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.

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{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]