Understand the difference between continuous and discontinuous inductor current, master ripple calculation and critical inductance.
In the previous chapter we built the Buck converter. But Buck behaves very differently under varying loads: at heavy load, inductor current never reaches zero (CCM); at light load, current 'breaks' to zero (DCM). This chapter analyzes both modes, derives ripple formulas, and finds the boundary condition for mode transition.
Each section has an interactive simulation. Focus on the inductor current i_l1 waveform: does it reach zero? How large is the ripple? Try changing L, C, R values to verify the formulas.
Under heavy load, inductor current remains positive at all times — this is Continuous Conduction Mode (CCM).
2Ripple magnitude is determined by L, f, VIN, VOUT. Formula: ΔI = (VIN−VOUT)×D / (f×L).
3When load current is small, inductor current drops to zero and stays there within each cycle — this is Discontinuous Conduction Mode (DCM).
4Critical inductance L_crit is the value where inductor current minimum just touches zero. L > L_crit means CCM, L < L_crit means DCM.
5The inductor determines current ripple, the capacitor determines voltage ripple. Formula: ΔVout ≈ ΔI_L / (8×f×C).