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Need someone to check my PSU design

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  • Need someone to check my PSU design

    So I need a PSU to take 11.5VDC to 14.5VDC and output 3.3v, 5v, 12v.

    The plans are to use 3 P-Channel mosfets (FDP6021P for 12v, SFP9540 for 5v and 3.3v) and 3 controller chips (LP2975).

    By my calculations, this should yield:
    3.3v: 10A
    5v: 13A
    12v: 24A

    Design Considerations:

    LDO - not a factor.
    132w w/ 11 volt drop ---> 10A

    LDO - not a factor.
    132w w/ 10 volt drop ---> 13A


    The LDO (dropout voltage) on the 12v rail is a concern, but LDO is calculated as follows:

    Rds_ON*I_load=dropout voltage

    Rds_ON ~ .03*20 = .6v drop in worst case scenario, closer to .15v drop in normal loading

    so in normal loading, the PSU would see about 11.7v at a moinimum (car off batteries discharged) but would stll get 11.5v to the MB, within ATX specs

    60w w/ 2.5v drop ---> 24A

    Any thoughts or suggestions? Yes, this can't keep a constant 12v output, but it should keep it within specs.

  • #2
    Seems like you are gonna have a **** load of heat dissipation and start-up would be harsh on your computer if it happens to be on.
    I have found you an argument; I am not obliged to find you an understanding.


    • #3
      already have a tank circuit, but dissipation will be a real problemo.

      am considering a PW200 and just the 12 regulator described above