SMPS power supply

 Hello again! we are back again with a blog on SMPS. You might have heard about SMPS powering your PC. It’s the same thing we are going to talk about.SMPS can power a lot of other things as well such as CCTV cameras, Motors, anything working on DC supply. We will be covering, What is SMPS basically, how it works and what are its types. The main section we will be covering will be of how to use it, What things you need to take care while using SMPS. We will also be comparing it with a linear power supply. There’s a short video also attached which will help you understand the same.

What is SMPS?

SMPS(Switched Mode Power Supply).It’s a module that consists of multiple inductors, capacitors and semiconductor devices such as diodes and MOSFETs. It converts AC Voltage to DC Voltage. We use it instead of a linear supply/power adapter because it gives better efficiency. It plays a major role in almost all electronic equipment (like mobile chargers, PC power supplies, etc).

It works on semiconductor switch type MOSFET to switch on-off the supply voltage at a particular switching frequency to control the output voltage. When you change the switching frequency it will change the output voltage.

so now that we know what is SMPS basically we will move on to its working and functionality. How things go inside.

How Does It work?

When we give AC Input to an SMPS, then initially it converts it into DC. This process of converting AC to DC is called rectification. It will be skipped when we give DC voltage. In PC power supplies the rectifier is designed as a voltage doubler by addition of a switch that operates manually/automatically. Now as the rectifier produces an unregulated DC voltage, it is sent to a filter capacitor. current drawn from the mains supply is in short pulses around the AC voltage peaks.

These pulses have high-frequency energy that reduces the power factor. Nowadays SMPS uses a special Power factor correction circuit to make the input current follow the sinusoidal shape of the AC input voltage, correcting the power factor. Power supplies that use active power factor correction usually are auto-ranging, supporting input voltages from ~100 VAC – 250 VAC, with no input voltage selector switch.

SMPS made for AC input can run from a DC supply, as the DC will pass through the rectifier unchanged.

SMPS working flow

                              Fig1.0 SMPS Workflow

Inverter stage

Also known as a chopper.

This stage converts DC, it doesn’t matter if it is from the input or from the rectifier stage as described above, to AC by running it through a power oscillator, whose output transformer is very small with few windings at a frequency of tens or hundreds of kilohertz. The frequency is usually above 20 kHz, to make it inaudible to humans. We do Switching in multiple stages (to get high gain) MOSFET amplifier. MOSFETs are a type of transistor with a low on-resistance and a high current-handling capacity.

Voltage converter and output rectifier

If the output has to be separated from the input, usually in the case of mains power supplies, the inverted AC has to be used to run the primary winding of a high-frequency transformer. This converts the voltage up or down to the needed output level on its secondary winding. The output transformer in the block diagram does this job.

If a DC output is needed, the AC output from the transformer is rectified. For output voltages above ten volts or so, ordinary silicon diodes are commonly used. For lower voltages, Schottky diodes are commonly used as the rectifier elements; they have the advantages of quicker recovery times than silicon diodes (allowing low-loss operation at higher frequencies) and a lower voltage drop when conducting. For even lower output voltages, MOSFETs may be used as synchronous rectifiers; compared to Schottky diodes, these have even lower conducting state voltage drops.

The rectified output has to be smoothed by a filter consisting of inductors and capacitors. For higher switching frequencies, components with lower capacitance and inductance are necessary.

Other types of SMPSs use a capacitor–diode voltage multiplier instead of inductors and transformers. These are mostly used for generating high voltages at low currents (Cockcroft-Walton generator). The low voltage variant’s called a charge pump.


The charger circuit has just two transistors, an

and rectifier diodes as active components.

A feedback circuit monitors the output voltage and compares it with a reference voltage. Depending on design and safety requirements, the controller may contain an isolation mechanism (such as an optocoupler) to isolate it from the DC output. Switching supplies in computers, TVs, and VCRs have these optocouplers to tightly control the output voltage.

Open-loop regulators do not have a feedback circuit. Instead, they rely on feeding a constant voltage to the input of the transformer or inductor and assume that the output will be correct. Regulated designs compensate for the impedance of the transformer or coil. Monopolar designs also compensate for the magnetic hysteresis of the core.

The feedback circuit needs the power to run before it can generate power, so an additional non-switching power supply is there on for standby.

Ok now as we know how it functions/works we will move to its different types and will give you short detail about each type.

