Lighting designs with flicker-free LED dimming

Posted on Feb 7, 2014

LED lighting, and the potential that it brings, is moving to the forefront of residential and commercial lighting markets. However, 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. Attempts to dim LED lamps have encountered a

Lighting designs with flicker-free LED dimming
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number of problems resulting in flickering and other undesirable behavior. This 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 while meeting new and emerging energy, power factor, THD, and EMI specifications. Incandescent-bulb-replacement LEDs contain an LED array connected in a series string and arranged to provide an even spread of light. The LED string must be driven by a constant current supply, which must be tightly controlled to ensure the level of luminous flux. 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; the required holding current is typically in the range of 8 to 40 mA. With LED lamps consuming less than 10% of the power of an equivalent incandescent lamp,...

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