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A common cause of LED lights flashing and treatment method

- Aug 23, 2016 -

The human eye can generally perceived frequency of 70 Hz light flashing, higher than the frequency does not perceive. So in LED lighting applications, if the pulse signal frequency is lower than 70 Hz low frequency component, the human eye will feel the shine. In the specific application, of course, there are many factors may lead to LED lights flashing. For example, in an off-line low power LED lighting applications, a common power supply topology structure type is to isolate the flyback topology. To meet energy star from linear solid-state lighting standard 8 w LED driver GreenPoint® Reference design as an example, as a result of flyback voltage regulator of sine square wave power conversion did not provide primary offset constant energy, dynamic self-supply (DSS) circuit may activate and flashing light. To avoid this problem, must enable primary bias to partial discharge in each half cycle, accordingly, need to choose appropriate constitute the bias circuit of capacitance and resistance value.

In addition, even if in use provide excellent support power factor correction, TRIAC dimming LED drive applications, the electromagnetic interference (EMI) filter. Caused by a TRIAC step (step) transient current inspire EMI filter inductance and capacitance in the natural resonance. If the resonant characteristics lead to fall below TRIAC maintain current input current, TRIAC will be closed. After a brief delay, TRIAC usually will conduction, inspire the same resonance. In the input voltage waveform of one and a half cycle, this series of events may be repeated many times, to form a visible LED flashing. In order to deal with this problem, a key demand of TRIAC dimmer is EMI filter input capacitance is extremely low, and the capacity to be able to through the TRIAC and winding impedance decoupling. According to the formula, adjustable capacitance decrease in optical module, can increase the resistance of the resonant circuit, the principle on inhibiting oscillation, restore to the circuit work.

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