SMPS SWITCHING POWER SUPPLY CIRCUIT DESIGN BASICS:

TUTORIALS, SCHEMATICS, THEORY, VOLTAGE REGULATOR TOPOLOGIES,
AND OTHER ONLINE RESOURCES

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The industry drive towards smaller, lighter and more efficient electronics has led to the development of switching-mode power conversion technology. Switching power supplies (SMPS) include power handling electronic components which are continuously commutating on and off with high frequency. These electronic switches effectively connect and disconnect energy storage inductor(s) and capacitor(s) to and from the input source or the output.

Volt-second balance in a continuous mode:
(Vin-V_Q-Vout)×ton=
(Vout+V_D)×toff
Solving for Vout:
Vout=(Vin-V_Q)D-V_D(1-D) ≈VinD, where D=ton/(ton+toff)- duty cycle

By varying duty cycle, frequency or phase shift of these commutations, an output parameter (such as output voltage) is controlled. Output filters are then "averaging" energy transfer rate and assure continuous current flow into the load. The DC gain of any converter is calculated based on the fact that in steady state, the net volt-seconds across an inductor over one switching cycle must be zero. The diagram to the right illustrates this concept for a buck converter.

The typical frequency (F) range of an offline SMPS is from 50 kHz to 500 kHz. DC-DC converters with low-voltage input operate up to several MHz. The high operating F results in the smaller size of switch-mode power supplies since generally the size of power transformers, inductors and filter capacitors is inversely proportional to the frequency. Switch mode operation also reduces energy losses and increases efficiency- when a switch is "off", its current is near zero; when it is "on", the voltage across it is low.

On the other hand, this mode of operation introduces the losses that occur during the transitions and which increase with operating frequency. It also introduces additional electrical noise (EMI) whose acceptable limits vary with the frequency. In most applications the limits for EMI begin at 150 kHz. Therefore the engineers often select F<150 kHz in order to place the fundamental harmonic below the requirement range. In general, the switcher's optimization is based primarily on size, efficiency, cost and EMI considerations. Realizing the switcher's advantages also requires the selection of the right components that can operate efficiently at the necessary frequencies.
There are about a dozen basic topologies used in practical power design. The best topology for a given application is selected based on the specific requirements for the PSU (including cost and time factors). Since a great deal of overlap exists in the topology usages, this selection is normally influenced by a personal experience of the designer. If it's your first project, you probably need to start with TI seminar books. They contain application notes and reference designs with practical circuits and calculation procedures.

Below you will find theory, SMPS schematics and design guides, power electronics tutorials and other free online resources for the engineers and hobbyists.

SWITCHING POWER SUPPLY DESIGN: TUTORIALS,
TEXTBOOKS

TOPOLOGIES: APPLICATION NOTES
and DESIGNS

SAMPLES of POWER SUPPLY SCHEMATICS FOR ENGINEERS AND HOBBYISTS

TI (formerly Unitrode) seminars: all manuals from 1983 to 2010

Linear and switching voltage regulator basics

What is SMPS? SWITCHMODE™ reference manual

Power factor correction (PFC) online handbook

SMPS design books

POWER ELECTRONICS TECHNOLOGY- HANDBOOKS,
LECTURES, GUIDES

Fundamentals of power electronics (instructor's slides- see their terms of use)

Interactive online textbook- rectifier circuits, basic converters, PSPICE and mathcad simulation for beginners

Electrical conversion reference textbook online- drivers, applications, and components

Mathematics of electric energy, power factor and THD- definitions and equations

Selection of converter topology

Switch mode voltage regulator schematics and formulas

Single transistor forward converter

Off-line forward converter with active clamp and reset

Flyback - the simplest SMPS

Phase shifted ZVT (soft switched) full bridge

Current-fed push-pull circuit

Current-doubler rectifier

Half bridge converter

Push-pull converter design procedure

SEPIC converter

Topologies and optimization of power factor correction circuits

High Voltage reference circuits

12 Volt AC-DC switching power supply: schematic, PCB, theory of operation

12VDC power supply with flyback

Switchmode PSU for car audio

Transformerless power supplies basics: resistive and capacitive circuits

SYNCHRONOUS
RECTIFIER CIRCUITS

SYNC THEREFORE I AM

Synchronous rectification aids low voltage supplys

Synchronous rectification review and analysis

Multi-output flyback with synchronous rectifiers

FIND POWER SUPPLY PRODUCTS BY SPEC

SMPS SWITCHING POWER SUPPLY CIRCUIT DESIGN BASICS:

TUTORIALS, SCHEMATICS, THEORY, VOLTAGE REGULATOR TOPOLOGIES, AND OTHER ONLINE RESOURCES

SWITCHING POWER SUPPLY DESIGN: TUTORIALS, TEXTBOOKS

TOPOLOGIES: APPLICATION NOTES and DESIGNS