# Homework Help: OP Amps Comparators

1. Oct 24, 2015

### 123ryoma12

1. The problem statement, all variables and given/known data
https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/73/73750-4bf3d2aa03a724fcf0b13a6b1111902f.jpg [Broken]

3. The attempt at a solution
V+ > V- for Vout to be +16V
V+ < V- for Vout to be -16V
V+ = -8x(in)
V- = (-15x18)/30 + (15x12)/30 = -3
My attempt on it was that -8X(in)V greater or equal to -3V for Yout to +16V
(EDIT: Then that would be Xin < 0.375 for it to be +16V
But the answer is saying the opposite.)

But this was the solution and it showed the opposite (that -8x(in) less that or equal to -3)

https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/73/73751-f11fe983c5d64cca6eb97cffb930e594.jpg [Broken]This was the answer

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Last edited by a moderator: May 7, 2017
2. Oct 24, 2015

### CWatters

Do you mean.. Yout is 16V if -8X(in)V greater or equal to -3V ?

In which case that is correct.

Their solution looks correct to me. As a check try setting Xin = 1V and work out Xout, Yin, Y+ and Yout.

3. Oct 24, 2015

### 123ryoma12

My mistake for not completing my answer.
And yes, that's what i meant, When -8(xin) was greater than -3 then the Vout would be +16V
Then that would be Xin < 0.375 for it to be +16V
But the answer is saying the opposite.

4. Oct 24, 2015

### 123ryoma12

Yout is -16V when Xin < 0.375

5. Oct 24, 2015

### CWatters

No the graph shows that when Xin is < 0.375 then Yout is +16v. For example at t=0.

6. Oct 24, 2015

### rude man

The output graph is wrong. The transition of Yout going from -16V to +16V occurs when Xout = -3V, not -1V as shown.

7. Oct 24, 2015

### rude man

No.

8. Oct 24, 2015

### 123ryoma12

Sorry guys, I just read the graph incorrectly.
Thanks for pointing that out.

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