Page 1 of 2 12 LastLast
Results 1 to 10 of 16

Thread: +5VSB questions

  1. #1
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    1,038
    Thanks Thanks Given 
    2
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default +5VSB questions

    There are a few aspects of the +5VSB rail that I'm a bit confused on.

    #1. How is it generated? I know it's separate from the main +12V/+5V/+3.3V, but I don't know exactly how. It normally has its own primary transistor and transformer and rectifier. What's the topology used?

    #2. How much power do motherboards draw from the +5VSB when off? I can't imagine them pulling more than 1-2A just to charge the CMOS battery and save data in the CMOS RAM.

    #3. How efficient is the +5VSB, usually? How much does efficiency vary?

    Thanks
    It's my PSU in a box!
    Ooo-ooh,
    My PSU in a box, baby!

  2. #2
    Join Date
    Feb 2009
    Posts
    1,090
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

  3. #3
    Join Date
    Mar 2009
    Location
    Kalamazoo, Michigan
    Posts
    1,072
    Thanks Thanks Given 
    0
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    Usually only older or cheaper designs use a two transistor design to generate the 5vsb. Better quality models use a IC such as a LM339 or so to generate the 5vsb. This is much better as it provides more protections like overvoltage, overcurrent, etc... all on one chip. Some units may also use a topswitch to generate the 5vsb which is also very reliable and a good way to do it.

    On a basic level, it's essentially a psu within a psu. Whatever is used to generate that 5vsb sends a current (I'm not too into the technical ratings and everything of the workings of the 5vsb, so somebody else can elaborate further and more info) to the 5vsb transformer which outputs the 5vsb (among other things) which is usually rectified by a diode and then filtered by a CLC filter like any other output.

    Now, thats what I know. Somebody else probably knows more and probably knows better, and I'm probably wrong on one or more things.
    Last edited by 370forlife; 08-13-2010 at 02:10 PM.
    Quote Originally Posted by JFK
    The American, by nature, is optimistic. He is experimental, an inventor and a builder who builds best when called upon to build greatly

  4. #4
    Join Date
    Oct 2006
    Location
    jonnyGURU forums, of course!
    Posts
    15,516
    Thanks Thanks Given 
    502
    Thanks Thanks Received 
    46
    Thanked in
    36 Posts

    Default

    You pretty much nailed it. A PSU within a PSU is the best analogy you could use.

    Motherboards used to use very little +5VSB. It used to only be used to keep the BIOS CMOS charged up and keep features like wake on KBD, LAN, etc. aware. But recently, companies have put all of USB on the +5VSB. This is to allow USB keyboards, mice, etc. to wake up a sleeping computer. This has increased the +5VSB load considerably. Anything you have plugged into your USB ports, cell phone, iPod, external HDD, etc. is drawing power from the +5VSB.

  5. #5
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    1,038
    Thanks Thanks Given 
    2
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    Hum, I didn't know that USB was on +5VSB. That changes things considerably. Do you know around when they started doing that?
    It's my PSU in a box!
    Ooo-ooh,
    My PSU in a box, baby!

  6. #6
    Join Date
    Oct 2006
    Location
    jonnyGURU forums, of course!
    Posts
    15,516
    Thanks Thanks Given 
    502
    Thanks Thanks Received 
    46
    Thanked in
    36 Posts

    Default

    I rememeber them starting to do it more often than not when the socket 778 came out, so about 2004-ish.

  7. #7
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    1,038
    Thanks Thanks Given 
    2
    Thanks Thanks Received 
    0
    Thanked in
    0 Posts

    Default

    What's your opinion on possible single-output PSUs and the future of the +5VSB.

    Intel's been pushing for everything to be single output for a while, they even talked about it at IDF in 2006 (http://www.intel.com/pressroom/kits/...transcript.pdf page 7). You can see the migration to +12V from ATX to ATX12V to ATX12V 2.x. Many enterprise servers already use single-output PSUs. So you can clearly see where the future of PSUs is going to be, they're going to eventually put everything on the +12V rail, if possible. This has obvious advantages. Cheaper, simpler power supplies that are more efficient? Sign me up. But there are obvious things I see that could put a wrench into things.

