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Thread: Making a PSU

  1. #1
    Variable Bitrate
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    Jul 2000
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    Ottawa, Canada
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    Post Making a PSU

    So I was going to try to make the newest Sproggy (2.5) PSU but found the transfomer expensive a a little hard to find.
    I was all set to peice together something from examples on numerous site but then i found the sproggy 2.0 (older).
    So i cut and pasted on the power good section from the 2.5, changed an IC to one that was readily available, added a capacitor or two and called it the 2.23.

    So here is what i have. Is there any big ugly errors that are going to fry my car battery?
    Any thing else i should consider?

    [SIZE=1]'91 Nissan Stanza

    [XXXXXXXXXXXXXXXXXXXX] XX% Completed -
    Car Totaled and i bought a 20G mp3 player

    http://machs-fuel.tk
    a DIY video projector page

  2. #2
    Low Bitrate
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    Oct 1999
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    N Ireland
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    108

    Post

    Hi

    I don't see anything wrong with what you've done. It should work fine. :-)

  3. #3
    Variable Bitrate
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    Feb 2000
    Location
    hoppers crossing, victoria, australia
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    Post

    the 7812k is only rated at 1.5amps http://www.microsemi.com/corporate/c...p?PARTID=43969

    thats not enough imo

    cheers pcman
    donate to my team in the ****box rally all proceeds go to the cancer council http://www.everydayhero.com.au/dodgy_mechanics

  4. #4
    Dustin Haug
    Guest

    Post

    Yep the 7812 isn't going to cut it for most systems. You'd be better off using a switching regulator for the 12V. You'll more current out and it'll be much more efficient.

  5. #5
    Variable Bitrate
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    hoppers crossing, victoria, australia
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    Post

    yeah
    or use 3 or 4 of em and run each thing of a sep 12v reg

    cheers
    pcman
    donate to my team in the ****box rally all proceeds go to the cancer council http://www.everydayhero.com.au/dodgy_mechanics

  6. #6
    Newbie
    Join Date
    Apr 2000
    Location
    NZ
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    19

    Talking

    The only thing wrong with the design is you will have to have the car running to give you 12V correctly.

    Think about using the LM2577T for the 12V and run the input from the 5V supply.
    This way the car can be off and you can still use the pc.

    more info on website

    cheers

    andi
    Andi

    http://www.andicorp.com
    Setup: P233MMX, 32MBRAM, 8.4GB HD, CUSTOM DC2DC, 40x2 LCD.

  7. #7
    Variable Bitrate
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    Post

    So would one LM2577 (3amps) be about enough for a basic system (MoBo, HD and character LCD?)
    [SIZE=1]'91 Nissan Stanza

    [XXXXXXXXXXXXXXXXXXXX] XX% Completed -
    Car Totaled and i bought a 20G mp3 player

    http://machs-fuel.tk
    a DIY video projector page

  8. #8
    FLAC
    Join Date
    Apr 2001
    Location
    Portland OR
    Posts
    1,244

    Post

    Originally posted by Machs_FueL:
    <STRONG>So would one LM2577 (3amps) be about enough for a basic system (MoBo, HD and character LCD?)</STRONG>
    The 2577 will only give you around less than one amp of output current for a given design. It says 3 amps, but that is the current it can sink through the inductor.

    On my box I am using a laptop power supply. 1 amp from 12 volts will run a low power mobo, and hard drive. (not including the 5 volt line)


    There are other linear regulators other than the 7812 that can do 5 amps. You still need to satisfy the input voltage of 1 volt higher than the desired output.

    Jeff_
    MPEGBOX - Plexiglass Computer
    www.mpegbox.com

  9. #9
    FLAC
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    Apr 2001
    Location
    Portland OR
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    Post

    Originally posted by andicorp:
    <STRONG>

    Think about using the LM2577T for the 12V and run the input from the 5V supply.
    This way the car can be off and you can still use the pc.


    andi</STRONG>
    Wouldn't it make more sense to take the input to the LM2577 from the 8-16 volt input rather than from the output of the 5 volt MAX787 ?

    How much current can you get out of the 2577 anyway?

    Jeff_
    MPEGBOX - Plexiglass Computer
    www.mpegbox.com

  10. #10
    Variable Bitrate
    Join Date
    Jul 2000
    Location
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    Post

    Ya i was thinking having the LM2577 right off the Vin, because that would give the PSU the ability to operate with out the car on

    hit reload and the diagram should change showing what i was thinking
    [SIZE=1]'91 Nissan Stanza

    [XXXXXXXXXXXXXXXXXXXX] XX% Completed -
    Car Totaled and i bought a 20G mp3 player

    http://machs-fuel.tk
    a DIY video projector page

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