|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. By varying duty cycle, frequency or phase shift of these commutations, an output parameter (such as voltage) is controlled. Output filters are then "averaging" energy transfer rate and assure continuous current flow into the load.
The diagram to the left illustrates this concept for a buck converter.
Volt-second balance for L in continuous mode:
Solving for Vout:
Vout=(Vin-VQ)D-VD(1-D). Neglecting VQ and VD: Vout≈VinD, where D=ton/(ton+toff)- duty cycle
The typical frequency (F) range of an offline SMPS circuit 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 switching losses that occur during the transitions and which increase with operating frequency. It also introduces additional electrical noise (EMI). Its acceptable limits vary with the frequency and with application. 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 SMPS design. The best configuration 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 may start with this guide to topology selection. Then see TI seminar books, which contain application notes and detailed reference designs with practical circuits and calculation procedures.
Below you will find theory, SMPS schematics and design guides, power electronics tutorials and other online resources for the engineers and hobbyists.
SWITCHING POWER SUPPLY DESIGN: TUTORIALS,
TOPOLOGIES: APPLICATION NOTES
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,
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
Half bridge converter
Push-pull converter design procedure
Topologies and optimization of power factor correction circuits
FIND POWER SUPPLY PRODUCTS BY SPEC
48VDC to DC 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