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SMPS – Switched-Mode Power Supply Working Characteristics

Switched Mode Power Supply (SMPS) is an electronic power supply circuit that converts electrical power supply efficiently with the help of a switching regulator. In other words, it is also known as Switching Mode Power Supply. In computers, it is used as a power supply unit to convert the voltage into the computer’s acceptable range.



SMPS stands for Switched-Mode Power Supply. It is an electronic power supply circuit that efficiently converts electrical power from one form to another. SMPS is widely used in various electronic devices to provide a stable and regulated output voltage or current.


The main principle behind an SMPS is to rapidly switch the input voltage on and off using high-frequency switching devices, such as transistors orMOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). This switching action allows the SMPS to regulate the output voltage or current by adjusting the duty cycle of the switching signal.

SMPS offers several advantages over traditional linear power supplies. It is more efficient because it operates in a switching mode rather than dissipating excess power as heat like linear supplies. SMPS can handle a wide range of input voltages and provide a stable output even with variations in the input voltage or load conditions. They are also usually smaller and lighter than linear power supplies, making them suitable for portable devices.

smp发现在不同的应用程序devices and systems, including computers, televisions, mobile phones, audio equipment, industrial equipment, and many other electronic devices that require a stable and efficient power supply.

SMPS has the power handling electronic components which converts electrical power efficiently. In order to reduce the overall power loss, the switched mode power supply uses a great power conversion technique.

History of Switched-Mode Power Supply

In the year 1977, the Switched-Mode power supply was introduced and was designed with Apple II. In 1980, an electronically produced signal generator was used alongside switched-mode power supply. However, in the mid 1800’s i.e, before the SMPS was actually introduced, to generate high voltages, induction coils were used. Later, in 1900’s Metal Oxide Semiconductor Field Effect Transistor (MOSFET) was used for power supplies.

Working of Switched-Mode Power Supply

The switched-mode power supply uses switching regulators which switches load current on and off in order to regulate and stabilize the output voltage. Between the off and on, the average voltage produces the appropriate power for a device.


Now, let’s understand the working of each stage from the above diagram –

Input Stage

In the input stage, a 50hz general AC supply is provided to the rectifier and filter circuit directly without using any transformer. The DC output here will have many variations and the value of the capacitor should be higher to handle the input fluctuations. The unregulated DC is then given to the central switching section of SMPS.

Switching Section

In this switching section, one of the fast-switching devices like PowerTransistoror MOSFET is used that switches on and off as per the variations and this output is given to the primary of the Transformer present in this section. The transformer used in this section are much smaller and lighter unlike the ones used for 60Hz supply. The power conversion rate is higher and hence they are efficient.

Output Stage

From the switching section, the output signal is again rectified and filtered in order to get the required DC voltage. This output is a regulated DC voltage which is thereafter fed to the control unit that acts as a feedback unit for the circuit and forms a close loop system. Any minute deviations found by the control unit is termed as error and is corrected instantly.

Control Unit

This is the feedback circuit which further has many sections.


The above-mentioned diagram explains the inner parts of a control unit. The output sensor senses the signal and combines it to the control unit. The signal is away from the other section so that any sudden spikes should not affect the circuitry. Reference voltage is given as one input along with the signal to the error amplifier which is a comparator which compares the signal with the required level of signal.

The final voltage is maintained by controlling the chopping frequency. This is controlled by comparing the inputs given to the error amplifier, whose output helps to determine whether to increase or decrease the chopping frequency. A standard PWM wave fixed frequency is produced by the PWMOscillator.

Features of Switched-Mode Power Supply

Here are some of the features of mentioned –

  • SMPS has the efficiency of 65-70%
  • Temperature can raise up to 20-40 degree Celsius.
  • The weight of SMPS is about 60kgs.
  • The magnetic material used is ferrite core.

Key Characteristics of Switched-Mode Power Supply

The switched-mode power supply is useful mostly where the switching of voltages is not a problem and where efficiency of the system matters. Below are some of the key characteristics of SMPS –

  • The voltages vary continuously as SMPS circuit operates by switching.
  • Switching device operates in both saturation or cut off mode.
  • The feedback circuit’s switching time controls the final output voltage.
  • One can adjust the Switching time by adjusting the duty cycle.
  • To avoid losing excess power in the form of heat, the SMPS continuously switches its i/p to control the o/p. This increases the efficiency of SMPS.

Applications of Switched-Mode Power Supply

SMPS finds its uses in:

  • Compute’s power supply
  • Mobile phone chargers
  • HVDC measurements
  • Battery chargers
  • Central power distribution
  • Motor Vehicles
  • Consumer electronics
  • Security systems
  • 空间站
  • Laptops etc.

Types of Switched-Mode Power Supply

SMPS, is a switched mode power supply circuit that is designed to get the regulated DC output voltage from an unregulated DC or AC voltage. There are four main types of SMPS like –

  • DC to DC converter
DC to DC Converter SMPS
DC to DC Converter SMPS
  • AC to DC converter
AC to DC Converter SMPS
AC to DC Converter SMPS
  • Fly back converter
Fly Back Converter SMPS
Fly Back Converter SMPS

  • Forward converter
Forward Converter SMPS
Forward Converter SMPS

The AC to DC conversion part in the input section is the key difference between AC to DC converter and DC to DC converter. For low power applications, the fly back converter is used. Apart from these, there are buck converter, boost converter which increases and decreases the output voltage based on the requirements. The other type of SMPS converters is – self-oscillating fly-back converter, buck-boost converter, Cuk, Sepic etc.


Mentioned below are some of the advantages of Switched-Mode Power Supply –

  • SMPS is very light in weight.
  • It is strongly anti-interference.
  • The production range of SMPS is large.
  • The switch-mode power source is small in scale.
  • The ideal use of power consumption is normally 60-70%.
  • Less heat generation, less power wastage.
  • SMPS reduces harmonic feedback into the supply mains.
  • The cost of manufacture is reduced.

Disadvantages of Switched-Mode Power Supply

  • Since SMPS is large, they have complexity.
  • The output of voltage is one.
  • In SMPS, the reflection of production is high and its control is weak.
  • It produces of noise.

Why one should choose Switched-Mode Power Supply?

Switched-Mode Power Supply involves some active and passive components unlike every electronic gadget and each of them have their own limitations and benefits as well-

  • The switching actions means the series regulator element is sometimes on or off. It has a very high-efficiency levels due to little wastage of energy as heat.
  • The switch mode power supplies can be compact due to the result of high efficiency and low level of heat dissolve.
  • Switch mode power technology also offers high-efficiency voltage conversions in voltage set-up or “Boost” applications and step-down or “Buck” applications.

Future Hold of Switched-Mode Power Supply

To summarize, in future, one can have more efficient SMPS that will have a better converter doing the most effective conversion process. The main focus areas for designers in making SMPS efficient would be as follows –

  • Higher output power
  • Increasing power density
  • Achieving higher current output and low voltage
  • Using a switching device like Schottky diode

To conclude, SMPS is one of the core electrical subjects. The pre-requisite knowledge of power electronics and analysis of network is very much essential. Thus, these two topics are the foundation for switched-mode power supply.

Read Also:Bridge Rectifier Circuit – Working, Types, Characteristics and ApplicationsWhat is MOSFET – Working, Types, Applications, Advantages & Disadvantages
Chakrasthitha is a B.E (Medical Electronics) and has work experience in MatLab and Lab View Software as Design Engineer at BCS innovations and Manipal hospital as Biomedical Engineer. She is an author, editor and partner at Electricalfundablog.


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