SWITCHING DC POWER SUPPLIES

INTRODUCTIONLINEAR POWER SUPPLYOVERVIEW OF SWITCHING POWER SUPPLIESDC – DC CONVERTER WITH ELECTRICAL

ISOLATIONCONTROL OF SMPSPOWER SUPPLY PROTECTIONAPPLICATION

IntroductionLike a linear power supply, the SMPS too converts

unregulated ac or dc input voltage to a regulated dc output voltage

The input voltage is first rectified and filtered using a capacitor at the rectifier output

unregulated dc voltage across the capacitor is then fed to a high frequency dc-to-dc converter

The high frequency transformer used in a SMPS

Linear Power Supplies

Disadvantages of LPS

The output fluctuates with input which is not desirable

Isolation is not possibleEfficiency is very lowBulky and noisy

SMPS Block Diagram

Switching DC Power Supply: Multiple Outputs

In most applications, several dc voltages are required, possibly electrically isolated from each other

Transformer Analysis

Transformer Analysis

Needed for high-frequency isolated supplies

PWM to Regulate Output

PWM OUTPUT WAVEFORM

Flyback Converter

FLYBACK CONVERTER WAVEFORM’S

Other flyback converters are:~ 1. Two transistor flyback converter 2. Parallelled flyback converter

But these are not commonly used

Forward ConverterDerived from Buck; idealized to assume that the transformer is ideal (not possible in practice)

Half-Bridge Converter Derived from Buck converter

Full-Bridge ConverterUsed at higher power levels (> 0.5 kW )

Input Filter Needed to comply with the EMI and harmonic limits

ConclusionOne of the most important applications of power

electronics is SMPSHigh efficiency and small weight and sizeIn SMPS multiple outputs are possibleLosses is minimum and only switching losses are

presentCurrent rating is mediumThe high frequency transformer used in a SMPS

Switched Mode Power Supply

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