Description

DRIVING CIRCUIT FOR AN ULTRA-BRIGHT LED LAMP

Technical Field

[1] The present invention relates to a high-luminance LED illumination apparatus that may be substituted for a fluorescent light tube, and more specifically, to a circuit for driving a high-luminance LED lamp that may be substituted for a fluorescent light tube, to which alternating or direct current voltage can be applied, wherein constant voltage and current are applied to an LED although strength of voltage or surrounding temperature is changed, thereby minimizing power consumption by constantly maintaining brightness of light and further minimizing power consumption by feeding back and reusing surplus power, as well as preventing damage of the LED. Background Art

[2] A light emitting diode (LED) is a diode that emits light when current is applied. If forward voltage is applied to a semiconductor of a specific element, electrons and holes move across the junction between a P-type semiconductor and an N-type semiconductor and recombine with each other, and the energy is smaller than when the electrons and holes are apart. The LED is a light emitting device that emits light by the difference of energy generated at the moment.

[3] The LED is a light emitting device that can be driven at low voltage, which has advantages of an extended lifetime, low power consumption, a fast response time, and a superior shock-proof characteristic, compared with other light emitting objects. Since the LED can be advantageously manufactured in a miniaturized and light form, application of the LED is expanded centering on a display purpose, and the LED increasingly tends to be used as a main illumination or outdoor display apparatus as luminance of the LED is improved. Although there is a limitation in luminance and colors in the early stage, it is possible to display natural full-colors as high-luminance blue-color LEDs are developed and manufactured, and thus all colors can be displayed if blue-color LEDs are combined with red and green-color LEDs. Therefore, the LEDs are spotlighted as being used as a component of displays, traffic lights, electric signboards, illumination equipment, and the like, which have characteristics of an extended lifetime, high-luminance, and high visibility.

[4] In addition, in the case of power LEDs having luminance that is at least ten times as high as that of conventional high-luminance LEDs, they are used for scenery illuminations, such as wall-recessed lights, indoor lights, under ground lights, flood lights, power liners, and the like, or special illuminations such as LED flash and the like. Generally, filament light bulbs, fluorescent light tubes, neon signs, and the like are

examples of an illumination apparatus installed in an indoor or outdoor advertisement material or signboard configured with channels of large-scaled screens, figures, characters, and the like, which are used to easily distinguish images in the daytime or nighttime.

[5] Among the illumination apparatuses, the filament light bulb that illuminates using light emitted by heat has a short lifetime since the filament is oxidized by the heat, and there is danger of fire since excessive heat is generated due to high power consumption. In addition, since the gas and fluorescent material filled in the fluorescent light tube are degenerated, the fluorescent light tube is inconvenient in that it should be frequently replaced due to a very short lifetime of 3,000 to 10,000 hours and disadvantageous in that brightness thereof is degraded as the lamp is aged. The fluorescent light tube is disadvantageous in that since fluorescent light tubes are not replaced in time although some of the fluorescent light tubes are out of order or getting dimmer, the effect of advertisement cannot be properly accomplished.

[6] Particularly, there is a problem in that since excessive labor costs are required to replace fluorescent light tubes when they are installed on a high-rise building or iron tower, all the fluorescent light tubes are replaced at the same time although some of them can be used still more, and thus unnecessary expenditure is required. In addition, since the neon sign among the illumination apparatuses is formed as figures or characters by curving and cutting neon tubes, they are disadvantageous in that costs for manufacturing and replacing the neon signs are high, environmental pollution is incurred since gases used for the neon sign contain mercury, and maintenance cost is much increased due to high power consumption.

