Numerical - maximum and minimum output voltages for IC voltage regulator with adjustable current and input voltage

Q.  What is the maximum and minimum output voltages for IC voltage regulator shown below if adjustable current and input voltage are 98.5μA and 40 V respectively with the variable range of resistances from zero to 5 k ohm ?

LM 317 IC Voltage Regulator      
- Published on 20 Oct 15

a. 30.16 V & 1.25 V
b. 29.66 V & 0 V
c. 27.99 V & 0 V
d. 31.49 V & 1.25 V

ANSWER: 31.49 V & 1.25 V
 
According to the equation of output voltage for IC voltage regulator,

Vout = Vref [1+ (R2/ R1)] + IADJ R2

Considering R2 at its minimum value = 0 ohm, the output voltage is evaluated by,

Vout (min) = 1.25 [1 + (0 / 210 )] + (98.5 x10-6) x 0
= 1.25 V

For maximum value of R2 = 5 k ohm, the output voltage is,

Vout (max) = 1.25 [1 + (5 x 103 / 210)] + (98.5 x 10-6 ) x 5 x 103

= 1.25 [1+ (5000 / 210)] + (98.5 x 10 - 6) x 5000
= 31 + 0.4925
= 31. 49 V

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