Notification 209 - Peak DRAIN-SOURCE voltage exceeds device breakdown (BVDSS)

CATEGORY

ISSUE / RESULT

FIX / REFERENCE(S)

Failure

The calculated peak DRAIN-SOURCE voltage (VDRAIN) exceeds the device breakdown voltage (BVDSS).

 

Failure of the PI Component  may result.  The worst-case conditions would be at full load or under overload / short circuit, at high-line AC input and at high temperature.

  • Decrease maximum AC input voltage (VACMAX)

  • Decrease the reflected output voltage (VOR) while reconsidering the primary clamp voltage rating and dissipation (applicable to Zener clamps).
    Note:     this may decrease the overall efficiency (N).

  • Consider redesigning the transformer, to minimize the primary leakage inductance (LL) and the associated LL induced spike.  See Application Notes AN-17, AN-18, AN-19 and Figure 1 below, for split primary construction details.

 

 

PI-1593-111535

Figure 1. Split Primary construction technique example, which reduces primary leakage inductance [ Application Note AN-19 ]

 

PI-1856-050696

Figure 2. DRAIN-SOURCE voltage waveform; where peak is less than BVDSS; assumes 265 VAC operation

[Worst-case calculation VDRAIN = VMAX + (1.4 x 1.5 x VOR) + 20, see Application Notes AN-26 (-FX) or AN-32 (-GX)]