with the LED light-emitting section 320, the control signal generator 310, and the switching section 300. The base substrate 11 may serve to radiate heat and disperse heat.

[33] The LED light-emitting section 320 has a structure in which at least one LED D is connected to at least one resistor Rl. An end of the resistor Rl is connected to a power source and the other end of the resistor Rl is connected to a plus terminal + of the LED. The resistor Rl is a protective resistor for protecting the LED D.

[34] Only one LED D is shown in Fig. 3. Fbwever, the LED light-emitting section 320 may have a structure in which plural connection structures of an LED and a resistor similar to the connection structure of the LED D and the resistor Rl shown in Fig. 3 are connected in parallel.

[35] The power source supplies excess current, which is larger by a predetermined level than normal current of the LED, to the LED D. The power source supplies the excess current to the LED D through the resistor Rl.

[36] The control signal generator 310 generates a control signal for controlling a supply time of the excess current by supply and interception of the excess current.

[37] The control signal generator 310 generates a rectangular wave or a PWM (Pulse

Width Modulation) signal with a constant period. The rectangular wave and the PWM signal are generally referred to as rectangular wave. The control signal generator 310 generates the rectangular wave in a program manner and can vary the period and the duty ratio of the rectangular wave. That is, the duty ratio and the period of the rectangular wave can be adjusted. The control signal generator 310 may include a micro processor (MPU: micro-processor unit) controlling the generation of the rectangular wave.

[38] The switching section 330 is connected between the LED light-emitting section 320 and the ground terminal and performs a switching operation in response to the control signal generated from the control signal generator 310.

[39] The switching section 330 switches the power source of the LED light-emitting section 320 in response to the control signal to repeatedly turn on and off the at least one LED D of the LED light-emitting section 320 with a predetermined time interval. The switching section 330 may include at least one field effect transistor (FET) or at least one transistor (TR) for fast switching. The switching section may include a switching element well known to those skilled in the art.

[40] The switching section 330 includes at least one resistor R2 and at least one switching element Q.

[41] The base of the switching element Q is connected to the resistor R2, the collector is connected to a terminal of the resistor Rl not connected to the LED D, and the emitter is grounded. When the switching element Q employs the field effect transistor, the gate of the FET is connected to the resistor R2, the source is connected to a terminal of the resistor Rl not connected to the LED D, and the drain is grounded.

[42] When the LED light-emitting section 320 includes only one LED, the switching section 330 also includes only one switching element. When the LED light-emitting section 320 includes plural LEDs, the switching section can include the same number of switching elements as the LEDs or a predetermined nunber of switching elements so that one switching element corresponds to a predetermined nunber of LEDs. For example, when the LED light-emitting section includes five LEDs, the switching section may include five switching elements in the one-to-one correspondence, or may two switching elements of which one switching element is connected to two LEDs and the other switching element is connected to three LEDs. The nunber of switching elements connected to the LEDs can be adjusted variously depending on the correspondence type.

[43] An operation of the thermal control apparatus 300 of an LED device will be described now with reference to Fig. 4. Fig. 4 is a graph illustrating a relation between time and current supplied to the LED D. Current Il shown in Fig. 4 represents normal current of the LED and current 12 represents excess current larger by a predetermined level than the normal current.

[44] First, the excess current L2 is supplied from the power source. When the control signal generator 310 generates the control signal, the supply time of the excess current 12 is controlled by the fast switching operation of the switching section 330 in response to the control signal.

[45] The supply time of the excess current 12 is adjusted on the basis of the fact that the destruction or thermal resistance of the LED is remarkably reduced at the time of instantaneously applying the excess current.

[46] The instantaneous excess current 12 supplied to the LED D enhances the efficiency of light, but causes the destruction of the LED due to the accumulation of heat when the supply time is great. Accordingly, the supply time of the excess current 12 is adjusted not to destruct the LED D. The supply time has the unit of βs (micro second). Then, when the excess current 12 is intercepted, the generated heat is radiated through the base substrate. When the heat is sufficiently radiated, the excess current 12 is applied thereto again. This operation is repeated.

[47] For example, as shown in Fig. 4, in the same way as supplying the excess current in a first time interval tl and intercepting the excess current in a second time interval t2, the excess current 12 is supplied in a third time interval t3, a fifth time interval t5, and a seventh time interval t7, and the excess current 12 is intercepted in a fourth time interval t4 and a sixth time interval t6.

