Forward pressure drop (VF) and forward current (if) relationship curve, it is known by the curve, when the positive voltage exceeds a certain threshold (about 2V), that is, usually referred to the conduction voltage, can be approximated to think that if and VF proportional. See table is the current main ultra-high-brightness led electrical characteristics. It is known from the table that the current super bright LED is up to 1A, and VF is usually 2~4v.
Because the light characteristics of LED are usually described as the function of the current, not the function of the voltage, the luminous flux (φv) and the relationship curve of the If, the constant current source drive is used to control the brightness better. In addition, the LED's positive pressure drop range is larger (up to 1V or more), and the Vf-if curve in the above diagram shows that the small change of VF will cause a larger, if change, resulting in a greater change in brightness. Therefore, the use of constant voltage source drive can not guarantee the uniformity of LED brightness, and affect the reliability of LED, life and light failure. Therefore, the ultra-high-brightness LED is usually driven by constant current source.
LED temperature and luminous flux (φv) relationship curve, from the following figure that the luminous flux and temperature is inversely proportional, 85 ℃ when the luminous flux is 25 ℃ half, and a 40 ℃ time output is 25 ℃ 1. 8 times times. The temperature change to the LED wavelength also has certain influence, therefore, the good heat dissipation is the LED maintains the constant brightness guarantee.