High reliability airport light topology: a new AC-LED topology

[Source: "High - tech LED - Technology and Applications " 1 February issue ]

C du/dt invisible damage to HV-LED

In the study of DC high voltage LED (HV-LED) lamps due to the presence of distributed capacitance C, after the "on-off-on-off..." impact test, the "Cdu/dt" transient process was found, possibly for DC high voltage LEDs. A reverse soft breakdown occurs, which is manifested by the LEDs that are originally consistently screened, and gradually differentiated; a high-priced high-end LED lamp in foreign countries, each LED is connected in parallel with a 5.6V Zener diode, eliminating the above-mentioned "C du /dt" It is possible to make the HV-LED in series with a hidden fault in which one LED has a reverse soft breakdown. Why do you only say "possible" without saying certain damage? Because the size of the distributed capacitor is greatly affected by the geometry, it is also greatly affected by the PCB layout. For example, if the distributed capacitance C is not large enough, or if the dt is large enough, the reverse soft breakdown of the HV-LED will not occur.

One reverse and one positive paired parallel AC-LED high reliability airport lights

AC constant current source i, power supply to two LEDs, one reverse and one positive paired parallel, and then connected in series to AC-LED, equivalent to each of the above LEDs are reverse-parallel 5.6V Zener diode, can effectively overcome "C du /dt" The soft breakdown risk of transients.

The list of switching impact test procedures for selecting some topologies is as follows:

The finally selected high-reliability airport lamp topology is a constant-current AC cable that penetrates into the distributed magnetic ring as the distributed variable-current magnetic ring primary winding N1; and the variable-current magnetic ring secondary N2, takes out the corresponding AC constant-current power, The AC-LED lamp characterized by the above number 4 is illuminated. The biggest advantage of this topology is that when one LED is damaged, other LEDs still work normally. This is the preferred topology for airport lights, tunnel lights, bridge lights, etc., with reliability as the preferred requirement.

Thoughts on LED utilization and light extraction rate of AC-LED

The AC-LEDs of the above No. 2 and No. 4, the positive half wave and the negative half wave respectively illuminate half of the LEDs. Therefore, many people think that the LED utilization rate of the AC-LED is 50%, which is a biased primary. in conclusion. We apply rare earth phosphors with rare earth lanthanum (Eu) elements that store light energy. When the LEDs are energized, the phosphors of another non-powered LED packaged in parallel are also excited to emit light. When one of the LEDs loses power, it is extinguished. When the other LED is powered on, it is similar to the principle that the capacitor can store charge. The rare earth erbium (Eu) phosphor stores light energy and simply breaks the illusion that AC-LED is regarded as 50% low utilization.

Selecting the formula containing rare earth lanthanum (Eu) and other light-storing elements in the phosphor can obtain AC power that adapts to different frequencies, and can lose power in a short time, but the human vision does not have the feeling of light flashing.

The LED lamp has a large current and the LED light output is also large (the key is that the LED junction temperature cannot be too high). Therefore, under the premise of the same junction temperature, the AC-LED can use a strong alternating current to illuminate each AC-LED lamp separately. (Under the premise that the human eye is flicker-free), a higher light output can be obtained.

We use 100KHZ AC frequency, only a small duty cycle AC pulse of 1us per half wave, and with the phosphor of the formulated light storage element formula, we can achieve extraordinary super high light output rate. Currently, this technology is applying for related patents. Will be described in detail later.

Unfinished

For more information, please refer to "High - tech LED - Technology and Applications" 1 February issue