Everything You Need To Know About Computer’s PSU

SMPS stand for Switch Mode Power Supply. It is mainly an electronic power supply device used in desktop computer systems. The main purpose of using an SMPS is to transfer power from AC source to DC applicants while converting voltage and current. It is mostly used in domestic products like personal computers. Switch-mode power supplies can tolerate a wide range of power frequencies and voltages, so its application increases. Due to the high volume of SMPS, they are now being used in the mobile phone charger too and the cost of mobile charger has been also decreased.

Switched-mode power supplies are used for DC to DC conversion as well, and because of this function of SMPS, heavy vehicles, in industrial settings such as telecommunications racks, bulk power and individual equipment items also uses DC/DC switched-mode converters to get the power supply, whatever voltages are needed.

SMPS also uses a switching regulator to convert electric power efficiently. The computer power supply changes A.C. (Alternating Current) to low voltage D.C. (Direct Current) to run peripheral devices. Nowadays computer uses SMPS as a primary power supply. Computer’s PSU is generally smaller and lighter as compared to a linear supply because of smaller transformer size and weight.

Mainly, SMPS switches elements includes, inductors, capacitors, transformer and all the different kinds of electrical components to regulate the output voltage and current.

Let’s Overlook To The Working Process Of A Computer’s Power Supply

The actual working of PC’s Power Supply is divided into four different parts and every section having its own important task to do to maintain the perfect power productivity. Here’s the list of all those different sections which I’m talking about:

  1. Input Rectifier: The first step is to convert AC into DC by the process called Rectification. The rectifier is a full wave diode bridgeor module that is used to produce an uncontrolled DC voltage to the Smoothing capacitor. The current drawn from the mains supply by this rectifier circuit occurs in short pulses around the AC voltage peaks. These pulses have significant high-frequency energy which reduces the power factor.
  2. Inverter: In this stage, DC is converted into AC through a power oscillator. The output transformer of power oscillator is very low with windings at a frequency ranging from tens to hundreds of kilohertz. These frequencies are above 20 kHz and inaudible to humans. The switching is done by MOSFET amplifier. This amplifier has low resistance with the high current handling capacity.
  3. Voltage Converter: If the output voltage is above 10 volts, then the silicon diodes are used. If the output voltage is lower than 10 volts, then the Schottky diodes are used as a rectifier. They have faster recovery time than silicon diodes and when conducting, the voltage drop is low.
  4. Output Regulator:  A filter consisting of inductors and capacitors is used for smoothing of rectifier output.  A feedback control loop is employed to regulate the output voltage by varying the duty cycle to compensate for variations in input voltage.

This Is How A PSU’s Back Panel Looks Like:

  • Fan: A fan is provided at the back panel. It is used to remove air inside the PSU.
  • Power Supply Port: This part draws electricity from your house socket and delivers it to the PSU.
  • Power Switch: A power switch is used to turn ON or OFF the PSU.
  • Voltage Switch: This part is used to switch the voltage from 110/115 V to 220/230 V or vice versa. If your PSU doesn’t have this part then it quite possible that the power connector of your PSU is universal or may be it is only made for a specific region only.

This Is How A PSU Connectors Looks Like:

While installing a Power supply unit into a computer, we need to connect all the vital hardware cables and connector to transfer the power supply to various components in the computer. Their generic specifications for various desktop systems are defined in Intel’s design guides, which are periodically revised.

  • PC Main Power Cable: This cable attached to the back panel of the PSU and used to power up the PSU device. It is visible from the outer side of the PSU.
  • SATA/MOLEX Power Cable: This cable connects PSU to the Hard Disk. SATA stands for Serial ATA or Serial Advanced Technology Attachment. SATA is better than PATA as its data sending speed is much higher than it.
  • ATX 24 Pin, Main MOBO Power Cable: This cable is the standard motherboard cable used in every computer’s motherboard and mainly this cable connects PSU to the motherboard and provides all the power needed by the motherboard. This cable either available in 2 cables or may be joined to a single cable.
  • 6 Pin Or 6+2 Pin PCI Express Power Cable: 6 Pin cable is used to provide the extra 12-volt power to PCI Express expansion cards. A maximum of 75 watts is generated by the PCI Express motherboard slots. Mainly it is created for the graphics card. 6+2 Pin cable is just like the 6 pin PCI Express power cable but with 2 more pins. The advantage of this cable is that it provides the max power of 150 watts.
  • 8 Pin CPU Power Cable: This cable is used to deliver the power supply to the processor.

#At Last, All The Extra Important Kinds of Stuff

Power RatingTotal power requirements for a high-performance computer with multi graphics card may range from 650 W to more than 1000 W, where normal personal computers usually require 300 to 500 W. The power consumption is calculated and around 40% greater than the power supplies are made. It is done to protect the system against overloading and performance degradation. The total power consumption of the system is the sum of all the power rating of all the components that takes the power from the supply. A power supply that is self-certified by its manufacturer will claim output ratings that may be double or more than what it actually provided.

EfficiencyA test done in 2005 states that, computer power supplies are 70-80% efficient. High-quality power supplies can be over 80% efficient. As a result, they are energy efficient, waste less energy in heat, require less airflow to cool. In 2012, The PSU’s became more efficient. Their efficiency may reach up to 90% at optimal load levels. Efficiency generally peaks at about 50–75% load. Now various actions are started to improve the efficiency of computer power supplies. Efficient power supplies save money as they waste less power and then that saved electricity will use to provide the power to the same computer.

Advantages And DisadvantagesOne of the main advantages of SMPS is that it is more efficiency than linear regulators because the switching transistor dissipates little power when acting as a switch. Some more advantages of SMPS include smaller size and lighter weight as the heavy line frequency transformers and heat generation are eliminated in SMPS.

Greater complexity, the generation of high-amplitude, high-frequency are the disadvantages. Cheap SMPS may cause interference with A/V equipment connected to the same phase, due to coupling with electrical switching noise back onto the mains power line.

PrecautionsAfter the power cord has been removed from the wall, the main filter capacitor may store up to 325 volts. Some of the SMPS lacks the bleeder capacitor which is used to discharge slowly the capacitor. If any contact is made with this capacitor, it may result’s a big electrical shock. The capacitor is sometimes made to connect with the primary and secondary sides of a transformer to reduce EMI (electromagnetic induction). If the transformer is one then it may result’s an electric shock.


  1. “8 Pin CPU Power Cable: This cable is used to deliver the power supply to the processor.” Shouldn’t you indicate the voltage of this cable?


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