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Basic Components of a Power Supply Unit

Jemuel is an electronics engineer, software engineer and author of articles about electronics, technology, personal development and finance.

A high voltage power vacuum tube power supply. It is capable of supplying +/- 1500 Vdc with 0 - 100mA output.

A high voltage power vacuum tube power supply. It is capable of supplying +/- 1500 Vdc with 0 - 100mA output.

Transformer

The transformer is a static device that transfers electrical energy from the primary winding to the secondary winding without affecting the frequency. It is used to step-up or step-down the AC voltage level and isolates the remainder of the electronic system from the AC power.

The primary winding of the transformer is connected to an AC voltage source that produces alternating current while the secondary is connected to a load. The primary and secondary windings are not physically connected to each other but due to electromagnetic induction following Faraday's law, there is an induced voltage in the secondary winding.

There are three main functions of transformers namely: stepping the voltage up, stepping the voltage down and providing isolation between the primary and secondary circuits.

A simple power supply used in desktop computers. This unit supplies the regulated voltage necessary for computer to operate properly.

A simple power supply used in desktop computers. This unit supplies the regulated voltage necessary for computer to operate properly.

A power supply is an electronic circuit that converts the voltage of an alternating current (AC) into a direct current (DC) voltage. It is basically consisting of the following elements: transformer, rectifier, filter and regulator circuits. Power supply units (PSU) are used in computers, amateur radio transmitters and receivers, and all other electronic equipment that use DC voltage as an input. Uninterruptible power supply is a must for computers which holds volatile data from time to time. Aside from protecting your computer from sudden shutdown, this prevents corruption of data due to power failure and low voltage.

Rectifier

The rectifier is a device used to change the AC power into pulsating DC. The basic rectifier is the diode. This diode is a unidirectional device that operates as rectifier in the forward direction. The three basic rectifier circuits using diodes are the half-wave, full-wave center-tapped and full-wave bridge type.

Purpose of Grounding Rectifiers

The transformer isolates the secondary winding from the primary source. The primary source may be grounded but your secondary winding is not because they are not connected. The secondary winding is not referenced to any potential. Applying a ground only gives the secondary circuit a reference potential.

Filter

The filter of the power supply is used to keep the ripple component from appearing in the output. It is designed to convert pulsating DC from rectifier circuits into a suitably smooth DC level. The two basic types of power supply filters are the capacitance filter (C-filter) and Resistor-Capacitor filter (RC-filter). The C-filter is the simplest and most economical filter available. On the other hand, RC-filter is used to reduce the amount of ripple voltage across a capacitor filter. Its primary function is to pass most of the DC component while attenuating the AC component of the signal. The RC filter is composed of resistors and capacitors. RC filters are used to filter a signal by simply blocking certain frequencies and passing others. Common RC filters are High-Pass filters and Low-Pass filters.

Ripple and Ripple factor

Ripple is the unwanted AC component of the signal after rectification. It is unwanted because it can destroy or damage the load. This is the main reason why filters are installed in power supply - to prevent high ripples. The job of the filter is to smoothen the signal and suppress the AC component or variations. Ripple factor is the ratio of the root mean square of the ripple voltage to the value of DC component at the output voltage. It is sometimes expressed in percentage or in peak-to-peak value. The ripple factor determines the effectivity of a filter being used in the circuit.

A sample full-wave bridge rectifier circuit with RC filter. The filter is used to reduce the AC component of the signal.

A sample full-wave bridge rectifier circuit with RC filter. The filter is used to reduce the AC component of the signal.

Voltage Regulators

A voltage regulator is designed to provide a very steady or well regulated DC output. It is always ideal to have a steady output voltage so that the load will operate properly. The output level is maintained regardless of the variation of the input voltage. The commonly used transistor voltage regulators are the series voltage regulator and the shunt voltage regulator.

Series voltage regulator

The series element controls the amount of the unregulated input voltage that goes to the output as a regulated output. The regulated output voltage is sampled by a circuit that provides a feedback to the comparator circuit and is compared to a reference voltage.


Shunt voltage regulator

The shunt voltage regulator provides regulation by shunting current away from the load to regulate the output voltage.

