大功率半导体的浪涌电流、I2t能力及短路.pdfVIP

Application Note Date: 30.05.2005 Page 1 AN-Number: AN2005-04 Department: SM TM Surge Current, I2t – Value and Short - Circuit Protection of High Power Semiconductors. According to DIN IEC 60747 the maximum rated surge current is the maximum allowable non periodical, sinusoidal 50 Hz or 60 Hz half 2 wave, without any following voltage and/or current stress. The I t – value is the maximum allowable value of the time – integral over this current, related to the indicated junction temperature. The semiconductors may lose, when stressed with maximum rated surge current, their blocking capability completely or partly, till the junction temperature wil l have decreased to the temperature range permitted for continuous work. This stress may be repeated at the earliest after several seconds and should occur only occasionally at a limited pulse number during the entire actual operating time of the semiconductor. Maximum rated surge forward current and maximum load integral are used to design the over-current protection of diodes and thyristors. As pure sine-wave currents in practice do not occur, the conversion to similar current forms of about equal pulse width can be made by the I2t – value. One differentiates between the following typical failure modes: • Outside short-circuit on the load side. • Internal short-circuit caused by a defect of a semiconductor, or by misfiring of a thyristor. Protection concepts: 1) Super fast semiconductor fuses These fuses, arranged in the branch or in the arm, disconnect within 2 one half wave. Their I t - value must be lower than that of the semicondu