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No.118, Qianwang Road, Baibu Town, Haiyan, Jiaxing City, Zhejiang Province, ChinaNormally the human eye is able to perceive light flickering at frequencies up to 70 Hz, and not at frequencies above this. 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 perceive flicker. Of course, in specific applications, there are many factors that may cause LED lights to flicker. For example, in offline low-power LED lighting applications, a common power supply topology is the isolated flyback topology.
ZF-002-3030-12W Backlit led panel
Taking the 8W off-line 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-Power Supply (DSS ) circuit may activate and cause the light to flicker. To avoid this problem, it is necessary to allow the primary bias to be partially discharged every half cycle, and accordingly, the magnitudes of the capacitors and resistors making up this bias circuit need to be properly chosen.
ZF-002-3030-12W Backlit led panelTaking the 8W off-line 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-Power Supply (DSS ) circuit may activate and cause the light to flicker. To avoid this problem, it is necessary to allow the primary bias to be partially discharged every half cycle, and accordingly, the magnitudes of the capacitors and resistors making up this bias circuit need to be properly chosen.
In addition, even in applications using LED drivers that provide excellent power factor correction and support TRIAC dimming, electromagnetic interference (EMI) filters are required. The transient current induced by the TRIAC step (step) excites the natural resonance of the inductor and capacitor in the EMI filter. If this resonant characteristic causes the input current to drop below the TRIAC holding current, the TRIAC will shut down. After a short delay, the TRIAC will usually turn on again, exciting the same resonance. This sequence of events may repeat several times during one half-cycle of the input power waveform, resulting in visible LED flickering.
To deal with this problem, a key requirement for TRIAC dimming is that the input capacitance of the EMI filter is extremely low, and this capacitance should 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, which in principle suppresses the oscillation and restores the desired circuit operation.
To deal with this problem, a key requirement for TRIAC dimming is that the input capacitance of the EMI filter is extremely low, and this capacitance should 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, which in principle suppresses the oscillation and restores the desired circuit operation.
