Sign in with
Sign up | Sign in
Your question

PSU Basic Knowledge

Last response: in Components
Share
a b ) Power supply
December 22, 2008 9:00:38 PM

Hello Everyone,

Antec would like to announce that we will try to increase our customer service by becoming a forum member.

With that said, we would like to provide you with information on PSU Basic Knowledge. Thanks for your support.


Q:What is Universal Input?


A:Universal Input means that the power supply (PSU) can be used in any country around the world, with any input voltage from 90~240VAC, without adjusting an input power selector switch.[/b]

Q:What is Active PFC and what are the benefits?

A:Without Power Factor Correction (PFC), the normal power factor for a PSU is less than 0.6, which makes it more difficult for the power plant to distribute electricity. Passive PFC can boost the power factor to around 0.7, but that is not a significant improvement. Active PFC can achieve 0.99 and increase the efficiency of the power plant 40%. This is very important in an environmental friendly era.

Q:What is the purpose of electromagnetic interference (EMI) filtering in a power supply?

A:An EMI filter is a required circuit for a PSU. The better the PSU, the better its EMI filter will be designed. The filter’s first job is to prevent the PSU noise from interfering with other electronic devices. Second, it prevents electromagnetic noise from the power grid and other devices from getting into the PSU. When using a bad PSU, there can be “snow” on the monitor and any nearby TV, or there may be static on the radio.

Q:What are Double Forward Converter circuits and their benefits?


A: Double Forward is the current mainstream of PSU design. It is has many advantages such as high efficiency, low failure rate and high Wattage. The design that it replaced is called Half-bridge. The old design had the advantage of low cost, but the wattage and efficiency could not be improved. Only low end systems are still using Half-bridge design.

  • When the circuit is off, each transistor is subject to half the load present in older designs.
  • When the circuit is goes into its off-state, leakage inductance spikes are clamped.

    Q:What are the benefits of Double Layer circuit board design?

    A: Double Layer has several benefits. The only drawback is higher cost.
  • An increase in copper foil area decreases loss in current flow.
  • Makes printed circuit board (PCB) layout easier and components can be arranged better.
  • Fewer jumpers, faster component insertion and easier board assembly.
  • Prevents solder cracking when using heavy components.
  • Better EMI performance.

    Q:For an induction coil, what is the effect of the cross-sectional area of the copper cable?


    A:Coils are measured by inductance. For two coils with the same inductance, it is better to use thicker wire. And with the same wattage, it is better with larger adaptor, larger induction coil or larger copper wire.

    Q:Is the capacitor an important factor to the life circle of PSU?

    A:Capacitors are probably the single most critical component. Using high capacity, high voltage ratings, and low ESR capacitors can greatly improve the PSU life circle. Selecting components with high heat ratings will also enhance the longevity of the unit. Some of the best quality components are of Japanese manufacture.

    Q: Does the temperature inside the PSU affect the output efficiency and life circle?


    A:Temperature greatly affects the life circle of many components, such as capacitors, resistors, fans, etc. If the temperature increases 10°C, the PSU’s lifetime will decrease by half. For example, if an output capacitor normally has a 3000 hours lifetime at 105°C; then at 95°C it can work 6000 hrs; and 96000 hours at 55°C. For efficiency, it is a different situation. Some components have higher efficiency at low temperature and some perform better when hot. For example, metallic oxide semiconductor field effect transistors (MOSFET) have higher efficiency at lower temperatures.

    Q:What are the differences between DC to DC circuit and general Magnetic Amplifier Circuit?

    A: DC to DC is going to be the main stream for future high-end PSU, and has the following benefits:
  • Since all of the 12 volt rails and other independent voltages ultimately start from a single 12V power supply, the min. load of 12V, 5V and 3.3V can be very small or zero. Because there is no min. load, it will not cause compatibility issues in different systems. Since 5V and 3.3V are transferred from 12V, there are always indirect load to 12V from one of each.
  • Antec has many power supplies designed with a main 12V core that gets broken out for separate rails. Since all power in our DC to DC design flows from the primary 12V core, all of the voltage rails can share from the same input pool of current for an optimal distribution of power at all times and across all voltages.
  • The DC to DC module uses low voltage MOSFET transistors which have low on-state loss. When transforming 12v to 5v or 3.3v, Magnetic Amplifier Circuits have 70 – 80% efficiency, but DC to DC can reach 90% or higher. It is more environmental friendly.


