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Original question:

PMP20873: PMP20873

PMP20873: PMP20873

Mownika Gudupuru
Intellectual 330 points
Part Number: PMP20873

In totempole, usually we have 2 Gan Fets and 2 Mosfets.  can we replace the two Mosfets which 2 Gan fets for faster switching action???

  • 0
    TI__Mastermind 26215 points

    Hi Mownika,

    In totem pole PFC, the MOSFETs act as a low frequency rectifier that operates at the line frequency. The main loss mechanism in these MOSFETs are conduction loss, not switching loss. Efficiency improvement would come from reducing Rdson or placing additional MOSFETs in parallel. GaN FETs in the rectifier positions would not provide much benefit since these switch at the line frequency.

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    Intellectual 330 points

    Hi Benjamin,

    Could u please elaborate the answer?? In the above mentioned reply you mentioned both mosfet and Gan operate at line frequency. So what was the difference.

    Also what happens if we use only Ganfets in the circuit??

  • 0 in reply to Mownika Gudupuru
    TI__Mastermind 26215 points

    Hi Mownika,

    The GaN FETs operate at the switching frequency but the silicon MOSFETs operate at the line frequency. The silicon FETs are rectifiers. With GaN, the 3rd quadrant voltage drop is often several volts, much higher than the body diode of silicon MOSFETs. For rectification you have to carefully manage the dead time or else this high 3rd quadrant voltage will lead to much larger conduction loss if you were to use GaN FETs for the rectifiers.

    Ultimately, you do not get any benefit from the improved switching performance of GaN because the rectifiers operate at such a low frequency and you actually have additional challenges because of the much large voltage drop when GaN operates in 3rd quadrant.  

    Best Regards,

    Ben Lough