T
treez
Guest
Hello,
The following article discusses sepic converter design when a coupled inductor is used.
https://www.ti.com/lit/an/slyt411/slyt411.pdf
Why does this article singularly fail to declare that the design of a sepic with coupled inductor should be based on the design of a flyback with equal primary and secondary inductances as occurring in the coupled sepic inductor?
In a coupled inductor sepic, the FET and diode currents are exactly the same as for a flyback.
It is the primary and secondary currents which usually differ between sepic and flyback (and obviously the flyback doesn’t feature the sepic capacitor current, as it has no sepic capacitor)
In fact, in a coupled inductor sepic, the primary and secondary current waveforms are virtually the same as in a flyback if the sepic capacitor is low value and the windings are closely coupled.
However, it is not usual to use low value sepic capacitors in closely coupled sepic inductors, as the low value sepic capacitor rings excessively with the leakage inductance.
In the coupled inductor sepic, when the sepic capacitor value is made higher value, then the primary and secondary currents do then differ from those in a flyback….they get lesser in RMS value than the flyback. –Also, the peak primary and secondary current desreases.-However, the FET and diode currents remain the same as in a flyback.
(obviously the flyback needs a prmary RCD clamp which the sepic does not….so the drain turn off voltage rises up to the clamp level in the flyback, so this is different to that in a sepic…however, the design is best completed with the analogy to the flyback borne in mind…..why does the above article fail to mention this?
The following article discusses sepic converter design when a coupled inductor is used.
https://www.ti.com/lit/an/slyt411/slyt411.pdf
Why does this article singularly fail to declare that the design of a sepic with coupled inductor should be based on the design of a flyback with equal primary and secondary inductances as occurring in the coupled sepic inductor?
In a coupled inductor sepic, the FET and diode currents are exactly the same as for a flyback.
It is the primary and secondary currents which usually differ between sepic and flyback (and obviously the flyback doesn’t feature the sepic capacitor current, as it has no sepic capacitor)
In fact, in a coupled inductor sepic, the primary and secondary current waveforms are virtually the same as in a flyback if the sepic capacitor is low value and the windings are closely coupled.
However, it is not usual to use low value sepic capacitors in closely coupled sepic inductors, as the low value sepic capacitor rings excessively with the leakage inductance.
In the coupled inductor sepic, when the sepic capacitor value is made higher value, then the primary and secondary currents do then differ from those in a flyback….they get lesser in RMS value than the flyback. –Also, the peak primary and secondary current desreases.-However, the FET and diode currents remain the same as in a flyback.
(obviously the flyback needs a prmary RCD clamp which the sepic does not….so the drain turn off voltage rises up to the clamp level in the flyback, so this is different to that in a sepic…however, the design is best completed with the analogy to the flyback borne in mind…..why does the above article fail to mention this?