    Q:How is a pulse-width modulation (PWM) fan quieter than a regular fan?

    A: PWM fans can run from 15% to 100% of their maximum speed. However, a traditional voltage control fan can only run from 35% to 90% of its maximum speed. Using a PWM fan and running the PSU at 50% load or less, the PSU will be much quieter. Any power supply running at high load will need to run its fan at high speed and will be audible.

    Q:What is synchronous rectification and what is its effect on the overall efficiency of the PSU?


    A:Synchronous rectification uses low voltage MOSFETs instead of a general rectifier, so its on-state resistance is lower. Synchronous rectification has lower loss so less heat is generated and efficiency is improved.

    Q:What is the effect of using DC to DC on the output voltages?


    A:The working frequency of a DC to DC voltage regulator module (VRM) is much higher than a Magnetic Amplifier Circuit. That means a DC to DC circuit can provide transient response times as low as 10 microseconds on rails controlled by the VRM. That’s a hundred times faster than standard power supply response times of 1 millisecond (1000 microseconds). This makes the output voltage more stable on the 5v and 3.3v rails, even if the load changes rapidly, and helps protect sensitive components.

    Q:Are multiple +12V outputs PSU more stable and reliable than single +12V output PSU?

    A:Multiple +12V outputs are mainly used for safety protection. Each output keeps the current within a safe range. Single +12V output is an old design; it is used to avoid wrong activating of protection circuit by mass power consuming from video card. However, it is very dangerous, because when short happens in any component; there will be no over-current protection. It is easy to cause fire, so Antec’s PSUs use multiple +12V outputs to avoid this danger. Some companies try to perpetuate a myth that power can be “trapped” on a rail. That’s just wrong. Each rail has its own circuitry for the protection of the PSU and the devices connected to it, but there’s no way one rail can limit the total power available on the others.

    Q:In regards to the size of DC output cable, is bigger always better?


    A:Basically, yes. However, there is still a cost/performance value which should be met and there are also electrical limitations of other components in your computer. Where larger amounts of current are required by components such as graphics cards, multiple wires tend to be used instead of one huge wire. One of the reasons for that has to do with how much current can flow into a motherboard or other printed circuit board at a single point. You gain more contact surface area for lower resistance and more connectors increase reliability of the connection due to redundancy.

    Q:What is the 80 PLUS® standard?


    A:From the 80 PLUS website, the 80 PLUS program is a unique forum that unites electric utilities, the computer industry and consumers in an effort to bring energy efficient technology solutions to the marketplace.
    The 80 PLUS standard has four classes: Standard/Bronze/Silver/Gold. Below is the information table. The basic principle is the efficiency must be at least 80% when the PSU is running at 20% load or higher.

    Fraction of Rated Load 20% 50% 100%
    80 PLUS 80% 80% 80%
    80 PLUS Bronze 82% 85% 82%
    80 PLUS Silver 85% 88% 85%
    80 PLUS Gold 87% 90% 87%

    Q:Is dual PCB better than single PCB?

    A:Yes. Dual PCB designs have more flexibility to arrange components and create an efficient air flow. Compared to single PCB, it will have better cooling efficiency.

    Q:How do I pick a good PSU?

    A:It is not easy for a general user to judge if a PSU is good or not. Here are some principles.
  • Choose a well-known brand.
  • Has the PSU passed safety certifications?
  • Is the wattage number the value for peak output or continuous output? Continuous is better.
  • Compare the weight with other similar products to see if it is too light.
  • (Not suitable for passive PFC power supply)
  • Compare the internal components, if they have size difference.
  • Does the PSU have the 80 PLUS certification.

    Q:What is the meaning and differences of working temperature of a PSU?

    A:Generally the working temperature of PSUs in the market is around 25℃ (environmental temperature). However, inside a case, because of CPU and video card, the temperature is usually higher than 25℃ (environmental temperature).

    Q:Why is Antec’s Signature PSU more expensive than other companies’ products?


    A:Antec started to design this series based on server standards, and then went beyond. All the components are the best choices and we also added many new designs seen here for the first time in a consumer power supply. The highest quality components. Insane levels of craftsmanship. Brilliant design. Cutting edge features. Put all of that together and you have the power supply equivalent of a high-end race car. Car companies build race cars in order to push automotive technology to new heights. Tough reviewers have noted that the Signature excels in absolutely every aspect of performance, and several reviewers have said that they have never seen a better PSU, ever. It’s also built to last; at 50℃ and running 24 hrs. at full load, we guarantee it for five years. Based on performance, this is not an expensive PSU. Think of it as a race car that you can afford!

