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I have been developing a 0-10v / 4-20ma analog output board

I have come across an issue when connecting to some certain loads I am experience signifcant oscillating where the output is swinging from 0v to the rail voltage (24v in this case).

Below is the schematic. The op-amp is an LM358

Analog schematic

J4 allows us to swap between 0-10 (1-2) and 4-20ma (2-3). AO_SIG1 is fed from an MCP4728.

Below are 3 captures from a scope, yellow channel is the output and blue channel is the output of MCP4728.

NO LOAD target 10v No Load

target 10v output with 1K resistor across output (A_OUT2+ - A_OUT2-) enter image description here

Target 10v output w. 10mA load set by a programmable load (DL24) enter image description here

I would appreciate any guidance to what could be the issue and how I might go about eliminating this oscillation.

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1 Answer 1

Reset to default
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Remove C19 or replace it with 100pF. It's adding a lot of phase shift to the feedback.

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  • \$\begingroup\$ Thank you, removing c19 does appear to stop the resonating. We're still getting some, now even when the output is disconnected. I will try and put a 100pf in place of the 1uF. \$\endgroup\$
    – Aaron N.
    Commented Feb 7 at 13:25
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    \$\begingroup\$ Put the 100pF cap from pin 1 to pin 2 \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Feb 7 at 13:29
  • \$\begingroup\$ Thanks for your assistance, very happy with the performance now. \$\endgroup\$
    – Aaron N.
    Commented Feb 7 at 15:27

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