High-Efficiency Asymmetrical Half-Bridge Converter Without Electrolytic Capacitor for Low-Output-Voltage AC-DC LED Drivers

• Published in: IEEE transactions on power electronics Vol. 28; no. 5; pp. 2539 - 2550
• Main Authors: Arias, M., Fernández Diaz, Marcos, Lamar, D. G., Balocco, D., Diallo, Almadidi Aguissa, Sebastián, Javier
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.05.2013; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: AC-DC converter; Applied sciences; asymmetrical half bridge; Boundary conditions; Capacitors; Capacitors. Resistors. Filters; Convertors; dc-dc converter; Dielectric, amorphous and glass solid devices; Electric currents; Electrical engineering. Electrical power engineering; Electrical machines; Electronics; Exact sciences and technology; LED drivers; Light emitting diodes; Lighting; Logic gates; low-output voltage; MOSFETs; Optoelectronic devices; Power supply; Reliability; self-driven synchronous rectification (SD-SR); Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Strontium; Topology; Transformers; Various equipment and components; Power converter; asymmetrical half bridge; Brightness; Power system stability; Driver; Power supply; Low frequency; low-output voltage; Implementation; Low voltage; Output voltage; Voltage stability; Power factor regulation; Multistage circuit; Bridge convertor; Lighting equipment; AC-DC converter; Multistage method; dc-dc converter; Up converter; Power electronics; Electrolytic capacitor; Topology; LED drivers; Switching; Light emitting diode; High efficiency; Ripple; Reliability; self-driven synchronous rectification (SD-SR)
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2012.2213613

Due to their high reliability and luminous efficacy, high-brightness light-emitting diodes are being widely used in lighting applications, and therefore, their power supplies are required to have also high reliability and efficiency. A very common approach for achieving this in ac-dc applications is using a two-stage topology. The power factor corrector boost converter operating in the boundary conduction mode is a very common converter used as first stage. It is normally designed without electrolytic capacitors, improving reliability but also increasing the low-frequency ripple of the output voltage. The asymmetrical half-bridge (AHB) is a perfect option for the second stage as it has very high efficiency, it operates at constant switching frequency, and its output filter is small (i.e., it can be also easily implemented without electrolytic capacitors). Moreover, the AHB is an excellent candidate for self-driven synchronous rectification (SD-SR) as its transformer does not have dead times. However, the standard configuration of the SD-SR must be modified in this case in order to deal with the transformer voltage variations due to the input voltage ripple and, more important, due to the LED dimming state. This modification is presented in this paper. Another important issue regarding the AHB is that its closed-loop controller cannot be very fast and it cannot easily cancel the previously mentioned low-frequency ripple. In this paper, a feed-forward technique, specifically designed to overcome this problem, is also presented. The experimental results obtained with a 60-W topology show that efficiency of the AHB may be very high (94.5%), while the inherent control problems related to the AHB can be overcome by the proposed feed-forward technique.