When should we choose continuous conduction mode (or discontinuous) when designing a boost converter?
DCM: more ripple current and inductor losses but easier to make stable. e.g. flyback but not scaleable > 200W , easy for no load. ( 1st order control system)
CCM: ideal for more constant loads with less input noise and less output ripple spectrum but more attention to fast reverse recovery diode losses.
- 2nd order system stability effects more difficult with wide load (gain) range.
Feedforward methods permit multiple outputs with tight magnetic coupling so on the main output needs to be regulated.
Interleave both methods for wide load range higher efficiency
add more phases to reduce ripple and more efficiency with load sharing.
Other modes: critical conduction mode and non-minimum phase (NMP) characteristic from right-hand pole (RHP)
2nd Order Effects means that if the loop phase margin drops to zero, it oscillates ( unstable). When you think adding a low ESR capacitor will help, consider the input capacitor, it reduces ripple but also phase margin. This problem was solved by design of the input filter, discovered by R. David Middlebrook at Caltech 1975.
"The Middlebrook Criterion is a graphical method for determining if the input filter of a switching mode power supply will cause instability or degrade performance parameters of a duty-ratio (voltage) programmed dc-to-dc converter switching-mode power supply. As usually applied, the output impedance of the input filter is overlaid on the open-loop input impedance of the switching-mode power supply at the worse-case conditions of low-line and full-load and low-line with shorted output." Ref
The key solution is to place the input filter resonance from P5 towards P4 to the left of P3 of the output filter.
The best authors in SMPS design were the late Abraham Pressman with updates by Keith Billings. Older versions are free at archive.org.