# Problem on Operational Amplifier

1. Feb 13, 2012

### lowqiumei

Hi,

Just I really short question. I have attached my assignment as a picture file. Don't worry I am not asking you to give me a solution.

I just want to know, in the question it tells us that there is a internal resistance of 1MΩ, and a supply voltage of 10V. I am really confuse, as all the questions i have did so far I have assume as ideal and has never taken consideration of internal resistance and supply voltage.

So my question here is, to find V_0, do I have to consider the internal resistance and supply voltage in my working?

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2. Feb 13, 2012

### Staff: Mentor

You should be able to sketch an equivalent circuit where the non-ideal characteristics are included, and then conclude whether or not they will affect the outcome.

3. Feb 13, 2012

### technician

the amplifier in your diagram has no negative (or positive) feedback, it is 'open loop'. Do you realise what that means.

4. Feb 14, 2012

### lowqiumei

Yes, So means I can no longer assume that there is no current flowing into operational amplifier and V+ is not equal to V-. And I also know that this is a voltage comparator.

5. Feb 14, 2012

### lowqiumei

Since it is a comparator, Am i right to say that when:
V+ > V- the output voltage will be +Vs
V- > V+ the output voltage will be -Vs

In this question since V- > V+, can i safely say that the output voltage will be -10v ?

6. Feb 14, 2012

### technician

Yes, that is correct (altho no sign is given for Vi I think you can assume that it is +)

7. Feb 14, 2012

### Staff: Mentor

In practice you can 'safely' say it if you've determined that the non-ideal characteristics of the op-amp won't leave the output in the active region rather than saturated (pegged to either supply rail). In this case the gain and input resistance happen to be sufficiently high so that this is not an issue.

8. Apr 11, 2012

### yasef

Operational Amplifier

I need a circuit that adds an AC signal with magnitude of 25mV and a variable DC signal between 0 to 5V, and applies it to a diode.

9. Apr 11, 2012

### Staff: Mentor

Re: Operational Amplifier

You might want to ask the question in the Electrical Engineering forum, or investigate "summing amplifier".