What are the common causes and solutions of LED lights flickering?

Usually the human eye can perceive light flickering at frequencies up to 70 Hz, and above this frequency it is not. Therefore, in LED lighting applications, if the pulse signal has a low frequency component with a frequency lower than 70 Hz, the human eye will feel flickering. Of course, in a specific application, there are many factors that may cause LED lights to flicker. For example, in off-line low-power LED lighting applications, a common power topology is the isolated flyback topology. Taking the GreenPoint® reference design of an 8W offline LED driver compliant with the "Energy Star" solid-state lighting standard as an example, since the sine-square-wave power conversion of the flyback regulator does not provide constant energy to the primary bias, the dynamic self-powered (DSS) ) circuit may activate and cause light flickering. To avoid this problem, it is necessary to allow the primary bias to be partially discharged at each half-cycle, and accordingly, the magnitude of the capacitors and resistors that make up this bias circuit needs to be properly selected.

In addition, electromagnetic interference (EMI) filters are required even in applications using LED drivers that provide excellent power factor correction and support TRIAC dimming. Transient currents caused by TRIAC steps can excite the natural resonance of inductors and capacitors in EMI filters. If this resonant characteristic causes the input current to drop below the TRIAC holding current, the TRIAC will turn off. After a short delay, the TRIAC will usually turn on again, exciting the same resonance. This sequence of events may repeat multiple times during one half-cycle of the input power waveform, resulting in visible LED flickering. To address this, a key requirement for TRIAC dimming is that the EMI filter has an extremely low input capacitance that can be decoupled through the TRIAC and the winding impedance. According to the formula, if the capacitance in the dimming module is reduced, the resistance of the resonant circuit can be increased, which in principle suppresses the oscillation and restores the desired circuit operation.

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