How to avoid LED flicker?

Whether an LED luminaire is flickering or not depends fundamentally on the solution through the LED driver. At present, LED driver simply meet the requirements of no flicker is also possible to do. There are roughly three ways to do this: 1. increase the output electrolytic capacitance; 2. use a valley-filling passive PFC scheme; 3. use a two-stage scheme (AC to DC, DC to DC).

The first option: increase the output electrolytic capacitance. Theoretically this solution can use electrolytic capacitors to absorb part of the AC ripple, but practical experience tells us: after the ripple is controlled within a certain range (10%), it is difficult to reduce it further, unless the electrolytic capacitors are increased regardless of the cost, and cannot be completely eliminated from the root.

The second way: using a valley-filling passive PFC scheme. This solution is also one of the most mainstream ways of dealing with it. Two large capacitors are used as well as three diodes for power factor correction, as there are large electrolytic capacitors behind the rectifier bridge, so that the AC ripple is absorbed and the current through the inductor or transformer to the secondary section is DC.

However, there are some problems with the valley-filling solution, the output of 40V or more cannot be made into a full voltage input of 90-265V, the valley of the output voltage of the valley-filling circuit is only half of the valley of the electrolytic filter circuit, the output voltage after rectification of the valley-filling rectifier is quite a bit lower than the output voltage after ordinary rectification, and it is possible that the valley-filling type may be used after the low-voltage input is underloaded. Furthermore, regardless of the isolated or non-isolated valley-filling scheme, the harmonic test cannot be passed at all. The power factor is not exactly above 0.95.

The third way: using a two-stage solution. By adding a DC to DC stage to our existing isolated power supply, the effects of AC ripple can be completely eliminated. The electrical parameters can also fully meet the certification standards. However, this solution is somewhat more costly and requires an additional power management chip and some peripheral circuits.

In summary, the valley-filling solution can solve the flicker problem of LED lamps, but there is an output voltage of more than 40V can not be made into a full voltage input, but the cost is relatively cheaper than the two-stage solution, for no flicker has strict requirements, the output voltage of more than 40V does not require a full voltage input customers can consider choosing such a flicker-free power solution. For customers with strict requirements for flicker-free and other aspects, a two-stage solution can be chosen.