Common causes and solutions for LED light flashing
Generally, the human eye can perceive light flicker with a frequency of up to 70 Hz, and it will not perceive it 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 the LED lights to flicker. For example, in offline low-power LED lighting applications, a common power supply topology is an isolated flyback topology. Taking the 8W offline LED driver GreenPoint® reference design that meets 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, dynamic self-powered (DSS) ) The circuit may activate and cause light flicker. In order to avoid this problem, the primary bias must be partially discharged in each half cycle. Accordingly, the capacitance and resistance of the bias circuit must be appropriately selected.
In addition, even in LED driver applications that provide excellent power factor correction and support TRIAC dimming, electromagnetic interference (EMI) filters are required. The transient current caused by the TRIAC step will excite the natural resonance of the inductor and capacitor in the EMI filter. If this resonance characteristic causes the input current to drop below the TRIAC holding current, the TRIAC will shut down. After a short delay, the TRIAC usually turns on again, exciting the same resonance. In a half cycle of the input power waveform, this series of events may be repeated many times, resulting in visible LED flicker. In order to cope with this problem, a key requirement of TRIAC dimming is that the input capacitance of the EMI filter is extremely low, and this capacitance must be able to be decoupled by the 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 operation can be restored.
