Active input current shaper without an electrolytic capacitor for retrofit lamps applications

Abstract

The evolution of solid-state lighting technology has transformed traditional solutions in lighting. High-brightness light-emitting diodes (HB-LEDs) have become very attractive light sources due to their excellent characteristics, namely high efficiency, a long lifetime, and low maintenance. It is evident that HB-LED drivers must be durable and efficient in order to enjoy these advantages. Moreover, to replace incandescent bulbs, the ac-to-dc HB-LED driver must be simple and have low size and comply with international regulations (i.e., injecting low-frequency harmonics into the mains supply). With the last modifications regarding low-power lighting equipment (i.e., < 25 W), the authors have traditionally focused their efforts on increasing efficiency by sacrificing sinusoidal input current, yet all their solutions obviate the suppression of the traditional electrolytic capacitor of ac-to-dc converters, highlighting that this is the price to pay for a simple and low-size solution. This paper, however, puts forward the design of a simple and low-size ac-to-dc HB-LED driver for retrofit lamps without an electrolytic capacitor in order to extend its lifetime. The solution proposed here derives from a well-known technique used in the past, the active input current shaper (AICS), but without an electrolytic capacitor in this case. If the electrolytic capacitor of an AICS is removed, then low-frequency ripple arises at its intermediate dc bus, adding some distortion in the line input current over the proper natural one of an AICS. However, this addition is slight in comparison to the proper natural distortion of AICSs. Moreover, the low-frequency ripple at the intermediate bus is not transferred to the output with the help of the rapid output dynamic response of the AICS, which prevents flicker. This paper presents a theoretical analysis that guarantees a compromise between compliance with international regulations and the use of capacitor technologies other than the electrolytic design. Finally, a 24-W experimental prototype has been built and tested to validate the theoretical results presented in this paper.