SEPIC or single-ended primary inductor converter is a type of Buck/Boost DC-DC Converter that provides a DC output greater than, less than, or equal to its DC input. It consists of two inductors, one is at the input and another one is connected to the ground and these two inductors are connected by a coupling capacitor.

The major advantage of a SEPIC converter is that its output voltage has the same polarity as that of the input voltage. This is called no-polarity inversion.

SEPIC converter circuit consists of input voltage source Vg, coupling capacitor C1, and output capacitor C2, two inductors L1 and L2, diode D, and load resistance. SEPIC converter circuits share the common ground between the input and output circuits. This converter exchanges energy between the inductor L1, capacitor C1, and inductor L2 to convert input DC voltage to require output voltage level.  Typically, a power transistor switch (S1) such as a MOSFET is used to control the amount of energy exchanged.  

Instead of using discrete inductors (L1 & L2), the SEPIC converter can also be designed using the coupling inductors which will improve the efficiency and reduce PCB area. Coupling inductors mean that two windings (L1 & L2) are connected in a single core.

Key benefits of SEPIC Converters:  

• When compared with a conventional buck-boost converter, the SEPIC converter offers benefits such as providing non-inverting output voltage, superior input current purity, and higher efficiency.
• When compared with a flyback converter (isolated buck-boost) that uses a transformer for isolation, the SEPIC converter offers benefits such as lower switching losses, low output voltage noise, higher efficiency, and allows the high frequency of operation.

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