LM317T Voltage Regulator with Pass Transistor

The heart of the LED chaser is the PIC 16F628A microcontroller, IC2. The program that runs on this chip controls the LEDs attached to the output port pins. Resistors R1 thru R8 limit the current through LED1 - LED8 to a safe level that won't damage the PICs I/O ports or LEDs. Resistor R9 provides a pull-up for the input connected to switch S1. R10 holds the PICs MCLR reset signal high. Capacitor C1 is used to decouple the 5 volt power supply to the PIC. The voltage regulator used is a LM2931-5.0, low-drop-out regulator and will maintain regulation with an input voltage down to 6 volts. Input voltage for the LED chaser should be between 6 volts and 14 volts to ensure power dissipation remains within limits. The LM2931-5.0 regulator is designed for battery powered and automotive applications and includes internal current limiting, thermal shutdown, as well as reverse battery connection without damage to itself or the circuit behind it. Capacitor C3 is important and must be fitted to prevent instability of the regulator output. i got this from: picprojects.biz



http://www.youtube.com/watch?v=KcsRgNZ116c&hl=en