LED control and failure mode

The circuit parameters of the protection device: select the main parameters of the LED protection device is a single LED rated current and rated power, forward operating voltage and constant current output voltage of the LED driver. Typical high brightness LED rated power between 1 watts and 3 watts. Rated power of high brightness LED maximum current consumption can be determined by the following formula:

Where I is the current, the P is LED rated power, and the VF is the LED forward voltage. LED can be used in a wide range of rated power, so these values vary accordingly. At the same time, the emission of different wavelengths (colors) of the LED has different voltage drop. For example, compared with the white LED, red LED usually has a lower VF, will consume more current. The main reliability problem is that if a high brightness LED fails to form an open circuit, the high brightness LED string how to operate continuously. This issue is critical in applications requiring high reliability of light sources.

Many outdoor applications are located away from the ground, so a small accident will turn into a big problem. In series, a single high brightness LED open circuit failure may cause significant costs and inconvenience, because the entire assembly must be maintained.

The LED Series in series is driven by a constant current, which is generated by the switching power supply which is driven by a series of LED strings into full brightness, color and intensity. The constant current source provides a better control of the LED group brightness and a more uniform LED group brightness. LED is a fragile solid-state device, in essence, is a diode, the structure is a P-N junction, in the forward bias, can emit light. The main failure mechanisms of LED are mechanical and thermal properties, including thermal cycling, thermal shock and LED at high temperatures (which may cause wire welding aging and failure). The possibility of a failure of the LED increases as a result of the oxidation of the metal and the weakening of the metal over time. ESD event or nearby lightning surge is another common cause of LED failure.