Second breakdown[edit]
For a device that makes use of the second breakdown effect see Avalanche transistor
The second breakdown is a failure mode in bipolar power transistors. In a power transistor with a large junction area, under certain conditions of current and voltage, the current concentrates in a small spot of the base-emitter junction. This causes local heating, progressing into to a short between collector and emitter. This often leads to the destruction of the transistor. Second breakdown can occur both with forward and reverse base drive. [2] Except at low collector-emitter voltages, the second breakdown limit restricts the collector current more than the steady-state power dissipation of the device.[3] Power MOSFETs do not exhibit secondary breakdown, and their safe operating area is limited only by maximum current (the capacity of the bonding wires), maximum power dissipation and maximum voltage. [4] However, Power MOSFETs have parasitic PN and BJT elements within the structure, which can cause more complex localized failure modes resembling Secondary Breakdown.