    Q:Why are there so many models of PSU with the 80 PLUS label when there aren’t anywhere near that many power supplies listed on the 80 PLUS website?


    A:To avoid fake certification, please check with the 80 PLUS official website to see if the products are on the certificate lists or not.

    1.Some companies will also change the hardware design to pass the certification, and then the products they send to market don’t meet the standard. Here are some of the tricks:

  • Cable length of test unit is shorter than the real product.
  • Thicker wires are used for testing. After passing the test, the design is changed.
  • Better electronic components are installed in the units sent for testing (or units are tested and hand-picked).
  • Use better fans and heatsinks or adjust the fan voltage in the cooling system.
  • Change EMI design or add jumper under it.

    2.It is really difficult for users to determine the internal design. The best way to choose is to select a well-known brand, do comparisons and read reviews.
  • More about : psu basic knowledge

    December 22, 2008 9:17:44 PM

    BRILLIANT POST, FINALLY A VAILD PERSON TO TALK ABOUT PSU's :)  Dear Sir, I would dare to suggest to add one more thing - explain split rails and true rails and also get into the modular design a bit more.This will complete the quizz. THANK YOU !

    THIS SHOULD BE A STICKY POST !
    a b ) Power supply
    December 22, 2008 9:20:13 PM

    Thanks for the great feedback and suggestion kenzz0, it's always appreciated.
    Related resources
    a b ) Power supply
    December 22, 2008 10:45:56 PM

    Taken From PC Power and Cooling Website:

    1. DOES A POWER SUPPLY UPGRADE MEAN A HIGHER ELECTRIC BILL?

    This is the biggest myth of all. First, it's important to understand that a power supply only delivers the power that's needed by the system, nothing more. If your PC currently has a 400W supply and the system needs 350W, it will still need and use only 350W - if the only change is upgrading to a 500W power supply (the upgrade makes sense since there are many advantages to running a power supply at a lower percentage of its rated capacity). Whether the electric bill goes up or down is solely determined by the efficiency of the new power supply. Greater efficiency means a lower electric bill because more of the AC power is converted into DC for the computer, rather than wasted as heat. The savings can really add up over time. For example, when the money saved in electricity over the course of its 3-year warranty is taken into account, the purchase price of the efficient Silencer 750 is less than $0.00. Here's the math:
    Model Efficiency @ 550W Input Power @ 550W
    Silencer 750W 83% 662W
    Standard 550W 73.8% 745W

    For the same output power, the Silencer 750 uses 83W less input power.

    3-year savings = .083KW x $0.10/KWH x 24 x 365 x 3 = $218.12

    2. DON'T BE MISLED BY EXAGGERATED WATTAGE CLAIMS

    To properly compare power supplies, wattage claims must state the maximum ambient temperature for continuous, full-load operation. Unfortunately for the consumer, this information is usually withheld, opening the door for manufacturers to exaggerate their wattage claims. They do so by assuming an unrealistic ambient temp of only 25°C (77°F), even though the actual internal power supply temp is at least 40°C (104°F). Since the proper full-load rating is 15°C higher for home use and 25°C higher for industrial use, these power supplies produce 33%-50% less power than their advertised ratings. See the derating chart on the right.

    Elevated Temperature Testing
    wattage comparison
    Turbo-Cool 510 spec: full load @ 50°C.
    "500W" Home PSU spec: full load @ 25°C, no load @ 70°C.

    3. DON'T LOSE POWER WITH MODULAR PLUGS

    Due to their look, convenience, and cost savings for manufacturers, modular plugs have become a popular power supply feature. Unfortunately, there has been little or no discussion of the impact of this feature on overall performance and reliability. The fact is, modular plugs limit power by adding to electrical resistance. The voltage drop can be as much as would occur in 2 feet of standard wire. Worse yet, modular plugs utilize delicate pins that can easily loosen, corrode, and burn, creating the potential for a major system failure. That's why professional system builders specify uninterrupted wire!

