What is an SMPS?
A switched-mode power
supply or in short SMPS is a power supply circuit that converts mains power
using switching devices that are turned on and off at high frequencies, and
storage components such as inductors or capacitors to supply power efficiently
for the load.
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Why Switched-mode power supply (SMPS) Used
Simple DC power supplies can be made with rectifiers followed by filter stages.
But they suffer from
the changes in the input or, at load.
This initiated the development of a linear regulator (series/shunt) circuits.
They maintain a constant voltage by varying their resistance to counterbalance input voltage change or, load current demand change.
Still, the efficiency of these systems is poor, they are heavy and not flexible enough to be chosen for every application.
So switched-mode power supplies (SMPS) were designed.
They use a high-frequency switch (transistor) with varying duty cycles to maintain the output voltage.
The output voltage variations caused by the switching are filtered output by an LC filter.
SMPS systems own their origin back to the days when valve or, tube car radios needed large HT supply, e.g., 150V DC to be generated from an automobile power system of nominally 12V DC.
Today we find their application in the most sophisticated PC power supplies (e.g., 200 Watt ATX SMPS).
Advantages of SMPS
- Low Weight and Smaller Size
- Higher Efficiency
- Wider AC input Voltage Range
- Reduced Cost
Disadvantages of SMPS
- Circuit Complexity
- Regulation
- Others
Applications
SMPS can be used in 3 configurations — (i) usual STEP-DOWN mode, (ii) STEP-UP mode or, (iii) INVERTED mode.
So, they are useful in large number of applications.
Some of them are listed below.
Linear regulators don't have such flexibility and don't have such versatile uses.
- STEP-DOWN mode: Generation of 5V supply for TTL based
circuit from 12V battery.
- STEP-UP mode: Generation of 25V from a 5V supply in
an EPROM programmer.
- INVERTED mode: Generation of double ended supply
(±5V or ±12V) from a single ended supply for operational amplifier.
