relationship between output voltage ripple and load current

[DimaKilani]

Hi all,

I designed a switched capacitor DC-DC buck converter. I want to measure the voltage ripples.

Q. what is the relationship between load current and output voltage ripple ?

I know that Vripple= Iload/C*fsw. Now when Iload is increased, fsw has to be increased to reach the output voltage level. which one has higher impact on Vripple ?! Iload of fsw ?

Regards,
Dima

 

[TuAtAu]

switching frequency is usually fixed. (depends)

In other words, to get a constant I load, you have to switch ON and OFF, and current across your inductor is going high (when ON) and going low (when OFF) like a triangle wave, then you filtered it with a capacitor to get the so called 'constant' DC voltage with ripple.

when I load is higher, in switched mode power supply, your ripple current across your inductor also higher, thus your ripple voltage also higher as well.

 

[dick_freebird]

On your output capacitor Iload=Cfilt*dV/dt so disregarding
the restoring charge pulse, in dt (=period - charge phase)
you would see a ripple voltage of Iload/Cfilt (with some HF
spikes superimposed).

Inductor ripple current is only V/L*dt, the average value
follows load but the ripple follows supply voltage and
frequency. Inductor selection to get a desirable (for
efficiency, current-mode-control stability and current-slew
tradeoff) ripple current is a design norm.