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10th March 2003 11:13 PM #1
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11th March 2003 04:45 AM #2
For an LM317:
When you use the regulator in the normal way (as shown in the datasheet), the equation for the output voltage is:
Vout = 1.25 * (1 + R2/R1) + Iadj * R2
If we use 240 ohms for R1, and 12V, ignore Iadj * R2 (because it's very small) then:
R2 = 240 * (12V / 1.25 - 1)
R2 = 2064 ohms
See http://neutrino.phys.washington.edu/...rICs/LM317.pdf
For an LM2914:
The equation is:
Vout = Vref * ((R1 + R2) / R1)
Vref is normally 1.275V, R1 is 1k, so:
R2 = R1 * (Vout / Vref - 1)
R2 = 1000 * (12V / 1.275V - 1)
R2 = 8412 ohms
See http://www.national.com/ds/LM/LM2941.pdf
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13th March 2003 03:42 AM #3
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13th March 2003 04:42 AM #4
If you use a 5k pot for R2, then use a 500 ohm resistor for R1, and adjust the pot until you read 12V on the output. (the value of the pot at this point should be about 4200 ohm)