Is the linear change in LED brightness difficult? PWM duty cycle helps you

First of all, it needs to be clear that the LED driver is constant current, and the PWM only changes the time ratio of the constant current to the current interruption, so the duty ratio and the output of the luminous flux are linear. As a luminaire, its output luminous flux changes linearly with time, but the human eye does not feel linear. The performance is that in the light-bright area, the small change of luminous flux also makes the light flux change greatly, and the luminous flux is compared. In a large area, a large luminous flux jumps, and the luminous flux perceived by the human eye does not change much.

In this set of drawings, all scales are evenly distributed. Figure 1 shows the relationship between the actual duty cycle and the luminous flux, which is linear; its corresponding human eye perception is shown in Figure 2, and the relationship between Figure 3 and Figure 4 is reversed.

To get the effect of Figure 4, the PWM duty cycle adjustment mode is like Figure 3. This is troublesome in the software processing of the microcontroller. There is a mathematical formula in the software processing to describe this curve, which may result in calculation. The duty cycle of a certain moment, taking up a lot of CPU resources to calculate; of course, there are other ways, such as using a large table to put the curve in the table, how much brightness is needed to go to the table to check the corresponding duty value Yes.

It should be noted here that the human eye like Figure 4 cannot be measured by the instrument. Therefore, the graphic given in the text is only a rough reference, and then adjusted according to the actual experience, until the brightness on the controller is added and the brightness is reduced. From the brightest to the darkest, the human eye feels that it is stepless and uniform. .

This article gives a way to adjust the PWM duty cycle from a software perspective to ensure that the brightness is linear. It is an article that is more biased towards the basic class. I hope everyone can gain something after reading this article.

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