Design the circruit No.2

Built and test the circuit shows below:

1. Components

     1 LM317 voltage regulator, 2 diodes, 1 LED, 3 resistors, 2 capacitors, 1 zener diode

2. Calculation

   Vref=1.25 Vout=5V and Vout=Vref(1+R3/R2)

   Then 5V=1.25 X (1+R3/R2)

             1+R3/R2=4

             R3/R2=3

              R3=3R2

    Check the data sheet of LM317

    R2=240R but i dont have 240R resistor, so i chose R2 270R. R3=3R2=810R dont have 810R resistor either, i chose 820R then.

   R1=V/I=(Vout-Vled)/Iled=(5V-1.8V)/20mA=160R

      

3.Design the layout

  I design the circuit show as below

  

4. Built the circuit

    Identify the terminals of regulater

     I build the circuit show as below and test the input voltage and output voltage

11.49V to input terminal for the voltage regulator

5.08V out off output terminal of the voltage regulator

     The circuit works fine.

5. Measuring and Explain

   Vs=12V
   Vd13=0.70V  
   That is the knee voltage of the diode

   Vd15=11.48V Vc15=11.48V 
   D15 and C15 are parallel after D13, so Vd15=Vc15=Vs-Vd13
   Vc16=5.08V 
   C16 is parallel with output terminal of the regulator, so Vc16=Vout
   Vr1=1.97V
   Vled=3.1V
   LED and R1 are in series and share the 5.08V output.
   Vr2=1.24V
   Vr3=3.83V
   available voltge of terminal in is 11.45V and available voltage of terminal out is 5.08V.