DocID024196 Rev 1

11/26

AN4242

Forward thermal runaway

2.2

Thermal runaway risk in transient phase

shown in Figure 7 and is described in the datasheet as the non-repetitive maximum surge

forward current.

In standard applications, the current waveforms are either shorter or longer and more

reflects the capability of the diode to sustain a surge current.

In an SMPS, during the transient phases such as the start-up phase, a power line drop-out,

a lightning surge or a short circuit, experience shows that some high surge current stresses

are applied to the diode. Examples are shown in Figure 8.

power line drop-out

Unlike the regular operating mode, the current stress duration is generally lower than 1 s. In

this case a thermal runaway phenomenon can be triggered and the advised limit to avoid

impedance:

STPSC606D

2 ms/div

2 V/div

10 A/div

5 ms / Div

5 A / Div

100 V / Div

h

c

IdSiC

200 ms / Div

5 A / Div

100V / Div

20 ms / Div

IdSiC

h

c