How to calculate VA rating and other things for Ferrite Core? (SMPS)

[FilipŠebík]

Hello, I want to make my own SMPS, but I can never find a way to calculate the VA rating for a ferrite core and I want to know who knows the equation for calculating VA rating and or the required turn/frequency for wanted or max wattage or something.

I would use this core FERROXCUBE ETD49/25/16-3F3 https://www.tme.eu/en/Document/882e54fb8772e021c51c30b1d1879eab/etd49.pdf
and I would like to make at least 500-600W variable voltage power supply (if the core is suitable), but I don't know the calculations required to do this. But for now let's have a fixed IN, OUT voltage and out A
Let's say the PSU will work with 230V AC, so 325V Peak, the power of 600 watts, Max current input of around 3 amps and the output voltage of 60 volts and output current of 10 amps and the switching topology is half bridge using mosfets.

How do I get the required turns/operating frequency and wire thickness for the primary and turns and wire thickness/turns for the secondary with the values that are written in the datasheet? I found this

Using the Ampere's law, you can get the following equation:

E = Ae² * B² / (2 * AL)

E: energy stored in the magnetic field
Ae: core's effective area
B: maximum flux density allowed by the core material
AL: core parameter, depends on Ae, magnetic circuit lenght and air gap lenght

You see, power (P) is enery by time. More energe and less time will result in a higher power.

P = E / t

The input power at the inductor is the energy stored (E) divided by ton. Ton is the duty cycle (D) divided by the switching frequency (fsw).

P = E / ton = E * fsw / D

This is an aproximate way to determine how much power you can obtain from a certain core. Actually there are losses by eddie currents, joule effect and stray flux.

But this equation needs the operating frequency for power calculation, so I can't learn much from it.
 
Helpful info
The 3F3 core parameters from Ferroxcube website:



PS: I am not asking you to calculate the things for me, just to help me and/or show us the equations for the things so it helps the people that will look for it

[sjsimmo]

Hi FilipŠebík,

I came across this website a while ago: http://schmidt-walter-schaltnetzteile.de/smps_e/smps_e.html when I was trying to design an smps lab power supply (I never got round to actually finalizing the design or building it though...).
It contains calculators which may be helpful with working out the suitability of your core, and required wire thickness. 
I'm sorry I can't help with doing the calculations though, I don't understand much about the mathematics myself...

Hope this helps,
- sjsimmo

[Mads Barnkob]

You have to choose a frequency on which you will design your SMPS around, it could be a range within those that you find from different smps driver ICs if you decided to use one of those.

But lets just say that chose 300 kHz, then you can adjust the driving parameters on the duty cycle, turning up/down on the power output.

The calculators that sjsimmo linked to looks very good for a start to get an idea of the topology, choosing a core/switches etc.