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Dear team,
When my customer doing simulation on below circuit configurations, they find TL082 ran into self-oscillation. When reduce the output capacitance from 330pF to 100pF, the oscillation disappear but when simulate this configuration, TL082 phase margin is -200dB. This doesn't make sense if they ran impropriate parameters?
Hi Zoe,
A few comments and questions:
1. Can the customer show how they simulated the circuit to find the phase margin? That value does not seem correct and it may be how the simulation was set up.
2. R81 looks to be used as an isolation resistor and if so, this resistor should be connected after the feedback loop (see example below).
Based on the fact that the oscillations disappeared after decreasing the capacitive load, it does appear to be a stability issue with the circuit. For reference, we have an FAQ with multiple resources on improving stability: FAQ - Documents on Op Amp Stability
Please let me know if you have any questions.
Thank you!
Best Regards,
Ashley
Hi Zoe,
In order to determine the phase margin in simulation, you will need to simulate an open-loop circuit by breaking the feedback loop and then generate the AC analysis curves. I've showed an example below.
This Precision Labs video also explains simulating for phase margin as well.
Is the capacitor in the feedback loop that is included in the simulation a part of the application? It will help with stability as well, so it is recommended to include. Can they also make sure they have the isolation resistor in the correct spot?
Please let me know if you have any questions.
Thank you!
Best Regards,
Ashley
Hi Zoe,
I agree with Ashley. Your circuit is not stable, even not when adding a 100nF in parallel to the feedback resistor:
But you could do it this way:
Kai
