When should we choose continuous conduction mode (or discontinuous) when designing a boost converter?

closed as too broad by Marcus Müller, Elliot Alderson, Andy aka, Finbarr, Dave Tweed Dec 7 at 14:15

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 2
    To me this is too broad a topic for this site - we try to focus on specific issues and provide specific answers. To fully answer this will require an extensive discussion of both control and power electronics theory. Perhaps you should narrow your question to only one of the three you posted - either advantages/disadvantages, applications, or choice. – Adam Lawrence Dec 5 at 16:51
  • 1
    @AdamLawrence took your advice. Erased the part of applications and I think the choice is covered with advantages/disdvantages because one can clearly infer whether to use one or another if we are aware of the advantages of each mode. – Miguel Duran Diaz Dec 5 at 16:55
  • DCM may have HUGE RINGING on the switching node, thus huge radiated EMI, or huge electric-field interference for microseconds. – analogsystemsrf Dec 5 at 17:07
  • 1
    I think it's not as clear cut as your question implies. I personally believe that if you design it to be in CCM for "fuller" loads then you have to accept that it will drop into DCM on light loads hence you don't really choose BUT if, in your question you can paint scenarios for a given load voltage, load current and supply voltage range (yes the supply voltage range is very important) then a fair comparison can be made. I think you'll find that it is difficult to constrain a design with requirements that make CCM an exclusive turn-to solution. – Andy aka Dec 5 at 17:45
  • Looks like your revised question has attracted some attention now, which is all we can hope for. Good to see! – Adam Lawrence Dec 6 at 13:07
up vote 7 down vote accepted

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)

CCM problem

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." enter image description here 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.

Not the answer you're looking for? Browse other questions tagged or ask your own question.