Understanding op amp circuit

[d4n13l]

Hi,

I'm starting with op amps, from the schematic, I get 0-1V from voltage divider, and I would expect to see the same voltage in the output of the op amp due to the negative feedback but it stays frozen at 1.9V no matter the +IN voltage. Could someone help me figure out why isn't it working?

[rstofer]

Check the data sheet.  The op amp probably can’t work within a couple of volts of the rails.

[Ultron81]

Yeah, what he rstofer said. If you want the input to drop to 0, you either need to supply a negative supply voltage to the op amp, or use a single-supply op amp that can go to 0V like a LM358.

[d4n13l]

It worked with the LM358, I didn't know that not all op-amps can be used like that. Thanks

[nigelwright7557]

Check the data sheet.  The op amp probably can’t work within a couple of volts of the rails.

Try a rail to rail op amp.
Not all op amps work close to the rails.
In fact some invert the output if close to the rails.

[David Hess]

The LM301 is a fabulous part for many reasons but those do not include input and output ranges which extend to the negative supply.

Note that even if the input voltage was higher, that circuit still would not work as shown because the LM301 requires external compensation to be unity gain stable.  Usually this would be a 33 picofarad capacitor between pins 1 and 8.  The LM358 you tried has the compensation capacitor built in.

[magic]

It worked with the LM358, I didn't know that not all op-amps can be used like that. Thanks

It gets worse. With other parts like RC4558 and TL072, tying IN+ to ground makes OUT and IN- fly to the positive rail.

Phase reversal also occurs in almost all JRC audio opamps, as they are variations of the same old 4558 topology. Probably many power amplifiers too, but you are unlikely to feed them signal which exceeds their negative supply rail and you are screwed anyway if you do.

[rstofer]

w2aew has a video that shows this output problem


Around 8 minutes in he shows output clamping.