Note that the “dB” value (change in B) in Figure 2B for the bipolar push pull transformer can be more than twice the “dB” value shown in Figure 1B for the unipolar forward converter (assuming the same core material). Bipolar operation is depicted graphically in Figure 2B. Both “B” and “H” cross zero value and reverse polarity.
The core in a push pull transformer has bipolar operation. “H” does not have to return to zero value. The flux density “B” and the magnetizing force “H” never cross zero hence always retain the same (or one) polarity. The core’s magnetic “B-H” loop remains in one quadrant of the “B-H” grid.
Unipolar operation is depicted graphically in Figure 1B. The core of the transformer in Figure 1A is operated in a unipolar fashion.
