Convert 120 AC to at least 70 V DC without Transformer

Discussion in 'General Electronics Chat' started by Javier Pernia, Aug 12, 2013.

  1. Javier Pernia

    Thread Starter New Member

    Aug 12, 2013
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    Hi Everyone, I need help with a power supply project, I need to convert 120 AC to anything lower than 70V DC @ 6A without using a transformer. In the Circuit I started to design, I use a bridge to convert 120 AC to ~170V DC and now I will like it to step down, without the use of a transformer, under 70 V DC for a 6 A load. What electronic components and circuits can I use? thanks for any help or any advise. :)
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Just Curious, why no transformer??
    Max.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    A switch-mode stepdown converter would do the job. Common in TV power supplies.
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    We do not support transformerless power supplies.
    Why won't you use a transformer to bring down the voltage to a range that is more manageble?

    Bertus
     
  5. #12

    Expert

    Nov 30, 2010
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    A transformer would be as cheap as, and work better than, the 1200 watt resistor you would need to lower the voltage. Besides that, if you do not use a transformer, this thread will be ended quickly by the policy of this website.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I did not know that!
    Is this just purely a safety concern??
    Max.
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    @ Max,

    Yep, this is basicaly a learning site.
    A lot of young people also visit this site and transformerless power supplies would be a great danger to them.

    Bertus
     
  8. #12

    Expert

    Nov 30, 2010
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    Yes. It's about safety. It's in the Terms Of Service statement. No transformerless power supplies.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Is there no voltage limit then on transformer fed supplies?
    I seem to remember a recent post here mentioning 1Kv?
    The NEC an NFPA recommend a limit of 30v or 50v in some installations for low voltage safety limit.
    The current practice for ungrounded industrial control is 24vdc?
    Max.
     
  10. #12

    Expert

    Nov 30, 2010
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    I have to wait for the moderators on the voltage limit, but I can say that a transformer isolated 1kv supply won't blow the op off his stool because it won't go through his butt to ground. Now, if he just has the sense to keep one hand in his pocket, the current won't go through his heart, either.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    You can get by without a power line transformer as long as you use a switch-mode converter with an isolated switch-mode transformer such as described here. That can be a lot smaller than the power line transformer due to the high switching frequency (transformer size is inversely proportional to frequency).
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    On a related note, it has long been my experience that it is generally not the newby to any new field that gets zapped or injured when venturing into a new field, it is the old hand, where familiarity breeds contempt!
    The new comer usually has healthy respect!.
    Max.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    I would tend to agree if not for residual capacitor charges. I also think fear alone is not enough to counteract ignorance, for instance not knowing what a high voltage wire looks like.
     
  14. #12

    Expert

    Nov 30, 2010
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    Respect, yes, even fear, but not a well rounded sense of the possible dangers. I took 3 hits across my chest that had enough energy to kill me before I was 28 years old. In the last 34 years, I have been shock free because of my, "well nourished sense of paranoia". (love that quote from WBahn:p)
     
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