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Expert Talk: What is a DC-DC Converter (SMPS)?

Open online SPICE simulator circuit link: learn_power_dcdc_overview_dcm.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:= 12 {use 5... 40}
{Output voltage [V]}
V_out:= 24 {use higher than V_in}

{Output current [A]}
I_out:= 1.5 {use 1 .. 2}
R_load:= V_out/I_out

{=== Control settings: change with care ! ===}
{Switching frequency [Hz]}
fs:= 100k {use 100k .. 300k}
{Duty cycle}
Duty:= 1-(V_in/V_out)
L_INIT:= I_out/(1-Duty) {inductor DC value}
C_INIT:= V_out {capacitor DC value}
T_on:= Duty*T
{Calculate components for CCM}
L_crcm:= (R_load*Duty)*(1-Duty)^2/(2*fs)
L:= 2*L_crcm
R_crcm:= (2*fs*L)/(Duty*(1-Duty)^2)


The success story of DC-DC converters began around 1970 with the start of the personal computing revolution.
All processing units needed highly accurate voltage rails in the range of 48 V down to 1 V with a broad range of
power requirements. The main advantage of DC-DC compared to linear regulators lies in the fact that they can
bridge high DC voltage drops in a very efficient way at very compact size.

Operating Modes
Hard switching: Transistors (MOSFETs, IGBTs) switch high DC currents and voltages at high frequency (simple circuit, high component stress)
Soft switching (Resonant): an added LC circuit makes current/voltages pass zero (lower switching loss but more complex control circuit)

DC-to-DC converters use magnetic components (inductor or transformer) to store and transfer energy. They can operate in two modes
Continuous Conduction Mode (CCM): the inductor current fluctuates but never goes down to zero
Discontinuous Conduction Mode (CCM): the current reaches zero during a switching cycle

Example Boost Converter (V_in= 12 V, V_out= 24 V)
1) first run the converter in CCM mode (default)
2) change the output resistor R_load to R_crcm (critical conduction mode)
3) simulate again and observe the conductor current in DCM mode
4) freely change the values in Interpreter window on the left, click on Run to calculate the components

Expert talk: how to design a Boost (step-up) Converter?

Non-isolated topologies for low voltages and power up to 150 W

Isolated topologies for high voltages and power up to 400 W

Boost in DCM mode
Boost in CCM mode

Other circuits
Technical Assistance

Infineon MOSFET Finder,
\a(Power Selection Guide,
\a(Automotive Power Guide

Buck Converter (step-down a DC voltage),
\a(Boost Converter (step-up a DC voltage),
\a(Buck-Boost Converter (invert a DC voltage),
\a(Cuk Converter (invert a DC voltage up or down),
\a(SEPIC Converter (step-up or down)

Flyback Converter,
\a(Forward Converter