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  • TI Thinks Resolved

SRK2000 LLC synchronous rectifier controller drain ringing

Prodigy 150 points

Replies: 4

Views: 228

Greetings!

I have built 7kwt 750-48v dc dc converter with LLC topology using ncp1396 primary controller and srk2000 secondary rectifier controller (when entering srk2000 or srk2001 in the part number field of the create thread form site says that there is no such part found).

on primary side i've got zvs achieved,M value of 6 and resonant frequency of LrCr around 47khz. secondary side has 2 turns on transformer and half wave rectifier with 2 sets of mosfets (3 mosfets in parallel on each side of the winding).center tapped on V out +. also i do have 22r+10nf rc snabbers on mosfets. srk2000 has custom gate drivers installed for driving heave gates in parallel. also i have put 5.1v zener diodes on the drain sensing inputs of srk2000  to protect it from a 100+v on inputs from drains.

Gate driving signals are more or less adequate,periodic.turn on is a little bit late,and turn of is not symetrical.one leg has longer width than other.

but my main concern is secondary ringing. Drains has 3x voltage spikes. i cannot say what the reason of that,but i cant tolerate such over-voltage.

This ringing at the front of a signal appears when load is connected to the rectifier. without load front and falls of a drain voltage is round and nice.

ZVS is achieved in primary half bridge even without a load,no problem with it.primary does not have voltage spikes.

Here how drain voltages look like

here is how gate driving signals look like ( turquoise trace2 and pink trace 3 are synchronous rectifier gate driving signals,yellow trace 1 is primary gate driving signal,and blue trace 4 is one of the synchronous mosfet drain.)

iam aware that its not a fault of a controller,it might be a fault of my design somehow (though design is very simple and i suppose typical as in datasheets) and i am asking for a help,i need it  desperately and have no one to ask for.

Thank you for your attention!

  • heres how secondary look like

    two halves of secondary and primary devided and spread on each side of a core (non magnetic gap heats up everything around).

    board with mosfets screwed to the heatsink and secondary synchronous controller board hangs ontop,soldered to the ground wire.

  • Hello Slavko,

    Thank you for describing your power supply design on E2E.  However, the devices you are using are not Texas Instrument devices, one is STMicro and the other ONSemi, and as such, we are unable to engage in this review.  Please contact either of those providers for assistance.

    Regards,

    ~Leonard 

     

  • In reply to LeonardEllis:

    Hi leonard! iam happy that you responded!
    sorry,i was not being attentive about brands.
    i would eager use Texas instruments controller for psecondary or/and primary. can you suggest one for me? is there are any LLC controllers with integrated syncronous rectification in TI production?
  • In reply to Slavko skala:

    Hi Slavko,

     I appreciate your willingness to look at a TI design solution.  Using the cross-reference tool on TI.com: http://www.ti.com/sitesearch/docs/universalsearch.tsp?searchTerm=ncp1396#linkId=8 , the UCC25600 might be a good replacement for the NCP1396: www.ti.com/product/UCC25600/toolssoftware .  Also look under the TI Designs section on this page, you will see several Reference Designs.

    And for the SRK2000, the LM27222 is one of many choices again using the cross-reference tool: www.ti.com/product/LM27222 .

    Let me say I am not an expert on this type of power supply design, so I am referring this to the Product Group will assist moving forward.

    Regards,

    ~Leonard 

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