# Problems with Pspice simulation(inverting op-amp)

#### 김찬우 1

Joined Oct 8, 2018
11
I am doing my pspice work and i cant understand why this results came out.

inverting gain should be -20k/10k=-2 so the output voltage is -10, but i got -6.769v

and other person's result is like below

i think he's and mine is same, i'm stuck in this problem.

#### ericgibbs

Joined Jan 29, 2010
12,197
hi 1,
What are the supply voltages to the OPA in your circuit.??
V+ and V- .?
E

#### MrAl

Joined Jun 17, 2014
8,059
Hi,

Yeah the supply voltage levels are very important especially with the ua741 because the output can not swing all the way to either rail. There could be as much as a 4v difference (maybe more) from rail to output at full swing either way.
The LM358 output on the other hand can get to within about 1.5v of the positive rail and to close to within 0v of the negative rail.

#### 김찬우 1

Joined Oct 8, 2018
11

i made other circuit and i found that amplification of vampl is working well according to the equation but the amplification of offset voltage is not accord to the equation.

#### ericgibbs

Joined Jan 29, 2010
12,197
hi 1,
The LM741 OPA is a very old amplifier with a very low performance specification.
Try a modern OPA.

Do you have an answer for my question in post #2.??

E

#### Jony130

Joined Feb 17, 2009
5,213
In Inverting configuration you need to add a negative supply (Vee) because for positive voltage at the output opamp wants to set the negative value at the output. So you need to add a negative supply into your circuit.

#### bertus

Joined Apr 5, 2008
21,235
Hello,

As said, for the schematic in post #4 you will need a negative power supply too.
Also the 5 Volts given will be to low, as the minimum voltage for the LM741 to work is 6 Volts.
Power the LM741 with + and - 15 Volts and the simulation will likely work.

bertus

Joined Mar 10, 2018
4,057
You are not meeting min supply on a 741 of +/- 10V for starters.

Regards, Dana

#### dl324

Joined Mar 30, 2015
12,661
LM741 are not for the faint of heart, or those who don't understand opamp specifications. When it was introduced, it was the best thing since sliced bread. That is no longer the case, though it is still useful. Particularly if you use vintage test equipment from that era; Tektronix used it in a number of their designs.

Joined Mar 10, 2018
4,057
A little moire info -

Regards, Dana.

#### ericgibbs

Joined Jan 29, 2010
12,197
hi,
This is a Homework question, we are supposed to guide the TS not give him a working solution.
E