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How huge? You can expect slight high frequency ripple on the output because the feedback does not operate instantaneously, due to stray circuit capacitance.It's not huge peak to peak. Any thoughts?
How huge? You can expect slight high frequency ripple on the output because the feedback does not operate instantaneously, due to stray circuit capacitance.
The square-wave response and AC Bode plot of your amp show no significant signs of oscillations, overshoot, or peaking, so the problem may be in the layout.
Do you have a 0.1uF ceramic decoupling cap directly from the V+ pin to ground?
Are all output signal wires and connections well away from the input connections?
It appears that your amplifier has a gain of less than one. 20k/75k=0.27
The LM324 is only compensated for unity gain, so it's very likely to oscillate. You will either have to increase the gain, or else add additional compensation.
It appears that your amplifier has a gain of less than one. 20k/75k=0.27
Your simulation is not actually using the LM324 model, instead you are using the built-in UniversalOpAmp2 model, which is a much faster opamp than a LM324. When I resimulated with the LM324, I get overshoot and ringing (marginal stability). If I add >30nF of capacitance across the 30Ω Load, then it oscillates just as you describe.
The problem is the additional phase shift in the feedback loop caused by the Darlington, amongst other things. The faster opamp has a better phase margin, so is less likely to take off...
It appears that your amplifier has a gain of less than one. 20k/75k=0.27
The LM324 is only compensated for unity gain, so it's very likely to oscillate. You will either have to increase the gain, or else add additional compensation.
I was simulating with the LM324, switched to see the difference and forgot to switch back before I posted. Sorry for the confusion.
Thanks its starting to become clearer. I took out the capacitor on my output(real circuit i made...not a simulation) and now believe it or not it is still oscillating but MUCH less. I had a .033uF in there which made it very bad. Do you think I could now take care of this much smaller oscillating with a 100pF in parallel with the feedback resistor in real life?
It's the equivalent non-inverting gain that's used to determine stability and that can never be less than 1. So an op amp compensated for a gain of 1 will always be stable with any value of inverting gain, even less than one.It appears that your amplifier has a gain of less than one. 20k/75k=0.27
The LM324 is only compensated for unity gain, so it's very likely to oscillate. You will either have to increase the gain, or else add additional compensation.
Why did you add >30nF of load capacitance. That's a lot of stray load capacitance.Your simulation is not actually using the LM324 model, instead you are using the built-in UniversalOpAmp2 model, which is a much faster opamp than a LM324. When I resimulated with the LM324, I get overshoot and ringing (marginal stability). If I add >30nF of capacitance across the 30Ω Load, then it oscillates just as you describe.
The problem is the additional phase shift in the feedback loop caused by the Darlington, amongst other things. The faster opamp has a better phase margin, so is less likely to take off...