Help, Cant get my first LM741 inverter circuit right.

Thread Starter

Scuttsy

Joined Jun 25, 2016
4
Hi everybody/anybody.
Im trying to configure my first (and basic) LM741 op amp inverter.
My Vcc is +5V, my input is a 1.5v DC battery, the positive connected to the inverting input pin 2, and the negative connected to non-inverting input pin 3.
Rf is 473k, Rin is 220k, so looking for a gain of about 2, and therefore looking for an output of about -3v, or thereabouts.
But using my multimeter, +ve lead on output, -ve lead on V-, I measure +2.06V
What am I doing wrong?
Thanks in advance
matthew
 
Are you supplies + and - 5v, or +5v and GND?

You need +/- 5v for this circuit to work.

Also, be careful using this op amp. It's output can only get within about 2v of any of its supply voltages. So, if you are using +5v and GND as the supplies, your usable output range may onlu be from +2v to +3v.

This is very common with op amps. Rail-to-rail versions will get you closer to the supplies. However, your circuit requires a dual supply.
 

Thread Starter

Scuttsy

Joined Jun 25, 2016
4
It is best to provide schematic along with the question.
Are you supplies + and - 5v, or +5v and GND?

You need +/- 5v for this circuit to work.

Also, be careful using this op amp. It's output can only get within about 2v of any of its supply voltages. So, if you are using +5v and GND as the supplies, your usable output range may onlu be from +2v to +3v.

This is very common with op amps. Rail-to-rail versions will get you closer to the supplies. However, your circuit requires a dual supply.
Oh, thanks very much.
Im trying to upload a photo, but cant for some reason. I posted the Q here too, can see photo there
https://electronics.stackexchange.com/questions/308741/help-cant-get-my-first-lm741-inverter-circuit-right
Have I connected my inputs correctly?
Thanks again
 

dl324

Joined Mar 30, 2015
9,154
That isn't a schematic, it's a picture of a breadboard with insufficient information to determine supply connections.

Your question was answered there. You're using a 40 year old design that has limitations that will trip up novices.

The datasheet shows that output voltage will be 1-3 volts below VCC, or 1-3V above the negative supply.
upload_2017-6-2_8-34-14.png
upload_2017-6-2_8-34-34.png

If you're operating with supplies of +5V and GND, typical output voltage swing will be 1-4V for light loads. Worst case, it would not function.

If you want to operate at 5V, you need a different opamp.

Note that I didn't say better. LM741 was used in many designs by designers who knew how to use it. When it was designed, it addressed deficiencies in other designs. One of the significant improvements was internal frequency compensation. These days, people tend to blame the tool when they choose the wrong one for the job...
 
You negative supply can not be GND, I believe this is pin 4.

Even with +/- 5v supply, the output can only reach +/- 3v.

The negative side of your battery must be connected to GND even while using dual supply.

You circuit is not powered correctly.
 

dl324

Joined Mar 30, 2015
9,154
My Vcc is +5V, my input is a 1.5v DC battery, the positive connected to the inverting input pin 2, and the negative connected to non-inverting input pin 3.
Rf is 473k, Rin is 220k, so looking for a gain of about 2, and therefore looking for an output of about -3v, or thereabouts.
Missed the fact that you configured the opamp for gain of about -2. We call that an inverting amplifier, not an inverter; that's a different thing.

upload_2017-6-2_9-24-28.png
What is the negative supply?
 
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