First I attached 2 docs they are .asc file (LTspice) so remove the .pdf to launch them.
You might need the .lib or I don't know what of the mosfet I used (IRFP4468). So, find a way to make it work (I have absolutely no idea how, still not familiar to LTSpice sorry) or use another Fet or use a switch instead.
You'll see that all is "work in progress", I assumed lot of things, used methods from ecircuitcenter.com. Many thing seem to work like they should.
You'll also discover that I find a way to High ripple current in the input capacitor.
I also discovered that I can't make a "all in one model", I was expecting that with our huge computering machinery I could find draw anything in a second,... but no.
It assumes the current is constant at its maximum, during the entire raise and fall times of the PWM wave. It's during these periods that current flows in and out of the capacitors. So it's a quite pessimistic approach, the current isn't obviously run at max for the entire switching period.
Understood!
You can have LTspice calculate the average and rms values for you - presss CTRL and click a waveform name. It will calculate for the part of the waveform currently being displayed, so remember to display only a part where the system is already stable.
Yes I discovered that. Very nice indeed
As I said before, it's decidedly non-trivial to come up with a model that's reasonably accurate at predicting the actual ripple current. And, it will be EXTREMELY controller-specific (based on the inductance, components, and so forth in the controller design), and even installation-specific because the length and routing of the battery wires, type/size of the battery, etc. will also probably play some role. So I'm not surprised that your model gives a result that can't possibly be true.
You are 1000% right
Also, I still think that ripple current isn't the most important spec for the capacitors. By the time you choose a set of caps which have the necessary capacitance and low enough ESR, the ripple current spec will most likely take care of itself.
Rated ripple current is the same as ESR in fact. We need one or the other from the datasheet and then apply the methodology of the supplier for specified T° and Frequency. But when I said that Ripple current is the key factor of the design, I meant the one "independant" from the chosen capacitor, design-dependant one. Sorry I can't explain better than that.
Last Note now using your formula (love it too)
Means that the lower the frequency the less ripple current.
Real Last note now
For Buck converter designs, which look like DC motor designs, capacitor input ripple current is generally chosen to be 1/2 of output current. I'm afraid that with Iripple = Imax*(tr+tf)/T we could find a ripple, way below 1/2 Iout.
Looking forward for your ideas and suggestions
Have a nice day