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PMP11282 Rev A - Problems with LLC

Gareth Franklin30
Prodigy 40 points
Other Parts Discussed in Thread: PMP11282, UCC27714

Hi,

I have built a PMP11282 Rev A Evaluation board in order to asses the interleaved/boost LLC combination. The interleaved boost works fine but I'm having some issues with the LLC.

The LLC runs but if I turn it on into a load (say 10A or more) or I do a large load change (say 2A to 12V) it blows the half bridge fets and the UCC27714 Hi/Lo Side Gate driver chip. The circuit has been built as per the documentation. The only change that I've had to do is with the resonant capacitor (C519). I couldn't get the part recommended in the BOM as it was out of stock so I've used four (4) 47nF/1000V ceramic capcitors with two sets of 2 capacitors in parallel placed in series to give me the required 47nF value (I did it this way as I has some problems with the ceramic capacitor flashing over during turn on when I only had a single 47nF/1000V capacitor).


If anyone has any suggestions as to why this might be occuring I'd appreciate it.

Thanks for your help.


Regards,

Gareth

  • 0
    TI__Expert 3200 points
    Hi Gareth,

    Let me forward to tis to a knowledgeable AE. Unfortunately he is traveling so the response may be delayed.
  • 0 in reply to Brian Johnson96
    TI__Expert 7260 points
    Hi Gareth,

    Ceramic capacitor is not preferred as the resonant capacitor in LLC application, this is because its capacitance changes with voltage, this makes the LLC resonant frequency not constant which may cause strange behavior. Also ceramic capacitor usually has high dissipation factor, this will cause extra power loss. Please use a film capacitor as suggested in the BOM.

    What is the package of the ceramic capacitor you used? The voltage across the resonant capacitor is high. If the physical clearance between the capacitor terminals is not wide enough, it may cause arc then short circuit.

    Regards,
    Bosheng
  • 0 in reply to Bosheng Sun
    Prodigy 40 points

    Hi Bosheng,

    Thanks for your suggestion. I shall replace the resonant capacitor with a film capacitor and see if that resolves my problem.

    The package that I have used is a 1210 surface mount ceramic. I had a problem with arcing on start up so I switched to using 4 of these (2 sets of 2 parallel capacitors in series) and that resolved that problem. I have read that it's better to use a split resonant capacitor as it reduces the voltage across the capacitor particularly on start up.

    Regards,

    Gareth

  • 0 in reply to Gareth Franklin30
    Prodigy 15 points

    hello Gareth

    My name is Clodoaldo Prado, I am technician in electronics and I live in Brazil in the state of Paraná.

    I wonder if it could do the assembly and testing in PMP11282 Rev A project?

    I'm dificulades to get inductors and transformers of this project such as RLTI-1154 inductor and transformer RLTI-1149.

    You could directly at Renco Electronics manufacturer, or you fabricated these components?

    Regards, Gareth