Notification 211 - The number of primary winding layers (L) is greater than recommended

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ISSUE / RESULT

FIX / REFERENCE(S)

Info

The number of primary winding layers (L) is greater than what is recommended, for the specified power level.

 

Too many primary winding layers increase the leakage inductance and the inter-winding capacitance of the transformer and can reduce overall supply efficiency while increasing the amount of energy that needs to be dissipated by the DRAIN voltage clamp circuit.

  • Reduce the number of layers (L), to below that recommended in Table 1.  Note: These recommendations are not ”design specific” so actual performance will depend on the transformer construction scheme used.  Split primary construction is recommended above 40 watts (see Figure 1).

  • Improving efficiency (N) will reduce the effect of parasitic elements; see Application Note AN-19  for high efficiency techniques.

  • See Application Notes AN-26 (-FX) or AN-32 (-GX)  for more information on wire size (AWG) calculation and techniques for improving efficiency.

 

Max Recommended Primary Layers

Power (PO)

L (max)

20 W - 40 W

3.0

> 40 W

2.0 *

Table 1. PI Expert maximum recommended primary layers versus output power levels.  *Split primary layers are recommended above 40 W.

 

PI-1689-111695

Figure 1. Example of split primary construction to reduce primary leakage inductance [ Application Note AN-19 ]