The switching power supply used as the LED driving power supply will contain a certain amount of ripple, so how do you view and handle the output ripple of the LED power supply?
Research by the Lighting Research Council (LRC) has shown that the flicker of LED lighting is frequency dependent and suggests the acceptance range of the stroboscopic effect, see the figure below:
Studies have shown that the output current ripple has no significant effect on the LED heating temperature, and has no significant effect on the power conversion efficiency of the LED lamp.
The output current ripple is closely related to the selected power topology.
In a conventional power supply, a large electrolytic capacitor is used to store energy, and a DC voltage is supplied to the switching stage, so that the output current ripple is low. However, the disadvantage is that power factor correction cannot be provided, and electrolytic capacitors are also called bottlenecks in life. Generally used only for 5W or less.
Most of the new switching power supplies have added PFC function to improve power factor, improve power efficiency and extend power life. For example, a single-stage PFC-corrected constant current output (CC) topology produces the highest conversion efficiency (>92%). However, the output ripple of this topology is high and concentrated in the 120 Hz (100 Hz) range.
In order to reduce the influence of ripple on the LED lighting effect (flicker), some standards stipulate the ripple ratio of the LED power supply. For example, a Japanese standard specifies a ripple ratio of less than 4%.
In addition, ripples need to be controlled to a certain level in certain applications, such as photography.
Another method is to inject the primary side ripple into the feedback terminal of the power IC to reduce the output ripple by about 25%. However, the consequence 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) reduces the ripple to less than 8%, which is an electronic filter implemented by a triode, which is equivalent to the addition of a first-stage conversion circuit.
Due to the insertion loss of the electronic filter, the conversion efficiency of the power supply will drop by about 5%.
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