Flickering in LED filament lamps is primarily caused by power supply fluctuations, driver circuit design flaws, or insufficient component performance. Essentially, it stems from periodic changes in current or voltage leading to unstable light output. Flickering not only affects visual comfort but can also cause headaches, eye fatigue, and other health problems with prolonged use. Therefore, optimizing circuit design to address flicker is crucial for improving the quality of LED filament lamps.
The stability of the driver circuit is key to resolving flicker. Traditional driver circuits using simple capacitor or RC voltage reduction schemes are prone to output current fluctuations due to component parameter variations. For example, capacitor value deviations or aging directly alter the voltage reduction effect, causing the LED filament lamp's operating current to deviate from its rated value, resulting in flicker. Optimized solutions require constant current driver chips that adjust the output current in real-time through a negative feedback mechanism, ensuring stable current even during voltage fluctuations. These chips typically integrate overvoltage and overcurrent protection functions, preventing increased flicker caused by transient interference from the power grid.
Power supply filtering design is also critical for suppressing flicker. Harmonics and surges in the power grid can be conducted to the LED driver circuit through the power lines. If filtering is insufficient, these interferences will be superimposed on the DC output, forming low-frequency ripple and causing LED filament lamps to flicker. Optimizing the filtering circuit requires a multi-stage filtering structure, such as connecting a large-capacity electrolytic capacitor and a ceramic capacitor in parallel at the input to filter out low-frequency and high-frequency interference respectively; adding a small-capacity capacitor at the output of the driver chip further smooths the current waveform. In addition, common-mode inductors can suppress common-mode noise on the power lines, reducing the impact of electromagnetic interference on the driver circuit.
Compatibility issues with the dimming circuit are a common cause of flickering. Traditional SCR dimmers are designed for incandescent lamps, and their dimming principle is to adjust brightness by cutting off a portion of the sine wave. However, this discontinuous current waveform causes instability in the input voltage of the LED driver circuit, leading to flickering. Solving this problem requires a dedicated LED dimming driver chip. Such chips can recognize SCR dimming signals and convert the discontinuous waveform into smooth DC or high-frequency pulses through internal circuitry, ensuring continuous current in the LED filament lamps during dimming. Some high-end driver chips also support digital dimming interfaces (such as DALI and PWM), enabling seamless integration with intelligent control systems for flicker-free dimming.
Component selection and layout directly impact circuit performance. The lifespan and temperature resistance of electrolytic capacitors are critical parameters. Using low-temperature-rise, long-life capacitors reduces output fluctuations caused by capacitor performance degradation. Inductors should be selected with low DC resistance and high saturation current to reduce their own losses and heat generation. In terms of circuit layout, the principle of "separation of strong and weak currents" should be followed, keeping sensitive components such as driver chips and filter capacitors away from the power input to reduce electromagnetic interference. Simultaneously, shortening the length of high-frequency signal traces reduces the impact of parasitic parameters on circuit stability.
While heat dissipation design is not directly related to flicker, it indirectly affects circuit reliability. When LED filament lamps are operating, the driver chip and electrolytic capacitors generate heat. Poor heat dissipation can lead to increased component temperature and performance drift, such as decreased capacitor capacitance and reduced chip efficiency, resulting in output current fluctuations. Optimizing heat dissipation requires starting with structural design and material selection. For example, using a metal substrate or thermally conductive adhesive to conduct heat to the lamp housing, or adding heat sink fins to increase the heat dissipation area.
Electromagnetic compatibility (EMC) design is an implicit requirement for addressing flicker. If the driver circuit is not EMC certified, it may affect other devices due to its own radiated or conducted interference, and may also malfunction due to external electromagnetic fields. Optimizing EMC requires adding components such as ferrite beads and filters to the circuit to suppress high-frequency noise; at the same time, a reasonable PCB layout should be designed to avoid signal lines forming loop antennas and reduce radiated interference.
Through driver circuit stability optimization, enhanced power supply filtering design, improved dimming circuit compatibility, optimized component selection and layout, improved heat dissipation design, and EMC design, the flicker problem of led filament lamps can be systematically solved. These measures not only need to be comprehensively considered during the circuit design stage, but also require rigorous testing and verification, such as using an oscilloscope to detect output current ripple and simulating flicker performance under different dimming scenarios, to ensure that the product meets flicker-free standards in actual use, providing users with a healthy and comfortable lighting environment.
