Generally, the human eye can perceive the flicker of light with a frequency up to 70 Hz, but it will not perceive the flicker above this frequency. 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 flicker. Of course, in specific applications, there are many factors that may cause LED lights to flash. For example, in offline low-power LED lighting applications, a common power topology is isolated flyback topology. GreenPoint, an 8W offline LED driver meeting the "Energy Star" solid state lighting standard ® For example, as the sine square wave power conversion of the flyback regulator does not provide constant energy for the primary bias, the dynamic self supply (DSS) circuit may activate and cause flashing. In order to avoid this problem, it is necessary to enable the primary bias to be partially discharged in each half cycle. Accordingly, it is necessary to properly select the capacitance and resistance values constituting the bias circuit.
In addition, electromagnetic interference (EMI) filters are required even in LED drive applications that provide excellent power factor correction and support TRIAC dimming. The transient current caused by TRIAC step will excite the natural resonance of inductance and capacitor in EMI filter. If this resonance characteristic causes the input current to drop below the TRIAC holding current, the TRIAC will turn off. After a short time delay, TRIAC will normally be turned on again to excite the same resonance. During a half cycle of the input power waveform, this series of events may be repeated many times, resulting in visible LED flickering. To deal with this problem, a key requirement of TRIAC dimming is that the input capacitance of the EMI filter is extremely low, and the capacitance should be decoupled by TRIAC and winding impedance. According to the formula, if the capacitance in the dimming module is reduced, the resistance of the resonant circuit can be increased. In principle, the oscillation can be suppressed and the desired circuit work can be resumed.