LEDs and dimmers

Using existing triac controllers and wiring offers a number of challenges for LED lighting. To maximize the success and adoption of solid-state lighting for retrofit lamps, the LED lamps should be capable of dimming when used with existing controllers and wiring.

Lighting designs with flicker-free LED dimming article explores the typical TRIAC dimmer, some of the challenges of using it with LED lighting, and two interesting new power management solutions that solve these issues.

A common lighting dimmer available today is the leading-edge TRIAC dimmer. For an LED lamp to be dimmable, the lamp’s power supply must interpret the variable phase angle output from the TRIAC controller to monotonically adjust the constant current drive.

The difficulty of achieving this while keeping the dimmer working correctly may result in flickering, audible noise, and blinking as the light level is adjusted. These are generally caused by a combination of false triggering or premature shutdown of the TRIAC and inadequate control of the LED current. For reliable dimming down to low levels, the TRIAC must remain conducting almost to the point where the AC voltage falls to zero.


  1. lcd digital signage says:

    led dimer can save mucm power, and it is green method.

  2. Tomi Engdahl says:

    Samsung LED light bulb teardown includes objective dimming numbers

    Notice that the incandescent bulb (yellow line) does not dim linearly with power. It’s main achievement is that it does dim down to zero. A CFL does a better job of dimming with power, and the Samsung LED light is very good, dimming quite linearly with power. However, it drops out at just under 20% of its max output light. (Which, however, more than meets the L-Prize spec.)

  3. Tomi Engdahl says:

    Efficient dimming for LED lighting

    Lighting control with traditional TRIAC need not cut efficiency

    Using LEDs for lighting is an ever-more-popular application because of its high efficacy and long life. Dimmable lighting applications in residential and commercial installations will account for over 50% of all lamps and luminaires by 2015. There is wide installation of a variety of dimmers for traditional incandescent lighting, so LED-based light lamps and luminaries must be compatible with these dimmers.

    Fluorescent-based lamps and LED-based lamps today provide similar efficacies, but LEDs have a slight advantage.

    To properly trigger a TRIAC dimmer, the LED driver must provide a path that is independent of the driver’s input capacitance. This current path should be disabled once the TRIAC dimmer is conducting to avoid unnecessary power dissipation. The LED driver must also provide sufficient holding current to prevent the TRIAC-based dimmer from falling out of conduction and causing phase angle misinterpretations and potential flickering.

  4. Tomi Engdahl says:

    Cirrus tackles dimmer compatibility challenges with digital LED controller

    Cirrus Logic’s initial entry into the LED lighting market indicates that the company believes the key to success in this highly-competitive sector lies in achieving near-100% compatibility with the existing base of old-fashioned TRIAC dimming switches. The company has tested its new CS161X LED controller family, based on Cirrus’ new digital TruDim technology, with over 200 dimmer switches from around the world, and says the controller achieved 97percent compatibility

    According to Cirrus, the closest competitive LED controller performed at 71%, and the average among today’s current LED controllers was 50% compatibility.

    The CS161X’s digital intelligence allows the controller to identify the type of dimmer in use and adapt its dimmer compatibility algorithm to provide smooth dimming that mimics the response of an incandescent bulb, a response not possible with analog controllers.

    Just how important is dimmer compatibility? The US Department of Energy and its Energy Star program clearly believe it to be important: Dimming compatibility was a requirement for the Department’s L-Prize LED bulb competition, but it didn’t set the bar too high: Contest rules stated only, “Must be compatible with at least three widely available residential dimmers.” In addition, dimming switches are most prevalent in the US, especially California, and relatively un-common in Asia.

    Interestingly, the newer, so-called “digital” dimmers are the most difficult dimmers to ensure compatibility. The Maestro digital dimmer from Lutron can routinely make LED bulbs fail, while the old-style dimmers pose less of a challenge. (The “digital” refers to the ability of the switches to set and remember dimming levels; they still use the familiar TRIACs to chop the ac wave signal.)

  5. Inteled says:

    Very interesting page.

  6. Leds Screen Manufacturer says:

    Interesting but unfortunatly short article.

  7. Tomi Engdahl says:

    Control device simplifies LED dimming

    Inspired LED’s Triac Analyzer allows low-voltage LED systems to be controlled using almost any standard triac wall dimmer with a 12-VDC or 24-VDC plug-in power supply. The compact device applies a voltage to the dimmer and determines how long the dimmer takes to start conducting current. The amount of time is directly proportional to the position of the dimmer’s slide, and the Triac Analyzer adjusts the output to the LEDs accordingly.

    The Triac Analyzer serves as a cost-effective alternative to conventional hardwired systems, but still offers customers the flexibility to adjust their lights from a standard wall dimmer.

    TRIAC Analyzer

  8. Tomi Engdahl says:

    Lamp Dimmers – Leading and Trailing Edge

    A demonstration of the difference between leading edge dimmers and trailing edge dimmers using an oscilloscope.

  9. Tomi Engdahl says:

    Dimmer Power Factor and Variac Dimming

    What happens to power factor when phase cut dimmers are used, and a demonstration of using a variable transformer to dim incandescent and LED lamps.


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