[7] Accordingly, advertisement illumination apparatuses using LEDs of semi-permanent lifetime, low cost, and low power consumption come to be used. Although the LED illumination apparatus has advantages of low power consumption, low heat, and semipermanent lifetime, a plurality of LEDs are used in combination only for a simple display function since luminance of the LEDs is low. In addition, high-luminance LEDs are manufactured and used recently as techniques are advanced. An LED illumination apparatus uses DC voltage generated through a diode or bridge circuit (a rectify circuit) after inputted AC voltage is dropped to required voltage through a transformer, and brightness of the LEDs is adjusted by controlling strength of voltage or current.

[8] However, although the LEDs require a stable power supply having constant voltage and current, it is particularly difficult to supply constant current. Furthermore, if the LEDs are exposed to outside and environmental conditions such as temperature, humidity, and the like are getting worse, there is a problem in that since abrupt change of current and voltage, which is incurred due to varying load, and ripples of the current

are insufficiently controlled, the LEDs are damaged due to abnormal operation.

[9] Furthermore, since the high-luminance LEDs can use a light source only when constant voltage is applied, there is a problem in that the high-luminance LEDs are limited to use only DC voltage currently and it is difficult to use the high-luminance LEDs without help of an expert technician. In addition, there is a problem in that since a circuit is configured based only on power used for the LEDs, power is severely wasted. Furthermore, durability of the LEDs is degraded since the amount of current is increased due to decrease of internal resistance of components as internal temperature of an LED illumination apparatus rises more than 80 degrees Celsius in summertime. Disclosure of Invention Technical Problem

[10] Accordingly, the present invention has been made in order to solve the above problems, and it is an object of the invention to provide a modular-type LED illumination apparatus that uses free voltage, which can be easily handled, installed, and used without difficulty of supplying constant voltage and help of an expert technician as is suffered in the prior art. Voltage of 10V to 250V can be used regardless of using an AC or DC power supply, and voltage is flattened by filtering ripple voltage that is generated when AC voltage is used. The voltage portion of the power consumed by the LED is maintained to be constant at all times within the range of power supply of 10V to 250V, and surplus power is fed back to minimize power consumption. In addition, although the temperature and voltage are changed, brightness of light remains constant, and the LED operates stably. Therefore, damage of the LED can be prevented, and thus the LED illumination apparatus can be used for an extended period of time.

[11] Another object of the invention is to provide an LED lamp that may be substituted for a fluorescent light tube as a modular-type LED illumination apparatus using free voltage, in which LEDs are buried with epoxy resin as a water-proof process, and thus durability is increased since erosion is prevented. Since surface emission is accomplished, the LED lamp can be easily distinguished from a far distance. Technical Solution

[12] In order to accomplish the above objects of the present invention, according to one aspect of the invention, there is provided a circuit for driving a high-luminance LED that is lit and emits light when current flows, the circuit comprising: a power supply unit for converting one input power to voltage appropriate to drive the high-luminance LED; a rectify unit including a plurality of bridge diodes, for converting the voltage generated by the power supply unit into DC voltage; a filter unit including a plurality of electrolytic condensers, for flattening voltage by filtering ripple voltage applied from the rectify unit; a voltage control unit including a regulator and a resistor, for

receiving the DC voltage passing through the filter unit and providing a PWM signal needed to drive the LED; a drive control unit including a field effect transistor and resistors, for controlling on-off and amount of current flowing through the LED; and a current control unit for controlling the amount of current by comparatively compensating a characteristic of current change of the LED affected by change of temperature.

[13] According to the present invention, the voltage control unit preferably includes a regulating integrated circuit for controlling over- voltage and over-current, a resistor element connected to an output terminal of the regulating integrated circuit in a series, for preventing damage and poor quality of the LED invited by over-current, and a condenser connected to a connection terminal of the regulating integrated circuit, for controlling and setting input power and power consumption.

[14] In addition, the current control unit for compensating temperature includes a diode, a condenser, and a coil, for feeding back over-current when the over-current flows through the high-luminance LED

[15] Although the present invention preferably corresponds to one power supply, it is apparent that a plurality of driving circuits can be configured in common so that a plurality of LEDs can be driven according to a plurality of different operating powers.

