# Why does the 741 op-amp saturate to the top rail when inputs both grounded?

I created the following circuit in MultiSim:

It shows a typical 741 op-amp with voltage rails connected to +/-5V and both inputs grounded. With (for all intents and purposes) equal voltages at the inputs, I would expect the output voltage either to be 0V, or very close to it (perhaps ~800mV or less).

Instead the op-amp saturates at the positive rail (or at least maximum Vout). Why not the negative rail? Why not 0V?

Would connecting pins 1 or 5 have an effect?

Regards

• Because opamps have "infinite" gain, which will take any microscopic difference to either of the rails. – Eugene Sh. Mar 12 at 20:19
• What you're seeing is called the input offset voltage. Simply put, the voltage the 741 actually amplifies is the difference between its inputs, plus its input offset voltage (and since we're talking about the 741 here, the input offset voltage can be quite high. The 741 is not a good op amp.) – Hearth Mar 12 at 20:20
• @Hearth Aha, thank you. I didn't consider Vos and therefore the op-amp is actually not comparing two identical voltages. – Benjamin Crawford Ctrl-Alt-Tut Mar 12 at 20:23
• Given the earlier comments, I think you need to have a look at the model you are using for the 741. Does it assume some value of offset voltage? What is the assumed value of the open loop gain? Without that information we can only guess at why you are getting the results you see. – Elliot Alderson Mar 12 at 20:23
• @ElliotAlderson The model is the default MultiSim 741 model whose contents is not decipherable by me. I think a sufficient explanation has been offered by Hearth, though. ... I have to ask if that's a reference to Mr. Robot or your real name? – Benjamin Crawford Ctrl-Alt-Tut Mar 12 at 20:32