    We already got rid of -5V back in 2003, and I expect to see -12V disappear within a year or two. What next? Probably +3.3V, since that's mainly just used for RAM and PCIe circuitry and could be easily regulated from +12V with VRMs, and obviously we're already seeing that in high-end enthusiast PSUs. But then there's the issue that many laptop 2.5" HDDs use +3.3V power, the SATA spec for laptops includes a +3.3V rail and many hard drives do make use of that. That right there drives a wedge between desktop and laptop hard drives unless manufacturers limit it exclusively to +12V and +5V.

    +5V is the next obvious target of course. Again, most motherboard functions that need +5V could just have it VRM regulated. But then you have HDDs and ODDs that use +5V circuitry. Those devices would require either a voltage step-down, or manufacturers would have to be persuaded to move to +12V circuitry. That could take some doing.

    And that leaves us with +12V and +5VSB. The +5VSB is currently needed for all the CMOS and BIOS circuitry, and now I learn it's needed for USB. I don't see the USB spec being rewritten for +12V any time soon, and I don't think a flash drive has room for a VRM. And there's the bigger issue that power supplies don't supply +12V while in standby, and when dealing with 1-2A loads on the +12V efficiency is going to be horrible on almost any current SMPS design. I've heard talk of switching +5VSB to +12V when mobos switch to UEFI, but at this point I have to wonder why.

    Moving from a +5V standby to a +12V standby would be a huge change and a big incompatibility point. I just don't see motherboard and PSU manufacturers and OEMs agreeing to such a huge change. Plus there wouldn't really be much advantage anyway since you'd still need a different switching mode or even entirely different "PSU within a PSU" in order for +12VSB to be efficient, which it would have to be to meet that "1W Initiative" thingy over in Europe.

    I expect the consumer PSUs of 2020 to be +12V and +5VSB, vastly different but still not single output.


    Anyway, just my rambling thoughts.
    It's my PSU in a box!
    Ooo-ooh,
    My PSU in a box, baby!

  8. #8
    Join Date
    Jul 2007
    Location
    Sweden
    Posts
    348
    Thanks Thanks Given 
    14
    Thanks Thanks Received 
    3
    Thanked in
    3 Posts

    Default

    jonnyGURU; Do you mean USB devices are running off 5VSB when the system is running aswell, not just in standby?
    I'm not saying you are wrong, but I did some tests on a old Socket 370 mobo, and most of the 5VSB power usage dropped when the system was booted, more info here;

    http://www.badcaps.net/forum/showthread.php?t=10428
    "The one who says it cannot be done should never interrupt the one who is doing it."

  9. #9
    Join Date
    Oct 2006
    Location
    jonnyGURU forums, of course!
    Posts
    15,516
    Thanks Thanks Given 
    502
    Thanks Thanks Received 
    46
    Thanked in
    36 Posts

    Default

    Quote Originally Posted by Per Hansson View Post
    jonnyGURU; Do you mean USB devices are running off 5VSB when the system is running aswell, not just in standby?
    I'm not saying you are wrong, but I did some tests on a old Socket 370 mobo, and most of the 5VSB power usage dropped when the system was booted, more info here;

    http://www.badcaps.net/forum/showthread.php?t=10428
    I said it hadn't started until 2004. Back when we were using Socket 370 boards, USB didn't use +5VSB!

    Yes... USB devices are running off +5VSB even when the system is running. I found this out when I was working for Ultra. We were working on a drive bay mounted powered USB hub. It got it's power from both the USB as well as a +5V from Molex. Suddenly, we got a lot of complaints from people that installing the device would cause their PSU's to trip off as soon as they were switched on! Turned out that the USB power was coming from +5VSB and we were adding power from the +5V and this was causing the PSU to trip. When we built Phobos @ BFG, we used the Enhance PSU we used because it had ample power on the +5VSB because the LCD panel ran off the +5VSB while the PC was off as well as on.

