Notification 217 - Gap Length (LG) is larger than the practical limit

CATEGORY

ISSUE / RESULT

FIX / REFERENCE(S)

Info

The required transformer gap length (LG) is longer than the practical limit (approximately SQRT(AE) / 10).

Excessive field fringing, near the gap, will result in higher losses.

• Decrease the size and the cross-sectional area (AE) of the core.  This decreases its effective un-gapped inductance (AL).

• Decrease the number of both the primary (NP) and the secondary (NS) turns.

• Decrease the current waveform parameter (KP), which will increase the primary winding inductance (LP).

• Decrease the size of the input bulk capacitance (CIN), which will decrease the minimum input voltage (VMIN).

• See Application Notes  AN-26 (-FX)  or AN-32 (-GX)  for details on how gap length (LG) is calculated.