PFC-SEPICLED driver
PFC stands for "Power Factor Correction", SEPIC stands for "Single-Ended Primary Inductor Converter", of course, LED stands for "Light Emitting Diode"
Integrating these three features in a single converter provides a high-efficiency, single-stage solution with good power factor for LED lighting. Figure 1 is a schematic diagram of a PFC-SEPICLED driver.
Figure 1. PFC-SEPIC converter can be controlled using a conventional PFC boost controller
An important feature of SEPIC is the lack of isolation. This structure can only be used in applications that do not require secure isolation. Think of a completely sealed application where users cannot access energized components such as street lights and high ceiling lights.
Most PFC converters use a boost topology that requires an output voltage that is higher than the peak line voltage. The SEPIC topology allows the output voltage to be higher or lower than the input voltage. This helps the controller to directly regulate the current in the LED string without the need for a secondary power stage.
Any PFC boost controller can be used to drive the PFC-SEPIC power stage. This is because the power switch is on the low side as it is in the boost topology.
The PFC boost controller forces the peak current in the switch to follow the input voltage sine wave, thus providing a good power factor. Unlike the boost topology, in the coupled inductor SEPIC, no input current flows when the switch is turned off. Therefore, the power factor is not as high as in the boost topology.
However, the power factor is easily maintained above 0.9, which is sufficient for most lighting applications.
Figure 2 is an example of line voltage and current and current harmonics, where the harmonics remain below the EN61000-3-2C requirements.
Figure 2. This topology not only provides good power factor, but also meets EN61000-3-2C standards.
Extremely efficient with this topology because:
1. Using a single stage to achieve PFC, power conversion and voltage regulation, can eliminate the disadvantages of double or triple conversion;
2. SEPIC's clamp capacitors retract the leakage energy in the coupled inductor, saving 2% energy or increasing efficiency compared to the flyback topology.
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