Driving LEDs with a PIC Microcontroller Application Note

Nowadays, applications increasingly make use of LEDs as a replacement for traditional light bulbs. For example, LEDs are frequently used in the design of automobile tail lights, signal lights, traffic signals, and variable message signs. LEDs provide several advantages over traditional light bulbs, such as smaller size and longer life. In many applications, the LEDs must be driven with intelligent control circuitry. According to the task at hand, this control circuitry must be able to fulfill various functions and tasks. In the following pages, solutions are provided for various application areas. These solutions are principal suggestions, not a concept ready for series production. One possible task for control circuitry is regulation of intensity, in case the LED brightness must be set to various levels. A solution is described in the section "Dimming". In addition, the specified brightness should be maintained at a constant level. Fluctuations in the supply voltage, for example, could lead to significant variations in current. In this case, one must insure that the current through the LEDs and thus the brightness is maintained at a constant level. This problem is covered in more detail in the section "Current Regulation". Another task for control circuitry is failure recognition. Modules consist of individual LEDs which can be tested for total failure. Additional information can be found in the section "Failure Recognition". A particular characteristic of LEDs is their strong temperature dependency. Since LED brightness is strongly dependent on temperature, the driver circuitry can carry out temperature compensation. Two possible approaches are described in the section "Temperature Compensation".