  10. #10
    Join Date
    Oct 2006
    Location
    jonnyGURU forums, of course!
    Posts
    15,516
    Thanks Thanks Given 
    502
    Thanks Thanks Received 
    46
    Thanked in
    36 Posts

    Default

    Quote Originally Posted by Phaedrus2129 View Post
    What's your opinion on possible single-output PSUs and the future of the +5VSB.

    Intel's been pushing for everything to be single output for a while, they even talked about it at IDF in 2006 (http://www.intel.com/pressroom/kits/...transcript.pdf page 7). You can see the migration to +12V from ATX to ATX12V to ATX12V 2.x. Many enterprise servers already use single-output PSUs. So you can clearly see where the future of PSUs is going to be, they're going to eventually put everything on the +12V rail, if possible. This has obvious advantages. Cheaper, simpler power supplies that are more efficient? Sign me up. But there are obvious things I see that could put a wrench into things.

    We already got rid of -5V back in 2003, and I expect to see -12V disappear within a year or two. What next? Probably +3.3V, since that's mainly just used for RAM and PCIe circuitry and could be easily regulated from +12V with VRMs, and obviously we're already seeing that in high-end enthusiast PSUs. But then there's the issue that many laptop 2.5" HDDs use +3.3V power, the SATA spec for laptops includes a +3.3V rail and many hard drives do make use of that. That right there drives a wedge between desktop and laptop hard drives unless manufacturers limit it exclusively to +12V and +5V.

    +5V is the next obvious target of course. Again, most motherboard functions that need +5V could just have it VRM regulated. But then you have HDDs and ODDs that use +5V circuitry. Those devices would require either a voltage step-down, or manufacturers would have to be persuaded to move to +12V circuitry. That could take some doing.

    And that leaves us with +12V and +5VSB. The +5VSB is currently needed for all the CMOS and BIOS circuitry, and now I learn it's needed for USB. I don't see the USB spec being rewritten for +12V any time soon, and I don't think a flash drive has room for a VRM. And there's the bigger issue that power supplies don't supply +12V while in standby, and when dealing with 1-2A loads on the +12V efficiency is going to be horrible on almost any current SMPS design. I've heard talk of switching +5VSB to +12V when mobos switch to UEFI, but at this point I have to wonder why.

    Moving from a +5V standby to a +12V standby would be a huge change and a big incompatibility point. I just don't see motherboard and PSU manufacturers and OEMs agreeing to such a huge change. Plus there wouldn't really be much advantage anyway since you'd still need a different switching mode or even entirely different "PSU within a PSU" in order for +12VSB to be efficient, which it would have to be to meet that "1W Initiative" thingy over in Europe.

    I expect the consumer PSUs of 2020 to be +12V and +5VSB, vastly different but still not single output.


    Anyway, just my rambling thoughts.
    It is an interesting "problem". You have to have some sort of stand by power at the PSU, regardless of the voltage. Even if the PSU was all +12V and all DC to DC regulation was done at the motherboard level, you might as well keep +5VSB. There's no advantage to changing that to +12VSB because it's still a separate circuit within the PSU and you'll need to step it down to +5V at some point to make it backwards compatible with USB, which is going to make things unneccessarily more expensive.

Similar Threads

  1. Corsair AXi PSU 5VSB reporting
    By red-ray in forum PC Power Supply Discussion
    Replies: 10
    Last Post: 08-08-2017, 12:55 PM
  2. Power Supply with 5A +5VSB
    By Stefan Payne in forum PC Power Supply Discussion
    Replies: 2
    Last Post: 01-25-2014, 06:19 PM
  3. Bad Axe 2 Questions... UPDATE: Now Crossfire questions
    By Jon Gerow in forum General PC Hardware
    Replies: 33
    Last Post: 02-07-2007, 05:27 PM
  4. +5VSB Question
    By NLight95 in forum PC Power Supply Discussion
    Replies: 9
    Last Post: 02-07-2007, 01:09 PM
  5. DFI motherboards and low +5VSB
    By Jon Gerow in forum PC Power Supply Discussion
    Replies: 5
    Last Post: 11-21-2006, 11:08 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •