SEPIC Converter Calculator

A SEPIC (Single-Ended Primary Inductance Converter) is a type of DC-DC power supply circuit that can step voltage up or down — unlike a basic buck or boost converter. Enter your input voltage, output voltage, output current, switching frequency, inductor current ripple, output voltage ripple, and expected efficiency into the SEPIC Converter Calculator to get the duty cycle plus all key component values: primary inductor (L1), secondary inductor (L2), coupling capacitor (Cc), output capacitor (Co), input current, and output power.

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Results

Duty Cycle (D)

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Primary Inductor (L1)

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Secondary Inductor (L2)

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Coupling Capacitor (Cc)

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Output Capacitor (Co)

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Input Current (Ii)

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Output Power

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Frequently Asked Questions

What is a SEPIC converter and how does it work?

A SEPIC (Single-Ended Primary Inductor Converter) is a DC-DC converter that can either step up or step down voltage while maintaining positive output polarity. It uses two inductors, a coupling capacitor, a diode, and a switching transistor to transfer energy from input to output.

What are the advantages of SEPIC topology over buck-boost converters?

SEPIC converters provide non-inverting output (positive polarity), continuous input current, and good isolation between input and output. Unlike buck-boost converters, SEPIC maintains the same ground reference for input and output.

How do I select the coupling capacitor for a SEPIC converter?

The coupling capacitor must be non-polarized and low ESR since it carries all the power. It should be rated for the peak voltage stress and sized to minimize voltage ripple. Ceramic or film capacitors are typically used.

What is the voltage conversion ratio for a SEPIC converter?

The voltage conversion ratio is Vo = Vi × D / (1-D), where D is the duty cycle. This means the output voltage can be higher or lower than input voltage depending on the duty cycle.

Why are two inductors needed in a SEPIC converter?

The two inductors (L1 and L2) can be separate components or coupled windings on the same core. L1 provides continuous input current while L2 helps with output current smoothing and energy storage.

What switching frequency should I choose for my SEPIC converter?

Higher switching frequencies allow smaller components but increase switching losses. Typical frequencies range from 50kHz to 500kHz. Consider efficiency, component size, and EMI requirements when selecting frequency.

How does inductor current ripple affect SEPIC converter performance?

Lower current ripple reduces core losses and improves efficiency but requires larger inductors. Typical ripple is 20-40% of average current. Higher ripple may cause discontinuous conduction mode.

What are the key design challenges for SEPIC converters?

Main challenges include coupling capacitor selection (high current stress), right-half-plane zero in control loop compensation, and higher component count compared to simpler topologies like buck or boost converters.