The use of series-resonant converters (SRCs) in light-emitting diode (LED) drivers has increased due to its simplicity and high efficiency. Furthermore, the use of a SRC provides reduction of the low-frequency ripple in the LED current, originated by the bus voltage ripple. Thus, an analysis of the SRC aiming to define a design methodology to improve the current ripple reduction provided by the SRC is proposed. Moreover, a discussion about the main factors that have influenced ripple reduction and the limits for this attenuation is presented, which have not been explored in the literature hither to.Introduction: Light-emitting diode (LED) current low-frequency (LF) ripple is a limiting factor for LED lighting systems [1,2]. Pulsating current might influence the performance of LEDs, such as maximum current limitation, efficacy, reliability, lifetime and optical performance, as flicker and chromaticity shift [2]. The LF ripple may also have an influence on the electronic driver design, especially in avoiding the use of electrolytic capacitors [1-4]. Thus, the reduction of LED LF current ripple is a relevant research topic.The use of a series-resonant converter as a power control (PC) stage for LED drivers is a good alternative to reduce the current ripple, besides providing simplicity and high efficiency for the system [1]. However, no previous work in the literature has performed an analysis about the factors that have influenced SRC LF current ripple reduction. Moreover, no study presented the limit of this ripple attenuation, or proposed a methodology for SRC design aiming at current ripple reduction. Therefore, this Letter proposes a SRC design methodology that analyses the main factors that have influenced LF current ripple, and defines the maximum ripple reduction provided by a SRC, which are completely new to the literature.

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-This paper presents a design methodology for LED (Light-Emitting Diode) lighting systems based on photo-electro-thermal (PET) interrelationships. The proposed methodology uses only LED datasheet information, which makes experimental tests unnecessary to obtain the design parameters. The methodology allows identifying several design specifications, such as, luminous efficacy, heatsink thermal resistance, LED junction temperature and forward current, essential aspects to produce a satisfactory lighting system. Thus, it is possible to define the lighting system features based on standards requirements to obtain the desired system results. Initially, a review of several PET theories is presented, and a new mathematical analysis is performed, in order to highlight the main contributions of the methodology. An LED bulb lamp design is presented to exemplify the methodology. Finally, experimental tests with the proposed LED lamp resulted in a luminous flux of 1271 lm, with a luminous efficacy of 112 lm/W, and LED junction temperature of 79.67 ºC. The errors between calculated and measured luminous flux, luminous efficacy and LED junction temperature were 3.70%, 1.88%, and 3.85%, respectively. These results validate the proposed methodology.