If there is one component vital to the operation of a computer, it is the power supply. Without it, a computer is just a box full of metal and plastic. The power supply converts the alternating current (AC) from your home to the direct current (DC) utilized by a computer. Your power supply is the heart and soul of your PC system, although it doesnâ€™t get nearly as much press as sexier components like the processor, hard drive and memory. It is essential that you know the difference between a good power supply and a barely adequate one before you shop. So, what should you look for in a power supply? Thatâ€™s the question our editors seek to answer with this valuable guide.
What Is A Power Supply, And What Does It Do?
Power supplies (often referred to as “switching power supplies”) use switcher technology to convert the AC input to lower DC voltages. The typical voltages supplied are:
The 3.3-volt and 5-volt types are typically used for digital circuits, while the 12-volt is used to run disk drive and fan motors. The main specification of a power supply is in watts. A watt is the product of the voltage in volts and the current in amperes or amps.
The switching power supplies used today are smaller and lighter than their predecessors. They convert the 60-Hertz (Hz, or cycles per second) current to a much higher frequency, meaning more cycles per second. This conversion enables a smaller, lightweight transformer to do the actual voltage step-down from 110 volts to the voltage needed by an individual computer component. The higher-frequency AC current provided by a power supply is also easier to rectify and filter compared to the original 60-Hz AC line voltage. This reduces the variances in voltage going to the sensitive electronic components of a PC.
Recently, the industry has settled on using ATX-based power supplies. ATX is an industry specification that means the power supply has the physical characteristics to fit a standard ATX case and the electrical characteristics to work with an ATX motherboard.
In a personal computer (PC), the power supply is the metal box usually found in a corner of the case. The power supply is visible from the back of many systems because it contains the power-cord receptacle and the cooling fan.
Power Supply Problems
The PC power supply is probably the most failure-prone item in a personal computer. It heats and cools each time it is used and receives the first influx of AC current when the PC is switched on. Typically, a stalled cooling fan is a prelude to power supply failure due to subsequent component overheating. All devices in a PC receive their DC power via the power supply.
A typical failure of a PC power supply is often noticed because of the burning smell just before the computer shuts down. Another problem can be the failure of the vital cooling fan, which prevents power supply components from overheating. Failure symptoms include random rebooting or failure in Windows for no apparent reason.
For any problems you suspect to be the fault of the power supply, use the documentation that came with your computer. If you have ever removed the case from your personal computer to add an adapter card or memory, you can change a power supply. Make sure you remove the power cord FIRST, since voltages are present even though your computer is off.
Get Familiar with Power Supply Lingo
When you buy a PC or replacement power supply, you should be familiar with the power supply itself. Learn everything you can about it. Here we define a few of the more common terms and values found in power supply Spec Sheets.
- Mean Time Between Failures (MTBF) or Mean Time To Failure (MTTF).
This value represents the calculated average total hours that the power supply is expected to perform for before it fails. Although power supplies will have MTBF ratings of 100,000 hours or more, be aware that these figures are rarely discerned from actual real-time testing. Most manufacturers determine these totals based upon the comparative failure rates of the power supply’s individual components.
- Overvoltage Protection.
Overvoltage Protection is a feature that prevents an electrical signal from being received if the voltage exceeds a certain safe amount. This helps prevent an electrical device from being overloaded possibly destroyed. Make sure the power supply you purchase includes Overvoltage Protection.
- Maximum Load Current.
Maximum load current is the greatest amount of current (expressed in amps) that can safely be delivered through a particular output. Maximum load current values are represented as individual amperages for each output voltage. With these figures, you can calculate the total amount of power the power supply can safely provide and how many devices using those various voltages it can support.
- Minimum Load Current.
This rating is the reverse of maximum load current. Minimum load current is the smallest amount of current (in amps) that must be drawn from a particular output in order for that output to function. If the current drawn from an output falls below the Minimum Load Current, the power supply could shut down automatically or even be damaged.
- Load Regulation.
When the current drawn from a particular output increases or decreases, the voltage changes slightly as well, usually increasing as the current rises. Load regulation is the percent change in output voltage as the load is changed from minimum to maximum, assuming a constant line and constant temperature. The load change may be other than no load to full load. For example: The load regulation could be given for 20% load to 100% load capacity.
The efficiency of a power supply is calculated by the ratio of the amount of power the supply draws to the amount of power the supply provides. This value is expressed in percentile. Be sure to purchase a power supply that falls within an acceptable range – the higher, the better! Greater efficiency translates to less heat inside the computer, which is always something to strive for. It is important to note that precision, stability, and durability are more important factors.
- Advanced Power Management (APM)
Advanced Power Management (APM) offers a set of five different states that your system can be in. It was developed by Microsoft and Intel for PC users who wish to conserve power. Each system component, including the operating system, basic input/output system (BIOS), motherboard and attached devices all need to be APM-compliant to be able to use this feature. Should you wish to disable APM because you suspect it is using up system resources or causing a conflict, the best way to do this is in the BIOS. That way, the operating system won’t try to reinstall it, which could happen if it were disabled only in the software.
- Power Supply Wattage
A larger supply may be needed if you use every available slot on the motherboard or every available drive bay in the personal computer case. It is not a good idea to have a 250-watt supply if you have 250 watts total in devices, since the supply should not be loaded to 100 percent of its capacity. A 400-watt switching power supply will not necessarily use more power than a 250-watt supply.
How Much Power Do I Need?
As you check out power supplies on our website, you will notice these products come in a number of wattage designations. How much power is necessary for the â€œaverageâ€ PC system depends on what you are going to use it for. A standard power supply from a respectable computer manufacturer is about 250- to 350W, and probably of average quality. Thatâ€™s more than enough for an average system consisting of a hard drive, an optical drive and a fair graphics card. If you are going to add more peripherals, you need to seriously consider upgrading your electrical capabilities.
The More Watts the Merrier
The fan that cools your power supply has to be a much larger job than the rest of the air coolers in your computer. This makes it one of the biggest, noisiest fans in your PC. If you opt for a higher-end power supply, you are going to notice that it produces significantly less noise. A newer, more efficient and power supply will deliver more power regulated evenly. It will operate at a reduced noise level as well. Some of the more expensive barebones PC models do not come with a power supply, which gives you the opportunity to choose your own. If you’ve added a lot of new components to your PC, you may be overtaxing your existing power supply, so look at getting a bigger, better one. Reputable manufacturers will typically include a chart of acceptable components.