Although a single surge does not cause any irreversible damage to the silicon wafer, it should not be allowed to occur too frequently. IFSM is the maximum allowed, non-repetitive and pulse-width dependent peak value of a half-sinusoidal surge current, applied at an instant when the diode is operating at its maximum junction temperature Tvjm. Although, in practice, the case temperature prior to a surge is always below Tvjm, both the junction and the housing are heated to Tvjm when the surge current limit is established. This worst-case test condition provides an additional margin to the real stress in an application.
During a surge, the junction heats up to a temperature well above its rated maximum value. Therefore, the diode is no longer able to block rated voltage, so the IFSM values are valid only for VR = 0 V after the surge, i.e. without reapplied voltage. Further information is provided in our Application Note "Surge currents for phase control thyristors".
If you want to purchase a product, need any pricing information or need help or support from ABB, please contact your local partner.