Switched Mode Power Supply (SMPS)

SMPS stands for Switched Mode Power Supply or switching-mode power supply. SMPS is a power supply unit (PSU) for electronic use that contains a switching regulator. While a linear regulator maintains the desired output voltage by dissipating excess power in a "pass" power transistor, the SMPS switches a power transistor at the faster rate between saturation (full on) and cutoff (completely off) with a variable duty cycle whose average is the desired output voltage. This process gives rectangular waveform as a result which is filtered by a low-pass filter with using inductor and capacitor.

The supreme benefit of using this process In SMPS is that it gives a better efficiency. It is because of the small dissipation of the power by the switching transistor in the saturated state and the off state compared to the semiconducting state (active region). Other advantages of Switch Mode Power Supply (SMPS) include smaller size and lighter weight which is greater in low frequency transformers which have a high weight. Moreover it generates lower heat from the higher efficiency.

Disadvantages of SMPS are:

• Greater complexity

• The generation of high amplitude

• High frequency energy that the low-pass filter must block to avoid electromagnetic interference (EMI)

• Ripple voltage at the switching frequency and the harmonic frequencies

SMPS can be categorized into four different types on the basis of its input and output waveforms, as follows.

• AC in, DC out: rectifier, off-line converter input stage.

• DC in, DC out: voltage converter, or current converter, or DC to DC converter

• AC in, AC out: frequency changer, cycloconverter

• DC in, AC out: inverter

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