simulate this circuit – Schematic created using CircuitLab

The feedback network I am using is a voltage divider with 4.7K and a 1K resistor. The node after the 4.7K resistor is connected to the inverting input of the amp. The node after the 1K is grounded. Attached is the hyperlink to the LF351 datasheet.

LF351 datasheet

  • 3
    \$\begingroup\$ Please use the tool and draw a schematic.(edit your question) or post one \$\endgroup\$
    – Voltage Spike
    Jul 29, 2019 at 0:16
  • 2
    \$\begingroup\$ You have a non-inverting amplifier with a gain of 5.7, and the max offset voltage at room is 10mV. So at the output you could see something like 57mV, probably a lot less, and it should not be saturating. Show a schematic clearly showing your input voltage, output voltage (what rail is it saturating to?) the supply voltages and any other connections. Then maybe we can help. Otherwise we have no way to guess. \$\endgroup\$
    – John D
    Jul 29, 2019 at 0:33
  • \$\begingroup\$ Wow i had no idea that circuit maker was there! Super useful and intuitive \$\endgroup\$
    – Sal M
    Jul 29, 2019 at 1:08
  • \$\begingroup\$ signal in is 1 V \$\endgroup\$
    – Sal M
    Jul 29, 2019 at 1:22

3 Answers 3


LF351 doesn't have rail-to-rail input capability, not even close.

With +/- 15 V supplies, the minimum common mode input voltage is specified as -11 V, with typical operation to -12 V. Translated to your +10.5/-0V supplies, this means you need to keep the input common mode voltage above 3 V (if you want to fuss around and take a risk) or 4 V (to be sure it will work).

You should either use a wider supply range (+/- 12 or +/- 15 V) or choose an op-amp better suited to the supplies you have.


The LF351 uses FETs are may be biased up to V+ but not within 3V above V-=0V

So your biasing to 0V is incorrect.

Better: Define your input and output range and thus define gain with offset specs.

  • then design your circuit.

You may consider an Op Amp that can sense near 0V or bias both inputs to V+/2


I have never seen an old LF351 but a TL081 is similar and has the "Opamp Phase Inversion" problem where the output saturates as high as it can go when an input has a voltage within 3V or 4V from the ground voltage in your circuit.

  • \$\begingroup\$ The TL081 is just the first op-amp that pops up as you place an op-amp in the schematic editor. OP was clearly too lazy to edit the op-amp and name it "LF351". \$\endgroup\$ Jul 29, 2019 at 3:47
  • \$\begingroup\$ Was not too lazy, I just did not see it. Schematic has been updated. I will be more careful next time. \$\endgroup\$
    – Sal M
    Jul 29, 2019 at 21:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.