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About power supply


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Type of Power Supply and their applications

Power supply is a device used to provide the electric energy to operate the devices running by electric power. It has many special way to provide electric energy to a specific system “ it is mother of the system “ ( Brown, 2001, p.1 ).

The basic function of power supply is to convert Alternative Current voltage to regulated  Direct Current voltage that required by electronic devices. A typical power supply has four different modules each of them has a specific function. Transformer is the first module and its function is to convert high voltage Alternative Current  to low voltage Direct Current. The second module is Rectifier and its main function is to convert low voltage Alternative Current to Direct Current. The third module is smoothing, the Direct Current produced by the rectifier is varying, so smoothing reduce this varying to small rippling. Last module is regulator, it set the Direct Current voltage to constant value by remove the ripples. This is a basic design of power supply. The design can be huge and complicated based on the requirements.

This essay will present the four major types of power supply which are Linear Regulators and Switching Mode Power Supply, Programmable Power Supply, Uninterruptible Power Supply.

The first type of power supply is Linear regulated power supply. It is the basic type of power supply. It produce the regulated output voltage by drop the input voltage. “it is though, a very electrically quiet power supply” (Brown, 2001, p.11). they are often used in ground based equipments and distributed power system.

Linear regulated power supply function is to convert varying Alternative Current input to regulated Direct Current output. The typical circuit use in this type has tow range. One allow more voltage at low current and the other allow more current at low voltage.

Linear regulated power supplies come in tow basic forms called series regulators and shunt regulators. Series regulated power supplies are most common form of linear regulated power supply. The power dissipated in series regulated device is the product of power supply output current and the voltage drop. Shunt regulated power supplies are simpler form of Linear Regulated power supply, but they are less efficient. 

Simplicity is the main advantage of linear regulated power supplies. It is used in systems that require extremely low noise. They are more suitable and cost effective for low power applications. It is used in ground based applications and distributed power systems. Since the linear regulated power supply has very low power output voltage ripple, it is used in low noise / low ripple applications such as communication and radio device where noise is very sensitive. It is more efficient in the application which output voltage is nearly equal to input voltage.

Second type of power supply is Switching Mode. It operates in ON-OFF mode. It uses switching circuits and energy storage elements such as capacitors and inductors to get the regulated output voltage. “These circuits are ideally lossless with 100% energy transfer” (Johnny, 2006, p.1).

The main advantage of Switching Mode Power Supply is the higher efficiency because of low power dissipation. Switching Mode Power Supply is used in domestic products which often have universal inputs. Mobile phones have changed their power supply technology from linear regulated to Switching Mode Technology. It is widely used in aircraft electric power such as airplane ground support.

Third type of power supply is Programmable Power Supply. It provide the power through a computer interface. It generally depends on both Linear regulated and Switched Mode technologies to produce accurate output power.

Programmable power supplies are mainly used in automated equipment testing. They are also used in ultrasonic vibration measurement tools.

Last type of power supply is Uninterruptible power supply. It is widely known as UPS or power back up. It is widely used as backup power to protect the devices from crashing due to sudden power loss.

There are three major categories of Uninterruptible power supply, offline -standby, online and line-interactive.

Offline /standby Uninterruptible power supply provides surge protection and battery back-up up to 20 minutes. When the input power supply falls below the starting level, then Uninterruptible power supply turns on its power circuit providing power backup to the device up in certain time (In this type 20  minutes).

Line-Interactive Uninterruptible power supply generally uses only one main power convertor to generate the power. The typical protection time varies from 5 minutes to 30 minutes.

The operation of Online Uninterruptible power supply is very similar to Standby or Line-Interactive type. The typical protection time varies between 5 minutes to 30 minutes. But, it provides electrical firewall between incoming utility power and sensitive electronic equipment.

They are mainly used for surge protection and back power for computers, data centers and telecommunication equipment. They are used to provide the electric isolation for the equipments which are sensitive to power fluctuations.

In conclusion, there are different sources of power being used to provide the power to the systems effectively and efficiently. For example, solar energy and wind power are being converting to electric energy to provide the power to large industrial applications. Power supplies are the heart of any system which requires electrical energy. They not only provide power but also provide the protection to the system against outside disturbances. Therefore, design and development considerations of a power supply are more important. As technology is growing, more advanced power supplies are being invented to provide best protection and efficient power to the devices.


Brown, M. (2001), Power Supply Cook Book, MA, U.S.A, Butterworth- Heinemann.

Bennet, C, Johnny (2006), Practical Computer Analysis of switched mode power supplies, FL, U.S.A, CRC Press.

Hoff, Michael. and Samstad, Jeffrey, Technical Comparison of On-Line VS. Line-Interactive UPS [online]. Available:

http:\\www.apcmedia.com/salestools/JSII-5YQSBR_R0_EN.pdf [accessed February 18, 2010]

Unknown. http://www.circuit-projects.com/power-supply/uninterruptible-power-supply-ups-basic-circuit-diagram.html, [accessed February 18, 2010]

Understanding Linear Power Supply Operation, Application Note 1554 [online]. Available:

http://cp.literature.agilent.com/litweb/pdf/5989-2291EN.pdf, [accessed February 16, 2010]

Unknown. http://www.kpsec.freeuk.com/powersup.htm, [accessed February 17, 2010]

Zhang, J, Henry. Linear Regulating and Switching Mode Power Supply Basics[online]. Available:

http://www.techonline.com/article/pdf/showPDF.jhtml?id=1931034931[accessed February 15, 2010]

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