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Expert Talk: Design a 220V Forward Converter in CCM mode

Open online SPICE simulator circuit link: learn_power_forward_220V_ccm_startup.tsc

{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:= 220 {use 100... 300}
{Output voltage [V]}
V_out:= 12 {use lower than V_in}

{Output current [A]}
I_out:= 2 {use 1 .. 4}
R_load:= V_out/I_out

N1:= 5 {Primary winding}
N2:= 1 {Secondary winding}
Ratio:= N2/N1 {voltage Ratio}
{=== Control settings: change with care ! ===}
{Switching frequency [Hz]}
fs:= 100k {use 100k .. 300k}
{Duty cycle}
Duty:= (V_out/V_in)*(N1/N2)
L2_INIT:= I_out {inductor DC value}
C_INIT:= V_out {capacitor DC value}
T_on:= Duty*T
{Component settings}
L1:= 1m
L2:= 50u
C:= 500u


Use the Forward topology if you need an isolated version (transformer) of the buck converter. It covers output
voltages that are smaller than the input voltage. There exist versions with one transistor or two transistors.
The Forward converter is used in ATX and telecom power supplies enabling high currents at low output voltages.

Output voltage (V_out): lower than the input voltage
Power rating P_out: up to 400 W
Isolation: galvanic with transformer

Continuous Conduction Mode (CCM)
V_out= (N2/N1) * D * V_in; Duty cycle D= T_on/T with conducting pulse width T_on, switching period T
N2/N1 is the transformer ratio with N1 windings on the primary and N2 windings on the secondary side

Component Ratings
MOSFET voltage class V_DS= 2 * V_in
MOSFET Current I_D= (1.5 * P_out)/V_in(min)
Diode voltage class V_R= 3 * V_out

Other Remarks
the inductance L1 on primary runs in DCM and needs to be demagnetized (not shown in circuit)
this limits the Duty cycle to 50%
the secondary side inductor L2 always runs in CCM

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= 220 V
V_out= 12 V (lower than V_in)
I_out= 2 A

Important Note (Disclaimer)
This is an idealized circuit for learning and experimental use. Test carefully when using calculated values for real hardware.

Expert talk: how to design a One Transitor Forward Converter?

Forward steady-state
Forward startup

Other circuits
Technical Assistance

Infineon MOSFET Finder,
\a(Power Selection Guide,
\a(300 W Forward with ICE1CS02