SMPS: Basics & Working of Switched Mode Power Supply

Switching mode power supply (SMPS) is used in a range of applications as an efficient and effective source of power. This is in major part to their efficiency. For anybody still working on a desktop, look for the fan output in the central processing units (CPU). That’s where the SMPS is. SMPS offers advantages in terms of size, weight, cost, efficiency and overall performance. These have become an accepted part of electronic gadgets. Basically it is a device in which energy conversion and regulation is provided by power semiconductors that are continuously switching “on” and “off” with high frequency.


The different kinds

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


The primary power received from AC main is rectified and filtered as high voltage DC. It is then switched at a huge rate of speed and fed to the primary side of the step-down transformer. The step-down transformer is only a fraction of the size of a comparable 50 Hz unit thus relieving the size and weight problems. We have the filtered and rectified output at the secondary side of the transformer. It is now sent to the output of the power supply. A sample of this output is sent back to the switch to control the output voltage.


Forward converter


In a forward converter the choke carries the current when the transistor is conducting as well as when it’s not. The diode carries the current during the OFF period of the transistor. Therefore, energy flows into the load during both the periods. The choke stores energy during the ON period and also passes some energy into the output load.


Flyback converter


In a flyback converter, the magnetic field of the inductor stores energy during the ON period of the switch. The energy is emptied into the output voltage circuit when the switch is in the open state. The duty cycle determines the output voltage.


Self-Oscillating Flyback Converter


This is the most simple and basic converter based on the flyback principle. During the conduction time of the switching transistor, the current through the transformer primary starts ramping up linearly with the slope equal to Vin/Lp. The voltage induced in the secondary winding and the feedback winding make the fast recovery rectifier reverse biased and hold the conducting transistor ON. When the primary current reaches a peak value Ip, where the core begins to saturate, the current tends to rise very sharply. This sharp rise in current cannot be supported by the fixed base drive provided by the feedback winding. As a result, the switching begins to come out of saturation.


Basic working concept of a SMPS


A switching regulator does the regulation in the SMPS. A series switching element turns the current supply to a smoothing capacitor on and off. The voltage on the capacitor controls the time the series element is turned. The continuous switching of the capacitor maintains the voltage at the required level.


Design basics


AC power first passes through fuses and a line filter. Then it is rectified by a full-wave bridge rectifier. The rectified voltage is next applied to the power factor correction (PFC) pre-regulator followed by the downstream DC-DC converter(s). Most computers and small appliances use International Electrotechnical Commission (IEC) style input connector. As for output connectors and pinouts, except for some industries, such as PC and compact PCI, in general they are not standardized and are left up to the manufacturer.




Like every electronic gadget, switching mode power supplies also involve some active and some passive components. And like every of those gadgets, it has its own advantages and disadvantages.


Let’s start with why you should go for a SMPS


  • The switching action means the series regulator element is either on or off. Very high efficiency levels are achieved as very little energy us dissipated as heat.
  • As a result of the high efficiency and low levels of heat dissipation, the switch mode power supplies can be compact.
  • Switch mode power supply technology also provide high efficiency voltage conversions in voltage step up or “Boost” applications and step down or “Buck” applications.


Then there’s the bad set


  • The transient spikes due to the switching action can migrate into other areas of the circuits if not properly filtered. These can cause electromagnetic or RF interference affecting other nearby items of electronic equipment, particularly if they receive radio signals.
  • To ensure that a SMPS performs as per the required specification can be a bit difficult. The ripple and interference levels are particularly tricky.
  • The costs of a switch mode power supply is calculates before designing or using one. Additional filtering further adds to the cost.


What would the future hold?


In the future, we could have more efficient SMPS aimed at a better converter doing the most effective conversion process. The focus areas for designers in making SMPS efficient would be:


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


Hon-Kwang Electric specialized in manufacturing switch mode power supply and related products. We provide series of switching power supplies to meet different demands of you. If you are interested in learning more details about switching mode power supply, please feel free to contact with Hon-Kwang.


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Uninterrupted Power Supply is the Answer to Productivity

Work disruptions due to power interruptions have been causing companies so many problems. One major problem that employers are concerned about is the possible decline in productivity of the employees and of the company in general due to these unexpected power interruptions. People naturally lose momentum if they stop in the middle of their work. This usually happens during power interruptions.

The unpredictability of power interruptions moves many employers to look for ways and means on minimizing work disruptions. Industries have never stopped in looking for solutions for a continuous power supply. They realized that efficiency is more or less facilitated by an uninterrupted power supply.

Efficiency and productivity are linked to each other. And both depend on how the person works within his environment. The work environment is a major factor since it can do a lot in motivating the worker. The reverse is also true. Once the work environment is neglected, productivity will naturally decline.

The necessity of a ups system is becoming more evident. Any workplace would surely require a continuous power supply. All businesses dream of an interrupted supply. From manufacturing to services, the role of power is indispensable. They are needed to provide lights and power to computers and other equipment. In hospitals for example, they are needed to sustain life.

