Electrical – NTE941M Non-inverting OpAmp Has Non-zero Output with 0V Input

operational-amplifiersingle-supply-op-amp

I have a non-inverting, single-supply, variable gain op-amp circuit configured in accordance with this diagram:

non-inverting opamp

  • Vcc: +16V
  • Rf: 800k Ohm Potentiometer
  • R2: 100k Ohm

I have the potentiometer set to ~200k Ohm for a gain of:

$$
A=(1+R_f/R_2)=(1+200k/100k)=3
$$

I have confirmed that this works experimentally (A=3.07). However, what puzzles me is that when \$V_{in}\$ is left floating I get an output of 6V instead of approx. 0V. Consequently, any input below approx. 2V yields no change in output.

Per the datasheet for this OpAmp, the maximum \$V_{os}\$ is 5mV, which even when amplified by 3, is nowhere near 6V.

Edit:

Below is a drawing of my circuit.
amplifier circuit

Best Answer

Extracts from the NTE941M data sheet: -

  • Common Mode Input Voltage Range is typically ±12 V on a ±15 V supply.

This means that if one supply of the op-amp is ground (0 volts) then you must have your input signal greater than typically 3 volts above ground or all bets are off.

  • Output Voltage Swing (for RL ≥ 10kΩ) is typically ±14 V on a ±15 V supply.

This means that you cannot expect the output to get any closer to the 0 volt rail than typically +1 volt above it.

any input below approx. 2V yields no change in output

Do you understand why now?

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