Types of SMPS

ports on a SMPS power supply

                                      Fig 1.1 SMPS Ports

The different types of SMPS include the following

  • D.C. to D.C. Converter
  • Forward Converter:
  • Flyback Converter
  • Self-Oscillating Flyback Converter

DC-DC Converter

On giving AC power it turns on and filters high voltage DC. It changes a very fast rate of speed and fed to the main side of the step-down transformer. This transformer is only a segment of the size of an equivalent 50 Hz unit, thus releasing the size and weight problems. The filtered and rectified o/p at the minor side of the transformer. Now then, it has to be sent to the o/p of the power supply. A sample of this output has to be sent back to the button to control the output voltage.

D.C to D.C Converter

Forward Converter

In a forward converter, the choke transmits the current when the transistor is leading as well as when it is not. The diode transmits the current through the OFF period of the transistor. Thus, the flow of current into the load during both the periods. The choke stores energy during the ON period and also permits some energy into the o/p load.

Forward Converter

Forward Converter

Flyback Converter

In this converter, the magnetic field of the inductor supplies the energy throughout the ON period of the switch. Output voltage circuit when the button is in open state, the energy collapses. The duty cycle controls the output voltage.

Self-Oscillating Flyback Converter

This is the most simple converter based on the principle of the flyback. Throughout the conduction time of the switching transistor, the flow of current through the transformer primary switches ramping up linearly with the angle equal to Vin/Lp. The induced voltage in the secondary winding and the feedback winding make the fastest recovery rectifier reverse biased and hold the conducting transistor ON. When the primary current touches a peak value ‘Ip’, where the core activates to saturate, the current inclines to increase very sharply. we cannot support them by the fixed base drive offered by the feedback winding. As a result, the switching activates to come out of saturation.

As now we’ve learned about the types of SMPS, let’s move to its uses.

What is the use?

SMPS is a famous and sometimes necessary choice for DC-DC power conversion. These circuits offer distinct benefits and tradeoffs when we compare it to another method of converting DC power. This blog will give a brief summary of the pros and cons of switch-mode power supplies, and also offers a simple review of their operation and theory.

Many major electronic DC devices get power from the standard power supply. But sometimes, standard power sources might not match the required levels by microprocessors, motors, LEDs, or other loads, especially when the source voltage isn’t in control. Battery-powered devices are prime examples of the problem: the typical voltage of a standard Li+ cell or NiMH stack is either too high/low or drops too far during discharge that it is not usable in a conventional application.

Old technology used linear power supplies to give the output voltage but energy dissipation was really higher(wastage of energy). Output has higher efficiency, stabilization and has lesser energy dissipation.

The most common application of an SMPS is the power supply unit of a computer.

Things required to test an smps

              Fig 1.2 Things Required for connecting an SMPS

Check the Video Linked above for connection of the SMPS.

Here we have used a Lubi SMPS. You can use a different one as well. Everything will be the same(might be some minor differences in specifications.

So Now that we’ve learned about its uses lets move to things that we need to take care of while using SMPS.

Things to take care while using an SMPS:

  • Don’t open the SMPS
  • Check connection properly the cable should not be touching the body of the SMPS.
  • Make sure to tighten the screws and connection.
  • Make sure you connect proper load as per the specifications otherwise it might burn.
  • use multimeter when adjusting voltage adjuster to check the changed voltage.
  • Don’t keep it in direct sunlight, humid atmosphere for a long duration.
  • Make sure to use cables of proper thickness so that cables don’t burn out.

So above mentioned are the things we need to take care/precautions while using an SMPS.

An example of Specifications is shown below.

specification SMPS

                            Fig 1.3 Specification of SMPS

Now let’s compare SMPS(Switched Mode Power Supply) with an LPS(Linear Power Supply) and see which is the better one SMPS or LPS.

SMPS vs Linear Power Supply

lps vs smps power supply

                               Fig 1.4 SMPS vs LPS

What’s your thought? Which is better? from my end both have their pros and cons. It depends on the requirement and usability.


SMPS are very important in giving us an efficient power supply. They give less heat and more performance as we compared it with Linear power supply(LPS). Many Devices work on DC voltage these days. SMPS provides a consistent and better supply with less heat dissipation.

Hope you like the blog, if you have any questions feel free to mention in the comments.

Thank you for reading till here. See you next time.

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