The human eye is usually able to perceive the light flashes of the frequency up to the same frequency, which is higher than that of the frequencies. Therefore, in the application of LED lighting, if the pulse signal frequency is lower than the low frequency component of the, the human eye will feel the flicker. Of course, in specific applications, there are many factors may cause LED lights to blink. For example, in the off-line low power LED illumination application, a common power supply topology is isolated flyback topology structure. In line with the "Energy Star" solid state lighting standard 8W linear LED driver Greenpoint® for example, because the sinusoidal square wave power conversion of the Flyback regulator does not provide a constant energy for the primary bias, the dynamic Self power supply (DSS) circuit may activate and cause a flicker of light. In order to avoid this problem, the primary bias must be able to discharge at each half cycle, and correspondingly, the amount of capacitance and resistance that comprise the bias circuit needs to be properly selected.

In addition, electromagnetic interference (EMI) filters are also required even in LED drive applications that provide excellent power factor correction and support triac dimming. The transient current caused by triac step is the natural resonance of inductance and capacitance in EMI filter. If the resonant property causes the input current to fall below the Triac maintenance current, the triac will be closed. After a short delay, the triac usually leads to the same resonance. During a half cycle of the input power waveform, this series of events may be repeated several times, resulting in a visible led flicker. In order to deal with this problem, the key requirement of triac dimming is that the input capacitance of EMI filter is very low, and the capacitance must be decoupled by triac and winding impedance. According to the formula, the capacitor in the dimming module can increase the resistance of the resonant circuit, restrain oscillation in principle, and restore the desired circuit work.