Problem on Operational Amplifier

[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?

 

[gneill]

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?

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.

 

[technician]

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

 

[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.

 

[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 ?

 

[technician]

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

 

[gneill]

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 ?

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.

 

[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.

 

[gneill]

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.

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