Contactless electronic ballast for high brightness LED lamps with mechanical dimming method

Advanced techniques in light-emitting-diode (LED) light sources allow LED lighting to appear in more and more applications. Besides providing the constant driving current source, LED ballast is usually isolated for safety specifications and dimmed for energy saving. Normally, LED ballast is designed with transformer for isolation and external circuits for dimming, increasing the challenges and complexity of the ballast design. To overcome the above limitations, this paper proposed a non-electrical dimming method based on a contactless transformer, taking full use of the transformer parasitical parameters to transfer energy by resonance. By adjusting the transformer air gap mechanically, the parameters in the resonance tank will change sensitively, which can be used for dimming control without additional components and control. In some extreme conditions, the proposed ballast provides a total environmentally-shield secondary enclosure with contactless transformer. Analysis, design example and prototype verification are given for the LED ballast and dimming control.