LED driver power supply technology
On LED open circuit protection protection utility
Date：2012-09-15
High power LEDs are increasingly being used in traffic lights, luminous billboards, street lights, airport runways, railway crossings, medical / surgical lighting and driving signal. Their long service life (high power white LEDs typically have a life of 35,000 to 50,000 hours), and low power consumption. However, LED will be caused by lightning, electrostatic discharge (ESD), overvoltage, overheating, and even power reverse and damage.
Series because the LED is usually string lights, string lights an LED open circuit due to a fault, all LED strings off. The LittELfuse LED open circuit protection device. Protector can each LED in parallel with the light string, it can bypass the open-circuit failure occurs LEDs continue to work to keep the rest of the string lights. When the overvoltage circuit and cause an overcurrent occurs in the lamp string, or reverse the electrode, the protection device will also effect.
When an LED fails open circuit, LED open circuit protection device will start conducting, to limit its voltage drops to 1.3V, and keep the remaining portion continues to work in series.
Design staff in order to do this, try a number of devices, such as Zener diodes, metal oxide varistors and SCR rectifier, but not open circuit protection and LED, because LED open-circuit protection is designed for this application design. Shown in Figure 1, the open fault when one LED, LED open circuit protection sensed this voltage rises, and starts conducting, limiting its pressure dropped to 1.3V or so, in order to maintain the light strings and the remaining part of the work.
LED open circuit protection devices have different characteristics and rated voltage optional. Some protection is designed as a single LED in the lamp protection string; allows designers to use a single device to protect two, three, four or five LEDs, in order to save costs. Littelfuse new generation of open LED protection, while providing ESD protection.
ESD and lightning protection
ESD assembly or field installation into the LED light string. Lightning can enter two ways to LED string lights: a nearby lightning strike may cause transients in the power supply, can be coupled to the LED drive and into the light string; nearby lightning strike may be on the LED driver power supply rail may also connected to the LED light string line to cause electrical transients.
The new generation of open LED protection, Littlefuse PLED 5 Series, you can deal with in ± 15kV air discharge, ± 8kV contact discharge ESD event, and the event of EFT ± 40A 5/50 ns (fast burst).
Reverse polarity protection
When a fitted PLED5 LED light string reverse pass on the power protector will start conducting these protected LED current shunt to protect them from harm. After the opposite electrode correction, the protector will turn off the the LED normal working.
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