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SEPIC Converter Inductor & Capacitor Sizing Calculator

The Single-Ended Primary-Inductor Converter (SEPIC) is a non-inverting DC-DC switching topology that allows output voltage to be greater than, less than, or equal to the input voltage.

Operating DC input voltage.

Regulated DC output voltage.

Maximum continuous DC load current.

PWM operating switching frequency.

Target inductor ripple current percentage relative to input current (typically 20% to 40%).

Allowable AC peak-to-peak voltage ripple on C_sep (typically 1% to 5%).

Calculated Result
32 µH

SEPIC Power Inductor (L1/L2)

Coupled Inductor (L₁ & L₂)

32 µH

Coupling Cap (C_sep)

20.8 µF

Nominal Duty Cycle (D)

50.0%

Peak Switch Current (I_pk)

5.38 A

Switch Voltage Stress (V_sw)

24 V

Output Filter Cap (C_out)

41.7 µF (1% ripple)

Calculation Breakdown

  1. SEPIC Operating Duty CycleD = V_out / (V_in + V_out) = 12 / (12 + 12) = 0.5
  2. Coupled Inductance SizingL = (V_in × D) / (ΔI_L × f_sw) = (12 × 0.5) / (0.75 × 250000) = 32 µH
  3. AC Coupling Capacitor RatingC_sep = (I_out × D) / (ΔV_c × f_sw) = (2.5 × 0.5) / [(12 × 0.02) × 250000] = 20.8 µF

SEPIC Power Component Specifications

Interactive visualization based on your current inputs

Value
0.013253850Duty Cycle (%)Inductance (µH)C_sep (µF)Peak Switch (V)Peak Current (A)ParameterValue

What Is the SEPIC Converter Inductor & Capacitor Sizing Calculator?

The SEPIC Converter Inductor & Capacitor Sizing Calculator determines key passive power components for Single-Ended Primary-Inductor DC-DC converters.

How Does the SEPIC Converter Inductor & Capacitor Sizing Calculator Work?

It computes nominal duty cycle, determines peak inductor ripple currents, and sizes L1, L2, and coupling capacitor C_sep for continuous conduction mode (CCM).

SEPIC Converter Inductor & Capacitor Sizing Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

D = \frac{V_{out}}{V_{in} + V_{out}}, \quad L_1 = L_2 = \frac{V_{in} D}{\Delta I_L f_{sw}}, \quad C_{sep} = \frac{I_{out} D}{\Delta V_{csep} f_{sw}}

Fundamental energy balance governing SEPIC dual-inductor topology with AC ground-isolated charge transfer.

How to Use the SEPIC Converter Inductor & Capacitor Sizing Calculator

  1. Enter input and output voltages and maximum load current.
  2. Specify PWM switching frequency in kHz.
  3. Set target inductor and capacitor ripple tolerances.

Step-by-Step Example Calculation

12V-to-12V Automotive Battery Stabilizer

Input Values:

inputVoltageVin:12
outputVoltageVout:12
outputCurrentIout:2.5
switchingFrequencyKhz:250
targetInductorRipplePercent:30
targetCapacitorRipplePercent:2
Worked Steps: Operates at 50% duty cycle, requiring 32.0 µH coupled inductance and 20.8 µF low-ESR ceramic C_sep capacitor.

Understanding Your Result

Coupled Inductance (L1/L2): Recommended minimum inductance in microhenries (µH).

Coupling Capacitance (C_sep): Required AC transfer capacitor value in microfarads (µF).

Switch Voltage Stress: Peak reverse voltage experienced by the power MOSFET and diode.

Factors That Affect the Result

  • Higher switching frequencies proportionally reduce required inductor and capacitor values.
  • Lower allowed ripple demands larger, bulkier passive components.

When Should You Use This Calculator?

  • Automotive battery conditioning (cold crank / load dump), battery chargers, solar MPPT regulators, and multi-chemistry power banks.

Assumptions & Limitations

  • Assumes continuous conduction mode (CCM) operation and negligible diode forward drop.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Conforms to Texas Instruments Application Report SLVA369 and Analog Devices technical guidance.

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