LED driving principle.p3.91 rental led display

　　The relationship curve between forward voltage drop (VF) and forward current (IF) shows that when the forward voltage exceeds a certain threshold (about 2V), commonly known as the conduction voltage, it can be approximately assumed that IF is proportional to VF. The electrical characteristics of the current main ultra high brightness LEDs are shown in the table. From the table, it can be seen that the maximum IF of the current ultra bright LED can reach 1A, while the VF is usually 2-4V.

　　Due to the fact that the optical characteristics of LEDs are usually described as a function of current rather than voltage, luminous flux( φ V) The relationship curve with IF, therefore, using a constant current source drive can better control brightness. In addition, the range of positive voltage drop variation of LED is relatively large (up to a maximum of 1V or more), and according to the VF-IF curve, a small change in VF will cause a significant change in IF, resulting in a significant change in brightness.

　　Temperature and Luminous Flux of LED( φ V) The relationship curve shows that the luminous flux is inversely proportional to temperature. The luminous flux at 85 ℃ is half that at 25 ℃, while the output at 40 ℃ is 1.8 times that at 25 ℃. The change in temperature also has a certain impact on the wavelength of LED, therefore, good heat dissipation is the guarantee for LED to maintain constant brightness.

　　Therefore, using a constant voltage source to drive cannot guarantee the consistency of LED brightness, and affects the reliability, lifespan, and light attenuation of LEDs. Therefore, ultra high brightness LEDs are typically driven by a constant current source.

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