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vcore from 12v line - needs regulation?

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  • vcore from 12v line - needs regulation?

    The most power hungry line of my mb is the cpu power, which I beleive takes its power not from the 3.3 or 5v, but the 12v line, which is then pwm'd down to 1.5v etc.

    As its pwm, its going to be very stable and I presume immune to variation on the 12v side, so why is this just not taken from the 13.8v car supply instead of an expensive psu?

    If its dropping it down to 1.5, why does it need 12 anyway, why not 10, 9 or even 8?

    go on , have I missed something simple, because I cant see why we cant just run the 12v rail at 10, would simplify dc-dc psu design if we could.
    Lez, more widely known as flez1966

  • #2
    Standards. PC components are made to work with the ATX standard. This dictates that all PC power supplies will have a regulated 12v, 5v, and 3.3v rail. Thus, motherboard manufacturers make their products so they work so long as 12v, 5v, and 3.3v are available. If you wanted to mod your motherboard so that it accepts 10V when it was engineered to accept 12V, then go for it, but you'd have to have an understanding of the electronics in place - just as much as the engineer who designed it.

    Basically, PCs are made to work inside of a strictly regulated power environment. Cars are made to work inside of a dirty, variable, and relatively unreliable power environment. The DC-DC psu is the complicated piece of electronics that bridges that gap quite nicely.

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    • #3
      Originally posted by RawsonDR
      Thus, motherboard manufacturers make their products so they work so long as 12v, 5v, and 3.3v are available. If you wanted to mod your motherboard so that it accepts 10V when it was engineered to accept 12V, then go for it, but you'd have to have an understanding of the electronics in place - just as much as the engineer who designed it.

      As an ex-electronics engineer, I have a vague idea where to poke, but Its like I said, its a pwm circuit reducing voltage, but to get the same voltage out from the in, it will need to increase the pwm width, I doubt that it wont be able to do this, but it may lead to increased current drain / flow through the pwm circuitry.

      I think I will give it a go, by cutting all the 12v lines from the pc and trying them from a 12 lead acid battery, and letting it fall in voltage overtime and let it fail to see when it does drop out, may take an hour etc, best have a cuppa and leave the camcorder running on it.

      If it works down to below 10v, then its simply a good 10v 10amp supply needed for it, well heatsinked 2n3055's etc

      Problem is while this may work for me, may not work for all, so may not be worth the effort, and just buying a large dc-atx supply may be easier than a low power dc-atx and a seperate vcore supply
      Lez, more widely known as flez1966

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