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why pwm is having low effecinecy at low loads?

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bharatsmile2007

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Hi all

can any one explain me "why pwm is having low efficiency for light load conditions in DC-DC converters?"

Thanks
 

Hi

I assume by light loads you mean large impedance load .

If that is the case, it is due the the "wasted power" would become dominant when duty cycle becomes small, i.e. low modulation index.
when that happens, you load power will decrease while "wasted power" maintain the same. That degrades your power efficiency overall.

Best Regards,
Linfei
 
To keep pwm mode at light load, you need to disable zero comparator. That means DC-DC will allow inductor current discharge to negative current. It is wasted current. So that DC-DC will lose Eff because of this current
 
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