Circuit requirements for dimmable LED lighting setup?

Discussion in 'The Projects Forum' started by dave.t.bucks, Jun 8, 2015.

  1. dave.t.bucks

    Thread Starter New Member

    Apr 26, 2015
    8
    0
    Hello,

    I want to make a simple 12 volt LED lighting setup for a stereo microscope. I want to use LEDs as I don't want the lights to emit any heat like standard bulbs, I want to use 12 volts to avoid any electrocution issues if I spill any liquids while using it.

    I want to use a pair of LEDs together, of about 300 lumen, such as these http://www.ultraleds.co.uk/12v-1-25a-15w-mini-power-supply-dc.html, as projected lighting from above and I would also like to add a separate lower powered (100-200 lumen) dimmable LED to act as a backlight.

    I understand that these sort of modern high light output LEDs require a constant voltage/current, and as such I will need a constant voltage LED driver such as this http://www.ultraleds.co.uk/20w-1-66-amp-constant-voltage-led-driver-power-supply-12v-dc.html ??

    Can I use a variable resistor alongside a dimmable LED with a constant voltage driver?

    I want to make the circuit as simple as possible.

    Thanks

    David
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    You need to define the LEDs you want to use. True LEDs need a constant CURRENT supply, not constant voltage. But your LEDs may have built-in accommodation for a regulated voltage 12V supply, so we need to know.

    This will have an impact on your dimming plans.

    In general, a variable resistor is too simple and is a poor solution; costly and poor control. The preferred approach is to use a driver that supports PWM (pulse width modulation). Everything you need can be bought inexpensively, so there's no need to build anything if you'd rather not.
     
  3. dave.t.bucks

    Thread Starter New Member

    Apr 26, 2015
    8
    0
    Thank you.

    I am flexible on the LEDs I wish to use, as long as they are a 12 volt and a G4 fitting (I say G4 as the physical framework I am working with held G4 type conventional halogen bulbs, so I couldn't use anything bigger than that). I am looking to use a LEDs which have a light output as bright or brighter than a 10 watt G4 capsule type halogen bulb. I have no fixed idea on which brand etc of LED to use, as I have limited knowledge. I need a pair of LEDs together for the projected light from above and a single LED for the transmitted light from below, I need to be able to switch between the pair of LEDS and the single LED, the latter of which needs to be dimmable.

    Where is the best place to get the driver and LEDs from?

    I would rather keep building to a minimum if possible as my knowledge is limited, but I am happy to do the basics.

    Thanks again.
     
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,282
    1,234
  5. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    I can't comment on where to find the bulbs. Personally I might start at the local Home Depot to get ideas and see what is already easily available.

    I see Mean Well drivers recommended often, but there is also a lot of cheap stuff available on e-bay. It kind of depends on what you need.
     
  6. dave.t.bucks

    Thread Starter New Member

    Apr 26, 2015
    8
    0
    Thanks, yes, that sort of bulb would be fine. As long as the bulb is no wider than 12mm, it will fit into the framework just fine.

    I'm in the UK, but I am sure I can find anything you suggest from the USA on sale in the UK.

    Is this the sort of driver I should get?

    Does the dimming switch work on the 12 volt or the 240 volt side of the driver?

    Thanks again

    David
     
Loading...