buck output ripple againts load variations

[alimjoco]

Does the output ripple of a a buck converter also depends on variation of load current? Or it only depends on the capacitor value, inductor current ripple, switching frequency and duty.

 

[mtwieg]

Output ripple = ripple current * impedance on the output, including the load impedance and capacitor impedance. The capacitor impedance should dominate the total output impedance, so load variations shouldn't matter significantly.

 

[alimjoco]

ah i see..since the total output impedance includes also the ESR va;ue(3m ohms), it seems that the total output impedance will be small right?? That is due to to the total parallel computation including the ESR..Am i right>?

 

[mtwieg]

Right, so as long as the impedance of the capacitor (which may be dominated by ESR depending on the cap) at the switching frequency is much lower than the load impedance, then the ripple will be determined by the capacitor only. Unless the capacitor is very inadequate, that should always be the case.