This application note series by Steve Sandler explores the measurement of the dynamic resistance of an LED and how to create a usable SPICE model from the data.
Today, LEDs dominate the lighting industry, replacing incandescent, CFL, and halogen bulbs. They are much more efficient at saving power, and as semiconductor devices, they should be much more reliable. Most LEDs are powered by constant current drivers in order to maintain uniform lighting in parallel strings with matching luminous intensity and color temperature. The stability of a constant current regulator depends on the dynamic LED impedance. This application note series explores the measurement of the dynamic resistance of an LED and how to create a usable SPICE model from the data.
The measurement of the LEDs forward-biased capacitance is also included, since that impacts driver stability and can be important for EMI assessment, particularly in cases where the LED current is pulse-width modulated for dimming.