Calculating the ripple current of the output filter of a full bridge smps? Answered
I have been designing an offline 100khz 720 watt full bridge converter for 24 volts dc out at 30 amps. I've calculated that at a minimum duty cycle of .3 and a voltage ripple of .03v I need a minimum of 7k uf. I read the output filter section of "The Power Supply Cookbook" and it gives this equation to get the peak to peak current ripple: I(pk-pk)=(2*Iout)/(min duty cycle). with a duty cycle of .3 this gives me 200A ripple current. With four caps each would need to be about 2000uf and a ripple current of 50A, which would be expensive. I've only every built flyback and boost converters so I wonder if the equation for peak to peak current ripple is only meant for those topologies, or perhaps I've calculated wrong. Is there a different equation I need to use or have I done something wrong? Any tips for selecting capacitors and what chemistry to use (tantulum/aluminum)? Thanks in advance I'm new to forward mode converters!