A Study of LED driver with Optimal PWM Control System

• Main Authors: Chen-Zu Wu, 吳承祖
• Other Authors: none
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/78976264470761111522

碩士 === 國立中正大學 === 光機電整合工程所 === 98 === Owing to the Light Emitting Diode (LED) with the advantages of high brightness, less power consumption, long lifetime etc, One traditional way of driving LEDs in general indoor lighting applications uses a resistor in series with the LED device. Although this driving scheme is simple and inexpensive, it suffers several disadvantages. Major drawback of a series connection of LEDs is their cumulative voltage drop that eventually limits the number of LEDs in a string. As a result, the linear regulators driving LED strings that have a below-maximum voltage drop operate with reduced efficiencies. In this LED driving approach, the only way to maintain operation of the linear regulators is to use LEDs with matched forward voltages, which inevitably increases the cost. Therefore, LED drivers employing linear current regulators, the drive voltage is provided by a switch-mode pre-regulator. The SMD802 is a peak-current control PWM IC with an internal high input voltage regulator that powers the IC from an 8-V to 450-V supply voltage. According to International Electrotechnical Commission (IEC) established the standard of Total Harmonic Distortion (THD) as IEC 61000-3-2. Knowing the power factor (PF) of electrical facilities and EMI noise filter are more important in these days. Evidence indicated that the LED driver indeed the kernel technology for switch power supply, combined with power factor correction (PFC) and EMI noise filter circuit. It is not only makes the LED driver in the universal voltage (85V ~265VAC) working environment, but also has a high efficiency (90%), high power factor (>0.9), wide power support (1W ~ 20W), pre-regulator output voltage and more efficient the highest point of LED driver temperature to control below 50oC.