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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 matthewenter image description here

Matt Cudmore
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    don't use 741, especially not on 5v rail, it needs min +/- 10v to work. – Neil_UK Jun 02 '17 at 14:41
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    Please have a look here: https://electronics.stackexchange.com/questions/304521/reasons-not-to-use-a-741-op-amp – PlasmaHH Jun 02 '17 at 14:47
  • @TonyM: it still is not single ended, and I would assume he tries 0-5V not -5-5V – PlasmaHH Jun 02 '17 at 14:55
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    With a single +5V powere supply, NO op-amp can possibly output a negative voltage. – Peter Bennett Jun 02 '17 at 15:07
  • @Neil_UK, the TI datasheet specifies +/-5V min but I take your very valid point :-) But I'd say don't use the 741 because: it's rubbish. And it's been rubbish since about 1980, far superseded ever since. At least use an LM358N, that'll do a 3..32V single-ended supply. No point investing learning time in a dead-end part, OP. – TonyM Jun 02 '17 at 15:29
  • Quite right - apologies and comment corrected, Neil_UK and @PlasmaHH – TonyM Jun 02 '17 at 15:30
  • Schematics are generally more useful than a picture of the circuit. – JRE Jun 02 '17 at 15:33

1 Answers1

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What am I doing wrong?

Top of the "reasons for not using the 741" list is the minimum supply voltage being nominally +/- 10V (although it will work down to +/- 5V without any guarantees). Running off a single 5 volt rail is rather a waste of time.

Next on the list is "Input voltage range is typically from -Vs + 2 volt to +Vs - 2 volt" so, even if you ran the 741 from a 20 volt supply, your 1.5 volt input would contravene #2.

looking for an output of about -3v, or thereabouts

7th on the list is "Typical output voltage swing is -Vs + 1 volt to +Vs - 1 volt" - this means the output is restricted to producing voltages that are within 1V above the negative rail and 1 volt below the positive rail so, if you are expecting an output of -3V you are going to be disappointed.

Listen, don't ever think of using this part - get some modern decent op-amps.

Andy aka
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