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IT4nextgen > Key Concepts > SMPS-Switched Mode Power Supply

SMPS-Switched Mode Power Supply

Last Updated February 23, 2023 By Subhash D 25 Comments

What is SMPS

SMPS or switched mode power supply is an electronic device that is used to convert AC to DC, AC to AC, DC to DC, and DC to AC voltages. The circuit consists of a transformer, rectifier, voltage regulator, and filter. The input supply is turned On and Off by MOSFETs and outputs a high-efficiency, regulated voltage. The SMPS used in computers is of AC to DC type supply.

SMPS Parts and Connectors

SMPS fan

Power-IN. The power-IN connector as shown in the figure is the input for the MAINS supply. A power cable is inserted here, the other end of which is connected to the main supply. The input supply gets converted to DC supply.

Power-OUT. The power-OUT connector is connected directly to the Power-IN connector from inside the supply unit. It supplies the same AC supply that is fed to the power-IN socket. The power-OUT connector is used to give supply to monitors or any display unit.

FAN. If you look at the back side of Computer-SMPS, you will find a FAN on the right side. The FAN as you can see blows the air out and is only used to dissipate the internal heat from the SMPS since the switching is done at high frequencies which creates a lot of heat inside.

ATX connector. As you can see in the image, it is a 24-pin female connector that is used to supply DC supply to the motherboards. Various color-coded wires connect to this connector and each colored wire supplies a distinct DC voltage which is explained in the chart below.

ATX connector
Wire colourDC Voltage
Red+5 V
Yellow+12V
BlackGround
Blue-12V
GreyPower Good
GreenPower On
Purple+5V StandBy
Orange+3.3V
Brown/Orange+3.3V Sense
White-5V (optional)

ATX-12V connector. The Latest SMPS power supplies are accompanied by an extra 4-pin connector which supplies 12 volts to energize the central processing unit and other components of the motherboard.

smps 12 v connector

AT Connectors. Earlier motherboards were used to support AT connectors( 6-pin each) also called P8 and P9 connectors to supply power to these motherboards(up to 486 boards).

AT 6-pn connectors
Wire Colour DC Voltage
Red+5V
White-5V
BlackGround or 0V
Blue-12V
Yellow+12V
Orange+ 5V ( PG)

4-PIN connectors. There are multiple 4-pin connectors that draw out from the SPMS unit. These connectors are used to supply DC power to various peripherals of a computer like a floppy disk drive, hard disk drive, or DVD-writers.

SMPS connector-4pin
Wire ColourDC Voltage Used For
Yellow+12 V Motors
BlackGND 
BlackGND 
Red+5VLogic circuit

SATA-output connector. To feed the power to the latest SATA hard drives, these connectors are used.

sata-connector

How to Test a Computer SMPS

check SMPS computer supply

To check the supply, whether it is working properly or not, you can test it before fitting it into the cabinet. There is a simple way to test the SMPS, you just have to short the green wired connector to any black colored(ground) connector. If the SMPS is working perfectly, the fan of the supply will start working.

Filed Under: Key Concepts Tagged With: Computer hardware

About Subhash D

A tech-enthusiast, Subhash is a Graduate Engineer and Microsoft Certified Systems Engineer. Founder of it4nextgen, he has spent more than 20 years in the IT industry.

Comments

  1. Saket says

    October 31, 2016 at 11:27 am

    Good information about amps connector voltages

    Reply
  2. Manoj Choudhary says

    February 25, 2017 at 11:25 pm

    Very helpful information

    Thanks

    Reply
  3. Amit Vishwakarma says

    March 25, 2017 at 8:50 pm

    Thank you so much your this info.is are so much help in my study love you so much thank thank you so much

    Reply
  4. Harapriya says

    April 29, 2017 at 12:37 pm

    Thank u so much for valuable information….

    Reply
  5. madhu says

    June 23, 2017 at 2:16 pm

    superb but need some changes

    Reply
  6. Vishwajeet Mishra says

    July 25, 2017 at 2:25 pm

    Great article for SMPS .

    Reply
  7. Vinoth says

    July 31, 2017 at 10:25 am

    Good info….

    Reply
  8. satyam says

    September 23, 2017 at 8:15 pm

    very good article

    Reply
  9. Ranjith says

    December 30, 2017 at 8:11 am

    Useful information thanks

    Reply
  10. Dennis says

    February 11, 2018 at 12:35 pm

    thanks all solved

    Reply
  11. Chhviraj says

    May 5, 2018 at 9:52 am

    Smps power problem solved

    Reply
  12. samir padhi says

    May 12, 2018 at 10:59 pm

    But there is no information about ampere that is carried by different colours wire which is very essential.

    Reply
  13. Sanjay says

    June 29, 2018 at 9:49 pm

    But what actually happens when we insert a ushape pin in green and black slots

    Reply
    • Subhash D says

      July 2, 2018 at 2:10 pm

      If the SMPS is OK, it will turn on and you can visually check that it’s FAN is in also in running mode.

      Reply
  14. Kavitha says

    August 26, 2018 at 8:47 pm

    Good

    Reply
  15. sairam says

    September 5, 2018 at 1:16 pm

    Thank you for the information. It is help full SMPS problem rectifying.

    Reply
  16. John says

    December 11, 2018 at 1:49 pm

    Thanks

    Reply
  17. Ritik says

    January 16, 2019 at 6:28 am

    I’m really thankful to u that u provide this information may I know that u have any. Id or u tube which I can follow it or subscribe it

    Reply
  18. smartth says

    March 16, 2019 at 9:21 am

    very very helpful
    just whole heartedly liked it

    Reply
  19. Chintu Ganguly says

    June 2, 2019 at 12:42 am

    when i start my computer before press power bottom cpu auto start and then auto off and then auto start and auto off continuous and there were no display how can i solved its problem ?

    Reply
  20. VARUN SHUKLA says

    September 29, 2019 at 12:31 pm

    Can I get (DC dual 40V),
    2 pieces (5-28 V) DC,
    4 pieces(12-24V) DC from a pc smps?

    Reply
    • VARUN SHUKLA says

      September 29, 2019 at 12:38 pm

      Can I get (DC dual 40V),
      1 piece (12- 24 V)DC,
      2 pieces (5-28 V) DC,
      4 pieces(12-26V) DC from a pc smps?

      Reply
  21. sabneet yadav says

    December 15, 2019 at 10:50 pm

    But there is no information about ampere that is carried by different colours wire which is very essential.

    Reply
  22. Santosh says

    July 11, 2020 at 7:59 pm

    What if blue wire voltage is -10

    Reply
  23. karan salve says

    November 4, 2020 at 9:30 am

    nice Information

    Reply

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