Voltage regulator 7805

The Adjustable Voltage Regulator LM317 III How do you determine the resistors R1 and R2 for a desired output voltage Vout? Suppose you want an output voltage Vout = 5 V. For this you use the formula... Vout = 1.25 × (1 + R2/R1) + (0.00005 × R2) As the the resistor R1 you usually choose a resistance in the range of several hundred Ω. Hence R1 = 220 Ω is a good choice. Now you can use this in the formula, and you get... R2 = (Vout - 1.25) / 0.00573 Since you want an output voltage Vout = 5 V... R2 = 655 Ω