EE 240 - HOMEWORK - Solution 1

EE 240 - HOMEWORK - Solution 1 - OUT ) SOLUTION V OUT =...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
EE240-A2-2010 Assignment #1 SOLUTION Power-Limited Voltage Divider The problem is to design a voltage divider (as in the circuit diagram below) in which the output voltage is a predetermined fraction, f, of the supply voltage, 12V, and the power drain on the voltage source is close to, but no more, than 100 mW. Therefore, you need to determine R 1 and R 2 that satisfy these conditions. Find the pair of R 1 and R 2 that gives the correct V OUT and has a total power drain from the source of 100 mW. Now for the real-life complication. Resistors don’t come in all values so after you determine the exact R 1 and R 2 to get the correct V OUT , select the closest available ones from the standard values for 5% resistors. Look for these values in the posted file, StandardR&C.pdf. Recalculate the power to make sure you are still within the limit and determine the percentage error in your V OUT . Percentage Error = 100 x (Obtained V OUT – Desired V OUT )/ (Desired V
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: OUT ) SOLUTION V OUT = f*12V *= 12V * R 2 /(R 1 +R 2 ) (R 1 and R 2 make a voltage divider) So R 2 /(R 1 +R 2 ) = f (1) To calculate the power drain, The source current is I = 12V/(R 1 +R 2 ) so the source power supplied is P S = I*12V = 144V 2 /(R 1 +R 2 ) = 0.1 Watt Therefore (R 1 +R 2 ) = 1440 (2) to get exactly 100 mW. Combine (1) and (2) to get R 2 = f*1440 R 1 = 1440 - R 2 . As an example, suppose f = 0.65. R 1 R 2 V OUT Then we want an output voltage of 7.80V with R 2 = 936 and R 1 = 504 . To stay within the power limit of 100 mW, we must pick the resistors that have (R 1 +R 2 ) > 1440. (This makes sure the current is restricted below the max allowed.) The closest values satisfying this are R 2 = 910 and R 1 = 560 ; R 1 +R 2 = 1470. Then the output voltage is V OUT = 12V* 910/(1470) = 7.429V instead of the desired 7.80V. Percentage Error = 100 x (7.429 - 7.80)/7.80 = - 4.75%....
View Full Document

This note was uploaded on 07/17/2011 for the course E E 240 taught by Professor Shankar during the Spring '10 term at University of Alberta.

Page1 / 2

EE 240 - HOMEWORK - Solution 1 - OUT ) SOLUTION V OUT =...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online