SMPS|Switched Mode Power Supply

Contents

PSU – Power Supply Unit

Power supply units provide the necessary power, voltage and current requirements for electronic devices.
Read also about UPS – Uninterrupted Power Supplies

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Theyusuallychangeactodcvoltage. – For example, 120 volts ac is changed to 12 volts dc.

Basic elements of power supply unit circuits

Transformer – steps ac voltage up or down.
Rectifier Diodes – change ac to “ripple” dc.
Filter Network – includes capacitors and inductors, smooth out the ripples.
Voltage Regulator – keeps the voltage constant.

cLASSIFICATION OF POWER SUPPLIES

Based on the regulation concept power supplies are classified as under,

power-supply-classification — Power supply unit classification

Linear Power supplies (LPS)

Linear Power supplies include a Mains transformer, rectifier, filter and regulator (series or shunt type).

In this the active device that provides regulation is always operated in the active or linear region of its characteristics.

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Any change in the output voltage due to a change in input voltage or load current results in a change in the drop across the regulator transistor( in case of series regulator) or a change in the current through the regulator transistor ( in case of shunt regulator) so as to maintain a constant output voltage across the load.

Switch Mode Power supplies

In a Switch mode power supply(SMPS), the active device that provides regulation always operates in a Switched mode i.e., It is operated either in cut-off or in saturation

What is SMPS?

Switched Mode Power Supply (SMPS) is an electrical power supply that incorporates a switching regulator to convert electrical power efficiently.
It transfers power from a source to a load, while converting voltage and current characteristics.

Voltage regulation is achieved by varying the ratio of on-to-off time.

Linear Mode Supply Vs SMPS

Comparison between Linear Mode Supply and SMPS

linear mode supply vs switched mode power supply

Types of SMPS

Fly back mode power supply
Forward mode power supply

Fly back Mode SMPS Power Supplies

Used where power requirement is less than 100W.
These are simple in design using minimum components and minimum circuit board space.
Reliable in operation and the efficiency is 70% to 80 %.

Forward Mode SMPS Power Supplies

Used for power requirement up to 200 watt.
Efficiency up to 90 %
Not very common due to complicated design. Mostly used for DC to DC conversion systems

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Functional Block Diagram of SMPS

Below is the smps block diagram

Advantages of SMPS

Lower weight
Smaller size
Higher efficiency
Lower power dissipation
Wide ac input voltage range
Reduced costs

Disadvantage of SMPS

The complexity of the circuit
tendency to RFI radiation
slower response to rapid load changes
less ability to remove output ripple.

Applications of SMPS

Machinetoolindustries
SecuritySystems (Closed circuit cameras)
SupportsupplieswithPLC’s
personal computers
MobilePhonechargers

Examples of SMPS

Zebronics 450 W, iball 600W, Antec 750W, Cooler master 550W, Seasonic 500w, UMAX 450W,Corsair 750W, Artis 400W

Working of SMPS

SMPS can be used to convert AC to DC, such as in a desktop computer power supply, or DC to DC, either step up or step down in many different Battery powered systems.

The input is the AC mains (line) supply the AC is rectified and smoothed by a reservoir capacitor before being processed by what is in effect a DC-to-DC converter, to produce a regulated DC output at the required level.

Fig. shows a block diagram example of a typical SMPS with an AC Mains (line) input and a regulated DC output.

The output rectification and filter are isolated from the High-Frequency switching section by a high-frequency transformer, and voltage control feedback is via an optoisolator.

The control section is typical of specialist ICs containing an HF oscillator, pulse width modulation, voltage, and current control and output shutdown sections.

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