Many people are not aware that LEDs may need overcurrent protection in spite of the integrated safety features that are found within the LED circuit. The manufacturers of LED lighting are concerned with the fact that the lack of adequate thermal management can lead to degraded lifespan and color output.
In addition, because LED drivers are usually semi-conductor devices, they can fail. Therefore, fail-safe overcurrent protection may be necessary.
The Danger of Damage
It is common for the optical behavior of the LED to vary considerably in temperature. The amount of emitted light lessens as the junction temperature increases. In some technologies, the wavelength emitted will change with the temperature. Without the proper management of the junction and current temperature, the efficiency will quickly drop. This will lead to a shortened life and reduced brightness.
Surges and transients of the power line may also decrease the life of the LED. A number of LED drivers are susceptible to damage as a result of improper polarity and voltage levels. Short circuits can also damage LED driver outputs.
The majority of LED drivers are designed to include integrated safety feature, such as thermal shutdown. They also include short and open LED detection as well. However, it may be necessary to use extra overcurrent protection devices in order to aid in the protection of ICs and other sensitive components.
An LED is driven by a constant current with a forward voltage of under 2V to 4.5V, depending on the current and color. The older designs depended on simple resistors that limited the LED drive current. However, the design of an LED circuit that is based on the usual forward voltage drop according to the manufacturer’s specifics may cause the LED driver to overheat.
The overheating of an LED circuit can happen if the forward voltage drop that goes across the LED reduces to a value that is considerably less than the usual declared value. In such as case, the amplified voltage of the LED driver may lead to higher overall power degeneracy that comes from the driver package.
LED applications utilize control and conversion devices that interface with a number of power sources like battery power, solar power or the AC line. This is done in order to control the power dissipation that comes from the LED driver. Protection such interfaces from damage caused by overcurrent and overheating is possible through the use of resettable polymeric positive temperature coefficient, or PPTC devices.
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