TOS question: Power factor correction circuits

Discussion in 'Feedback and Suggestions' started by Lestraveled, May 12, 2015.

  1. Lestraveled

    Thread Starter Well-Known Member

    May 19, 2014
    1,957
    1,215
    I have a question concerning the "transformerless power supply" restriction in the TOS.

    I use Vicor power conversion modules often in my designs. They are transformer based converters and carry isolation certifications from almost all standards organizations around the world. These are DC in, and DC out modules.
    Countries are beginning to require power factor correction (PFC) standards on consumer products, and to power a Vicor module from the mains, a PFC circuit must be added between the mains and the Vicor module.

    The question: Is it acceptable to discuss power factor correction circuits on this forum, that operate directly from the mains, yet are part of a power supply that is ultimately fully transformer isolated?
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    If this is meant to feed a mains device,AC in/AC out, the is no problem. If you are converting a line voltage into DC that can be accessed, either directly or indirectly, without a transformer then it is a violation.

    I would need to see a schematic.
     
  3. Lestraveled

    Thread Starter Well-Known Member

    May 19, 2014
    1,957
    1,215
    Oh well
    The PFC circuit does convert AC to DC and of course, and the DC is accessible. So I accept your no answer. I hope you didn't mind me asking.
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Can you isolate the AC portion at all? The thing is to prevent an possible path from line to people in the event of failure, Optoisolators do this, as well as transformers.
     
  5. Lestraveled

    Thread Starter Well-Known Member

    May 19, 2014
    1,957
    1,215
    Bill, that is exactly what the vicor module does. It has a 3000 Vrms input to output isolation spec (VI-2XX),(better then most opto-isolators). I'll make a functional block diagram and post it shortly, along with data sheets. My working schematic is not up to date.

    Thanks for just considering this.
     
  6. Lestraveled

    Thread Starter Well-Known Member

    May 19, 2014
    1,957
    1,215
    Below is a functional block diagram of a PFC circuit supplying a vicor power conversion module. Attached are the data sheets for the Linear Technologies LT1248 PFC controller and the Vicor VI-2xx family data sheet (please note the isolation spec for the converters). The PFC circuit is to provide the Vicor module with the correct operating voltage and to present a resistive load to the mains. The vicor module provides all of the line isolation.
    The design I have been working on is similar to the page 11 schematic on the LT1248 data sheet, but is a buck converter instead of a boost converter.

    Bill, I am sure the this is on the edge of acceptable verses not acceptable, in terms of the TOS. Power factor correction is becoming more important around the world. Soon it will be requirement for residential appliances.

    I will abide by your call.

    [​IMG]
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    For this particular design to pass muster here youwould need an isolation transformer after the filter.
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Dicknpointed out the post about isolation, canyou reference the specs please?
     
  9. Lestraveled

    Thread Starter Well-Known Member

    May 19, 2014
    1,957
    1,215
    I assume you mean the isolation specs of the Vicor module. The isolation spec is at the top of page three, " Dialectic Withstand Characteristics".
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Ok, I'm willing to buy in. Sorry about the hassle.
     
  11. Lestraveled

    Thread Starter Well-Known Member

    May 19, 2014
    1,957
    1,215
    Wow, Thank You Bill.

    I will be blowing the dust off of the prototype soon. This design has been very challenging, and I probably will ask for assistance in the Projects area. So, depending how things go with the design, it may be a few weeks before I post anything.

    When I am working on the prototype I do use an isolation transformer with a variable transformer on the line voltage.

    Bill, I understand that this design is close to the limits of the TOS, and I will do my best to stay on the "good" side of the line. The direction that a thread takes is sometimes difficult to control, so if you (the moderators), become uncomfortable with the content of the posts, I will accept a "cease and desist" order without insult.
     
  12. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    I've never had a quibble about the TOS concerning "LEDs to mains" projects as it is an essential tool in keeping those just learning from literally killing themselves. I’ve kept mute on certain topics where I have done some work (such as light dimmers) where they are intrinsically dangerous during development and need a keen sense of safety to survive the process.

    But the whole “"Transformer-less power supplies" is always a gray area.

    Why? Even a "Transformer-supplied power supply" has a section where there are direct connections to the AC line, and are potentially hazardous. Now in no way do I have any worries that Lestraveled will do dumb things in his efforts one must keep in mind that the output of a power supply, while isolated from the AC line, can be dangerous just by itself.

    Why? Well, there is no implied limit to the output voltage it can make. To do it’s thing a power factor corrector (PFC) circuit must boost the input voltage it sees. A rectified AC line voltage is some 160-170 volts, and the PFC will boost this to 300VDC. Get your body across that and it hurts, line isolated or not.

    All things considered I would allow posts on PFC as by itself it is an advanced topic that will only attract advanced people.
     
  13. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Generally I don't worry about light dimmers, or electric motors, or light bulbs. The codes in various countries are very similar, the hardware to do this safely in every hardware store. Anytime you are using a capacitor instead of a wall wart I have to get involved.
     
Loading...