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Power LEDs have changed the world of illumination. The number of experimentation on the ouput of power LEDs is the highest in the electronic hobby world. Before going through the intricacies of the luminance of power LEDs we must first know the characteristics of LEDs. A white LED is generally biased at a voltage range of 2.5 to 3.5V DC. Depending on the wattage of LED, the input current is determined. White LEDs are used for illumination purposes and are available right from 0.1Watt to 3Watts in general, with the same voltage characteristic but different current rating. Though very simplistic, it is interesting to use the following serially connected white LEDs in a chain. Here in this circuit 25 LEDs in a series have been considered a safe zone operation. We decide the bias voltage to be 3V DC in each of this rung. The total potential required to bias the LEDs is 25x3= 75V DC. A bridge rectifier is employed to rectify 120V AC line without any filter circuit being employe...

This is a Step-Up Booster Powers Eight White LEDs Project . Simal white LEDs are capable of delivering ample white light without the fragility problems and costs associated with fluorescent backlights. They do pose a problem however in that their forward voltage can be as high as 4 V, precluding them being from powered directly from a single Li-Ion cell. Applications requiring more white LEDs or higher efficiency can use an LT1615 boost converter to drive a series connected array of LEDs . The high efficiency circuit (about 80%) shown here can provide a constant-current drive for up to eight LEDs . Driving eight white LEDs in series requires at least 29 V at the output and this is possible thanks to the internal 36-V, 350-mA switch in the LT1615. The constant-current design of the circuit guarantees a steady current through all LEDs , regardless of the forward voltage differences between them. Although this circuit was designed to operate from a single Li-Ion battery (2.5V to 4.5V), ...