Dual PSU Regulation

Discussion in 'Off-Topic' started by R!f@@, Jan 4, 2010.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    IMHO this is not a novice question?

    So I prefer professional opinion on this.
    I have designed and build PSU ranging from 0V to 30V Variable both with CC and CV @ almost 10A output current capability.
    So to say voltage regulation is not new to me.

    Now I have a new objective. I am mainly involved in R&D.
    At this moment I am learning PIC and am proud to say that I have written my very first ASM file in MPLAB, and build and programed a PIC12F629 successfully. Even though this is as simple as lighting a LED, :D
    this is a very huge step for me being this my only weakness.
    I have finally found the documents that suite me, even though I say this was not easy thing to find for oneself.

    This step taken from me is encouraged by the very members of this forum, in here are a few I like to thank you personally, I know these people know whom I am talking about even though I did not name them. I will let others to guess :).

    But what I like most is to build,and have been building for the last few years are hi end hi fi with almost no distortion in the sound, and I am almost achieving this, that is incorporating class A amps in home hi-fi's.
    In order to do this I have to have a solid PSU even at the design stage.
    Strict regulation to minimize heavy loading and loss to test the power capability and distortion. May be some might not agree, but I am not going to debate on it, so please do not comment on this matter. I will ask for opinion when I have something to show and talk about that is working.

    Almost every good audio tech knows that Audio amps need dual supplies, even though it does not need to be regulated but needs a serious amount of capacitors for sustained amount of music power typically for powerful bass reproduction and to minimize voltage sagging.
    Now when it comes to voltage regulation I have never tried to regulate the negative side, even to produce a regulated dual supply, I have always used two separate PSU which are regulated from the positive side, what I am saying is the regulating or control element is located at the positive rail of the supply. I can series connect the two and I have a dual supply.

    What I like to know is won't the regulation be better in the negative side if the negative regulator is located in the negative rail of the supply instead of the positive side of the negative supply.
    Confusing isn't it :p.

    I like to be sure about this so I can built a positive and a negative rail tracking PSU.

    Any thoughts?

    Rifaa
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    Then I build an dual linear power supply starting from scratch I often build it as two separate power supply and connect the output so I end up with a dual supply. The reason for this is that positive voltage regulators are more common so the selection is better. And I find it more practical that the two units share all the parts. The regulation will be independent
     
  3. studiot

    AAC Fanatic!

    Nov 9, 2007
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    In general with linear regulators if you wish to adjust down to zero volts you need a rail of the opposite polarity to the one being regulated to maintain a reference.
    With switched mode regulators you can avoid this and even generate a regulated rail of the opposite polarity.

    Going back to linear, if you provide a small negative supply, regulated by at least a zener, you can use this as your reference point for the positive rail regulator. The positive rail is then used as a reference for the negative rail.

    By doing this you can achieve tracking regulation of both rails with a single pot. You also have the ability to earth the centre zero.
     
  4. R!f@@

    Thread Starter AAC Fanatic!

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    I'll make this a little simple.
    For audio purpose I do not need to adjust down to zero.
    Typical range is from ±12V to say ±80V or so. Current limited built in of course

    For high voltages I have to go for a floating regulator. This way I can achieve higher voltages with low voltage components.
    I will be using a couple of regulators individually switched via relay to the appropriate tapping to the power transformer. This way I can always be able to minimize heat dissipation and use low wattage components to regulate high current.
    I still haven't figured out the basic schema but I know I can do this.

    I can track with a dual pot and have a fine adjust VR wired separately to each rail. The PSU will have meters for both V and I measurements for both rails.

    Question is the negative rail regulation. Do you suggest for best performance that I should use a negative rail regulating element or a positive rail element in the negative supply.
    Or regulate both rails from the positive side and series them at the output only, which means that the only common connection will be at the out put of the two supplies where the ground reference is produced for dual purpose, but for this I have to use two separate windings or two transformers. this can be done I think.
    What would be the effect theoretically.

    Rifaa
     
    Last edited: Jan 4, 2010
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Well it really depends why you want +/- rails.

    I think you will find a good enough dual pot expensive and difficult to source for close tracking.
    If you want to be able to have asymmetrical rails, with sustained different current draws then the two transformer solution is best. Otherwise you will load one half of a CT trnasformer significantly more than the other which will eventually lead to core magnetisation.
    Since this solution provides esentially two separate isolated supplies you can in theory make them both negative or both positive regulated or one of each. However the bipolar solution makes earthing easier, especially for a high power audio amp. Draw out some schemes, including the rectifiers, and you will see what I mean.
    If on the other hand you merely require equal rails with substantially equal current draws than a CT transformer is the likely the most economical and compact. If you do this, of course, you have to regulate both ends as you are measuring against the middle. ie you require a positive and negative regulator. I favour symmetry in this case. And earthing is easily accomodated by earthing the centre.
     
  6. R!f@@

    Thread Starter AAC Fanatic!

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    Audio amps will load almost equally to both rails, but if intend to use the dual supply as separate PSU for two different loads, core magnetization will be there.
    Separate TX will give me cheaper solution, with more common components that are easy for me to get, like regulating the positive rail.
    And leaves me with a better supply with more connection options if I needed more that one positive supplies for other projects.
    Am I right or what?

    Rifaa
     
  7. studiot

    AAC Fanatic!

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    That's about it mate!
     
  8. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    Thanks

    Rifaa
     
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