I'm trying to make a linear regulator using an op amp and a pass transistor.
Here is the circuit:
From my limited understanding you can predict the stability of the circuit's feedback loop by looking at the loop gain. By plotting V(fb)/V(in) I'm told the circuit has a phase margin of ~75 degrees and a gain margin of ~25dB.
When tested on a breadboard however the output is oscillating at around 7kHz at 100mV pp. I can reduce the frequency of this oscillation by increasing R5. I can also reduce the amplitude down to nothing by increasing C2 to 68nF (though I would like to avoid this to keep the response time down). The question is, What is causing the discrepancy between LT spice and reality?
Bode plot:
Scope trace:
No comments:
Post a Comment