• Switched-Mode Power Supply (SMPS) is an electronic circuit which converts the power using switching devices that are turned on and off at high frequencies, and storage components such as indicators or capacitors to supply power when the switching device is in its non-conduction state. It can be abbreviated as SMPS.
• The switched-mode power supply is also called switch-mode power supply or switching-mode power supply. Its efficiency is high. That’s why we use it in the variety of electronic types of equipment which require a stable and efficient power supply.
• We can classify switched-mode power supply by the type of the input and output voltages.
The four major categories are as follows:
• AC to DC
• DC to DC
• DC to AC
• AC to AC
Working of switched-mode power supply
The working of a basic AC to DC switched-mode power supply is as shown in diagram:
• Input rectifier stage: we make use of this stage to convert AC into DC, and the circuit which has DC input does not require this stage. In this, the rectifier produces unregulated DC. We pass this unregulated DC through the filter.
• Inverter stage: This stage converts DC into AC by running it through a power oscillator. The DC supply can come either directly from the input or from the rectifier stage which is explained above. The output transformer of power oscillator is tiny with few windings at a frequency of 10 or 100 KHz.
• Output transformer: if we want to isolate the output from the input, the inverted AC is used to draw the primary windings of a high-frequency transformer. It converts the voltage up or down to the required output level on its secondary windings.
• Output rectifier: if we want the DC output, then the AC output from the transformer is rectified.
• Regulation: in this, the output voltage is monitored by the feedback circuit and then compares it with the reference voltage.
Classification of the switched-mode power supply
We can classify the switched-mode power supply by circuit topology. It can be of two types: isolated and non-isolated topologies.
• Isolated topologies: This type of topology includes a transformer. Thus, it can produce an output of higher or lower voltage than the input by adjusting the turns ratio. For some topologies, we can place multiple windings on the transformer so that it can produce various output voltages. While some converters make use of a transformer for the storage of energy, while others make use of a separate inductor.
Various isolated topologies are as follows:
• Flyback converter
• Forward converter
• Push-pull converter
• Half-bridge converter
• Full-bridge converter
• Non-isolated topologies: This type of topology make use of non-isolated converters, which are the simplest. There are three basic types of non-isolated converters which make use of a single inductor for storage of energy. In this, we assume the input voltage to be higher than 0. If it is negative, we will negate the output voltage.
Various types of non-isolated topologies are as follows:
• Buck topology
• Boost topology
• Buck-Boost topology
• Split-pi topology
• SEPIC topology
• Cuk topology
Advantages of the switched-mode power supply
• Efficiency: in this, the little energy is dissipated in the form of heat as switching action is there in this supply. That’s why its efficiency is high which is from 68% to 90%.
• Compact: the size of the switched-mode power supply is small. So, they can be made more compact.
• Flexible technology: we can make use of this technology to provide high-efficiency voltage conversions in voltage step up or “Boost” applications or step down or “Buck” applications.
• Its power density is high.
• It has regulated and reliable outputs instead of variations in input supply voltage.
• Their weight is also less as compared to other linear power supplies.
• It has wide ac input voltage range.
Disadvantages of the switched-mode power supply
• Noise: The biggest problem of the switched-mode power supply is the transient spikes that occur in the switching action. These spikes can cause electromagnetic interference which can affect other electronic types of equipment that are nearby.
• External components: we can also design a switch mode regulator using a single integrated circuit, typically there is the requirement of external components. In some of the designs, the series switch element may be incorporated within the integrated circuit, but where any current is consumed, the series switch will be an external component. These external components require space and add to the cost
• Expert design needed: There is the requirement of some experts so that it can perform the necessary specifications.
• Prices: we have to make the careful considerations of the costs of a switched-mode power supply before designing the system. If the additional filtration is required, then it adds to the value of the system.
Applications of the switched-mode power supply
• It is used in machine-tool industries.
• It is used for security systems.
• It is used in personal computers.
• It is used in closed circuit cameras.
• It is used in mobile phone chargers.
• It is used to support supplies with PLC’s.