- Joined
- Apr 22, 2005
- Location
- A Labyrinth
*Update, see notes at end and messages throughout this discussion.
Why do I care about Dual Rail and which PSUs are the best. I've seen a lot of questions concerning multi-rail PSUs, drooping and what's nest to buy. I decided to write this technical brief on PSUs based 2005 systems from years of knowledge in DC and AC electronics. My hope is that although more on the techinical side than most care about, you will be able to choose a great power supply for the Dream system and get better OC from it.
The magazines state look for the heavy PSUs and expect to pay a little more for a good one. This is true and I'll explain the inner reason in a minute. While you may see a lot of resemblance between different units they can vary significantly. There's only so many semiconductor, inductors and fans available and you may see the same parts on cheap PSUs as you see on expensive ones. That is why you have to research a little to find what you really need. If you are using old P3s, Slot or Socket A equipment then you can probably just get a decent 350Watter and run till the insulation falls of the wiring. However if you are running P4 prescotts, A64s and/or SLI then what you put in as a power source is going to mean the differece between Tinker and Overclocker.
The Nature of PSUs.
No all PSUs are not created equal! Naturally, most expensive PSUs uses more components, heavier transformers/coils and bigger heatsinks. Quality does also play in as well which will also drive up cost. Unlike mobos and slot cards, PSUs reguire more manual labor to place and solder components. It's not a task that robots can pick, place and wave solder to a board. Wires have to be run and large components have to be connected. This all drives up the cost we have to pay. Cheaper ones reduce the component sizes and filters circuits used to regulate the current arriving at you V-modds and overclocked CPUs. To do it right, it takes heavy transformers, chokes, capacitors and MOSFETs to deliver/
Transfomers, Coils and Chokes
These are the voltage converters and energy storage. Starting from house current at 120 or 240 volts, a isolation/stepdown transformer usually converts the voltage down a lower voltage from 25 to 50 volts. The I/S transformer also provides current isolation should something short. Without it, a direct short could send house current of 20 or more amps at 120volts blowing your chips all over the inside of the case. Most of the newer PSUs are replacing the primary transformer with a choke which provides the current isolation but eliminates the voltage step down. A Choke being a coil of wire on an iron or ferite core will only allow the amount of current defined by the wire gauge to flow through. Just like comparing a fire hose to your garden hose, which one do you want for putting out fires and which one to water your flowers with. Coils and chokes also store energy and lessen the effect of power surges and spikes as well as assist in voltage regulation. The larger the transform or coil the more energy it stores and this stored energy will determine if you OCed processor will run or crash when pushed. This is one of the differences I've seen in the better power supplies; they all have large coils and transformers in them. By far PC-Power&Cooling has such a largest transformers and coils in their units. So large that it looks like the airflow is blocked in reality, the air forced to pass around coils and closer to the heatsinks providing better cooling.
Phase Locked Loop (PLL)
These circuits, most are on chip, are the voltage watch dogs that monitor the voltage and bark louder if the voltage drops to increase current. This PLL is running as a voltage controlled pulse width modulator in PSUs. You would find one for each voltage supplied and each rail in multi-rail power supplies. What these low power but tight controlling voltage coupled oscillators do is respond to current demands in your PSU width differnt pulse widths. These PLLs are what drive the MOSFETs by switching on long enough to allow enough current through to maintain a predetermined voltage. When demand is low, the on times will be short. As current demand increases, the on-time will widden to allow more current through to keep up the voltage. This is where the term Phase Locked Loop comes from. The PLL is locked in step with current demand staying in tight control of voltage. The better quality supplies are very responsive to these fluctuations and will hold tight voltages.
MOSFETs
Theses are the providers of current. Their purpose is take the incomming voltage and provide for the current demand. This is where the term "switching power supply" comes from. The PLLs are sinaling the MOSFETS to turn on and off at the right intervals to supply the right amount of current to maintain tight voltages. Earlier I talked about transformers and chokes and how they transform voltage and current depending on circuit design. Due to the huge power demands it's important that these MOSFETs get the power they need to be able to deliver to the demands of ever more power hungry CPUs and GPUs. How MOSFETs are so effective in power regulation is that they use a low power signal from the PLLs and respond by switching large volumes of current at high speeds. You can search "Metal-Oxide Semiconductor/Field-Effect Transistor" for what these little beasts are and how they work. In our PSUs they act like a large dam holding back water with a valve that is easy to open and close, and it can be done quickly. The height of the dam represents the voltage the amount that can flow through the valve is the current. This height represents potential, the higher the level the greater the potential and the ability to supply for demands of current. This ability to respond to high current demands is why 12 Volts is used to provide power to your CPU. At 5 Volts the dam is not high enough to create enough pressure to respond when current demand increases and voltage suffers by drooping. The side effect to these higher voltages and increased current is heat generation. Good fans and headsinks are going to mean longer life and less of a possiblity of MOSFET failures. They are tough but subject to thermal breakdown at high temps.
