New-Tech Europe | March 2016 | Digital edition

Power Control for LED Lighting

European Editors - Publitek Marketing Communications

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filament. This, in turn reduces the filament’s light output. Because of the comparatively long time that it takes for the filament to heat up and cool down, this switching is not noticeable to the user except possibly at the very lowest settings of the dimmer. However, with LEDs, which have much shorter response times, the low switching frequency of the main supply means that attempting to use a similar strategy to control the light output will result in significant flickering. As a result, LEDs require specialized power supply circuits that can deliver a more consistent voltage and current output to provide power that minimizes flicker without compromising efficiency. Although it is possible to manipulate light levels from LEDs by altering the current supplied to them, this results

in a drop in power efficiency at lower current levels. A power LED provides its best efficiency at the highest rated current. So, dimming behavior is still best obtained using pulse- width modulation (PWM) techniques, turning the LED on and off at higher frequencies than would be supported by traditional mains-based dimmer circuits. In a PWM-based power converter, a reference signal fed back to the controller is used to determine whether the transistor that feeds power to the load should be on or off. The reference is compared to a periodic signal created by a ramp generator. While the reference signal is higher than the ramp, the transistor is switched on. When the reference signal falls below the ramp, the transistor is switched off. The

mart lighting is one of the keys to the smart home.

Radio and network control can be used to alter the level of lighting either by direct control from the user, employing a dedicated remote control or with the help of a smartphone app, or automatically based on time of day. However, LED power control for lighting requires special consideration. Circuitry developed for traditional dimming control does not work well with the requirements of solid-state lighting. Most dimmers installed in homes are based on a phase-cut circuit. The advantage of this type of circuit is that it is very simple to design and is robust. The circuit works by simply cutting the supply to the bulb for a portion of the AC cycle, reducing the overall voltage supplied to the

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