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Do you agree that this Full Bridge SMPS is in both CCM & DCM at the same time?

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treez

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Hello,
Do you agree that this 100W Full Bridge SMPS is in both CCM and DCM at the same time?
Due to the magnetising current being very large compared to the power current, the current in the output inductor indicates CCM operation, but the primary current indicates DCM operation.
(LTspice sim attached, also pdf schem and waveforms.
 

Attachments

  • FULL BRIDGE _CCM and DCM.TXT
    13.4 KB · Views: 80
  • Full Bridge SMPS _i(pri)=blue, i(OutputInductor)=red.pdf
    60.1 KB · Views: 132
  • Schematic _FULL BRIDGE _CCM and DCM.pdf
    23.2 KB · Views: 130

Re: Do you agree that this Full Bridge SMPS is in both CCM & DCM at the same time?

I think transformer model is not so accurate to consider simulation result/graphic true.
 
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Re: Do you agree that this Full Bridge SMPS is in both CCM & DCM at the same time?

I agree that the simulation model of the transformer is not totally accurate, but I believe it is good enough to be correct in showing that the primary current is in DCM , but the current in the output inductor indicates that the full bridge is in CCM. I believe this would be the case in a real converter built in the lab.
 
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Re: Do you agree that this Full Bridge SMPS is in both CCM & DCM at the same time?

There's nothing wrong with the transformer model, these sort of wavforms are to be expected.

When there is more than one energy storage inductor in the converter (like with a transformer coupled converter with finite magnetizing inductance), CCM and DCM don't completely describe the waveforms' shape. Sometimes we instead use the terms complete energy transfer mode or incomplete energy transfer mode to describe whether all stored energy in the inductor(s) equal to zero at the start of a switch cycle. For a single inductor converter, complete/incomplete energy transfer modes are equivalent to DCM/CCM modes, respectively. In your case you are operating in incomplete energy transfer mode. A more convenient way to view the waveforms is by summing the flux in each winding and looking at total flux, and you will see that it never settles at zero.
 

Re: Do you agree that this Full Bridge SMPS is in both CCM & DCM at the same time?

Thanks, from a control point of view, is the above Full Bridge SMPS in DCM , or CCM? I believe its DCM.
 
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