Buck converter efficency

[Max01800]

I know that, for a buck converter if the Output voltage is constant and the load current increases, the efficency should incresse. But after a certain value of the output current, the efficency starts decreasing. Can somebody tell me why ?

 

[crutschow]

But after a certain value of the output current, the efficency starts decreasing. Can somebody tell me why ?

The dissipation from the resistance of the controlling MOSFET and power inductor increase the losses as the output current goes up.
So higher current converters use MOSFETs and larger inductors with lower resistance.

 

[Easy peasy]

at higher loads the I^2 R losses of every component carrying current, AC ( capacitors ) or DC goes up with I^2 - so yes, above a certain load the efficiency drops off - even the wires connecting the output to the load ( and the power source to the buck converter ) contribute to this.

 

[D.A.(Tony)Stewart]

The numerator is linear with current.
The denominator has mainly fixed losses and 2nd order losses