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Thread: anybody have any knowledge on ATX psu's

  1. #1
    Variable Bitrate
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    anybody have any knowledge on ATX psu's

    Ok so I'm finally close to finnishing my presslab forward converter, I have a very stable +12, -12 +5, -5, 5Vsb and 3.3 Volt output, it will actually powerup my whole setup. So all great, but.... I want to use the ATX way of turning on and off my psu and this is what I just can't get to work. When my PSU is allready running, I push the powerbutton and the comp. starts up but when I connect everything so that the powerbutton also powers up or down the psu, the mobo won't come on.
    Why is this!?!? why can I use the ATXswitch only when the PSU is allready running... I'm going nuts over this!!

    I'm hoping anybody can help me, I've bothered presslab so much the last 48 hours I feel kinda guilty 'bout bothering him again..

    thanx....
    marsjell
    If at first you don't succeed.........
    destroy all evidence you tried

    for info on t6369c LCD or Presslab's powersupply check:
    http://www.namms.tk <=updated!!

  2. #2
    Rob
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    The way ATX works is that the 5v standby is allways on (hence the name) and the power button turns everything else on & off. I hope that helps.

    Rob
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  3. #3
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    The PS_ON line that connnects to your motherboard (not sure what color wire or what pin, it differs depending on the power supply) should be normally pulled high by the 5vsb line, and when the motherboard wants the power on it pulls it low (to ground.) I believe this line should be connected to the shutdown pin of the PWM chip.

    I'm starting work on a forward convertor of my own, I have my transformer wound, but I haven't ordered the parts to build the input side.

  4. #4
    Variable Bitrate
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    Yeah but that's just my problem...

    I've rebuild a "normal" atx PSU so that it runs on 12VDC. On the primary side I have a lead which turns on the PS when connected to GND. When the powerbutton is pushed, the mobo pullsdown the voltage on the poweronlead to 0V. So I connected my on/off lead to this lead. This seems to work, my PSU powers up, all voltages are at the correct level but the mobo doesn't startup.

    When I connect my on/off lead to gnd, my PS immediatly startsup If I now push the powerbutton on the mobo it does startup....

    this is my problem, why does my PS have to be running before I turn on the mobo, why can't I start my mobo & PS at the same time??

    Mobes: That's exactly what I have done, but somehow it won't work that way...
    If at first you don't succeed.........
    destroy all evidence you tried

    for info on t6369c LCD or Presslab's powersupply check:
    http://www.namms.tk <=updated!!

  5. #5
    Live and Kickin'
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    A normally closed relay between PS_On and ground should do the trick.

    The relay is closed when PS_On is connected to ground (everything is on) and it is open when PS_On returns 5V (everything is off)

    The relay should control the power to everything but +5v standby, which should always be on.

  6. #6
    FLAC Mastero's Avatar
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    try this
    Attached Images Attached Images  

  7. #7
    Variable Bitrate
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    mastero: what does it do? remember, I don't have a sproggy, I've modified a regular atx psu
    If at first you don't succeed.........
    destroy all evidence you tried

    for info on t6369c LCD or Presslab's powersupply check:
    http://www.namms.tk <=updated!!

  8. #8
    FLAC Mastero's Avatar
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    its simple mars all you need is three parts to make it work ...

    the design i posted is outdated ..

    parts required

    78L05

    IN4007

    5vdc SPDT relay.


    thats it now the working theroy...

    Assuming your PSu works like a AT psu as when you apply power the mobo kicks on ...

    the pin 14 of the ATX connectors is called the PS-on when you apply ground to this the PSU power is full so what i have done is used a 78L05 to give me the stby volt which is required for the softstart .. assuming you have two wires + and - on your psu ...
    connect the + to the input of the 78L05 and ground to ground also connect the ground to you PSU not the output of the 78L05 goes to the 4007 diode -->/--- then to the relay and to the +5stby pin on the ATX connector...

    Now connect the +12 which is connected to the 78L05 to the relay path as shown and connect the other point of the relay coil to the pin 14 then connect the contact path of the relay to your PSu's +12 input so when you apply ground to pin 14 the relay kicks on an the +12 is supplied to your PSu for FULL POWER

    I hope you get all this



    Mastero

  9. #9
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    Originally posted by marsjell
    mastero: what does it do? remember, I don't have a sproggy, I've modified a regular atx psu

    how? i'm trying to do the same thing, but i'm not sure how exactly to do it.. i've been tracing out the different voltages on the PCB (started yesterday) and any help would be great.

    btw i checked out your website, and the PSU section isnt finished..

  10. #10
    Variable Bitrate
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    Kamikaze, I'll try to get everything I know up tomorrow (my day off) so then you should get some help from my website...

    Mastero: I have a problem explaining what happens when.

    I'll try again.
    When I connect everything like I should, everything seems to work ok. I have my 5vsb (based on mixim787) powering my mobo. When I push the powerbutton on my mobo, the PSU starts, all voltages are ok (+5,-5,+12,-12,+3.3), but the mobo doesn't boot.

    Now when connect the shutdown from the PWM to ground (so that it works like an at-psu, connect inputvoltage=>PSU starts) my mobo DOES boot, after pushing the powerbutton on the mobo?

    schematic:

    ATX power: mobo pwrbutton on =>ps on => no boot
    AT power: ps on=> mobo pwrbutton on =>boot!

    does this make any sense??? (I mean my english, my problem etc.)

    judging from your reactions, I think you don't understand (thanks to my crappy english) what my problem is....
    If at first you don't succeed.........
    destroy all evidence you tried

    for info on t6369c LCD or Presslab's powersupply check:
    http://www.namms.tk <=updated!!

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