kvos

hey guys, i need some help, i am new to electronics., i am in the process of building a voltage regulator for my delta ehe 10 watt, 12 v fan fan . i want to use a LM2941 regulator, my question is-what combination of potentiometer/ resistors will give me a voltage range that is closer to to 12v. the only problem is that i dont understand diagrams that well. if anyone can direct me to a site that can help me . i have got a guide that shows me a 'how to' with a lm317t regulator. any help would be appreciate it. thank you .

Phasor

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

kvos

thanks Phasor for the reply. so with lm2914 , if i use a 5K ohm potentionometer ,the resitor needed is a 42 K ohm to acheve as close a output voltage to 12. thanks heeps.

Phasor

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)