A simple low-pass RC circuit is a single pole system and it's stable. In a DC-DC buck converter, we have a conjugate double pole due to the LC filter. Yet, we employ several techniques such as D-CAP or Type I/II/III compensation. Can someone tell me why?


1 Answer 1


Because you add feedback around the native double pole system. This makes the characteristics of the system different from those of the L.C alone, and necessitates loop compensation.

  • \$\begingroup\$ Can you please elaborate a bit? \$\endgroup\$
    – Arshiya
    Commented Jul 20, 2022 at 6:25
  • 1
    \$\begingroup\$ A passive 3-pole or 4-pole system without feedback is always stable. Only feedback can make a system unstable (intentionally or not). Self-excitement is possible with feedback only. \$\endgroup\$
    – LvW
    Commented Jul 20, 2022 at 7:15
  • \$\begingroup\$ So, for proper regulation at the output end, we add a feedback loop and that basically gives a -360° phase shift and the circuit starts to oscillate. So we need some sort of compensation to avoid this, right? \$\endgroup\$
    – Arshiya
    Commented Jul 20, 2022 at 16:15

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