This is why investors would always consider the reliability of the power of a country before pouring in their money. Power interruptions would definitely be a negative factor since most investors would always look for a stable power supply. Manufacturing companies would always choose to invest in a country with a stable power supply. This will enable them to keep on manufacturing. It would also allow them to save money since they will not have to spend extra for back up generators which they will have to use in the event of power interruptions.

Ultimately, to provide continuous power supply, a stable and reliable power plant may be necessary. These power plants would supply the power requirement of each city. There are many types of power plants. Some of these plants use coal and other fossil fuels such diesel and bunker fuel. However, the more desirable solutions are the power plants that utilize renewable energy such as geothermal, wind, water and solar energy. These energy sources not only promote awareness of the need to take care of the environment but also provide a more reliable and cheaper energy.

The motivation to have uninterrupted power supplies moved scientists and engineers to continually seek to tap these renewable sources of energy. Among these possibilities, the geothermal poses the greatest potential. Unlike solar and wind energies, the geothermal is available the whole day. The volcano does not stop producing the steam which the geothermal power plant taps for power generation. This continuous supply of steam would then guarantee an uninterrupted power supply to different industries. This makes this energy source the answer to many worries of government. Investors would be more than willing to gamble if they are assured that the playing field is more or less stable.

Why an uninterrupted power supply is the answer to better productivity. See the website for more information.

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To Eliminate Noise from a Switch Mode Supply

A switching mode power supply is very efficient in its working. Although, the supply is designed in such a way that it produces noise that is inaudible to the human ear, it sometimes gives a lot of noise especially when it gets old.

The good news is that if your switching mode power supplies producing a lot of noise there are ways in which you can eliminate the noise.


High-pitched whine with a fan

The noise is caused by lack of lubrication in the fan bearing. To eliminate the noise you should lubricate the bearing. This calls you to unplug the device from the power supply and remove the fan’s bearing protective plating. You should then put a few drops of sewing machine oil directly onto the bearing.

You should note that some protective plating is held by screws while others are held by a thick sticker.

High-pitched whine without a fan

This noise is usually caused by external electromagnetic interference (EMI). To solve it you need to move the power supply away from anything that produces a large amount of EMI. Some of the objects that tend to produce a lot of EMI include: large speakers, large batteries, fluorescent lights and flat-screen monitors.

If you remove the supply from these objects and the noise persists, it must have been caused by a dry capacitor. You should remove the capacitors together with the soldering iron and then replace them with new capacitors.

You should note that capacitors have the ability of causing massive electronic shock; therefore, after unplugging the power supply you should leave it unplugged for at least three hours before you remove the capacitors.

Low-pitched hum

If the low-pitched hum is annoying, you should put the supply in a metal casing in order to shut the noise in the casing. All you should do is to visit your local store and find a casing that will fit your entire power supply unit. You should then place the supply inside the casing and screw the casing shut.


These are some of the ways in which you can eliminate the noise in a switching mode power supply unit. If you do all of the above and the noise persists, you should take your device to a professional who will rectify the problem for you.

To ensure that your device lasts for a long time without developing problems, it’s good that you buy your device from a reputable seller.

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Manufacturer of Switching Power Supply, Adaptors – Hon-Kwang

Hon-Kwang was founded in 1981. Head office is in Kaohsiung, Taiwan. Hon-Kwang is a maker of power supplies & specialized in the design and manufacture for the domestic and foreign market.

Hon-Kwang specialized in manufacturing switching mode power supply and series AC/AC adaptors, AC/DC adaptors with different output rating, I/P voltage. Also, LED power supplies with 5W, 7W, 10W up to 250W are provided. Hon-Kwang switching mode power supplies feature universal input, high efficiency and short circuit protection.



Hon-Kwang Electric Co., Ltd.

Address: 246, Feng-Jen Road, Feng-Shan Kaohsiung Hsien, Taiwan

TEL: +886 (7) 743-0206

FAX: +886 (7) 742-2305


Power Supply and Redundant Power Supply – Sure Star

Sure Star was striving to provide a wide selection of industrial power supply products and rack mount power supply, server power supply and redundant power supply. Sure Star has grown to one of the leading brands in the IPC power supply industry. Our company mission is to focus on providing customers with a combination of cutting-edge technology, high quality production, and remarkable customer service. Our ability to design according to the customers’ requirements has given a renown reputation, as our engineers have the keen ability and ample resources to make an OEM project run smoothly and efficiently. If you want to find out more about the very best in industrial power supply, rack mount power supply, server power supply and redundant power supply contact with us.

industrial power supply

industrial power supply

ADD: No. 2-1, Daan Rd., Shulin Dist., New Taipei City, Taiwan
TEL: (886 2) 2682-2505
FAX: (886 2) 2682-2515