The Transformer

A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling with no moving parts. A transformer comprises two or more coupled windings, or a single tapped winding and, in most cases, a magnetic core to concentrate magnetic flux. A changing current in one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings. Michael Faraday built the first transformer, although he used it only to demonstrate the principle of electromagnetic induction and did not foresee the use to which it would eventually be put.



The secondary has more turns than the primary. Intake low voltage like 12v and step-up them in 220v. UPS is an good example of this.


The secondary has fewer turns than the primary. Intake high voltage like 220v and step-down them  in 3v, 6v, 12v. charging Adopter is a good example.

Electronic Components

As a computer professional, you should be familiar with the more common types of electronic components within a power supply. Here is a description of the basic components found on circuit boards inside a computer.


A resistor is a component that is meant to be inserted into an electrical path, to restrict the flow of electricity. Most resistors come with two connecting wires, one at each end, so they can be added to the circuit. The value of a resistor is measured in Ohms, and the higher this value is, the less current will be able to flow through it.



The Mnemonic

B.B. ROY of Great Britain had a Very Good Wife

Black is also easy to remember as zero because of the nothingness common to both.

I.C (Integrated Circuit)

In electronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon chip, or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material.

There are two main advantages of ICs over discrete circuits: cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography and not constructed

one transistor at a time. Performance is high since the components switch quickly and consume little power, because the components are small and close together.

PC Power Supply

It is a very important part and most often overlooked when the specifications of a computer are being written for a purchase or an upgrade. Computer owners boast of their motherboard, processor, RAM and Hard Disk etc. What they forget to care about is the power supply.

Primary Function and Operation

  • The power supply provides the electrical power used by the computer.
  • The power supply in a personal computer system is designed to convert 230V and 50Hz AC power into +3.3V, +5V, and +12V DC power.
  • Some power supplies require, you to switch between the two input ranges, where’s others auto-switch.

Positive DC Voltages

  • Normally, the digital electronic components and circuits in the system (motherboard, adapter cards, and disk drive logic boards) use the +3.3V or +5V power, and the motors (disk drive motors and any fans) use the +12V power. The table below lists these devices and their power consumptions.

Power Consumption Ratings for PC Devices

VoltageDevices Powered
+3.3VChipsets, DIMMs, PCI/AGP cards, miscellaneous chips
+5VDisk drive logic, SIMMs, PCI/AGP cards, ISA cards, voltage regulators, miscellaneous chips
+12VMotors, voltage regulators (high output)
  • The power supply must deliver a good, steady supply of DC power so that the system can operate properly.
  • Devices that run on voltages other than those specified in the above table must be powered by onboard voltage regulators. For example, RIMMs run on 2.5V that is supplied by an onboard regulator, and processors are supplied by a voltage regulator module (VRM) that normally is built into the motherboard as well.
  • The main function of the +12V power is to run disk drive motors as well as the higher-output processor voltage regulators in some of the newer boards.
  • Usually, a large amount of +12V current is available from the power supply, especially in those designed for systems with a large number of drive bays for disk drive motors.
  • In the newer CPU voltage regulators, the +12V supply is used by any cooling fans in the system—which, of course, should always be running.
  • Most fans in desktop systems run on +12V, portable systems can use fans that run on +5V, or even +3.3V.

Negative DC Voltages

  • PC power supply also generates–5V and –12V.
  • The –5V is required on the Industry Standard Architecture (ISA) bus for full backward compatibility.
  •  –5V and –12V are supplied to the motherboard via the power supply connectors, the motherboard normally uses only the +3.3V, +5V, and +12V.


The Power Good Signal

  • The power supply actually prevents the computer from starting up or operating until all the power supply voltages are within the proper ranges.
  • The power supply completes internal checks and tests before allowing the system to start. If the tests are successful, the power supply sends a special signal to the motherboard, called Power_Good.
  • This signal must be continuously present for the system to run. Therefore, when the AC voltage dips and the power supply cannot maintain outputs within regulation tolerance, the Power_Good signal is withdrawn (goes low) and forces the system to reset. The system will not restart until the Power_Good signal returns.

The Power_Good signal (sometimes called Power_OK or PWR_OK) is a +5V (nominal) active high signal (with variation from +2.4V through +6.0V generally being considered acceptable) that is supplied to the motherboard when the power supply has passed its internal self tests and the output voltages have stabilized.

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