Capacitors
Caps, short for capacitors store energy just like a battery but for shorter duration and faster cycles. With the MOSFETs being switched on and off by the PLL circuit, the power coming through is choppy. This is where the Caps come into play to filter or reduce this chop or ripple to a smooth even voltage. It's quite simple, they store energy during peaks and release it during valleys. The larger capacitors are the better they perform, skimping here will reduce the OC-ability of your system and stress components by allowing this ripple through.
Dual Rails
What a Dual Rail PSU provides is 2 seperate 12V power circuits. This really helps when dealing with A64 (X2 and FX ) and Prescott CPUs along with SLI video cards. Dual rail allows the CPU to run on one rail while the rest of the system uses the second rail. This isolates the heavy surge demands of the cpu from the load of drives and video cards. Drives do add to demand but the largest surge they create is during startup when the rest of the circuits are held asleep by the MOBO reset system. Video cards are starting to create heavier demands but they still don't come close to the power a cpu draws in bursts. These CPUs today can gobble up huge amounts of current flatline earlier PSUs with single rails and lower current. This current demand gets Ber with higher frontside busses, memory bandwidth and OCing the multiplier. This is due to the fact you are pushing circuits to switch at extemely high rates and this act of switching is causing these surges on the PSU that will affect any components in the same rail. A dual rail 450watt PSU should perform as good as a 500 to 550 watter since the it has the high demand seperated from the heavy load. The above average computer OCed is drawing in the 150 to 200 watts of continuos power it's the surges that are creating the need for hugher wattages. If you also note that the efficiency number is about 75% on good PSUs. This means that 125 watts of a 500 watter is lost to heat, filtering and regulation leaving you with 375 watts of power. But lets face it, the little used -12v line is wattage not available. The 3.3 and 5 volt rails are less used so thats close to half the total wattage not available to the important 12 volt supply. What you typically end up with is 225 to 350 watts on the 12volt rail(s). I've seen 50 watt swings on a P4C and 120watts running. With most of the demand on the 12volt rails, I might be looking at 100 to 125 watts to spare. This spare is important because of the swings the power supply needs more headroom to absorb the swings and keep the voltages inside tolerance. Think of dual rails as garden hoses and spigots. Hook up 2 pulse sprinklers with 2 hoses and one of those Y adaptors with a 3rd hose and trigger head on the end. Hook this to a single spigot and turn the water on with the trigger head closed and the sprinklers should have good pressure and covering distance accross the yard. Next take the trigger head and start washing the car and watch what happens to the sprinklers as you squeeze and release the trigger. Now move the 3rd hose to a seperate spigot and repeat the test. Now using the 3rd hose will have little or no effect on the sprinklers. You have a choice bigger spigots or more spigots.
Closing words
PSUs are getting better and good ones are becoming more mainstream driving down prices. If you re OCing PSU you will need a good to best quality PSU with good fans to improve it's ability to perform. Just like you would'nt wear a parka cutting grass in the summer, don't smother your PSU with wires or poor airflow.
*Updated Notes on this origional topic. Due to a inaccurate number from the intel 800 group of dual processors and what I also learned from other people weeks after this thread was posted a number of Chips will shut down some of the dual-rail PSUs. My original calulations were from Extreme and 800 dual Intel CPUS was far below the actual numbers some OCer are seeing. My origional number for Intel Prescotts, was about 150 watts, but from later findings this number exceeded 200 watts and would flatline the 16 to 18 amp rails on most PSUs. This may also apply to other Prescott and newer CPUs that are being pushed up to 4 and 5GHZ, units on Phase Change cooling and all Duals. This will also mean Xeons, Itaniums and Optirons that hit these high wattages are included in the "Get A Bigger PSU" crowd. For these chips you will need more than 20 amps on the rail that the CPU is on. This will mean a high wattage PSU whether it is single or dual rail starting at 550 or better. Unfortunately it looks like CPU power is exceeding what the PSU makers are putting on the market faster than they can update the power throughput.
I didn't mention AMD Athlon CPUs for the fact most are well under 150 watts AMD did an excellent job of producing a fast and efficient CPU. If you manage to get more than 175watts through your Athlon 64/X2 then you will also have to do a little more looking to find a beefier PSU.
