Detecting thyristor effect is essential in HBLED module test

摘要

Testing high-power, high-brightness light-emitting diode (HBLED) modules is increasingly challenging. One crucial characterization function is the ability to detect which modules are affected by the thyristor effect, so that they can be sorted out during production test. The thyristor (or snapback) effect is simply an unwanted capacitance in series with an LED's junction. This effect is problematic because it causes a delay in the turn-on of an LED and it demands a higher LED turn-on voltage, neither of which is a desirable quality. For anyone who manufactures LEDs or designs them into their products, the delay in turn-on is the most serious problem because it creates undesirable inconsistencies in the level of the light output, which can be seen as a dimming or a shift in the color of the light output when compared with the output of LEDs that do not exhibit this effect. The higher LED turn-on voltage required means power is wasted (current times voltage equals power, so requiring a higher voltage to achieve the same current equals higher power). Given that current is delivered to the LED via pulses, the LED is switched on and off hundreds or thousands of times a second, so the cumulative amount of wasted power due to the thyristor effect can be quite significant.