11/26/2023 0 Comments Peak flux densityWhen Q1 turns OFF, the magnetizing current in the primary winding immediately stops. As a result, there's no usable transformer action during the ON period of Q1. Hence, the secondary windings effectively don't exist, or at least the primary can't “see” them. The phasing of the secondary windings and rectifier diodes is such that the secondaries aren't conducting during this period. This is positive, and an increasing current is flowing in the primary (the magnetizing current). When Q1 is ON the input voltage is applied to the start of the primary winding (the dot end). Look again at the phasing of the windings and diodes in Fig. However, the secondary voltages aren't related to the primary to secondary turn's ratio, as they would normally be with a true transformer. They have additional windings called the secondaries. More accurately, they're inductors or chokes, depending on the mode of operation. A common difficulty in the design of such converters is the so-called “transformer.” We can see how its design requires more care and understanding than its counterpart in the forward converter.ĭesign difficulties stem from the fact that flyback transformers aren't really transformers. If one output is closed-loop voltage stabilized, then all other outputs will be semi-stabilized, (within limits of loading and voltage typically required in many applications). In multiple output applications, the addition of a secondary winding, a single diode, and an output capacitor is all that's required for each additional isolated or common output. A major advantage of this topology is its low cost and simplicity. 1 shows a typical off-line flyback converter found in a low-power multiple output application. Now, let's examine one more example of the function of an air gap in a ferrite core, while providing a better understanding of flyback transformers. We found even a small air gap benefits discontinuous forward designs, as the residual flux value will be nearer zero, allowing a larger working flux density range. In that article, we found that although an air gap won't prevent saturation in true transformer applications, it does reduce the slope of the B/H loop, reducing permeability and inductance, and increasing the magnetizing current in the primary. Let's return to the question, “Why Have an Air Gap?” initially posed in the Power Design article in the December 2002 issue of Power Electronics Technology. For the PDF version of this article, click here.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |