Analysis and Practical Evaluation of Dimmable Passive Light-Emitting Diode Drivers for Smart Lampposts

Passive light-emitting-diode (LED) drivers have recently been adopted by the lighting industry in street lighting applications due to their high robustness against extreme weather conditions, long lifetime, and high percentage of recyclable components. With the increasing trend of smart lamp posts, there are new requests for dimmable passive street lighting systems. This article presents a novel dimmable technology for passive LED drivers. By adding a switchable parallel capacitor across the input current-limiting inductor, a small freewheeling period between the inductor and capacitor can provide an artificial dead angle, which reduces the power for a passive half-bridge voltage doubler LED driver. The operating principle of this new dimming mechanism is explained, and a full analysis is included. The new dimmable mechanism has been practically confirmed in a 120-W passive LED system. The theoretical and practical results are in good agreement.