# Expert Talk: Design a 24V Cuk Converter in CCM mode

## Open online SPICE simulator circuit link: learn_power_cuk_24V_ccm_startup.tsc

Expert talk: how to design a Cuk Converter?

Use the Cuk topology if you need an inverted output voltage with opposite polarity of the input voltage and

need to cover output voltage ranges which are both higher and lower than the input voltage. The basic form

is non-isolated but there exists an isolated version.

Overview

Output voltage V_out: inverted, absolute can be higher or lower than input voltage

Power rating P_out: up to 150 W

Isolation: not available for the basic version (an isolated version is also possible)

Continuous Conduction Mode (CCM)

Output voltage V_out= - (D * V_in) / (1 - D); Duty cycle D= T_on/T with conducting pulse width T_on, switching period T

Current Ripple I_LR= (V_in * D * T) / L

Component Ratings

MOSFET voltage class V_DS= V_in

MOSFET current I_D= I_in

Diode voltage class V_R= V_out - V_in

Other Remarks

the input and output currents of a Cuk topology are continuous

the buck-boost converter currents are discontinuous

Example Converter

set your CCM converter spec in the Interpreter window on the left, click on Run to calculate the components and simulate it!

V_in= 24 V

V_out= -12 V (inverted, absolute of V_out higher or lower than V_in)

I_out= 1 A

Important Note (Disclaimer)

This is an idealized circuit for learning and experimental use. Test carefully when using calculated values for real hardware.

+

{1. click here to set application parameters}

{2. click on "Run" to calculate components}

{3. click on "OK" and Simulate Transient }

{Input voltage [V]}

V_in:= 24 {use 12... 40}

{Output voltage [V]}

V_out:= -12 {negative of V_in}

{Output current [A]}

I_out:= 1 {use 1 .. 2}

R_load:= -V_out/I_out

R_load=[12]

{=== Control settings: change with care ! ===}

{Switching frequency [Hz]}

fs:= 100k {use 100k .. 300k}

{Duty cycle}

Duty:= -1/((V_in/V_out)-1)

Duty=[333.3333m]

L1_INIT:= I_out {inductor DC value}

L2_INIT:= I_out {capacitor DC value}

C1_INIT:= V_out

C2_INIT:= V_out

T:=1/fs

T_on:= Duty*T

T_off:=T-T_on

ControlT2:=T_on

ControlT4:=T_off

{Calculate components for CCM}

C1:= 4u

L2:= 2m

C2:= 50u

L_crcm:=(L2*R_load*T*(1-Duty)^2)/(2*L2- (R_load*T*(1-Duty^2)))

L_crcm=[27.3973u]

L1:= 5*L_crcm

L1=[136.9863u]

\a(Power Selection Guide,https://edit.infineon.com/dgdl?fileId=5546d4625607bd13015621522aa012cb)

\a(Automotive Power Guide

Technical Assistance

Other circuits

Cuk startup

Cuk steady-state