The present invention generally relates to light emitting diodes (LEDs), and in particular to a single LED chip comprising a number of LED cells connected in series for enhancing brightness and increasing the overall operation voltage to match with the electrical potential of the electric main.
Brightness is one of the major concerns of light emitting diode (LED) devices. The most commonly employed method in enhancing the brightness of the LED devices is to increase the chip size of an LED chip. In the industry, the LED chip size has been increased from 9 milxc3x979 mil to 25 milxc3x9725 mil to the recently developed 40 milxc3x9740 mil. The working current for the LED chip has increased from 20 mA to 50 mA and has reached 500 mA recently. Such a working current leads to an overall voltage drop of around 2-4 volts for direct current which is much lower than the regular voltage supplied by the electric main which is 110-220 V in general. Thus, expenses for power transformation and regulation, as well as related equipments, are very high.
FIGS. 7 and 8 show a conventional circuit arrangement for LED devices in which the LED cells are connected in parallel. Such an arrangement increases the overall current consumption while requiring only a small voltage drop. Thus, the difference in voltage between the LED device and the electric main is significant.
It is thus desired to provide a serial arrangement of LED cells in a single LED chip for overcoming the problems discussed above.
An object of the present invention is to provide a serial connection structure of LED cells inside a single LED chip for increasing the voltage drop and maintaining a low working current.
Another object of the present invention is to provide an LED module that is connectable with an electric main with simplified and thus low-cost interfacing devices.
To achieve the above objects, in accordance with the present invention, there is provided serial connection structure of a light emitting diode device. The device comprises a substrate having a major surface on which a number of LED cells are formed and arranged in a two-dimensional array. The LED cells have a p-type semiconductor and an n-type semiconductor. The n-type semiconductor of each LED cell is electrically connected to the p-type semiconductor of the adjacent LED cell whereby the LED cells are connected in series. The p-type semiconductor of the starting LED cell and the n-type semiconductor of the ending LED cell are connected to conductors for electrical connection with an external power source. The arrangement of serially connected LED cells allows enhancement of the brightness of a single LED device when the chip size of the LED device is increased. The working voltage is also heightened and the working current can be maintained low. Interfacing equipments between the LED device and external power source can be simplified.