I was having trouble designing a small headphone amplifier that used lm358 as input stage. After verifying the push-pull output stage was correct and that every DC point was correct too (output resting at VCC/2, bias at correct voltage etc), I started to question the opamp's functionality.
I tested a simple circuit using lm358 in multisim with a single 9V supply, and I found out that, somewhy, the output voltage swings only from 6.6V to 2.4V (This is, VCC/2 +-2.1V).
Is that supposed to be like that? I didn't expect it to go all the way from 9V to 0V, but I expected it could at least swing from 8V to 1V.
Here's a screenshot of my circuit, showing the oscilloscope output for it. I'm using an AC input with 0.4V amplitude, so the output was expected to swing between 8.5V and 0.5V, but it only goes from 6.6V to 2.4V:
The datasheet emphasizes the large output swing for this chip. So I expected it to go further. Is this correct?
Thanks!
Best Answer
Here is what is probably a better simulation using LTspice and a TI model for the LM358. I modified the circuit slightly, using 5.6K/3.9K for the bias divider to center it near the middle of the no-load output range (~3.7V). Input is 370mV.
You can see it saturating badly on the first cycle, then it settles down towards the middle of the range.