How to deal with flashing LED lights, usually the human eye can sense the frequency of light up to 70 Hz flicker, above this frequency will not be perceived. Therefore, in LED lighting applications, if the frequency of the pulse signal is lower than 70 Hz, the human eye will experience flicker. Of course, there are several factors that can cause LED lights to flash in a specific application. For example, in off-line low power LED lighting applications, a common power topology is an isolated flyback topology. To avoid this problem, the primary bias must be allowed to discharge in each half-cycle, and accordingly the capacitance and the resistance of the bias circuit must be properly chosen.
In addition, electromagnetic interference (EMI) filters are required even in LED driver applications that provide excellent power factor correction and support TRIAC dimming. The transient current caused by the TRIAC step can excite the natural resonance of the inductor and capacitor in the EMI filter. If this resonant characteristic causes the input current to fall below the TRIAC holding current, the TRIAC will shut down. After a short time delay, the TRIAC usually turns on again, inducing the same resonance. In one half cycle of the input power waveform, this series of events may be repeated several times, resulting in visible LED flicker. In order 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 capacitor must be able to be decoupled through the TRIAC and the winding impedance. According to the formula, if the capacitance in the dimming module is reduced, the resistance of the resonant circuit can be increased, and in principle the oscillation is suppressed and the desired circuit operation is restored.
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