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I am trying to design a half bridge isolated DC DC converter but I am encountering some issues.

  1. Is there an effective way to come up with a minimum value of capacitors C1 and C2. In all the papers that I read, they just seem to come up with a value as big as possible. The tricky thing is that I will not use any electrolytic capacitors, only film and ceramic ones in my design. This means that I cannot really use a very high value, but I am however using a very high switching frequency (100-500kHz probably). So I hope that this might reduce the need for a very large capacitor.

  2. It seems from Link 1 that there might be a problem regarding converter stability when a current mode controller is used. I am wondering if this converter could cause a problem when voltage mode control is used and the converters are placed in parallel... As I have always read that you need current mode control in order to put SMPS in parallel. Does anybody have any experience in this area regarding the stability of half bridge converters and paralleling them?

I have added a quick drawing for completeness.

Half bridge converter

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  • \$\begingroup\$ 1. Yes. Calculate the voltage droop for maximum load at minimum input voltage. How much can you trade off against turns ratio? 2. Parallel converters will always pose problems. Current mode control is one way to attenuate but not always solve the problem. If price isn't an issue, look in to ADP1046 or it's bigger brother for current sharing and phase shredding. \$\endgroup\$ – winny Oct 6 '16 at 13:20
  • \$\begingroup\$ Why the setup with C1 and C2 ? Why not one smoothing cap and one switch. This is what 9 out of 10 switching power supplies use. Think about what happens when those caps are very small. What will happen ? What value do you need these caps to be to not make that a problem ? Prove that with a calculation. Converter outputs in parallel: why do you need that ? You want voltage regulation but that is no good why is that ? After you've answered these questions look at stability because that is even more complex. \$\endgroup\$ – Bimpelrekkie Oct 6 '16 at 13:22
  • \$\begingroup\$ I'm really curious about the point behind paralleling SMPS. Even if the output power is an issue, this is a half-bridge and practically it is capable of providing nearly 1kW! Anyway, regarding your 1st question: In a HB converter, you want the mid-point to be as fixed as possible, so the divider caps must be large enough. Also, ESR and ESL are the things you must consider. \$\endgroup\$ – Rohat Kılıç Oct 6 '16 at 14:59
  • \$\begingroup\$ Well it's quite simple because they are all working on a different location and they will be connected to a common DC bus. Btw, the power of each converter will be about 300W. FakaMoustache, what do you mean with the setup with one switch? A flyback or forward? \$\endgroup\$ – Simon R Oct 7 '16 at 6:16
  • \$\begingroup\$ And I want to be sure that the system is stable because otherwise it might not be such a good idea to put all the work in it:) \$\endgroup\$ – Simon R Oct 7 '16 at 6:37

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