Based on knowledge and reading by Alabama Cajun June, 2005.
Why do I care about Dual Rail and which PSUs are the best. I've seen a lot of questions concerning multi-rail PSUs, drooping and what's nest to buy. I decided to write this technical brief on PSUs based 2005 systems from years of knowledge in DC and AC electronics. My hope is that although more on the techinical side than most care about, you will be able to choose a great power supply for the Dream system and get better OC from it.
The magazines state look for the heavy PSUs and expect to pay a little more for a good one. This is true and I'll explain the inner reason in a minute. While you may see a lot of resemblance between different units they can vary significantly. There's only so many semiconductor, inductors and fans available and you may see the same parts on cheap PSUs as you see on expensive ones. That is why you have to research a little to find what you really need. If you are using old P3s, Slot or Socket A equipment then you can probably just get a decent 350Watter and run till the insulation falls of the wiring. However if you are running P4 prescotts, A64s and/or SLI then what you put in as a power source is going to mean the differece between Tinker and Overclocker.
The Nature of PSUs.
No all PSUs are not created equal! Naturally, most expensive PSUs uses more components, heavier transformers/coils and bigger heatsinks. Quality does also play in as well which will also drive up cost. Unlike mobos and slot cards, PSUs reguire more manual labor to place and solder components. It's not a task that robots can pick, place and wave solder to a board. Wires have to be run and large components have to be connected. This all drives up the cost we have to pay. Cheaper ones reduce the component sizes and filters circuits used to regulate the current arriving at you V-modds and overclocked CPUs. To do it right, it takes heavy transformers, chokes, capacitors and MOSFETs to deliver/
Transfomers, Coils and Chokes
These are the voltage converters and energy storage. Starting from house current at 120 or 240 volts, a isolation/stepdown transformer usually converts the voltage down a lower voltage from 25 to 50 volts. The I/S transformer also provides current isolation should something short. Without it, a direct short could send house current of 20 or more amps at 120volts blowing your chips all over the inside of the case. Most of the newer PSUs are replacing the primary transformer with a choke which provides the current isolation but eliminates the voltage step down. A Choke being a coil of wire on an iron or ferite core will only allow the amount of current defined by the wire gauge to flow through. Just like comparing a fire hose to your garden hose, which one do you want for putting out fires and which one to water your flowers with. Coils and chokes also store energy and lessen the effect of power surges and spikes as well as assist in voltage regulation. The larger the transform or coil the more energy it stores and this stored energy will determine if you OCed processor will run or crash when pushed. This is one of the differences I've seen in the better power supplies; they all have large coils and transformers in them. By far PC-Power&Cooling has such a largest transformers and coils in their units. So large that it looks like the airflow is blocked in reality, the air forced to pass around coils and closer to the heatsinks providing better cooling.
Phase Locked Loop (PLL)
These circuits, most are on chip, are the voltage watch dogs that monitor the voltage and bark louder if the voltage drops to increase current. This PLL is running as a voltage controlled pulse width modulator in PSUs. You would find one for each voltage supplied and each rail in multi-rail power supplies. What these low power but tight controlling voltage coupled oscillators do is respond to current demands in your PSU width differnt pulse widths. These PLLs are what drive the MOSFETs by switching on long enough to allow enough current through to maintain a predetermined voltage. When demand is low, the on times will be short. As current demand increases, the on-time will widden to allow more current through to keep up the voltage. This is where the term Phase Locked Loop comes from. The PLL is locked in step with current demand staying in tight control of voltage. The better quality supplies are very responsive to these fluctuations and will hold tight voltages.
MOSFETs
Theses are the providers of current. Their purpose is take the incomming voltage and provide for the current demand. This is where the term "switching power supply" comes from. The PLLs are sinaling the MOSFETS to turn on and off at the right intervals to supply the right amount of current to maintain tight voltages. Earlier I talked about transformers and chokes and how they transform voltage and current depending on circuit design. Due to the huge power demands it's important that these MOSFETs get the power they need to be able to deliver to the demands of ever more power hungry CPUs and GPUs. How MOSFETs are so effective in power regulation is that they use a low power signal from the PLLs and respond by switching large volumes of current at high speeds. You can search "Metal-Oxide Semiconductor/Field-Effect Transistor" for what these little beasts are and how they work. In our PSUs they act like a large dam holding back water with a valve that is easy to open and close, and it can be done quickly. The height of the dam represents the voltage the amount that can flow through the valve is the current. This height represents potential, the higher the level the greater the potential and the ability to supply for demands of current. This ability to respond to high current demands is why 12 Volts is used to provide power to your CPU. At 5 Volts the dam is not high enough to create enough pressure to respond when current demand increases and voltage suffers by drooping. The side effect to these higher voltages and increased current is heat generation. Good fans and headsinks are going to mean longer life and less of a possiblity of MOSFET failures. They are tough but subject to thermal breakdown at high temps.
