INTRODUCTIONTOLEDPOWERSOURCES-Molex.pdfVIP

INTRODUCTION TO LED POWER SOURCES BY JEFF CIARLETTE ? MOLEX INC INTRODUCTION Properly powering a light emitting diode (LED) or group of LEDs is different than powering most electronics. While most electronics require a constant voltage source, LEDs require a constant current source. Most power supplies will provide a set voltage, such as 5V, and have a maximum current rating. The power supply will maintain this voltage and provide enough current to meet the demand of the circuit it is powering. This means a dedicated power supply would need to be implemented to drive any LEDs in a circuit. For an LED to properly operate, the power supply must have a high enough voltage to turn on (illuminate) the LED and it must provide a controlled constant amount of current to the LED. The voltage required to illuminate the LED is called the forward voltage (Vf). The amount of current the LED uses when illuminated is called the forward current (If). Forward current is typically specified as a maximum value. Current above this rating can damage the LED. LED light output varies with the forward current. Decreasing the forward current decreases the LED light output. active. The forward current requirements are usually 10mA to 20mA. There is little requirement for a precise amount of current for these types application, since there is usually only one LED used for indication and slight variations in luminous intensity from one indicator to a nearby indicator are not important as long as each indicator is visible and relatively of the same brightness. The power required to power LEDs used for lighting is much greater than that used for indicator LEDs. As a result, efficiency becomes a concern. Some methods of powering LEDs are very inefficient and result in large power losses. These losses are usually counterproductive, as LEDs are often chosen to increase efficiency of lighting systems over other methods, such as incandescent lighting. LEDs in these applications may require hundreds o