SMPS (Switch Mode Power Supply)

A switch mode power supply (SMPS) is a also known as a switched power supply or switcher. It is an electronic power supply that incorporates a regulator to convert electric power efficiently. An SMPS transfers power from a DC or AC source to DC loads as a personal computer while converting into voltage and current characteristic. In linear power supply transistor of switching mode supply continually switch between low dissipation. A hypothetical ideal switch mode dissipates no power. In contrast, a linear power supply regulates output voltage in the pass transistors. The important advantage of SMPS is higher electrical efficiency. In laboratory there is a adjustable switch mode power supply is available.

The size of switch mode power supply is smaller and lighter than linear supply because the transformer can be smaller. This is because it operates high switching frequency. The reduced transformer size topology and the requirement for electromagnetic interference suppression designs in a much greater components. Switching regulators are uses as replacements for linear regulators when higher efficiency. They are however, more complicated. A simple designs have a poor power factor. Generally, all types of SMPS have a cooling fan which helps to cool power supply.

How SMPS Works

A linear power supply (non-SMPS) uses a linear regulator to provide a efficient voltage by dissipating power in ohmic losses. A linear regulator regulates either output voltage or current throwing the electric power in form of heat. Its maximum power efficiency is voltage-in/voltage-out since the volt difference is wasted. In contrast, a SMPS changes output voltage and current by switching ideally loss storage elements like inductors and capacitors. Ideal switching elements have no resistance when “no” and carry when “off”.

So converters with ideal components operates with full efficiency. In reality, these ideal components do not exist, so a switching power supply cannot be 100% efficient. In SMPS, the output current flow depends on input power signal. The storage elements and circuits are uses on the pattern use to drive the switching elements. The density of these switching waveform has energy at relatively high frequencies.


Advantages and Disadvantages

The main advantage of the switch power supply is efficiency up to 96% than linear regulators. The switching transistor dissipates little power when acting as a switch. It have smaller size, lower noise and lighter weight from the elimination of heavy line-frequency transformer. In switching mode supply a transformer is also smaller than a traditional line frequency. Therefore it requires a smaller amount of expensive raw materials. Disadvantage is greater complexity, the generation of high amplitude or a high frequency energy.

Types of SMPS

Non-isolated topologies SMPS

A non-isolated converters are simplest power supply. They have three basic types using a single inductor for energy storage. The voltage limit is 30v AC or 42.4v peak or 60v DC. The buckboost topologies are all strongly related. The all input, output and ground come together at one point. One of the three passes an indicators on the way while other two passes through switches. One of the two switches must be active. A topology can be change simply by relabeling the connectors.


Isolated topologies SMPS

All isolated topologies includes a transformer. They can produce an output at higher or lower voltage input by adjusting the turns ratio. For energy storage some converters use the transformer while other use a separate inductor.


Zero voltage switch SMPS

In zero voltage switch each switch cycle delivers a quantized energy to the converter output. switch turn-on and turn-off occurs at zero current and voltage. It is also known as a valley switching which reduces EMI in the power of to methods:


  • By switching the bipolar switch when the voltage is at a minimum to minimize the hard switching effect that causes EMI.
  • A zero voltage switch mode power supply requires a small heatsink where a little energy is lost as heat. This allows them to be small.


A switch mode power supply unit is very domestic product such as personal computers often have universal inputs. SMPS accept power from mains supplies throughout the world. A manual voltage switch may be requires. A switch mode power supply can tolerate a wide range of power volt and frequency. The high volume of chargers have always been particularly cost cheap. The first ever chargers were linear power supplies.

Nowadays, the demand for even lower no-load power requirements in the applications have flyback topology. It is being uses more widely. Generally, a switched mode power supply is used for DC to DC power supply. In heavy vehicles that use a normal 24V or 12V for accessories may be furnished through a DC/DC switch-mode supply. In industrial sector like telecommunications racks the power is maybe low DC voltage.


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