Hi,
After watching the power supply design videos of Dave, I got inspired to build my own. For my power supply however, I would like to replace the LT3080 with an op amp plus series pass transistor. The circuit worked fine when I used a resistive load, and I was able to change the output voltage by changing V3. But as Dave warned for in his video, I run into stability issues when adding a capacitive load. Of course I could just use the LT3080 to fix my problem, but for educational purposes I would like to fix this problem without one. I've added my circuit as an attachment to this post.
I am taught the basics of control systems / barkhousen stability criteria at university. So I did the analysis, derived the transfer function and plotted the transfer function in Matlab. This showed a phase margin of 36 degrees, which I guess is not enough and causes the oscillations. What they did not teach in our classes however, is how to actually solve this problem. I could of course decrease the output capacitance, but if I ever use a load with a capacitance greater than 20 uF, the circuit starts oscillating. Does anyone have a suggestion what I could do to solve this problem?