Abstract:
A light emitting device utilizing a plurality of light emitting diodes (LEDs). LEDs with R/G/B colors are specially arranged to obtain a better light mixing effect. A specially designed heat sink structure is provided to enhance the heat dissipation of LEDs so as to increase the LED density, to decrease its volume and to elongate its lifetime. Furthermore, a newly designed network buffer means is provide for easy connection of the LED system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention generally relates to a light emitting diode (LED) lighting device. 
     2. Related Art 
     When a plurality of light emitting diodes (LEDs) of the same color or different colors are connected in series into several series of LEDs, it is likely to have different VF values in individual LEDs (1.8 V to 2.1 V for red ones and 3.6 V to 4.0 V for blue and green ones) which result in uneven electric currents. This phenomenon of uneven electric currents would damage LEDs with larger currents flowing through and make LEDs with smaller currents unable to have sufficient luminosity. 
     Since the relation between the luminosity of the LED and the electric current flowing through is not linear. In the prior art, the control of the LED luminosity can only be achieved by changing the duty cycle of lighting the LEDs. This technology has been widely used in LED signs for over 20 years and become a fairly mature technology. 
     The above-mentioned control can be achieved by a software program performed on a microprocessor, a digital logic circuit, or a devoted integrated circuit (There are already IC factories designing and producing this type of ICs for LED signs). A PWM logic circuit  120  composed of digital devices can increase the frequency of the lighting cycle of the LED. The software control through a microprocessor can only go up to 350 Hz (i.e. a repetition rate of 350 times per second). This frequency can not be perceived by naked eyes. However, from a camera one can apparently see the blinking. This blinking can even be observed by a relative motion between the eyes and the lighting unit. Thus, it is bad for image production. 
     When a large number of LEDs are located together and arranged in one direction in a usual way, the emitted light would have speckles (i.e. uneven color mixing). The wavelength and luminosity of the light emitted from the LED of a specific color are limited by the LED production technology to certain ranges. If an equal number of red, green, and blue LEDs are employed, different electric currents have to provided for LEDs of different colors so as to obtain a light spectrum similar to the natural light. Accordingly, in the long run, LEDs with larger currents flowing through decay faster in the luminosity whereas LEDs with smaller currents flowing through decay more slowly. 
     Moreover, the LED also generates heat when emitting light. There is no problem in heat dissipation for a single LED. Since the luminosity of a single LED is not high enough, many LEDs have to be collected for a substantial operation power. If so, the heat generated by the LEDs would be harmful to themselves. If the heat generated by the LEDs can not be dissipated immediately, the density of LEDs can not be increased to reduce the device volume and its lifetime may be shortened. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide a light emitting diode (LED) lighting which can conquer the problem with blinking and overheating. 
     Digital network has a wide application in computer systems. The device also uses the digital network. However, a normal network driver can only control about 32 terminal devices. Once a plurality of devices are connected together, a proper buffer has to be inserted to increase the driving power or to extend the network outreach. Therefore, several network connection methods are proposed. Nevertheless, all network buffer circuits are designed to be fixed. Once the devices on the network are changed or rearranged, they have to be redesigned and reconnected. Since LED lighting devices has a strong mobility, fixed buffers are not suitable. Some apparatuses adopt the method of adding a buffer at each level to simplify the connection complexity, yet this method still has some danger because once some device is out of order, all devices after it are disconnected from the network and cannot work. 
     Furthermore, any device on the network system needs an independent address while installation. This is very inconvenient in certain circumstances. Another function of the present invention is to allow the main control system to send out an address update command after the network and all devices finish installation for each device to setup its address on its own without assigning individually. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described with reference to the accompanying drawings of which: 
     FIG. 1 is a structural block diagram of the present invention; 
     FIG. 2 is a schematic view of an LED arrangement according to the present invention; 
     FIG. 3 is a cross-sectional view of a lamp base with the LED heat dissipation according to the present invention; 
     FIG. 4 is a block diagram of the digital network applied to the present invention; 
     FIG. 5 is a block diagram showing the network system functioning principles according to the present invention; 
     FIG. 6 is a three-dimensional view of a embodiment lamp base with a water proof structure according to the present invention; and 
     FIG. 7 is a cross-sectional view of a embodiment lamp base with a waterproof structure according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is designed by the research and development groups of our company by accumulating decades of experience and the application of the latest light emitting diode (LED) technology in LED signs. Most of the base devices are derived from the LED sign system. 
