negative voltage from power supply?

Discussion in 'General Electronics Chat' started by GRNDPNDR, Mar 13, 2014.

  1. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    This may sound a bit dumb but I'm curious if it's possible to get a negative voltage out of a benchtop power supply, for working with things like op amps that require a negative rail.

    the outputs on my PS include a "ground" plug between the positive and negative but the documentation is sparse, and I'm not really sure if this is feature/function of any power supply.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Flip the leads.. ;)
    The "ground" is chassis ground and is not tied to the output at all..

    Or do you mean a negative and positive from the same output.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U need to make a virtual ground circuit from a single ended supply to drive an opamp with dual rail voltage.

    I believe Bill made a circuit of the sort
     
  4. #12

    Expert

    Nov 30, 2010
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    You need to measure and find out if, "ground" is chassis ground or common for the 2 pins marked plus and minus.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    If you want both a positive and negative supply you can make a virtual ground (also called virtual ground or rail splitter) at 1/2 the supply voltage. Here's a discussion on that.

    Edit: The "ground" plug is likely just a connection the the power supply chassis and the mains safety ground.
     
    Last edited: Mar 13, 2014
  6. bance

    Member

    Aug 11, 2012
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    I have a dual output supply, I just connect -ve from one output to +ve of the other and make that my circuit ground....

    Before you do that check that the -ve output of both channels have no continuity. ie they are not connected to each other or you will have a dead short.
     
  7. chipwitch

    Member

    Mar 29, 2013
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    Crutschow, in the blog you linked to, can you explain a couple things? In the second image, I recognize the voltage divider. What's the purpose of the caps?

    Also, the explanation for why that circuit is less than ideal, that follows seems far more complicated than it needs to be. Only yesterday did I watch a video that finally explained op-amps in a way I comprehended. So, the one in the example throws me. I just don't have a firm enough grasp on them yet. Isn't the author just trying to explain that a low impedance load will unbalance the voltage? Or is there some other aspect being illustrated?
     
  8. Shagas

    Active Member

    May 13, 2013
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    Is the 'ground plug' a normal plug like the positive and negative voltage?
    Check with your multimeter if it is really ground . If it is then you should be able to measure a negative voltage when connecting your 'com' lead of your multimeter to the ground and the red lead of your multimeter to the -ve voltage plug.
     
  9. Metalmann

    Active Member

    Dec 8, 2012
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    "..curious if it's possible to get a negative voltage out of a benchtop power supply".




    I just checked my adjustable power supply, and zero.
    No reading from + or -.....and the center yellow post.

    Set at 12 V, I get 12 V reading at the red and black posts only.

    I get zero reading from any variation of the yellow; and black and red posts..

    What does yours read?
     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Most of the time it's the earth connection. Sometimes called ground.

    A dual rail ground is not connected to earth directly.
     
  11. bance

    Member

    Aug 11, 2012
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    As R!f@@ says....

    Check for continuity between the (Green/yellow) output and the ground pin on the power supply plug!
     
  12. Brevor

    Active Member

    Apr 9, 2011
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    If you only need low current for op amps check out the Microchip TC1044S it's a 98% efficiant charge pump, I used one once in a low power op amp circuit it worked very well. It has a frequency boost feature for audio circuits that puts the clock frequency up in the 40 Khz range to avoid noise.
     
    Last edited: Mar 13, 2014
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Need to check for low R between earth pin of power plug to the PSU out put ground/earth pin.
     
  14. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    Wow, I forgot about this thread, then come back and it's full of replies.

    My power supply is a Mastech HY3005F-3.

    each channel has "Black, Green, Red" being negative, ground and positive respectively.

    I'll see if I get a reading from Ground and negative, but after reading these replies I'm doubting it will, not that I expected I would in the first place but I had to check.

    I often toy with opamps so now I'm going to need a way to have a negative voltage from a single rail supply. The charge pump(s) before-mentioned might be an option.

    Maybe build some kind of little box that I can plug my power supply into and out comes dual rail voltage.
     
  15. #12

    Expert

    Nov 30, 2010
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    Most opamps are so low power (less than 10 ma) that a pair of 9V batteries will get you at least a 40 hour week of experimentation.
     
  16. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    The whole reason I bought a power supply though is so I wouldn't have to use cobbled-together items, or multiple wall warts for powering various circuits.
     
  17. bance

    Member

    Aug 11, 2012
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    Before I had a bench power supply, I only had a variable wall wart...

    So i made a litttle board with an LM7660 and a couple of cap's and it worked fine for op-amp circuits....
     
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