SEPICS work best if the inductors are bi-filar wound on top of each other
Thanks, i appreciate that, but we are stuck with using the cheapest off the shelf sepic inductors available, we cannot get custom wound cores so we must stick with the MSD1583 series, this has the lowset leakage of any sepic inductor (coupled)
Its so weird that the coupled inductor sepic is exactly liek the flyback, (ie if you just take the cap out of the sepic).
...when designing a coupled inductor sepic, i presume that one uses the same method as for the flyback?
..........the non coupled inductor sepic , i have found, needs such heavy damping of the resonance of the L's and C's that its unusable above about 2W....dont you think?
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OK, new findings, my sepic inductor (coupled) is 22uH, and the sepic capacitor is 2u2, so these have a resonant frequency of 23KHz, and this is too close to my switching frequency, and is giving rise to the resonating currents that are overheating the coupled sepic inductor.
Coming away from the hardware and using the simulator, using a much bigger faradic capacitor value gives far less rms current in the coupled sepic inductor coils.
So here is a secret of the industry.
"If you are doing a sepic converter with a coupled inductor, then use the biggest faradic value of sepic capacitor that you can, in order to reduce ringing and losses due to the ringing currents"
....This is a "gem" of information...a real golden nugget, please feast at your leisure, as you will not find this written in any article anywhere concerning the sepic converter with coupled inductor.
(just to mote, when doing a sepic converter with separate inductors (not coupled), you should always the lowest faradic value of capacitor that you can.)
Anyway, what is the maximum voltage seen by a sepic capacitor in a sepic converter with a coupled sepic inductor.?
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More of note regarding the sepic
SimonBramble, your article was great, to augment it further, you could add how you select the sepic capacitor value, and how the resonant frequency of the L and C cannot be anywhere near the feedback loop frequency, ....the loop crossover frequency must be much less than this resonance, otherwise it will ring like mad, especially the non coupled version.
Also, for the non coupled version, the switching frequency cannot be anywhere near the L,C resonant frequency....the switching frequency must be eiether miles above , or miles below , the L,C resonant frequency.