Advantageous Effects

[16] The present invention is effective in that power consumption is minimized by maintaining brightness of light and further minimized by feeding back and reusing surplus power, as well as preventing damage of LEDs by applying constant voltage and current to the LEDs although strength of voltage and surrounding temperature are changed. [17] Accordingly, the present invention is effective in that it is possible to provide an

LED lamp that may be substituted for a fluorescent light tube, which can be used in conventional fluorescent illumination equipment without change or modification of a power supply apparatus.

Brief Description of the Drawings [18] FIG. 1 is a diagram showing a driving circuit of a high-luminance LED lamp that may be substituted for a fluorescent light tube according to an embodiment of the invention. [19] FIG. 2 is a diagram showing a driving circuit of a high-luminance LED lamp that may be substituted for a fluorescent light tube according to another embodiment of the invention.

Mode for the Invention [20] Hereinafter, the present invention will be described with reference to the ac-

companying drawings.

[21] FIG. 1 shows a circuit for driving a high-luminance LED according to an embodiment of the present invention. A power supply unit 100 comprises a surge protective element SVR, a coil L _x , and a condenser C _x and converts one input power into voltage appropriate to drive the high-luminance LED. Here, the power supply unit 100 may use a power supply apparatus, such as a general AC-DC converter, AC line transformer, or the like, preferably one that may generate one constant voltage and constant current.

[22] Power supplied to the power supply unit 100 is applied to a rectify unit 200 comprising bridge diodes Dl to D4 and converted to DC voltage, and a filter unit 300 comprising a plurality of electrolytic condensers Cl to C4 operates not to affect components and the LED by charging and discharging voltage having an irregular peak waveform supplied from the rectify unit 200. In addition, the filter unit 300 flattens the voltage by filtering ripple voltage that is generated when AC power is used in order to provide the same condition as that of using DC power.

[23] On the other hand, the DC voltage passing through the filter unit 300 is inputted into a voltage control unit 400 and provides a PWM signal needed to drive the LED, and the voltage control unit 400 comprises a regulator ICl, a resistor Rl, a condenser C5, and a zener diode ZD.

[24] The regulator ICl of the voltage control unit 400 controls over- voltage and over- current, and the resistor Rl and the condenser C5 are connected to the output terminal of the regulator ICl in a series and prevent damage and poor quality of the LED incurred by over-current.

[25] Accordingly, the voltage portion of consumed power is maintained constantly and supplied through the process of blocking the over-current by the resistor element Rl, and thus damage and poor quality of the LED can be prevented.

[26] A driving control unit 500 comprising resistors R3 and R4 and a field effect transistor FET is connected to the gate terminal GATE of the regulator ICl in order to input a pulse width modulation signal. Here, the gate terminal GATE of the regulator ICl controls on-off and brightness of the high-luminance LED.

[27] On the other hand, if abnormal voltage is outputted to the output terminal of the resistor element Rl of the voltage control unit 400 due to extreme change of input power or surrounding temperature, surplus power except the current consumed by the LED is collected and reused through a diode D20 of a current control unit 600, unlike a conventional method of consuming surplus power by emitting heat, and thus waste of power can be minimized.

[28] As described above, although power is supplied within a certain voltage range regardless of using DC or AC voltage, constant voltage and current are stably supplied at

all times, and thus brightness of the high-luminance LED is maintained constantly.

[29] FIG. 2 shows another embodiment of the invention. Comparing with FIG. 1, since another embodiment is the same as the embodiment described above except that two inputs INPUTl and INPUT 2 and two outputs LEDl and LED2 are generated and two high-efficiency LED fluorescent light tubes are driven, detailed description will be omitted. Industrial Applicability

[30] Although the present invention has been described with reference to several preferred embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications and variations may occur to those skilled in the art, without departing from the scope of the invention as defined by the appended claims.