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Thread: Has anyone tried modifying a 110v atx PSU to 12v DC?

  1. #11
    Constant Bitrate
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    Post

    Why not just build a 3.3volt stepdown with a MAX788 and run it off of an AT DC/DC power supply or from the cars 12volt source? This way you can get the 3.3volt source for an atx board, and then just wire it into a standard ATX connector? Just a thought!

  2. #12
    Newbie
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    Question

    It sounds like a wonderful idea, but I have a couple of worries. My main concern is the whole "power good" circuit. What is it and does an ATX PC need it? I think its like -5v or something like that. So far, the cheapest price I have heard for a DC-DC ATX PSU is $102.

  3. #13
    Retired Admin Aaron Cake's Avatar
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    Cool

    Power Good is 5V, activated about 100mS after the supply voltages stabilize. You can mimick the signal with a simple RC network.

    ------------------
    Aaron Cake
    London, Ontario, Canada

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  4. #14
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    Question

    RC? As in Resistor Crossover maybe? I'm a pretty dedicated cheapskate, so if I can glean enough info to design a big PSU, I'll do it and post the design. So far, I'm thinking about modifying Sproggy PSU, daisy chaining the MAX ICs to gain more power handling (if that's possible). That would take care of the power issue, but as for the power good signal, i don't know

  5. #15
    Retired Admin Aaron Cake's Avatar
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    Cool

    Resistor-capacitor. The simplist timing circuit possible. I don't think I have an example posted anywhere, but any electronics text should provide the necessary info for this two component circuit.

    ------------------
    Aaron Cake
    London, Ontario, Canada

    Player: Cyrix 200, 32MB RAM, 10.2Gig Quantum HD, Onboard EtherNet/Sound/Video, Custom Lexan Case, Arise DC-DC, Win95 Kernal w/Custom Player
    Car: '86 Mazda RX-7 w/Basic Performance Upgrades
    Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
    Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
    "If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

  6. #16
    Raw Wave Rob Withey's Avatar
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    Post

    RC as in Resistor-Capacitor I would guess. Use an inline resistor from the 5V line to charge a capacitor. The voltage on the capacitor rises more slowly than the voltage before the resistor. This still gives you a slowish edge - a schmitt trigger would sharpen this up if this still causes grief.

    The delay can be altered by the values of R and C. Bigger R means smaller charge current and a longer delay. Bigger C means more charge needed to raise the voltage on the capacitor, and a longer delay.


    Rob

    Originally posted by HappyPuppy:
    RC? As in Resistor Crossover maybe? I'm a pretty dedicated cheapskate, so if I can glean enough info to design a big PSU, I'll do it and post the design. So far, I'm thinking about modifying Sproggy PSU, daisy chaining the MAX ICs to gain more power handling (if that's possible). That would take care of the power issue, but as for the power good signal, i don't know


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    Old Systems retired due to new car
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