    4. MARKETING MYTH vs. WARRANTY REALITY

    As with all consumer products, the fine print in the warranty will often contradict a manufacturer's marketing hype. Unfortunately, this is especially true for computer power supplies. Take for example this quote direct from the product box of a leading manufacturer: "we've earned a stellar reputation for producing stable, reliable, industrial-grade PC power supplies". Now compare that statement to what is specifically excluded in the company's "legendary 3-year warranty":

    Sample of What is NOT covered -

    a. commercial and industrial use
    b. wear and tear from moving parts
    c. that the product will meet your requirements.

    In conclusion, don't be mislead by marketing hype, avoid superficial gimmicks, and read the warranty carefully before purchasing your next power supply.

    5. AN SLI CERTIFIED POWER SUPPLY WILL ALWAYS POWER HIGH-END GRAPHICS CARDS?

    We went through three power supplies before we found one that consistently worked with these high-end graphics cards and an FX-60. We initially started with a Silverstone 600W SLI certified power supply, but running some games resulted in the system powering down under full load. We next moved onto a higher rated Thermaltake PurePower SLI certified 680W unit. But while most games ran most of the time, the system would still occasionally shut down. Finally, we ended up using PC Power and Cooling's massive TurboCool 850 SSI. This just goes to show that if you really want to build something that pushes the bleeding edge, make sure you have the right power supply.

    ExtremeTech Review Feb 12, 2006

    6. SHOULD AN ATX POWER SUPPLY BE COOLED WITH A 120MM FAN?

    Most low-noise ATX power supplies today utilize a top-mounted 120mm fan rather than a rear-mounted 80mm fan. The 120's favorable reputation is based on the fact that under low to medium load conditions, the 120mm fan provides sufficient cooling at low RPM and low RPM fans are generally very quiet.

    However, problems occur with this design when the load exceeds 50%-60%. Because the 120mm fan consumes about 1.5" of vertical space inside the PSU, heat sinks, capacitors, and other components are about 30% smaller in height compared to a PSU with a rear-mounted fan. The smaller parts can handle less current, so the maximum power available with the 120mm design is limited. And, because the heat sinks have less surface area, more air flow is needed with this design to keep the thermal situation under control. With 80%-100% load, the 120's fan speed can double and the noise level can jump by up to 20dB.

    In conclusion, for systems that require more than 50% of the power supply's capacity, a well-engineered PSU with a rear-mounted 80mm fan will provide superior performance and reliability (due to larger components) at a noise level comparable to a PSU equipped with a 120mm fan.

    7. ARE TWO POWER SUPPLY FANS BETTER THAN ONE?

    No. A power supply with two fans doesn't exhaust any more air from the case than a power supply with one. That's because due to space limitations, only one fan can be used for exhaust, while the other is limited to spot cooling. Possible explanations for a 2-fan PSU include: thermal engineering problems; an attempt to exaggerate the wattage rating by spot cooling the transformer; or an attempt by the marketing department to create a new gimmick.

    8. ARE MULTIPLE 12-VOLT RAILS BETTER THAN A SINGLE 12-VOLT RAIL?

    With all the hype about multiple 12-volt rails (ads claim that two rails is better than one, five is better than four, etc.), you'd think it was a better design. Unfortunately, it's not!

    Here are the facts: A large, single 12-volt rail (without a 240VA limit) can transfer 100% of the 12-volt output from the PSU to the computer, while a multi-rail 12-volt design has distribution losses of up to 30% of the power supply's rating. Those losses occur because power literally gets "trapped" on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system.

    Since the maximum current from any one 12-volt rail of a multiple-rail PSU is limited to 20 amps (240VA / 12 volts = 20 amps), PCs with high-performance components that draw over 20 amps from the same rail are subject to over-current shutdowns. With power requirements for multiple processors and graphics cards continuing to grow, the multiple-rail design, with its 240VA limit per rail, is basically obsolete.

    PC Power and Cooling is once again leading the industry. All of our power supplies now feature a large, single 12-volt rail. The design is favored by major processor and graphics companies, complies with EPS12V specs (the 240VA limit is not a requirement) and is approved by all major safety agencies such as UL and TUV.3

    http://www.pcpower.com/technology/myths/#m8
    December 22, 2008 11:04:58 PM

    Quote:
    With all the hype about multiple 12-volt rails (ads claim that two rails is better than one, five is better than four, etc.), you'd think it was a better design. Unfortunately, it's not!