[48] The time lengths of the first time interval tl, the third time interval t3, the fifth time interval t5, and the seventh time interval t7 may be equal to each other or may be different from each other. The time lengths of the second time interval t2, the fourth time interval t4, and the sixth time interval t6 may be equal to each other or may be different from each other. Particularly, when the time lengths of the second time interval t2, the fourth time interval t4, and the sixth time interval t6 are short, that is, when the excess current is supplied again in a state where the heat is not sufficiently radiated, the deterioration and the accunulation of heat may occur. Accordingly, a sufficient time length should be guaranteed.

[49] Here, the high-level length of the rectangular wave as the control signal is equal to the supply time length of the excess current 12 and the low-level length of the rectangular wave is equal to the interception time length of the excess current 12. This is natural because the supply and interception of the excess current 12 is controlled by the rectangular wave.

[50] The level of the excess current 12 and the supply time and the interception time of the excess current can be controlled to interlock with each other. For example, when the level of the excess current 12 is raised, the supply time length of the excess current 12 can be reduced and the interception time length of the excess current 12 can be reduced. The level of the excess current 12 can vary variously. When the level of the excess current 12 is once determined, the supply time and the interception time of the excess current 12 is controlled. The time may be several tens βs to several hundreds βs . The times can be defined by plural experiments. Since a packaging method and an LED bonding structure are different every element and a degree of heat transmission is different every structure, the time values should be acquired from the experiments by characteristics of elements. The experiment result is input to the control signal generator 310 to control the rectangular wave.

[51] By performing the above^nentioned operations, it is possible to elongate the lifetime of the LED, to suppress the generation of heat from the protective resistor Rl connected to the LED, and thus to remove the generated heat. Accordingly, since the known problem that a large-current element should be used due to the continuous supply of the current smaller than the normal current can be solved and the size of a package can be reduced, it is possible to accomplish a decrease in size and an enhancement in reliability. Particularly, since a large-scaled heat radiating plate need not be used, it is advantageous in a decrease in size.

[52] By changing the brightness and the intensity of illunination of the LEDs using a variety of colors of the LEDs, it is possible to provide a variety of chromaticity.

[53] Fig. 5 is a graph illustrating a temperature distribution in the LED bonding structure.

[54] As shown in Fig. 5, the temperature forms a peak at a bonding position of the LED 9 and decreases as the distance from the bonding position of the LED 9 in the base substrate 11 increases. The temperature of the LED device is stabilized in the range of 13⁰C to 4O⁰C as a whole. Accordingly, since the peak temperature is lowered by 2O⁰C or more, it is possible to prevent or minimize the destruction of the LED due to the deterioration of the LED and the accumlation of heat. Reference numeral 10 represents an LED bonding material which is not described here.

[55] The above^nentioned embodiment is only an example for the purpose of clear understanding of the invention, and thus should not be understood to limit the invention. It will be easily understood by those skilled in the art that the embodiment can be modified in various forms without departing from the basic spirit of the invention.

Claims

[1] A thermal control method of an LED device comprising the steps of: applying excess current larger by a predetermined level than normal current to at least one LED; and repeatedly switching supply and interception of the excess current to the at least one LED and controlling a supply time of the excess current to the at least one

T KD

[2] The thermal control method according to claim 1, wherein the supply time of the excess current is determined such that the at least one LED is not deteriorated and destructed, and an interception time of the excess current is determined on the basis of an amount of heat emitted from the at least one LED.

[3] The thermal control method according to claim 2, wherein the at least one LED is bonded to a base substrate for radiating heat and dispersing heat.

[4] A thermal control apparatus of an LED device comprising: an LED light-emitting section including at least one LED; a power source supplying excess current, which is larger by a predetermined level than normal current of the at least one LED, to the at least one LED; a control signal generator generating a control signal for controlling a supply time of the excess current by supplying and intercepting the excess current; and a switching section connected between the LED light-emitting section and a ground terminal so as to perform a switching operation in response to the control signal.

[5] The thermal control apparatus according to claim 4, wherein the control signal is a rectangular wave or a PWM signal.

[6] The thermal control apparatus according to claim 4, wherein the switching section includes at least one switching element having at least one field effect transistor (FET) or at least one transistor (TR).

[7] The thermal control apparatus according to claim 4 or 6, wherein the at least one

LED is bonded to a base substrate for radiating heat and dispersing heat.