1. In offline low-power LED lighting applications, a common power topology is an 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, the primary bias must be able to be partially discharged in each half-cycle, and accordingly, the magnitude of the capacitors and resistors that make up this bias circuit needs to be properly selected.
2. Usually, the human eye can perceive the flicker of light with a frequency of up to 70 Hz, and it will not perceive it above this frequency. Therefore, in the application of LED lighting, 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.
3. Electromagnetic Interference (EMI) filters are required even in LED driver applications that provide optimal 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 a half cycle of the input power waveform, resulting in visible LED flickering.
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