Capacitors
Caps, short for capacitors store energy just like a battery but for shorter duration and faster cycles. With the MOSFETs being switched on and off by the PLL circuit, the power coming through is choppy. This is where the Caps come into play to filter or reduce this chop or ripple to a smooth even voltage. It's quite simple, they store energy during peaks and release it during valleys. The larger capacitors are the better they perform, skimping here will reduce the OC-ability of your system and stress components by allowing this ripple through.
Dual Rails
What a Dual Rail PSU provides is 2 seperate 12V power circuits. This really helps when dealing with A64 (X2 and FX ) and Prescott CPUs along with SLI video cards. Dual rail allows the CPU to run on one rail while the rest of the system uses the second rail. This isolates the heavy surge demands of the cpu from the load of drives and video cards. Drives do add to demand but the largest surge they create is during startup when the rest of the circuits are held asleep by the MOBO reset system. Video cards are starting to create heavier demands but they still don't come close to the power a cpu draws in bursts. These CPUs today can gobble up huge amounts of current flatline earlier PSUs with single rails and lower current. This current demand gets Ber with higher frontside busses, memory bandwidth and OCing the multiplier. This is due to the fact you are pushing circuits to switch at extemely high rates and this act of switching is causing these surges on the PSU that will affect any components in the same rail. A dual rail 450watt PSU should perform as good as a 500 to 550 watter since the it has the high demand seperated from the heavy load. The above average computer OCed is drawing in the 150 to 200 watts of continuos power it's the surges that are creating the need for hugher wattages. If you also note that the efficiency number is about 75% on good PSUs. This means that 125 watts of a 500 watter is lost to heat, filtering and regulation leaving you with 375 watts of power. But lets face it, the little used -12v line is wattage not available. The 3.3 and 5 volt rails are less used so thats close to half the total wattage not available to the important 12 volt supply. What you typically end up with is 225 to 350 watts on the 12volt rail(s). I've seen 50 watt swings on a P4C and 120watts running. With most of the demand on the 12volt rails, I might be looking at 100 to 125 watts to spare. This spare is important because of the swings the power supply needs more headroom to absorb the swings and keep the voltages inside tolerance. Think of dual rails as garden hoses and spigots. Hook up 2 pulse sprinklers with 2 hoses and one of those Y adaptors with a 3rd hose and trigger head on the end. Hook this to a single spigot and turn the water on with the trigger head closed and the sprinklers should have good pressure and covering distance accross the yard. Next take the trigger head and start washing the car and watch what happens to the sprinklers as you squeeze and release the trigger. Now move the 3rd hose to a seperate spigot and repeat the test. Now using the 3rd hose will have little or no effect on the sprinklers. You have a choice bigger spigots or more spigots.
Closing words
PSUs are getting better and good ones are becoming more mainstream driving down prices. If you re OCing PSU you will need a good to best quality PSU with good fans to improve it's ability to perform. Just like you would'nt wear a parka cutting grass in the summer, don't smother your PSU with wires or poor airflow.
*Updated Notes on this origional topic. Due to a inaccurate number from the intel 800 group of dual processors and what I also learned from other people weeks after this thread was posted a number of Chips will shut down some of the dual-rail PSUs. My original calulations were from Extreme and 800 dual Intel CPUS was far below the actual numbers some OCer are seeing. My origional number for Intel Prescotts, was about 150 watts, but from later findings this number exceeded 200 watts and would flatline the 16 to 18 amp rails on most PSUs. This may also apply to other Prescott and newer CPUs that are being pushed up to 4 and 5GHZ, units on Phase Change cooling and all Duals. This will also mean Xeons, Itaniums and Optirons that hit these high wattages are included in the "Get A Bigger PSU" crowd. For these chips you will need more than 20 amps on the rail that the CPU is on. This will mean a high wattage PSU whether it is single or dual rail starting at 550 or better. Unfortunately it looks like CPU power is exceeding what the PSU makers are putting on the market faster than they can update the power throughput.
I didn't mention AMD Athlon CPUs for the fact most are well under 150 watts AMD did an excellent job of producing a fast and efficient CPU. If you manage to get more than 175watts through your Athlon 64/X2 then you will also have to do a little more looking to find a beefier PSU.
Based on knowledge and reading by Alabama Cajun June, 2005.
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