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SWITCH-MODE
POWER SUPPLY
Power electronics deals with four forms of power conversion.
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ac-dc conversion called rectification
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ac-ac conversion ,
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dc-ac conversion and
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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:
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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,
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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,
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step up or step down an unregulated dc input voltage to produce
a regulated dc output voltage ,
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invert the input dc voltage using usually a circuit such
as the Cuk converter, and
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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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