Are Buck converters dim-able / switchable ?

Discussion in 'The Family Room' started by videoman3857, May 2, 2017.

  1. videoman3857

    videoman3857 Full Time Elf

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    To put it in a nutshell.
    Can Buck step down converters be switched at reasonably high speeds ?
    Will they be damaged by the switching ?

    What I am doing:
    I have low voltage micro leds (fairy lights) on copper wire in existing star frames.
    I want to add more strings of these lights and set them up so they twinkle - 2 alternating channels.
    The controller I need to use (LOR CMB16) has two spare channels, however it supplies 30 volts to the other 16 channels. Ergo Buck step down controllers inline to control the voltage on each channel
     
  2. smartalec

    smartalec Im a SmartAlec what can i say! Community Project Designer

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    30v for a stepdown to 12v i know gets very hot an needs heatsinks for starters..
    but when you disconnect the 30v the caps on the stepdown board will take a couple of seconds to discharge..
    so No fast switching cant be done with that setup..
     
  3. OP
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    videoman3857

    videoman3857 Full Time Elf

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    Thanks SmartAlec.
    looks like I'm going to have to reconfigure some of my display to incorporate some 5 volt lights
    so I can use duel voltage on the board and control them that way.
    The buck converter would have been convenient - and less time consuming. Oh well, back to the drawing board.
     
  4. smartalec

    smartalec Im a SmartAlec what can i say! Community Project Designer

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    OK i will let you in on the well known secret..
    just about all DC controllers around Switch the Negative.. Not the Positive..
    so there for it does'nt matter what voltage you run the lights on, as its switching the negative..
    so +5v to lights (from stepdown or power supply) an gnd (negative) wire goes to the controller to be switched..
    just like your +30v goes to the lights an the negative goes to the controller to be switched..

    just remember all negatives from the power supplys or steps downs need to be joined together.

    hows that sound? happyer now..lol
     
  5. David_AVD

    David_AVD Good news, everyone!

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  6. OP
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    videoman3857

    videoman3857 Full Time Elf

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    Thank you so much Guys. I'm Forever learning.
    You saved me a tonne of heartache and $
    This why I ask questions. This is why I am attending the Brisbane mini.
    This why I love this site.

    So, if I use the buck converter to supply positive to the led string and use the -ve from the controller;
    can I now switch the led string at a reasonably high rate, or do I still have the capacitor discharge problem ?
    Substituting a 5 volt power supply for the buck converter is not a problem - the buck converter is more convenient.
     
  7. multicast

    multicast Senior Elf Generous Elf

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    Yes, that is a better way of doing it. Most buck converters will be operating in the 100kHz to 1Mhz ( depending on their design ).. Your resoanbly high rate will likely be in the order of 1Khz or lower. You'll not have a problem at all.
     
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  8. OP
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    videoman3857

    videoman3857 Full Time Elf

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    That's great news . Thanks.
     
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