A typical schematic diagram of LM317. The major component, LM317 IC is used as adjustable voltage regulator.

A typical schematic diagram of LM317. The major component, LM317 IC is used as adjustable voltage regulator.

IC Voltage Regulators

A regulator Integrated Circuit (IC) unit contains the circuitry - the reference source, comparator, amplifier, control device, and the overload protector - inside a single IC. There are also adjustable voltage regulators which allow the user to set the desired output level. Other IC regulators have fixed output values. It is said that IC regulators are superior compared to transistor voltage regulators when it comes to linearity of the output voltage.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: "C" filter is short for Capacitance filter. You also mentioned about “RC" filter. What does “RC“stand for in reference to a power supply unit?

Answer: The RC filter is a Resistor-Capacitor electrical circuit composed of resistors and capacitors. RC filters are used to filter a signal by simply blocking certain frequencies and passing others. Common RC filters are High-Pass filters and Low-Pass filters.

Question: Why do we have to ground the rectifier?

Answer: The transformer isolates the secondary winding from the primary source. The primary source may be grounded but your secondary winding is not because they are not connected.

The secondary winding is not referenced to any potential. Applying a ground only gives the secondary circuit a reference potential.

Comments

Israel Josiah on August 09, 2019:

What are the components that can cause a Desktop monitor from not powering?

umar dukul on June 28, 2019:

list the companent of atx and at power suply unit

muhammad umar dukul on June 28, 2019:

thanks

Bogi on December 02, 2018:

What is the rate of Rh and Rl if Vn =40v???? Vout should be from 0 to 40v?

Aowais on September 12, 2018:

What is the power supply box made out of in computer

Sanmesh Sanjay Nikam on September 11, 2018:

it is very use-full to me

Thank You

ani on September 06, 2018:

nice

Taiwo Tajudeen on July 23, 2018:

Why do we have to ground the rectifier in the design of the rectifier shown above?

what is the most important part of the computer on June 26, 2018:

what is the most important part of the computer

jerson on June 03, 2018:

You can UPS to removed fluctuation....

marv on April 22, 2018:

please can you tell me five functions of power supply unit

Issaaya khamusini fiftybob on March 07, 2018:

Thank you for this. I like electronics.

rickynaidoo007@gmail.com on October 05, 2017:

How to learn the direct current voltages and ac current voltages in an electronic circuit?

Jemuel Omboy (author) from Cebu, Philippines on July 22, 2017:

Hi Mahmud. AC voltage do fluctuate, and if you want to convert it into non-fluctuating, it becomes DC. If you meant that you want to convert AC to DC then you can use the rectifying circuit, filter and voltage regulator for steady output.

Thanks!

weerasinghe on June 21, 2017:

Thanks a lot dear!!!,my congratulations!!!

Mahmud on June 05, 2017:

My question is , in case the fluctuation in input voltage this will reflect in output voltage , and in case if i need to purify the AC voltage (fluctuating ) to pure ac without fluctuation there is any electronic circuit to solve this issue ?

Asmin karkee on June 03, 2017:

Thanks A Lot!!!!!!!!!!!!!!!!

Evans on March 07, 2017:

This is soo helpful

Bhuvana on February 10, 2017:

so useful

alex on February 08, 2017:

thanks its a good one

BRANDT on November 15, 2016:

THANK YOU SO MUCH! :)

Jemuel Omboy (author) from Cebu, Philippines on October 07, 2016:

You're welcome Koobake!

Koobake on September 27, 2016:

Thank you so much

Jemuel Omboy (author) from Cebu, Philippines on February 20, 2016:

You're welcome, Michael. Good luck on your project!

michael on February 15, 2016:

thankyousomuchsir....i hope this project will be ok:)

Nadia Batool on December 09, 2015:

This is Nice

Jemuel Omboy (author) from Cebu, Philippines on August 23, 2015:

You're welcome Amit and Rebecca! Hope this helps you.

sapinoso,Rebecca on March 09, 2015:

Thanks a lot!

Amit on February 25, 2015:

Thanks! very much buddy