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| Electronic Projects Design/Ideas/Reviews Are you building an electronic project or want to? Maybe you need some assistance? Come and submit your electronic questions here and let our experienced members find a solution. |
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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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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)
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