    Here are the facts: A large, single 12-volt rail (without a 240VA limit) can transfer 100% of the 12-volt output from the PSU to the computer, while a multi-rail 12-volt design has distribution losses of up to 30% of the power supply's rating. Those losses occur because power literally gets "trapped" on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system.

    Since the maximum current from any one 12-volt rail of a multiple-rail PSU is limited to 20 amps (240VA / 12 volts = 20 amps), PCs with high-performance components that draw over 20 amps from the same rail are subject to over-current shutdowns. With power requirements for multiple processors and graphics cards continuing to grow, the multiple-rail design, with its 240VA limit per rail, is basically obsolete.


    FALSE - MARKETING MESSAGE

    Quote:
    PC Power and Cooling is once again leading the industry. All of our power supplies now feature a large, single 12-volt rail


    The truth lies behind on how the PSU is actually built - true multirail or split multirail
    The true multirail power supplies are actually the best solution because the power distribution is optimized, having different curent capabilities for the computer requirements eg : 15A for mainboard, CPU voltage regulator etc and 40A for the video cards - two completely diferent 12V rails with different power outputs and independent voltage regulators.
    I guess PC P&C is trying to keep costs down feeding marketing rumours between customers. BUILDING A REAL GOOD POWER SUPPLY IS AN EXPENSIVE ART AND THERE ARE NOT MANY ARTISTS IN THIS INDUSTRY ;) 
    December 23, 2008 3:44:18 AM

    "A:Multiple +12V outputs are mainly used for safety protection. Each output keeps the current within a safe range. Single +12V output is an old design; it is used to avoid wrong activating of protection circuit by mass power consuming from video card. However, it is very dangerous, because when short happens in any component; there will be no over-current protection."

    Taken from http://www.hardwaresecrets.com/article/553: On the PC Power & Cooling S75CF 750W test review. A single rail PSU.

    available on the othersProtections: over current (OCP, tested and working)

    http://www.jonnyguru.com/forums/showthread.php?t=3990

    In most cases, multiple +12V rails are actually just a single +12V source just split up into multiple +12V outputs each with a limited output capability.

    The only "problem" the occurs with multiple +12V rails is that when a +12V rail is overloaded (for example: more than 20A is being demanded from a rail set to only deliver up to 20A), the PSU shuts down. Since there are no "limits" on single +12V rail PSU's, you can not overload the rails and cause them to shut down..... unless you're using a "too-small" PSU in the first place. Single +12V rails do not have better voltage regulation, do not have better ripple filtering, etc. unless the PSU is better to begin with.

    There are a few units that actually have two +12V sources, but these are typically very high output power supplies. And in most cases these multiple +12V outputs are split up again to form a total of four, five or six +12V rails for even better safety. To be clear: These REAL multiple +12V rail units are very rare and are all 1000W+ units (Enermax Galaxy, Topower/Tagan "Dual Engine", Thermaltake Tough Power 1000W & 1200W, for example.)


    different rails, which doesn’t make sense as they aren’t used at the same time (maybe there is one or two extremely high-end motherboards that do, but they are the exception, not the rule).

    If you had a power supply with split +12V rails and powered your TEC's with Molexes, you would be putting your TEC's on the same +12V rail as the hard drives, optical drives, fans, CCFL's, water pump.. you name it, just as you did with the Molex to PCIe adapters. The power supply could, essentially, shut down on you in the middle of using it. A power supply with a single, non-split, +12V rail would not have any kind of limit as to how much power is delivered to any particular group of connectors, so one could essentially run several TEC's off of Molex power connectors and not experience any problems if one had a single +12V rail PSU

    The only "problem" the occurs with multiple +12V rails is that when a +12V rail is overloaded (for example: more than 20A is being demanded from a rail set to only deliver up to 20A), the PSU shuts down. Since there are no "limits" on single +12V rail PSU's, you can not overload the rails and cause them to shut down..... unless you're using a "too-small" PSU in the first place. Single +12V rails do not have better voltage regulation, do not have better ripple filtering, etc. unless the PSU is better to begin with.

    The bottom line is, for 99% of the folks out there single vs. multiple +12V rails is a NON ISSUE. It's something that has been hyped up by marketing folks on BOTH SIDES of the fence. Too often we see mis-prioritized requests for PSU advice: Asking "what single +12V rail PSU should I get" when the person isn't even running SLI! Unless you're running a plethora of Peltiers in your machine, it should be a non-issue assuming that the PSU has all of the connectors your machine requires and there are no need for "splitters"
    !