Common Causes And Treatment Methods of LED Lights Flickering

Usually, the human eye can sense the frequency of 70 Hz of the light flicker. Therefore, in LED lighting applications, if the pulse signal frequency is lower than 70 Hz of low-frequency components, the human eye will feel the flicker. Of course, in specific applications, 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 isolated flyback topology. GreenPoint & reg, an 8W off-line LED driver that meets the Solid State Lighting Standard of Energy Star, is taken as an example of reference design. Since the sinusoidal 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 trigger flicker. In order to avoid this problem, it is necessary to enable the primary bias to discharge at each half-cycle portion, and accordingly, the capacitance and resistance values that constitute the bias circuit need to be properly selected.

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 induced by the TRIAC step (step) will excite the natural resonance of the inductor and the capacitor in the EMI filter. If this resonance characteristic causes input current to TRIAC to maintain current, TRIAC will turn off. After a short delay, TRIAC usually leads to the same resonance. This series of events may be repeated many times during a half cycle of the input power waveform, resulting in a visible LED flicker. To deal with this problem, a key requirement of TRIAC dimming is that the input capacitance of the EMI filter is extremely low, and this capacitance can be decoupled through TRIAC and winding impedance. According to the formula, if the capacitance of the dimming module decreases, the resistance of the resonant circuit can be increased, and the oscillation can be suppressed in principle and the desired circuit can be restored.