ICL7107 to power and test on the same PC SMPS

Discussion in 'The Projects Forum' started by jj_alukkas, Jun 13, 2011.

  1. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
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    5
    Hello all,

    I am using a pc SMPS for making a lab power supply and plan to add a variable output on one of the 12v lines with an lm317 chip. So I also have a plan to integrate a ICL7107 based voltmeter on the variable line, but I would like to know If I can power the chip from the (-5)-0-(+5) lines of the smps and the same time monitor the 12v line will have the variable regulator. I already have a built voltmeter, just want to know if this would work as ICL7107 needs a different line to power it other than the one it is tested on. I am putting this possibilty in case the smps has separate transformer windings for 12 and 5 rather than regulating the 12v line to 5v.

    Thanks
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    1,605
    I *think* I get what you want to do. When you say "power" you mean the meter will get its +/-5V power from the same module as supplies the 12V you wish to further regulate down to a smaller voltage. The meter reads this smaller voltage.

    Yep, that should work fine, as everything coming out of the pc SMPS has the same ground. If you had separate supplies then you would have to add the connection to common up the grounds.
     
  3. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    Thanks for your reply.

    Actually, you got the good part of my question :) The other part is that, the chip I use in my voltmeter module, *cannot* use the same supply as what it will be measuring to supply the power for running itself, i.e, +/-5V!

    And I would like to know if the 12v and 5v supplies coming from a PC SMPS are isolated from each other (except for ground which is common) and the 5v is not derived from 12v using a regulator or other means. Hope you got what I asked. The purpose is to provide supply voltage for icl7107 from 5v as well as enable it to measure its 12v!! Could I get some idea on this please?
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    There is no Isolation in a PC supply whatsoever besides input & output.
    In a PC supply all the voltages are separate and derived from it's own tx winding.

    I believe u won't have a problem in powering the voltmeter while measuring one of it's output.
     
  5. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    I happened to get this ckt diagram for a 200w pc smps.. from what i can make out of this, it seems to me that the 12v and 5v lines are seperate!! Could anybody verify this please?

    [​IMG]
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    The circuit has separate secondary voltages but as you see they are not isolated
     
  7. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    So is it supposed to work?
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I dunno if it is suppose to but what I know is, it wouldn't hurt to try.
     
  9. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    Yes, thats exactly what Im gonna do :) Thanks. Will keep posting.
     
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