SEPIC converter
CCM two-inductor sizing, coupling-capacitor stress and explicitly checked conduction limits.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
CCM conversion: |VO|/VIN = D/(1−D); ΔIL = VIN D/(L fs)
Assumptions
- Ideal CCM, negligible transfer-capacitor ripple in the inductor slopes, and in-phase triangular winding ripple.
- Transfer-capacitor RMS uses the small-ripple approximation; use a capacitor rated for RMS current and DC bias.
- Coupled mode assumes equal self-inductances, aiding flux and equal winding voltages; effective ripple inductance is L(1+k). Leakage spikes and imperfect winding matching are omitted.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Minimum input voltage
- 9.6 V
- Nominal input voltage
- 12 V
- Maximum input voltage
- 14.4 V
- Output-voltage magnitude
- 5 V
- Minimum load
- 0.02 A
- Maximum / design load
- 1 A
- Switching frequency
- 200000 Hz
- Chosen inductance
- 0.000047 H
- Nominal output capacitance
- 0.0001 F
- Parallel output capacitors
- 1
- Capacitance retained after bias/tolerance
- 0.7
- Each output-capacitor ESR
- 0.02 Ω
- Minimum controller current limit
- 4 A
- Inductor saturation current
- 4 A
- Inductor construction
- separate
- Coupling coefficient
- 0.95
- Second inductor / winding inductance
- 0.000047 H
- Effective transfer capacitance
- 0.00001 F
Results
- Output voltage target
- 5 V
- Chosen L1
- 0.000047 H
- Chosen L2
- 0.000047 H
- CCM duty
- 0.294118
- Input-side average current
- 0.416667 A
- Output-side average current
- 1 A
- First-inductor ripple
- 0.375469 A
- Second-inductor ripple
- 0.375469 A