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Selecting the best White LED driver topology

Published on Mar 15 2011 // Lighting Display circuits

Incandescent, and we bid Farewell to the ERA Will. Throughout the 20th Century, Edison invented the incandescent has withstood the test of LAMP Time, become the standard tool for General Illumination. But the new Lighting Technology – Light-emitting especially DIODE (LED) – Will eventually replace incandescent and fluorescent Lamps. When the Whole World because of Rising Energy costs and Save Energy Budget, incandescent Lighting Technology is clearly on the Wrong Side. Energy Consumed in an incandescent 97% is Wasted. Fluorescent Although Slightly Better, but Still 85% of Wasted Energy. Moreover, the average Life of these two Lights are only about 5,000 hours. In addition, fluorescent also use the Toxic Mercury Lamps, Light is the color emitted Rough. Both techniques can not be Compared with White LED – IT only 10 times the Life of the former, NOR the use of Toxic substances, and almost any color of Light. More Importantly, IT is no less fluorescent Light Conversion Efficiency.

  Thus, in General Lighting applications, the Transition to Energy LED Technology Will Greatly reduce consumption. A recent US Department of Energy Research study forecasts that by 2025, will be widely promoted in the white LED saves 10% of global electricity, save money to 100 billion U.S. dollars. Sandia National Laboratories, said that energy savings means that the global annual carbon dioxide emissions of power plants to reduce 350 million tons. Government leaders have begun to notice this. For example, recently announced a decree Australia end the use of inefficient incandescent lamps, as reducing greenhouse gas emissions and reduce household energy spending plan.
  Although large-scale white LED lighting today an ideal solution, but if the drive LED should spread to every electronic device in a light bulb, the designer also faces no small challenge. First, space constraints required LED drive must be compact and efficient. Also to be considered thermal factors, the reliability of its equipment for the lighting has an important effect brought to the design density limit. Finally, designers must carefully consider the impact of their products EMI.
  Because users can not access drives, designers can lower power (= 3 W) lighting business based on product type, non-isolated (COTS) sensors buck and buck / boost switch mode power supplies (SMPS) converter . The two circuits do not require transformers, and has many other advantages. This article will compare these two topologies, and discuss the trade-off for each topology.
2 Topology
  Figure 1 shows a basic configured as a buck converter (1a) and a basic buck / boost converter LinkSwitch-TN. LinkSwitch-TN in a single-chip IC integrates a power MOSFET, oscillator, simple on / off control scheme, a high voltage switched current source, frequency jittering, current limit and thermal-by-week shutdown circuitry, which simplifies the conversion design, and reduced component count. It is self-powered through the DRAIN pin, so no bias supply and associated circuitry. As a substitute the following for the 360mA range of linear and non-isolated power capacitor type of low-cost-effective solutions, LinkSwitch-TN with a first-class linear regulators and complexity of the regulatory function of higher efficiency than passive solutions, the power factor is higher than the capacitor-type program.
   Shown in Figure 1a buck converter has many advantages. First, it enables a selected corresponding LinkSwitch-TN devices and sensors to maximize the power output values. It also reduces the power switch and freewheeling diode voltage stress. In addition, the buck converter output flowing through the sensor is slightly lower than the average current buck / boost converter flows through the sensor output average current.
   Buck / boost converter configuration than the buck converter has a major advantage: it is and load the output diode in series. In a buck converter, if the MOSFET short circuit, input and output directly connected. If the buck / boost converter MOSFET short circuit occurs, the output diode reverse biased to block the channel between the input and output.
   In both converters, the AC input is from the D1, D2, C1, C2, RF1 and RF2 rectifier and filter. Two diodes enhance the performance and spread resistance line surge EMI. Designer must use a fuse on RF1 fire resistance, but is only used in the RF2 on a fire resistance. Linkswitch-TN in the on / off control is used to adjust the output current. Once the current feedback pin exceeds 49 µA,, MOSFET switch will fail to prepare for the next switching cycle.

Selecting the best White LED driver  topology.