How Do You Calculate the Correct Resistor Values for a Simple Voltage Regulator?

[bengaltiger14]

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.

 

[Lambduh]

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.

 

[thomate1]

I would first like to commend you on your experimentation and efforts in designing a voltage regulator. It is important to understand the principles and calculations behind the design in order to ensure its effectiveness and reliability.

In terms of determining the value for R1, the formula you have used is correct. The voltage divider equation, Vout = (R2/(R1+R2)) * Vin, is commonly used to calculate the output voltage in a voltage regulator circuit. In this case, Vin is 10V and Vout is 7V, so the equation becomes 7 = (R2/(R1+R2)) * 10.

Using your values of R2 = 100 ohms and Rload = 1000 ohms, we can rearrange the equation to solve for R1:

R1 = (R2 * Vin)/(Vout - Vin) = (100 * 10)/(7 - 10) = 1000 ohms

This confirms that the value of R1 should be 1000 ohms when R2 is 100 ohms and Rload is 1000 ohms. When Rload varies from 1000 to 1500 ohms, the value of R1 will also vary accordingly.

To further validate your calculations, you can also use the power equation to check if the power dissipated by R1 is within a safe range. The power dissipated by R1 can be calculated as P = (Vin^2)/(R1+R2). In this case, P = (10^2)/(1000+100) = 0.1W, which is a safe value for most resistors.

In conclusion, your calculations and algebra are correct in determining the value of R1 for your voltage regulator circuit. It is important to double check your calculations and also consider factors such as power dissipation to ensure the effectiveness and safety of your design. Keep up the good work in your scientific endeavors!