     FIG. 1 is a structural block diagram of the present invention. The invention comprises three groups of LEDs in red, green and blue  100 , 101 , 102 , three groups of electric current driving circuits  110 , 111 , 112 , a PWM wave generator logic circuit composed of digital components  120 , a small microprocessor  130 , an infrared (IR) receiver  140 , a button switch  150 , nonvolatile memory  160 , and a digital network receiver  170 . 
     LEDs of each color are connected in series into several series of LEDs  100 ,  100   a,    100   b,    101 ,  101   a,    101   b,    102 ,  102   a,    102   b,  each of which is driven by an individual electric current driving circuit  110 ,  110   a,    110   b,    111 ,  111   a,    111   b,    112 ,  112   a,    112   b.  This can prevent the phenomenon of uneven electric currents due to different VF values of individual LEDs(1.8 V to 2.1 V for red ones and 3.6 V to 4.0 V for blue and green ones) when connected in parallel. 
     As described in the background, the luminosity of the LED is not linearly proportional to the electric current flowing through. In the prior art, the control of the LED luminosity can only be achieved by changing the duty cycle of lighting the LEDs. This technology has been widely used in LED signs for over 20 years and become a fairly mature technology. The control can be achieved by a software program performed on a microprocessor, a digital logic circuit, or a devoted integrated circuit (There are already IC factories designing and producing this type of ICs for LED signs). A PWM logic circuit composed of digital devices can increase the frequency of the lighting cycle of the LED. The software control through a microprocessor can only go up to 350 Hz (i.e. a repetition rate of 350 times per second). The present invention utilizes a devoted digital logic circuit  120  to generate PWM signals with the frequencies above 30,000 Hz. This then provides a steady, non-blinking light source. Also, since the burden of the CPU is reduced (more than 80% working time of the high level CPU would be occupied for generating PWM signals using the microprocessor), thus a lower level microprocessor can be employed to increase the system stability. 
     Since a digital logic circuit is adopted to generate PWM signals, the microprocessor  130  of the present invention can devote to receiving display messages transmitted from a network receiver  170 , converting the messages into serial or parallel signals  131  required by the digital logic circuit  120  and sending to the digital logic circuit  120 . A digital network usually contains more than two devices working together, thus the microprocessor  130  determines the order or method of reading data from the net through the network receiver  170  according to relevant information stored in EEPROM  160 . This is somewhat like defining addresses, yet the present method is more flexible because the contents of the EEPROM  160  can be updated by following a specific procedure via a digital network. It is not like those devices which define addresses by manually setting switches or other mechanical methods. The invention further comprises an infrared (IR) receiver  140  so the operator can enter some commands to change the function mode of the device via an IR keyboard. These commands are stored into the EEPROM  160  after entering confirmation to be the reference for the next starting of the device. Since the device of the present invention is normally installed at places that people can not reach by hands, the IR setting become more convenient. Furthermore, IR input devices can be more easily made to be waterproof than usual mechanical ones, so this is an advantage of the present invention when waterproof is needed. 
     The button switch  150  in FIG. 1 is an auxiliary setting, which is usually used for making initial setup of newly built models in the factory and is of no use after being installed. 
     The above-mentioned operations and functions can be completed by a software program on a microprocessor  130 . Modifying the software program can change the functioning method and order. 
     If a large number of LEDs are place together without special arrangement, the light emitted therefrom usually has speckles (i.e. uneven color mixing). Our research team made hundreds of arrangements and actual tests and finally determined that the arrangement shown in FIG. 2 has the least speckles. Therefore, the present invention uses the most proper ratio R:G:B=3:4:3 to make the electric currents flowing through all color LEDs close to one another. The LED arrangement in FIG. 2 follows this principle. 10 LEDs as a unit  210  form a base arrangement unit, which includes 3 red LED, 3 blue LEDs, and 4 green LEDs. The whole LED lighting unit is made up by following this rule. Each LED is separated from one another by 5.9 mm to 6.1 mm, which is determined to be the best spacing for machining process thermal density and the device size. 
