Cuk Converter Design

Cuk converter operation principle animation

On this page are presented basic design equations of the Cuk 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 L1 : $r_1=\frac{I_{L_{1ripple}}}{I_{L1_{AVG}}}=\frac{I_{L_{1ripple}}}{I_{i}}=\frac{V_i*(1-D)}{I_o*L_1*f_s}$

Current ripple ratio L2 : $r_2=\frac{I_{L_{2ripple}}}{I_{L2_{AVG}}}=\frac{I_{L_{2ripple}}}{I_{o}}=\frac{V_i*D}{I_o*L_2*f_s}$

Voltage conversion ratio : $V_{o}=-V_{i}*\frac{D}{1-D}$

RMS current in input capacitor: $I_{C_{i}}=\frac{1}{2*\sqrt{3}}*\frac{V_{i}}{fs*L_1*(\frac{V_i}{|V_o|}+1)}$

RMS current in output capacitor: $I_{C_{o}}=\frac{1}{2*\sqrt{3}}*\frac{V_{i}}{fs*L_2*(\frac{V_i}{|V_o|}+1)}$

RMS current in coupling capacitor: $I_{C_{c}}=I_{o}*\sqrt{\frac{D}{1-D}}$

Peak switch current: $I_{Q1_{max}}=I_o*(1-\frac{D}{1-D})+\frac{V_i*D}{2}*(\frac{1}{L_1}*\frac{1}{L_2})$

Peak diode current: $I_{D1_{max}}=I_o*(1-\frac{D}{1-D})+\frac{V_i*D}{2}*(\frac{1}{L_1}*\frac{1}{L_2})$

Suggested reading:
1. LM2611 1.4MHz Cuk Converter
2. Cuk Converter Analysis
3. Switching Power Supply Design and Optimization

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

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