Applying a Novel Current Balancing Circuit to LED Lighting

• Main Authors: Sheng-Chien Chou, 周勝千
• Other Authors: 胡國英
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/56f64d

碩士 === 國立臺北科技大學 === 電機工程系所 === 97 === In this paper, a current balancing cicuit is presented and applied to driving paralleled light-emitting diode (LED) strings. As generally acknowledged, LEDs are getting more and more popular instead of incandescent lamps, halogen light bulbs and street lights. Therefore, a single LED string does not provide enough illumination, and hence paralleled LED strings are indispensable. There are some features of the LED given as follows: (i) LED illumination is proportional to the driving current; and (ii) slight variations in voltage on the LED cause significant variations in current in the LED. Based on the mention above, the constant current control has been widely used to drive the LED up to now. Concerning the high efficiency and small volume of the LED product, it is indispensable for using the power electronics circuit to tackle energy conversion. However, up to the present the paralleled LED strings are driven based on the fact that each LED string is independently controlled, thereby causing the corresponding circuit to be complicated and the resulting cost to be high. Consequently, the proposed LED driving circuit is presented herein and has the following features: (i) it is simple in structure; (ii) it is suitable for different types of converters, such as buck converter, forward converter, resonant converter, etc.; (iii) there are two stages in such a LED driving circuit, one is a front-ended buck converter to provide a constant current for LED strings, and the other is a current balancing circuit to balance current among LED strings; and (iv) it has easy expansion by modifying the current balancing circuit. In this paper, mathematical derivation and software simulation are used to verify the feasibility of the proposed topology whereas some experimental results are provided to further demonstrate its effectiveness.