Efficiently dimming LED strips

Discussion in 'General Electronics Chat' started by IamTed, Jun 12, 2013.

  1. IamTed

    Thread Starter New Member

    Jun 12, 2013
    Hi everyone,
    I'm new to the forum and hope you can set me straight.
    For the past many years, I have had fluorescent lights under my kitchen cabinets. They were ok, but I never really liked them, so I ordered up a reel of LED flexible strip lights. After installing them, I found that the light was nicer, the profile was much lower, so you couldn't see a fixture under the cabinets and the power consumption was about a third of the fluorescents. Bonus!

    Now here is the fun part. The lights are plenty bright to use for work lighting. What I want to do, is to also use them as a "night light". My dilemma, is that I don't want to throw away all the power savings that I gained by switching to the LEDs. The transformer that I am using is an electronic dimmable one that is designed for powering MR16s. I could just put a standard triac dimmer in line with it, just like it is designed for, but seeing that LEDs don't dim like incandescents, I'm worried about possibly having an annoying flicker. The other options that I have thought of are using a PWM circuit to dim them or maybe a voltage regulator after the PSU to drop the voltage. I am not concerned about the change in color temperature that would occur with dropping the voltage.

    Currently, the strips all in total are drawing 1800mA at 12 volts. I am not needing the dimming to be variable, it will either be operating at 100% or at the dimmed output for "night lighting".

    As for the 120 volt triac dimming option, if I go that way, it will be with off the shelf, CSA/ULc approved stuff, so I am fully aware of the safety issues. I am just including it in the option list to compare the efficiency compared to the other LV options.

    What is the best option that won't have most of my money going up in heat while running in the "night light" mode, while having the long term bonus of reliability?
  2. Brownout

    Well-Known Member

    Jan 10, 2012
    I'd say PWM is the best option. There is a plethora of ways to implement it, so I won't try to offer a schematic. The easiest way would be a simple 555 timer circuit, but the slickest way would be a uC, which can be programmed for different settings that depend on different conditions (time of day, etc) But getting spun up on uC's takes alot more time....
  3. crutschow


    Mar 14, 2008
    I would try the Triac dimmer circuit if the transformer is designed for it. (Do the LEDs have any additional supply module?) I don't think flicker or the change in color temperature will be a problem.

    I have some ceiling LEDs that are designed for dimming and they dim nicely with a standard wall dimmer, although they don't dim as much as an incandescent bulb.
  4. IamTed

    Thread Starter New Member

    Jun 12, 2013
    Crutschow, nope, the strips are just 3 LEDs in series with a SMD resistor. No controls circuit was included with them, just feed them 12V. I too have some 120V LED GU10 dimmable lamps that I installed outside on a dual brightness motion detector. When in the dimmed mode, they are brighter than the halogens were, but I haven't tried actually dimming one. I figure that they have a PWM designed into the driver circuit.

    Brownout, I have considered going with PWM, but I thought that I had read somewhere that it wasn't the most efficient way to go.
  5. Brownout

    Well-Known Member

    Jan 10, 2012
    PWM is very efficient, and you get 0 - 100% dimmability. Although, a standard line dimmer would be easier to implement.
  6. jay1028

    New Member

    Nov 9, 2008
    I would connect the leds to a 12v transformer of at least 2 amp rating and use a dimmer that is made for dimming 'magnetic low voltage', the transformer is considered magnetic versus electronic in a switching supply.


    I use the MLV series to control MR16 track lights that use a transformer and there is no flicker as long as you use the correct dimmer. I have under counter xenon lighting and they use switching supplies and not transformers and they require the ELV series of dimmer.

    Just a thought.

    These dimmers are designed to control 110V to the lighting,(not 12V) hence the 12 v xfmr required. I just noticed that they have an Electronic LED Driver, but I don't know anything about that.
    Last edited: Jun 12, 2013
  7. creakndale

    Active Member

    Mar 13, 2009
  8. Metalmann

    Active Member

    Dec 8, 2012

    That's what I used for kitchen under-cabinet lighting. I received four, but will have to repair one...it was DOA, and not worth shipping back. They gave me credit instead. I may be asking you guys how to troubleshoot, and repair it in the future.;):D

    I used the 5 meter strips, with the 5050-600 LEDs. Plenty bright. Think I use around 32 feet total, and not finished yet.:cool:
  9. JMac3108

    Active Member

    Aug 16, 2010
    PWM is the most efficient way to dim LEDs.

    You can reduce the current through LEDs to dim them, but the color will change. This is probably not a problem in your application, but is an issue when you're dimming LEDs in an LCD backlight. In that case, PWM is used so that the LEDs maintain the desired color at low brightness.
    Metalmann likes this.