My EE skills are pretty limited, but gradually improving. I am trying to increase the current capability of an analog output device by introducing the signal to an op-amp (LF 356N) circuit. My current configuration is as shown in the image -- however, I am seeing a steadily decreasing negative voltage on the output side.

For example, I activate my 12V and 24V power supplies, and the output signal will start around -1V and in the span of nearly a minute, it will decrease and plateau around -9.5 V.

Can someone please suggest what I may be doing wrong? enter image description here

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    \$\begingroup\$ What's your input during this time? Also, your opamp is missing +- symbols on its input \$\endgroup\$ – BeB00 May 16 '18 at 2:13
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    \$\begingroup\$ Rather than letting your input float, try grounding it. You can do this directly, or connect a 10k resistor between the input and ground. \$\endgroup\$ – WhatRoughBeast May 16 '18 at 2:21
  • \$\begingroup\$ My input is a DC pseudo-random signal ranging between -10V and +10V. For the op-amp, + on top, - on bottom. Okay, I will try grounding my input signal. Thanks! \$\endgroup\$ – Austin Prater May 16 '18 at 17:29

If your analog input is AC coupled you will need a path to ground for the input bias current of the amplifier. A resistor (say 100K) to ground from the non-inverting input will suffice for that op-amp.


simulate this circuit – Schematic created using CircuitLab

| improve this answer | |
  • \$\begingroup\$ Hey Spehro, my input is a DC pseudo-random signal ranging between -10V and +10V. I'll give the resistor a shot. Thanks! \$\endgroup\$ – Austin Prater May 16 '18 at 17:47

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