DC-DC Buck Converter Issue
Just an experiment:







simulate this circuit &ndash; Schematic created using CircuitLab

As you can see, I've made two adjustments to the circuit:


Reduce the value of R2
Replace C3 with a resistor


With C3 as the feedback, the oscillation was very chaotic. Changing it to a resistor stabilized the oscillation at around 7.3 kHz. There's a nasty startup transient, but I'll leave that as an exercise for the reader.