Points to Know about Your Computer Power Supply Unit

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September 2nd, 2010 · No Comments · Power Supply

Computer power supplies are the main source of energy for any desktop computer. Their operating scheme, the meaning of colored wires inside, and the relationship between voltage and current to output power is outlined in this article. How to measure power supply voltages is also demonstrated.

Power Supply Unit Basics

Ever wonder what is happening inside your computer supply? Computers cannot run without a source of energy. They require a proper power unit in order to be fed. Since the first computers, power supplies have been used for feeding every electronic device or circuit inside a computer. But how do these electric generators work and provide electricity to the computers? There’s no magic inside. A power supply simply draws AC (alternating current) voltage from an electrical source and converts it to DC (direct current) voltage.

A computer power supply unit consists of several components inside. There are coils, capacitors, an electronic circuit board to regulate current and of course a fan to cool down the whole unit inside a power supply. Fans are the number one failure reasons for power supplies. It’s true- a $5 fan may cost you more than ten to twenty times that amount when it fails.

Besides these components, several cables should be attached to the circuit board with a specific number of wire sets in distinguishable colors. These sets of wires are used to transmit different voltages to the main board and other devices connected to it. A computer power supply draws 110 volt of electricity from wall outlet which is in the form of AC voltage and converts it to much smaller voltages in DC form.

Today’s modern power supplies are equipped with several safety circuits checking flowing current continuously. If any kind of extreme condition exceeding its power output capacity is detected, the power supply simply shuts itself down and prevents any possible further harm to itself or to the mainboard.

Computer Power Supply Voltages

In a computer mainly three types of DC voltage are required to run. 12 Volts is necessary to feed the mainboard itself as well as any new age graphic cards, 5 Volts is required for the chassis and CPU fan or USB ports, and 3.3 Volts is used for the CPU itself. 12 Volts is also applicable for specific “smart” chassis fans. Thus in broader sense, a computer power supply can convert 110 Volt electrical current (or 220 Volt for the European scheme) to +12V, -12V, +5V, -5V, and +3.3Volt.

The electronic circuit board in a power supply is responsible for forwarding the converted electricity through dedicated cable sets in order to feed the devices inside the computer. With the help of the components cited above, AC voltage is transformed into clean direct current. Nearly half of the work done by a power supply unit is carried out by capacitors inside. They help regulate the smooth, clean currents to precious circuits in your computer.

But be warned. Even if your computer is unplugged, there is still chance of electricity being stored inside your PSU even days after you pulled its plug. That’s what capacitors are used for. They store energy to be used for a continuous work flow.

Power versus Voltage Output

What makes a computer power supply unique and capable of feeding the computer with sufficient energy is simply its capacity to produce power measured in Watts in almost every unit out there. Yes, every power supply has a decent capacity in terms of maximum power they can produce within a certain time period, and this specific capacity often leads to confusion as well.

Let’s make things more clear. Since power means voltage multiplied by current from Electricity 101, computer power supplies can be interpreted as a power source to the extent limited by their capacity to produce maximum Watts per operating cycle. This capacity is regularly misjudged by consumers. (Manufacturers are responsible for this confusion.) Because real capacity can be calculated by adding up all the voltage outputs of every bit of wire set multiplied by maximum current they can produce. This specific capacity reflects the real output power of a power supply, but manufacturers prefer to use a broad numbering format which may lead to false interpretation of real output power.

Power Supply Unit Color Codes

Inside power supplies you see bunch of colored cable sets coming out with different sockets or connectors and different numbers of wires each. Color codes of power supply cables are as follows:

1. Black Wires: Those are used to provide a ground for the current. Every other color should be paired with a black wire.
2. Yellow Wires: This color denotes +12Volt
3. Red Wires: This color denotes +5Volt
4. Blue Wires: -12Volt
5. White:Wires -5Volt
6. Orange Wires: 3.3Volt
7. Green Wires: Control wire to check DC voltage
8. Purple Wires: +5V on standby mode

source: http://www.brighthub.com/computing/hardware/articles/58559.aspx

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