     The present invention has a good improvement in heat dissipation due to the lighting of the LED lighting device. The invention adopts the passive and active methods for heat dissipation. The passive heat dissipation is shown in the cross-sectional view of a lamp base with the LED heat dissipation as in FIG. 3. A chip  302  is the LED  301  is the object that radiates light and heat. The heat would be spread out via a metal wire  303 . This metal wire is the so-called hot pole. The metal wire  303  of the LED  301  is welded onto a solder pad  305  of a circuit board  304 . The whole circuit board  304  gets in contact with a heat sink  307  (usually aluminum) using a soft thermal conducting silicon chip  306  as the medium. All the heat generated on the LED  301  is readily spread to the ambient air. To speed up the heat transfer on the chip  302 , the solder point of the hot pole on the PCB layout can be enlarged so as to increase the contact area of the solder point  305  and the heat pad  306 . Therefore, the heat transfer rate can be increased. 
     In addition, when collecting more LEDs  301  on a larger lighting device, it is not so easy to have heat dissipation purely by radiation from the heat sink  307  to the air. An active heat device, a fan  308  can be included to facilitate the heat dissipation. 
     The device according to the present invention provides a resolution to the problems existing in a conventional digital network. As the block diagram of the digital network applied to the present invention shown in FIG. 4, the device comprises a set of in-connectors  401 , a set of out-connectors, a set of network receiving circuits  403 , a set of network buffers  405 , a set of relays  405 , and a set of relay driving circuits. When the relay  405  is not active, the out-connector  402  is directly connected to the in-connector  401 . This device is simply connected to the network. When the relay  405  actions, the connector  402  is connected to the network receiver  403  through a network buffer  404  and a relay  405 . It is equivalent to have a network buffer insert into the network. The driver  406  for controlling the relay  405  is preprogrammed to action at a proper time according to the rules set by a microprocessor. Taking the LED lighting device of the present invention as an example, a unit needs three addresses (corresponding to R/G/B colors) and the network driver can drive 32 devices. Therefore, the rules can be set as when the device addresses are defined at 0, 96, 192, 288, 384 . . . , the network buffer of the device automatically join the network so that the network can be indefinitely extended and at the same time the high reliability can be guaranteed. 
     Each independent address set by any device on the network of the present invention is defined by itself after all device installations are completed and the main control system sends out the address update command. It is not necessary to set the addresses individually. FIG. 5 depicts a block diagram showing the network system functioning principles according to the present invention. There is one more relay  507  in FIG. 5 than in FIG. 4, but the rest is the same as FIG.  4 . The new relay  507  mainly separates the connector  502  from the network so that the devices thereafter  5   b,    5   c  can not receive network signals. When the power is just turned on or the device receives some command from the network, the microprocessor  509  controls the relay  507  to action and to separate the connector  502  from the connector  501 . The network signals sent by the main control system  520  can only reach the first device  5   a.  The main control system  520  can give the address setting command to the first device  5   a  via the network  510 . The microprocessor  509  in the device then stores the address to EEPROM  508  for future reference and restores the relay  507  so as to connect the network to the next device  5   b.  Since the second device  5   b  has not received any command, it is still in the standby state. Thus, the second address setting command given by the main control system  520  would reach the second device  5   b,  but not the third device  5   c.  As such process goes on, the main control system  520  can perform address settings for all devices installed on the network. This kind of device does not need to take into account the settings of each device while installation. The main control system sends out a setting command after all installations are completed. So the whole system building can be speeded up. 
     The present invention provides a structure that can facilitate heat dissipation. Aside from heat dissipation, the structure also provide a structure that is waterproof and can be assembled quickly. Referring to FIGS. 6 and 7, the structure comprises two semispherical main heat sinks  601 ,  701  which are formed with fins  602 ,  702  to increase the surface area and an aluminum cup connected back to back  603 ,  703 . Soft heat conducting rubbers  605 ,  705  are inserted between the main heat sinks  601 ,  701  and the aluminum cups  603 ,  703  to facilitate heat transfer and to lower the imperfect heat contact between the two objects  701  and  703  due to machining errors. The LED lighting units  606 ,  706  are assembled via soft heat conducting rubbers  607 ,  707  on the aluminum cups  603 ,  703 . The heat generated by the LED can be immediately dissipated. The reason for using cup shape elements is to increase the heat contact area without increasing the weight of materials (as compared with using thick aluminum plates). 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.