Since light emitting diodes (LEDs) can realize colors, they have been widely used for indicating lamps, electric display boards and displays. The LEDs have also been used for general illumination because they can realize white light. Since such LEDs have high efficiency and longer life span and are environment-friendly, their applicable fields have been continuously expanded.
Meanwhile, an LED is a semiconductor device which is formed of a p-n junction structure of semiconductors and emits light through recombination of electrons and holes. In general, the LED is driven by a current flowing in a direction. Thus, when the LED is driven using an AC power source, there is a need for an AC/DC converter for converting an AC current to a DC current. With the use of an AC/DC converter together with LEDs, installation costs of LEDs increase, which makes it difficult to use the LEDs for general illumination at home. Therefore, to use LEDs for general illumination, there is a need for an LED package capable of being directly driven using an AC power source without an AC/DC converter.
Such an LED lamp is disclosed in U.S. Pat. No. 5,463,280 entitled “LIGHT EMITTING DIODE RETROFIT LAMP” issued to James C. Johnson. The LED lamp includes a plurality of light emitting diodes coupled in series, a means for limiting a current, and a diode bridge. Since an AC current is converted to a DC current through the diode bridge, the LED lamp can be driven by an AC power source.
However, since the LED lamp have serially coupled LEDs with individual LED chips mounted thereon, the process of coupling the LEDs is complicated, and the size of the LED lamp considerably increases since the LEDs occupy a large space.
In the meantime, since the luminous power of an LED is substantially in proportion to an input power, increase of electric power to be input into the LED enables high luminous power. However, the junction temperature of the LED increases due to the increase of the input electric power. The increase of the junction temperature of the LED results in decrease of photometric efficiency that represents the degree of conversion of input energy into visual light. Therefore, it is necessary to prevent the junction temperature of the LED from rising due to the increased input power.
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