Understanding comparators

1. Mar 4, 2012

Lildon

1. The problem statement, all variables and given/known data

I'm just not sure how to do this at all really. My instructor never talked about gains and I can't find anything useful on the web. Any help is appreciated.

2. Mar 4, 2012

Staff: Mentor

A differential amplifier amplifies the difference between the + and - input voltages by some gain factor A.

Vout = A(V+ - V-)

3. Mar 4, 2012

Lildon

so then it would be Vout = 1,000,000 * 1uV?

4. Mar 4, 2012

Staff: Mentor

What's the voltage on V+? What's the voltage on V-? What's their difference?

5. Mar 4, 2012

Lildon

V+ is 1uV and the other is grounded right? so 1 - 0 = 1uV * 1,000,000. I have hardly been taught this and I'm supposed to just figure it out. is V- not 0?

6. Mar 4, 2012

Staff: Mentor

Your diagram does not show V- as grounded. What's it connected to?

7. Mar 4, 2012

Staff: Mentor

Nooo.

The op-amp symbol is a triangle, and here it is pointing to the right. That's the output. The vertical side on the left is where the inputs are located. There are two of them, one towards the top of that vertical line, and it's marked + because it is the non-inverting input. The other input is located lower down on that vertical line, and it's marked - because the output will have a component that is the inverse of this.

The op-amp also needs to be powered from a battery or some dc power source, and by convention the connections for the dc source are drawn coming out of the oblique sides of the triangle: emerging from the top is the connection to the + terminal of the battery or dc source, and emerging from the bottom oblique side is the connection to the - terminal of the battery. In some cases, instead of having a negative dc source, the designer returns that connection to ground (0 volts), and that's the case here. The vertical line you see at the lower oblique side of the op-amp symbol is not an input, it's the power supply pin of the op-amp going to ground.

8. Mar 4, 2012

Lildon

Okay that makes more sense. I wasn't sure if he was talking about the positive and negative terminals of the voltage source or if it was the the amplifier. Thanks for explaining it.

9. Mar 5, 2012

Staff: Mentor

so now it would be Vout = https://www.physicsforums.com/images/icons/icon5.gif [Broken]

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