1. Field of Invention
The invention relates to a structure of light-emitting diodes (LED), and particularly to a structure of LED dies with an alternating current (AC) loop (a structure of AC LED dies).
2. Related Art
A light-emitting diode (LED) emits light based on its semi-conductive characteristics, in contrast to the heating light-emitting principle of a fluorescent lamp, and is thus called a cold light. The LED provides a number of advantages such as high endurance, long lifetime, compactness, low power consumption and so forth. Furthermore, no pernicious material such as mercury is contained in the LED. Therefore, there are high expectations with respect to the LEDs for being a light source in daily life in the current lighting market.
However, prior LEDs are generally limited in their acceptable power levels. Most LEDs may be fed with only low DC voltages and may be damaged if high voltages or AC voltages are applied thereon. Because of this, a DC voltage conversion circuit is generally used to transform the external power supply used by such LEDs. In operating an LED by use of a low DC voltage, the LED has its characteristic curve of the current-voltage relation, as shown in FIG. 1A. As shown, when the voltage is forwardly applied, the LED is conducted and light is emitted there from. On the other hand, if a reverse voltage is applied, the LED breaks down and no light is emitted. Further, in practical usage the LED is often connected in series or parallel with several such LEDs, such as those used in traffic light apparatuses such as stop light apparatuses. As shown in FIG. 2, the externally supplied AC voltage 11 is first reduced in its level by means of a conversion circuit 12 and then converted into a DC voltage corresponding thereto. Then the converted DC voltage is fed into a plurality of LEDs connected with one another in series or in parallel as mentioned above, in which LEDs cannot be used when reverse power is supplied.
However, once a single LED arranged among the plurality of LEDs is damaged, the set of LEDs in which the damaged LED resides is also likely to become damaged and the whole of the loop formed with the damaged LED included is badly affected. To reduce this occurrence, the number of LEDs connected in series is generally reduced as much as possible. Unfortunately, the total amount of wires used for these LEDs in a specific application is unavoidably increased and the power consumption increases correspondingly. Furthermore, the voltage at an end of one of the wires is insufficient and thus causes uneven luminance of the LEDs.
There is another serious problem with a low DC voltage operated ALInGaN LED. When such a LED is assembled and processed, electrical static discharge (ESD) is apt to occur. When this occurs, an instantaneous high reverse voltage is burst forth and the LED is damaged.
To resolve the above-mentioned shortcomings, circuit assembly and die manufacturing are two generally adopted solutions.
The circuit assembly scheme may be seen in U.S. Pat. No. 6,547,249. This patent discloses an additional diode arranged in a reverse orientation and connected in parallel to protect an LED-based circuit to prevent sudden ESD or an exceptional current or voltage attack. In another U.S. Pat. No. 5,936,599, LEDs in an LED based circuit are arranged in a reverse orientation and connected in parallel, and inductors and capacitors are introduced in the circuit. In this case, an AC voltage and a high voltage may be used by the LEDs. However, although the problem of high power consumption may be overcome by such circuit assembly schemes, the corresponding large volume of the LED based circuit considerably limits its actual applicable range.
An example of the die manufacturing scheme may be seen in U.S. Pat. No. 6,547,249, in which LED dies are manufactured as a matrix form and connections of the LED dies are arranged in the same orientation in series and in parallel. Although such LEDs may be operated with a high voltage, they may still not be applied with an AC voltage. In this patent, an arrangement for protection of breakdown of the LEDs is also provided by connecting a diode with the LEDs in a variety of combinations where the LEDs may also be arranged in mutually reverse orientations and connected with each other but should be disposed over a submount and then connected with the LED matrix in parallel. According to this patent, the LED die 91 has a structure shown in FIG. 1B, and has an equivalent circuit shown in FIG. 1C, in which the LED 91 is connected in parallel with two mutually oriented Zener diodes 92 and 93, or a connection may be provided to form a loop as shown in FIG. 1D. The current-voltage relation curves corresponding to the equivalent circuits in FIG. 1C and FIG. 1D are shown in FIG. 1E and FIG. 1F respectively.
Also referring to U.S. Pat. No. 6,635,902, the LED dies are also manufactured as a matrix form while the LEDs are oriented the same and connected in series. Although the LEDs may be operated with a high voltage, they also have the problem of not being capable of operation with AC voltage.