Low Flicker or Flicker free AC to DC conversion

Discussion in 'Electronics & Electrics' started by lawrencep93, Mar 21, 2019.

  1. lawrencep93

    lawrencep93 Member

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    I was wondering if anyone knew the best power supply or an add on circuit to smooth out the flickering from most AC to DC conversions.

    I want to build a project RED and Infrared LED light therapy device with minimal or no flickering that plugs into 240v.

    So far I am going to make one which is just 10m rolls of LED strip lights and soldering some wire to each strip then plug it into a cheapo 6w AC to DC power supply that came with the strips, but I want to have something with minimal or no flickering with out having to go to a battery set up.

    The other future project I want to try is mounting 1 or more 100w LED chips to an old heat sink with a fan, so the voltages will be a little different, I also have a spare 700w PC power supply I could maybe use for the second project if I work out a way to house and cool 6 of these LED chips which will make use of the 700w PSU, just need to check the voltages leaving the power supply as I think the fans will be 12v and the LED chips are 24v so will need something to step the voltage down for the fan.
     
  2. aXis

    aXis Member

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    Just about any switchmode AC-DC converter *should* will give you a stable, flicker free output.

    If not you can try adding some extra LC filtering on the output.
     
  3. theSeekerr

    theSeekerr Member

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    Any appropriately designed DC power supply will achieve flicker-free output.

    Even the simplest option of a rectifier followed by a capacitor bank won't visibly flicker provided the capacitor bank is sized adequately (the right search term for this would be something like "rectifier ripple voltage")

    A switchmode supply won't flicker visibly because any flicker will be at several thousand hertz, well beyond the threshold of perception even for very conservative estimates. Most power supplies you can buy are switchmode. I'd be very surprised if it were an issue with any appropriately sized supply.
     
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    lawrencep93

    lawrencep93 Member

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    Thanks for the replies, the whole point is to mimic some expensive therapeutic devices, so flickering needs to be kept to an extreme minimum to the point where you can't pick it up on a high speed camera.

    Where do you guys buy such a power supply?
     
  5. aXis

    aXis Member

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    For a start, what is the construction of the LED light strip. Does it have integrated constant current LED driver, integrated current limiting resistors, or no current control at all?

    If it has a driver included that may have some inherent flickering. If it's one of the other two, all you have to do is supply a ripple free voltage or current supply respectively. Smoothing can be done with capacitive & inductive filters, even several stages of them.
     
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    lawrencep93

    lawrencep93 Member

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  7. mtma

    mtma Member

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    Connecting that to a 12V laptop style power brick (not a LED driver) will practically give you a no flicker result.
     
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    lawrencep93

    lawrencep93 Member

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    Oh sweet might try that, I will cut the strips up and solder a wire across each side, I will try just off a direct power brick from an old laptop then.
     
  9. aXis

    aXis Member

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  10. dakiller

    dakiller (Oscillating & Impeding)

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    LED flicker is mostly from dimmers that dim LED's by switching them on and off really fast, Pulse Width Modulation (PWM). It is the cheapest and easiest way to dim an LED, so you have to design something that will cost more circuit wise to do it a different way.

    If you don't want to dim that strip lighting, connecting it to any normal 12v DC supply will run them flicker free.

    If you want to be able to dim them, you need a variable constant current driver (of which I don't have anything to recommend off the top of my head)
     
  11. RobRoySyd

    RobRoySyd Member

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    If they're LED strips with integral current limiting resistors a variable constant current supply is not what's needed. A variable voltage DC supply will work fine.

    For sure flicker is a problem with video cameras, I tried some cheap LED dimmers and looked OK to the eye but the flicker with my camera was horrendous.

    One concern is the actual sensors in video cameras are most sensitive to IR. There's an IR cut filter in front of the sensor but start flooding a scene with IR and some can get through the filter and then you'll get some weird colour problems e.g. synthetic black fabrics gets a magenta tint.
     
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    lawrencep93

    lawrencep93 Member

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    I won't be diming them just using full power, the flicker rate has a biological effect in photobiomodulation treatments, I just wanted to build my own RED LED PBM panel because treatments can cost $100/hour for full body beds, and products like Joov run into the $1,000's. I will eventually make booster 100w chip LEDs using a cooling fan as well
     
  13. RobRoySyd

    RobRoySyd Member

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    $100 / hour does seem expensive but Joov for what it is not so much so. Take a look at what lights for film and television cost.
    Have you tried these treatments and are you thoroughly convinced they do some good?

    If you are then most likely it involves some interesting physics / chemistry that AFAIK would require a specific wavelength of IR. If that's not the case and any wavelength will work then heat lamps give off heaps of IR. I've got an IR light of around 1KW gathering dust you could have for freight. I suspect it was used for paint drying / baking.
     
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    lawrencep93

    lawrencep93 Member

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    The LED light beds are expensive.

    Need specific wave lengths hence the LED use, I can find the LED's just setting it up is the harder bit.

    Thanks for the offer on the IR light, but I don't want too much heat
     
  15. RobRoySyd

    RobRoySyd Member

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    All the electronics stuff is easy, it's the mechanical stuff that's the hard part. As for the bed have you thought about starting with an old tanning bed?
     
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    lawrencep93

    lawrencep93 Member

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    I did think of starting with that but I don't have the room for one, I was just looking at making a panel I can put on my wall.

    When I move house I might make one in the spare room so I don't have to go to the Dermatologist to do my UVB therapy, then I might do half UVB globes and the other side with all red and infra red LED's as the two work better together for my Psoriasis.
     
  17. RobRoySyd

    RobRoySyd Member

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    So sorry to hear you've got that. Seems a lot of people have it in odd places and it gets misdiagnosed.

    As for the panel easiest would be to use LED strips. I have a contact in China who has made LED strips to spec for me. The problem though is they will only ship DHL which gets expensive (USD 35) for small quantities. If that doesn't scare you off let me know and I'll see what they can do. Psoriasis is common in Asia so I'd guess they'll be making the things used to treat it.
     

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