LED is a light emitting semiconductor device similar to an ordinary diode. As forward current flowing through the P-N junction of the semiconductor material, photons are released as a results of electrons moving across the diode and falling into P- type layer. Depending on the photon’s frequency, it could either be invisible to human eye (infrared portion) or be part of the visible light spectrum. The latest development in LED technology involves coating blue LED with phosphor to create white LED. The electrical characteristics of LED can be described with the V-I curve similar to a diode as below:
White LEDs are generally used for lighting applications, the brightness of such device increases proportionally with the increase in forward conduction current. Due to the rise in demand for high power, high luminance white LED in the lighting industry, specifications are being standardized. Forward voltage is typically within the range of 3.0~3.5V with forward current of 350/700/1050mA resulting in power rating of 1/2/3W for a single chip. Chip on board (COB) LED modules have also been developed to have a matrix of chips on a small PCB to increase light output.
LEDs require direct voltage (DC) to drive. There are two types of driving methods: Constant Voltage (CV) and Constant Current (CC).
- January 16, 2015
- Lenny Peng