The switching power supply used as the LED driving power supply will contain a certain amount of ripple, so how to treat and deal with the output ripple of the LED power supply? Research by the Lighting Research Council (LRC) shows that the flicker of LED lighting is related to frequency, and proposes the acceptable range of stroboscopic effects, see the following figure:
Studies have shown that the output current ripple has no significant effect on the heating of the LED, and at the same time has no significant effect on the power conversion efficiency of the LED lamp.
The output current ripple is closely related to the selected power supply topology. In traditional power supplies, large electrolytic capacitors are used to store energy and provide DC voltage for the switching stage, so that the output current ripple is very low. But the disadvantage is that it cannot provide power factor correction, and the electrolytic capacitor is also called the bottleneck of life. Generally only used in occasions below 5W.
The output current ripple is closely related to the selected power supply topology. In traditional power supplies, large electrolytic capacitors are used to store energy and provide DC voltage for the switching stage, so that the output current ripple is very low. But the disadvantage is that it cannot provide power factor correction, and the electrolytic capacitor is also called the bottleneck of life. Generally only used in occasions below 5W. Most of the new switching power supplies add PFC function to improve power factor, improve power supply efficiency and extend power supply life. For example, a single-stage PFC-corrected constant current output (CC) topology can produce the highest conversion efficiency (>92%). However, the output ripple of this topology is relatively high and concentrated in the 120Hz (100Hz) range. In order to reduce the impact of ripple on the LED luminous effect (flicker), some standards specify the ripple ratio of the LED power supply. For example, a Japanese standard stipulates that the ripple ratio is less than 4%. In addition, some specific applications (such as photography) also need to control the ripple to a certain level.
Another method is to inject the primary-side ripple into the feedback end of the power IC, which can reduce the output ripple by about 25%, but the consequence of this is to reduce the PF value (~0.7), and the overall conversion efficiency of the power supply is not affected. The use of an active ripple current filter (ARF) can reduce the ripple to less than 8%, that is, an electronic filter realized by a triode, which is equivalent to adding a first-level conversion circuit. Due to the insertion loss of the electronic filter, the conversion efficiency of the power supply will drop by about 5%.
