Hi,
The attached (LTspice and PNG schem) shows a Two Transistor Forward and also a Buck converter. Both are converting 390Vin to 100Vout at 500W, and at 100kHz.
It is seen that the 500W Buck is not really useable, as it is likely to be so noisy that even its own control would be compromised. The 2 Tran forward has a leakage inductance in the transformer, and this reduces the di/dt in the switchs and diodes. Also, it reduces the peaks of the turn on spike currents. They both need snubbing, but the two tran forward needs far less. Also, if an artificial “stray” inductance is added to the Buck, then it simply causes way too high losses in the Buck’s semiconductors.
As such, we see that transformer isolated converters have another very important use. That is, Noise reduction when power is high.
However, virtually all the offTheShelf bobbins for SMPS transformers are designed with mains isolation clearance/creepages in mind. This makes them too big, for those cases when the isolation spec is not strict. Also, a 1 layer coil will start and terminate on the same side of the bobbin….(for isolation purposes). This is not necessary for “less strict” isolation. As such, the new bobbin range should have bobbin pins placed such that a 1 layer coil would start at one end of the bobbin tube, and terminate at the other…no straggly awkward bit of wire being straggled across the bobbin for termination. Also, the bobbins should have entrance and exit “flaps” such that a coil , eg primary coil, can come on and off the bobbin without taking up room needed for the secondary coil round the bobbin edges.
Also, bobbin pins should not be so weakly joined to the bobbin plastic. At the moment, any multi strand coil (for higher current) needs much heat when terminating to the bobbin pin, and inevitably the heat melts the pin out of the bobbin plastic. As such, simple bobbin clasps are needed, and the transformers can then be soldered to the PCB directly. Or alternatively, soldered to a separate, optional “Plinth”. The plinth would have metal pins very well embedded into the plinth plastic such that they don’t loosen when termination soldering is done.
So why do we not have these bobbins available to us?