SEPIC Converter Design

SEPIC converter operation principle animation

On this page are presented basic design equations of the SEPIC converter. Below the equations there
is an interactive online simulation circuit along with component selection steps. In addition to basic components the
circuit also contains eventual parasitic elements of the main converter components.

Key design equations:

Continuous conduction mode (CCM):

Current ripple ratio : $r=\frac{I_{L_{ripple}}}{I_{L1_{AVG}}}=\frac{I_{L_{ripple}}}{I_{i}}=\frac{I_{L_{ripple}}*V_{i_{min}}}{I_{o}*V_{o}}$

Voltage conversion ratio : $V_{o}=\frac{V_{i}*D-V_{DS_{Q1}}*D-V_{D1}*(1-D)}{1-D}$

RMS current in input capacitor: $I_{C_{in}}=\frac{I_{L_{ripple}}}{\sqrt{12}}$

RMS current in output capacitor: $I_{C_{o}}=I_{o}*\sqrt{\frac{V_o+V_{D1}}{V_i}}$

RMS current in coupling capacitor: $I_{C_{s}}=I_{o}*\sqrt{\frac{V_o+V_{D1}}{V_i}}$

RMS switch current: $I_{Q1_{RMS}}=I_{o}*\sqrt{\frac{(V_o+V_i+V_{D1})*(V_o+V_{D1})}{V_i^2}}$

Suggested reading:
1. Designing A SEPIC Converter
2. Analyzing the Sepic Converter
3. Switching Power Supply Design and Optimization

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Open project to simulate circuit, see "Notes" for component selection info - the circuit is simulatable online