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TPS62140: Efficiency and Input voltage relation

Part Number: TPS62140

Hi ,

Can anyone please explain why increasing input voltage will decrease the efficiency of the buck convertor ?

As shown in the datasheet graph.



  • Vignesh,

    In general higher input voltage will increase the switching losses in the converter, therefore lowering the efficiency.

  • Hi 

    Can you please explain me why?



  • Vignesh,

    The efficiency is:

    Pout / Pin


    Pout / (Pout + Pdiss)


    Pdiss is primarily composed of losses in the IC and losses in the inductor.  There are other losses as well, but they can generally be ignored.  The IC losses are what we are concerned with here.  At the first order they can be approximated by"

    Pdiss (IC) = quiescent losses + conduction losses + switching losses + gate charge losses + dead time losses.

    The switching losses are equal to (Vin * Iout * (trise + tfall) *Fsw) / 2


    Vin is the input voltage

    Iout is the output current

    trise is the rise time of the switch node voltage

    tfall is the fall time of the switch node voltage

    Fsw is the switching frequency

    The switching loss will increase as Vin increases. Since that loss term is in the denominator of the efficiency equation, as it increases, the efficiency will decrease.