LM317- ADJUSTABLE VOLTAGE REGULATOR -DESIGN



The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying up to 1.5 A over an output-voltage range of 1.25 V to 37 V. It requires only two external resistors to set the output voltage. It includes current limiting, thermal overload protection, and safe operating area protection regulators.
  • Output Voltage  Adjustable From 1.25 V to 37 V 
  • Output Current -1.5 A
  • Maximum input voltage =40V
FIG 1- PINOUT
RESISTOR – DESIGN
Aim – design an voltage regulator of 3.3V

FIG 2 –SAMPLE APPLICATION CIRCUIT


From data sheet of LM317,
Output Voltage Vo  =  1.25(1+R2/R1)
3.3  =  1.25(1+R2/R1)
Assume one resistor and find next one.
Let R1 = 220 ohms
3.3  =  1.25(1+R2/220)
2.64=  1+R2/220
1.64=  R2/220
R2= 360
Use near standard resistor of 330 ohms