2
\$\begingroup\$

I am providing 1.8 V as supply in a single supply voltage follower circuit. Now my concern is if I put negative voltage (Range -1.3 V to -500 mV) in the non-inverting pin, what will the output from the voltage follower circuit?

\$\endgroup\$
2
  • 2
    \$\begingroup\$ Check the datasheet of the OP amp you intend to use. Usually, input voltage below the negative supply violates the maximum rating of the op amp. So you should avoid it all together. \$\endgroup\$
    – Klas-Kenny
    Dec 7 '21 at 21:03
  • \$\begingroup\$ It's unlikely to be specified, as the input voltage you want to use is outside the permitted input range. It will depend on the particular opamp. The two most likely values are hard against one or the other rail. But it could be something else. The opamp may survive if you limit the input current with a series resistor. \$\endgroup\$
    – Neil_UK
    Dec 7 '21 at 21:31
7
\$\begingroup\$

Typically for 0~-300mV nothing much will happen except the op-amp will be railed near ground at the output.

Below -300mV, especially -500~-600mV or more (at room temperature), significant current will start to flow in the internal isolation and protection junctions. The output may shoot up to the positive rail (called "phase reversal") or do nothing much, but at some point, with many op-amps, the current may get to the point where permanent damage takes place.

Adding series current-limiting resistance may prevent that, but it's a not typically a good thing to do. Other op-amps on the same chip may be affected, for example, or supply current and heating may increase.

\$\endgroup\$

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.