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Switch Mode Power Supply
Power electronics deals with four forms of power conversion.
- ac-dc conversion called rectification
- ac-ac conversion ,
- dc-ac conversion and
- dc-dc conversion.
DC-DC converters were referred to as choppers earlier, when SCRs
were used. Nowadays, IGBTs and MOSFETs are the devices used for
dc-dc conversion and these circuits can be classified as switch
mode power supply circuits. The abbreviation or acronym for switch
mode power supply is SMPS.
A switch mode power supply circuit is versatile. It can be used
to:
- step down an unregulated dc input voltage to produce a regulated
dc output voltage using a circuit known as Buck Converter or
Step-Down SMPS,
- step up an unregulated dc input voltage to produce a regulated
dc output voltage using a circuit known as Boost Converter or
Step-Up SMPS,
- step up or step down an unregulated dc input voltage to produce
a regulated dc output voltage ,
- invert the input dc voltage using usually a circuit such as
the Cuk converter, and
- produce multiple dc outputs using a circuit such as the fly-back
converter.
A switch mode power supply is a widely used circuit nowadays
and it is used in a system such as a computer, television receiver,
battery charger etc. The switching frequency is usually above
20 kHz, so that the noise produced by it is above the audio range.
It is also used to provide a variable dc voltage to armature of
a dc motor in a variable speed drive. It is used in a high-frequency
unity-power factor circuit.
This chapter
describes the basics, operation and design of switched-mode power
supplies. The pages to follow contain:
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