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TIDM-1007: Issues when using normal MOSFET instead of GaN device

Ted Huh
Intellectual 2610 points
Part Number: TIDM-1007

Hi Manish,

My customer built their own totempole CCM PFC board using TIDM-1007 design.

They used normal MOSFET for highspeed switch. and when my customer and I tested build level 1 and level 2 DC, It worked OK.

However, when we tried to test level 2 AC, highspeed switches blew up.

so I checked every hardware and software for 2 weeks, but everything was normal. but still blew up when we try level 2 AC.

today I found the reason through TI journal below

it says :

"Because of the reverse recovery issue, a regular MOSFET cannot be used in a continuous-conduction mode (CCM) totem-pole PFC,
therefore Q3 and Q4 need to be gallium nitride (GaN) FETs, which have no reverse recovery."

but still I can't understand why this makes MOSFET broken. if current flows as the picture below, It seems there's no problem even if we use MOSFET instead of GaN.

Could you explain the reason more specific?

Best Regards,

Ted

  • 0
    TI__Mastermind 43730 points

    Ted,

     

    “It seems like using MOSFET instead of GaN was wrong.

    So could you explain why we can’t use normal MOSFET when we do TTPL CCM PFC?”

     

    I am not clear on the question, on one hand, you are saying using MOSFET was wrong and then you are asking why we cannot use MOSFETs?

     

    We do use Si MOSFET switches for the low switching frequency leg (Q1 and Q2). This is primarily done because of cost. They could be replaced with GaN if need be.

     

    The high-frequency legs theoretically could use Si as well but, Si MOS in general have higher reverse recovery losses which will in general, affect efficiency and a single hard switching event could possible destroy the FETs, and hence they are not practical.

     

    Please see https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8118374, see page 189, column 2first para. 

     

    Table 1, that gives a good comparison and also underscores based on devices available, that GaN is better for Totem Pole PFC.

     

    Regards

    Manish Bhardwaj