Circuit identification? - Page 1
Forum section: electronics / beginners

author: etstudent
author_rank: Regular Contributor
timestamp: November 07, 2012, 08:45:11 pm
content: I need to identify what circuit this is. It I think its an inverting amp? What in the picture is the biggest clue to what this circuit it? Thanks for any help.

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 07, 2012, 08:57:53 pm
content: Hint: It has 2 inputs...

author: jeroen74
author_rank: Frequent Contributor
timestamp: November 07, 2012, 09:01:08 pm
content: I think most people would appreciate it when pictures like this are not 1.9mbAnyway, the circuit is a differential amplifier. It amplifies the voltage difference between the inputs. The potentiometer allows you to adjust the amplification factor.The give away is the feedback from output to the inverting input, and the voltage divider on the non-inverting input.

author: etstudent
author_rank: Regular Contributor
timestamp: November 07, 2012, 09:05:25 pm
content: I know I keep forgetting to take the picture on a lower resolution, apologize for that. Differential amp is not an option, only Inverting amp and non-inverting are the choices. Why would that be? Thanks for the help.

author: jeroen74
author_rank: Frequent Contributor
timestamp: November 07, 2012, 09:08:02 pm
content: Homework assignment?Check it yourself on Wikipedia:http://en.wikipedia.org/wiki/Opamp

author: etstudent
author_rank: Regular Contributor
timestamp: November 07, 2012, 09:18:40 pm
content: Its not homework, its a knowledge check at the end of the chapter. Its not something being graded, its for my own knowledge. I will look through the wikipedia page you linked me to, thanks.

author: etstudent
author_rank: Regular Contributor
timestamp: November 07, 2012, 09:24:45 pm
content: Got it, my instinct was right. Its a inverting amp based on the picture and configuration in the circuit on the wikipedia page. Thanks guys, I'm gonna have a few more questions in this "knowledge check".

author: etstudent
author_rank: Regular Contributor
timestamp: November 07, 2012, 09:34:45 pm
content: Same circuit. If the voltage at e2 is zero, the circuit could function as a?My guess is it would turn the circuit into a noninverting amp? That is just using common sense, and an educated guess.

author: jeroen74
author_rank: Frequent Contributor
timestamp: November 07, 2012, 09:46:05 pm
content: Yes, as a plain inverting amplifier. If the input it at 0 volts, it's as if the resistors aren't there. I'm guessing though that in real circuits, some real life opamp non-idealities come into play, like input bias current.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 07, 2012, 11:43:27 pm
content: its an opamp in differential configuration as jeroen said, with bias and gain adjust. though i dont know how the biasing calculated.

author: etstudent
author_rank: Regular Contributor
timestamp: November 08, 2012, 12:27:23 pm
content: New question about a D-A converter.If your D-A converter is calibrated to give an analog output of 4.3 for a binary input of 0111, what will its output be for binary input of 1111?I just don't get it, is there a formula I'm missing or just common sense? Any help I will be greatly appreciative, thanks.

author: jeroen74
author_rank: Frequent Contributor
timestamp: November 08, 2012, 01:38:42 pm
content: One D/A count is 4.3 volts divided by 7, or 0.614..V. So fullscale is then 15*0.614...=9.214...VWhat was your answer?

author: etstudent
author_rank: Regular Contributor
timestamp: November 08, 2012, 02:11:20 pm
content: Right! Thank you, I overlooked a part of the question. I got it right after looking at it again. I looked at it again after I posted this question, and I saw where I was off. Thank you again.

author: etstudent
author_rank: Regular Contributor
timestamp: November 08, 2012, 06:15:26 pm
content: New question for ya, let me know if I'm correct in my answer.Question is this, If the input voltage to the circuit is 5V, the output voltage is?By my calculations its .23V? Thanks for the help again.

author: jeroen74
author_rank: Frequent Contributor
timestamp: November 08, 2012, 06:43:08 pm
content: Yes 0.23VFirst divider divides by 100, amplifier amplifies by 1+(68/18)=4.77777... so overall 4.7777/100=~0.0475V*0.047=0.235V

author: etstudent
author_rank: Regular Contributor
timestamp: November 08, 2012, 08:10:06 pm
content: Hmm, I just added up all the resistors and divided that by 5V. Same result though.

author: etstudent
author_rank: Regular Contributor
timestamp: November 09, 2012, 04:22:50 pm
content: One more circuit here to analyze. The question is, what happens if I move the potentiometer input from pin3 to pin2?Is it Pin1 voltage goes negativePin1 voltage falls sharplyPin1 voltage rises sharplyPin1 voltage stays the sameI'm kinda lost on this one, i can't find it in my book where it suggests what would happen. Thanks for any help again.

author: etstudent
author_rank: Regular Contributor
timestamp: November 11, 2012, 07:43:30 pm
content: Sorry I didn't include the circuit, oops my bad.

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 11, 2012, 07:50:56 pm
content: If you move the potentiometer input from pin 3 to pin 2, pin 3 will float. Nobody can tell you what is going to happen.(Am I the only one thinking we are doing your homework?)

author: etstudent
author_rank: Regular Contributor
timestamp: November 11, 2012, 08:57:25 pm
content: Its not homework. Its not graded, and I believe the answer is the voltage at pin 1 will drop sharply. Its just an end of the chapter knowledge check 10 questions. Thanks for the help though I appreciate it.

author: etstudent
author_rank: Regular Contributor
timestamp: November 12, 2012, 11:33:19 pm
content: Thanks to everyone for the help, I got 8 of 10 right in the knowledge check end of the chapter. Onto a new set of studies, this set deals with industrial computers. First chapter was interesting so far, fascinating really. Again thanks for all the help, I appreciate it.