LED drive driving principle;
The relationship curve between forward voltage drop (VF) and forward current (IF). It can be known from the curve that when the forward voltage exceeds a certain threshold (about 2V), which is generally called the on-voltage, it can be approximately considered that IF and VF is directly proportional. See the table for the electrical characteristics of the current major super-bright LEDs. As can be seen from the table, the highest IF of the current super bright LED can reach 1A, and the VF is usually 2 to 4V.
Because the light characteristics of LEDs are usually described as a function of current, not a function of voltage, the relationship between the luminous flux (φV) and IF, so using a constant current source drive can better control the brightness. In addition, the LED's forward voltage drop has a relatively large range (up to more than 1V), and from the VF-IF curve in the figure above, it can be seen that a small change in VF will cause a large change in IF, which will cause a change in brightness. Major changes. Therefore, driving with a constant voltage source cannot guarantee the consistency of LED brightness, and affects the reliability, life and light decay of the LED. Therefore, the super bright LED is usually driven by a constant current source.
The relationship between the temperature and the luminous flux (φV) of the LED shows that the luminous flux is inversely proportional to the temperature. The luminous flux at 85 ° C is half that at 25 ° C, and the light output at 40 ° C is 1.8 times that at 25 ° C. The change in temperature also has a certain effect on the wavelength of the LFD. Therefore, good heat dissipation is a guarantee for the LED to maintain a constant brightness.