Ripple Current and Flickering of LED

Ripple Current and Flickering of LED

Hello, today we are going to talk about the flicker, or strobe flicker.

First let’s try to make the difference of flicker and strobe flicker clear. flicker normally indicates the instability of the light system, which can be obviously noticed by human eyes. And the flicker frequency is unstable but normally below 100Hz. And strobe flicker always refers to the ones with higher and stable frequency which is the twice of line voltage frequency. In China it is twice of 50Hz while in US it is 120Hz. In this video, we are focusing on the strobe flicker.

There are quite a few applications where the light quality needs to be strobe flicker free, such as hospital, roadway, sports stadium, theatres, workshops, schools, etc.. To avoid the strobe flicker, we need to know what causes the flicker firstly.

The obvious reason of flicker is the lumen output fluctuation from the light source, and we know that the drving current of the led is almost proportional to the lumen output. So the root cause is the driver current ripple. So to remove the flicker, we need to look for the low ripple driver solutions.

There are quite a lot of both low ripple and high ripple led driver designs, for lighting engineers, it is not easy to determine which driver design you choose, and the best way is to check the experimental results by measuring the LED current or light lumen output. But the pity is that there is still no real standard released telling you how much current ripple you should have to be flicker free. Fortunately we have some reference drafted by IEEE, which shows the recommended relation between the current ripple and frequency to avoid the strobe flicker.You could contact me by my email in the last page to get a copy.

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So from this recommended curve, we know that for the 100Hz current ripple, the pk to pk value should be 8% x 2 Irms = 16% Io, and for 120Hz current ripple, the pk-pk value should be 19.2%Io

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