Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

How does Ideal Op-amp behave?

Status
Not open for further replies.
saad

saad

Advanced Member level 4
Joined
Jun 8, 2005
Messages
101
Helped
10
Reputation
20
Reaction score
7
Trophy points
1,298
Location
Pakistan
Activity points
2,080
Consider the ideal opamp in inverting configuration.

if i increase the value of feedback resistor outof bound the gain increases as expected but output fails to converge for certain value of R2 (in this case after 14 KΩ) input is 2 V p-p sine wave @ 1KHz.

why does this happen?

please note that this problem does not occur if i use uA741 instead of ideal opamp

Please be to the point in answering. and post as quickly as possible

Regards,
Saad
 

Hi

What opamp are U currently using and facing this problem?
 

try putting some load at the output of the amplifier. The 741 output has a path to ground where as the ideal opamp otuput does not.
 

Adding of load resistance does not work either :cry:


i m using PSpice. Actually if it is the problem of software then uA741 should also not work.

plz try to investigate it.

Regards,
Saad
 

Can you show waveform diagrams with normal and bad work and what r1/r2 you use ?
May be you have static overrange ?
 

plz post the waverform u generated , and the value of the resistors ..dat wud be a lil help to us and u
 

Google search: op-amp for everyone

From texsas instruments.

LizardK
 

You have to consider the supply voltage as the output peak voltage for the 741 cannot higher than (supply voltage - 1V), and the load resistance cannot be higher than 2kohm.
So you will know how much the output you can get and think of that with 2Vp-p input, how much the gain you can get.
nguyennam
 

ideal opamp has no offset voltage means there is same voltage applied between inverting and non inverting end
 

Hey dude,
I tried to simulate your circuit in PSPICE and MATLAB..Can u post the waveforms so that we can have a better understanding .....
 

saad said:
why does this happen?
Saad
Click to expand...

what just happen that you didn't mention the details so please put all details you have and I hope we can help you..
:D
 

saad said:
why does this happen?
Click to expand...

Hi saad
I've simulated your circuit in proteus simulator it support Pspice too.
I realized that your problem is not with R2 you can increase it to any value but first you have to change positive rail voltage of the OP-AMP to high value to make the OP-AMP gain the input voltage to the required voltage at output as well as the negative rail voltage
here I've set them to 1000v and -1000v while the voltage gain is 900000ohm/100000ohm = 9
so the largest output voltage will be 12*9=108
I hope this is helpful



I've uploaded the simulated circuit

enjoy!!!!!!!!:D
 

Hi Dear saad!

Well you know theorically you can increase the gain as much as you want. But in practice you are limited due to the Devices. In this case when you increase the gain and gain effects the output voltage, so the opamp have to support the load with more current. Unfortunately output current is not following and opamp would be overloaded. For example consider a 741u, maximum output current is only 25 mA. On the other hand output voltage is to be less than power supplies, you provide for opamp, i.e. if you support omamp with +10v and -10v you can not get more than +10v at output.

Thanks!
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top