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A novel twin-bus converter using n + 1 active switches is proposed for the n-string LEDs to be dimmable from true zero to the rated current level. With the proposed twin-bus structure, the n-switches that perform the current-loop regulation can operate at very high frequency because of significantly reduced voltage stresses, while achieving high efficiency over a wide load range. With operating frequency exceeding 1 MHz in the test case, the proposed LED driver demonstrates ultra compact size inductor and fast slew rates of the LED current. The dimming controlled switch, however, can operate at a low frequency to ensure high-efficiency operation without light flicker. The detailed power stage operating principle and control scheme of the individual string current for the presented converter are described. Experimental results of a 3-string 50-W LED driver hardware prototype show that the independent string current can be regulated from zero to the desired 350 mA for dimming control. A peak efficiency of 98.3% was achieved with 1.08 MHz switching frequency.Index Terms--High efficiency, DC-DC converter, light emitting diode, Dimmable LED drive, offline LED lighting 978-1-4244-5287-3/10/$26.00 ©2010 IEEE

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SUMMARYThe AC-DC power supply for LED lighting application requires a long lifetime while maintaining highefficiency, high power factor and low cost. However, a typical design uses electrolytic capacitor as storage capacitor, which is not only bulky but also with short life span, thus hampering performance improvement of the entire LED lighting system. In this article, a SEPIC-derived power factor correction topology is proposed as the first stage for driving multiple lighting LED lamps. Along with a relatively large voltage ripple allowable in a two-stage design, the proposal of LED lamp driver is able to eliminate the electrolytic capacitor while maintaining high power factor and high efficiency. To further increase the efficiency of LED driver, we introduced and used the twin-bus buck converter as the second-stage current regulator with Pulse Width Modulation (PWM) dimming function. The basic operating principle and the deign consideration are discussed in detail. A 50-W prototype has been built and tested to verify the proposal.

SUMMARYIn this paper, a single-stage integrated bridgeless AC/DC converter is proposed. As compared to its counterpart that is composed of totem-pole boost power factor correction (PFC) cascade fly-back DC/DC converter, the studied circuit has less components number while overcoming the limits of the totem-pole type. Thus, it is suitable to the low-power LED lighting applications. Furthermore, when both PFC inductors L b and magmatic inductance L m of the transformer TR1 operate at discontinuous current mode, the bus voltage v CB can be used to decouple the ac input and constant dc output power. Thus, the approach of increasing bus voltage ripple is employed to eliminate electrolytic capacitors and obtain long operation lifetime. Additionally, it is able to be compatible with our studied twin-bus configuration for increasing the overall efficiency. A 50-W hardware prototype has been designed, fabricated, and tested in the laboratory to verify the proposed converter validity.