Feature Story

Minimizing Flicker in LED Lighting Applications

Learn How Richtek LED Lighting Solutions Minimize LED Light Flicker

All light sources that ultimately derive their power from the AC mains are likely to flicker. LEDs are particularly worse compared to incandescent lamps because LEDs react quickly to current variation. Most flicker manifest itself as periodic light fluctuation at double the AC line frequency, but incompatibility between lamps and peripheral lighting components can cause random lower frequency flicker as well.
Although 100/120Hz flicker is not perceived by most humans, it can still lead to irritation and eye fatigue. Therefore flicker is one of the key parameters that need to be considered when it comes to replacing traditional lights with efficient, long lasting LED lighting.
Luminaire manufacturers are eager to solve this problem to win more customers switching to LED lamps. This article explains LED flicker phenomena in relation to driver topology and LED characteristics and introduces several Richtek solutions to minimize LED light flicker.

Flicker Definition

Most often, flicker is calculated by using the IES RP 16-10 standard method. For periodic signals the percent flicker is defined as:
A comparison between different light sources reveals various flicker percentages. But how much flicker is allowed?
At this moment, there are no standards that define the maximum allowed flicker for LED lamps. But many Luminaire manufacturers define the percent of flicker to be less than 30% in the 100Hz/120Hz range.
LED light luminance is directly related to the current through the LED. To minimize light flicker, the current variation through the LED needs to be minimized as well. It is important to realize that LED driver topology together with LED string characteristics play an important role in the design of low flicker LED lamps.

Richtek LED Lighting Solutions to Minimize Flicker

There is a trade-off between converter power factor and LED output ripple. Reducing the converter power factor can be used to minimize LED current ripple and flicker.
If high power factor is required, a way to minimize flicker is to increase the converter output filter capacitance. However, size and cost need to be considered.
One could also choose LEDs with higher dynamic resistance, or operate the LED “closer to the knee” which increases dynamic resistance as well.
Another way to reduce flicker is to add a linear post regulator or ripple removercircuit.

Verification Tool

For final verification of the design, a simple light flicker measurement tool can be used in combination with an oscilloscope.
This tool is quite simple to build from readily available components, and is very useful for checking the light variation of different LED lighting applications.
For more information, please see the application note “MinimizingFlicker in LED Lighting Applications

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PFC flyback topology: RT7302, PFC Buck topology: RT8487,
Linear topology: RT7321 and PFC MR-16 LED driver: RT8479

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