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Original question:

TIDA-010015-AC to DC power supply _Transformer sample and datasheet availability

TIDA-010015-Board Splitting exercise

balasubramani r
Expert 1170 points
Other Parts Discussed in Thread: TIDA-010015

Hi Everyone 

Since some size consideration we are planning to split the TIDA-010015 board in two stage like follows

Stage 1-Input, Filter, PFC boost section section in one board
Stage 2-LLC, Secondary section in one board. 
Later these board will be stacked together for full functionality.
So we would like to hear across from all technical team regarding this split, what could be the challenge if done this splitting process and what need to be taken care. Shall we proceed like this? How much size reduction shall be expected?
Please advise . 
  • 0
    TI__Expert 3860 points
    Hi Balasubramani,

    There is no problem in splitting the board into two if it is done at the PFC output. The output is high voltage DC with very little high frequency ripple. However, care has to be taken to provide local decoupling for the LLC stage (assuming that the bulk capacitor is part of the PFC stage) to contain HF current locally.

    I am not sure about getting any size reduction though. If you take a look at the design, you can see that the board is almost fully filled in all three dimensions. You get size advantage with stacking only if there is some unutilized space in the stacking dimension. But if your system has more available space say in Z axis, stacking in that direction will help you get space saving.

    The main pitfall of stacking two switching stages is the noise interaction between these two stages. There can be a pathway to get fringe fields from magnetic components to get coupled directly to the EMI filter, reducing its efficacy. Common mode coupling is also possible through parasitic capacitances. So shielding the EMI filter portion is a good idea if you are planning to stack the stages.

    Regards,

    Salil
  • 0 in reply to Salil
    Expert 1170 points

    Hi Salil, 

    Thanks for the detailed information. Local Decoupling in the sense an additional Bulk capacitor to be used in LLC input right? 

    Apart from shielding any special care need to be taken? Please advise

  • 0 in reply to balasubramani r
    TI__Expert 3860 points
    Hi Balasubramani,

    No. A high voltage ceramic or film capacitor capable of supporting the input ripple current of the PFC stage is sufficient. You may also split the total value of bulk capacitor into two, and use one each at the output of PFC and input of LLC stages.

    Shielding and decoupling are the important concerns I can think of. High voltage isolation requirements also are required to be met.

    Regards,

    Salil
  • 0 in reply to Salil
    Expert 1170 points

    Hi Salil,

    In reference to the above thread for minimizing the form factor , if my power design starting with 120VAC is the maximum input  (Ideal case 110V AC to 24DC is our requirement) then accordingly if i design, then the related passive components size get reduced right? do we really need to boost 390V? is there any specific requirement to have 390V DC at PFC output or we can set the PFC boost voltage to some other voltage ?   

    in that case if my output load is LED load(almost resistive load) then do we really need PFC boost section?

    Please advise.

  • 0 in reply to balasubramani r
    TI__Expert 3860 points
    Hi Balasubramani,

    Yes, the size of passive components willl be smaller with lower input voltage range. No need to boost to 390V. You need to boost only to 200V. There will be efficiency improvement in both PFC as well as LLC sections.

    The requirement of PFC is not because of the final load. It is because of the bulk capacitor in the AC-DC section. This is going to be present with or without the PFC section. Without PFC section, the charging of this capacitor is going to introduce current distortion. Please see this training to understand the need of active PFC: training.ti.com/power-factor-correction-pfc-basics

    Regards,

    Salil
  • 0 in reply to Salil
    Expert 1170 points

    Hi Salil,

    "Shielding and decoupling are the important concerns I can think of. High voltage isolation requirements also are required to be met."

    High voltage isolation in sense what you are meaning here. Do we need any other isolation technique to be introduced in this power supply? please advise. 

  • 0 in reply to balasubramani r
    TI__Expert 3860 points

    Hi Balasubramani,

    What I meant was that while splitting the board and stacking them one over the other, it is likely that the high voltage clearance and creepage requirements get impacted. This was a caution to pay attention to see if any potential situation for high voltage isolation violation develops due to the new physical arrangement of components.

    Regards,

    Salil

  • 0 in reply to Salil
    Expert 1170 points

    Thanks Salil for the clarification.