1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Design of a Voltage Regulator

  1. Nov 19, 2008 #1
    I am to design a simple voltage regulator(resistors only) to deliver 7.00 volts to a load with a 10v power supply. The circuit will be 1 resistor in series with two parallel resistors. The last parallel resistor being Rload (which can vary from 1000 to 1500 ohms).

    Through experiment, I found that I could use a 100 ohm resistor for R2 which would make R1 a 40 ohm resistor. My problem is determining the value for R1 through calculation.

    R2 and Rload at 1000 ohms is 91 ohms. So I use the formula: (91/(91+R1)) * 10 = 7.0. Is the right in determing R1? If you plug 40 for R1 is works.

    I just need calculations proving this and I think I am having algebra problems solving for R1.
  2. jcsd
  3. Nov 19, 2008 #2
    I think the easiest way to do this is just pick a value for Rload and set R2 to the same value. So their resistance is effectively half of one of their values. For simplicity i chose 1k ohms.

    Then since you know you want the value across them to be 7 volts use ohms law to solve for the current. I = V / R. I = 7v / 500 ohms this gives 14mA.

    To solve for the value of the first resistor use ohms law again in the form of R = V / I. We can do this because we know the current flowing through the series circuit and we know we want 3V across the first resistor.

    R = 3V/ 14mA, R = 214 ohms.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook