Buck 48Vin, 40Vout, 5 A out. at full power.This circuit supply a LED panel. The feedback signal is the panel current converted to voltage at FB pin (from INA168).
Other components: 22uH (flat wire inductor from Coilcaft), 47uF output, 10 Ohm/1nF snubber on SW node, 0.007 Ohm current sense (Kelvin connected), F=180kz
The current output range is from 5A down to ~30mA. Output votage swing for this current range is from 40V to around 30V.
The circuit is stable in the whole range, but at critical conduction, which falls at ~ 1A output current; it breaks out into 3-10kHz oscillations, depending on Rcomp and Ccomp values. I tried to place my compensation zero in few different places, following the movement of Rload /Cout pole with load. To no avail.
Also I have noticed instability in the DCM region, just at the valleys of the SW ringing, due to resonance between L and switch output capacitance. I was able to eliminate these, but not at the critical conduction spot, by decreasing Q of the inductor with an RC snubber across it.
I need to stabilize my buck at critical conduction point. Compensation strategy anyone?
Jack
