I am attempting to calculate the power rating of R1 and R2 on page 1 of the datasheet of the LM317 voltage regulator (https://www.onsemi.com/pub_link/Collateral/LM317-D.PDF). I will use 240Ω for R1 as suggested by the datasheet and 2.05KΩ for R2 to yield 12 volts.
The datasheet on page 7 reads "
the LM317 develops and maintains a nominal
1.25 V reference (Vref) between its output and adjustment
terminals. This reference voltage is converted to a
programming current (IPROG) by R1 (see Figure 17), and this
constant current flows through R2 to ground."
1) Would the power rating of R2 be as follows:
P=(Vref)(minimum load current)
= 1.25 X 0.01
= 0.0125
So use a resistor with a power rating greater than or equal to 0.025W (double calculated power rating or 0.0125+0.0125)
2) How do I calculate the power rating of R1?
The datasheet on page 7 reads "
the LM317 develops and maintains a nominal
1.25 V reference (Vref) between its output and adjustment
terminals. This reference voltage is converted to a
programming current (IPROG) by R1 (see Figure 17), and this
constant current flows through R2 to ground."
1) Would the power rating of R2 be as follows:
P=(Vref)(minimum load current)
= 1.25 X 0.01
= 0.0125
So use a resistor with a power rating greater than or equal to 0.025W (double calculated power rating or 0.0125+0.0125)
2) How do I calculate the power rating of R1?