Driving principle of LED driving; Forward pressure drop (VF)And forward current (IF)
The relationship curve, from the curve, when the forward voltage exceeds a certain threshold (About 2 V)
, That is, after the commonly referred turn-on voltage, it can be approximately considered that IF is proportional to VF.
See table is the electrical characteristics of the current main ultra-bright LED.
According to the table, the * height IF of the current ultra-high brightness LED can reach 1A, while VF is usually 2 ~ 4V
Since the light characteristics of LED are usually described as a function of current, not voltage, luminous flux (φV)
The relationship curve with IF, therefore, using constant current source drive can better control brightness.
In addition, the change range of LED's forward voltage drop is relatively large (* Large up to 1V or more), And by VF in the above figure-
IF curve, we can know that the small change of VF will cause larger, IF change, thus causing larger change of brightness.
Therefore, the use of constant voltage source driving can not guarantee the consistency of LED brightness, and affect the reliability, life and light decay of LED.
Therefore, ultra-bright LED is usually driven by constant current source. LED temperature and luminous flux (φV)
The relation curve, from the following figure, we can know that the luminous flux is inversely proportional to the temperature, the luminous flux at 85 ℃ is half of that at 25 ℃, and the time output at 40 ℃ is 1. 8 times that at 25 ℃.
The change of temperature also has certain influence on the wavelength of LFD. Therefore, good heat dissipation is the guarantee for LED to maintain constant brightness.
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