Notification 213 - Peak DRAIN-SOURCE voltage is within 20 V of device breakdown (BVDSS)

CATEGORY

ISSUE / RESULT

FIX / REFERENCE(S)

Information

The calculated peak DRAIN-SOURCE voltage (VDRAIN) is within 20 volts of 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 highest rated ambient temperature.

• Verify the worst-case DRAIN-SOURCE voltage by measuring a prototype on the bench, before accepting this design.
  Preferably, the following design modifications should be made:

• Select a larger core size.

• Revise the transformer’s construction, to minimize the primary leakage inductance (LL) and the associated LL induced spike.  See Application Notes  AN-17 , AN-18 and AN-19 .

• Decrease the reflected output voltage (VOR).

• Reduce the voltage rating of the primary clamp Zener diode (which will decrease overall efficiency by increasing clamp dissipation).

• Decrease the maximum AC input voltage (VACMAX), if possible.

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