Introduction to Semiconductor Devices

A: A permanent clamp explains the bidirectional short, the surviving fuse, and why the LDO is burning power with no load. B explains leakage and heat but not a dead short both ways. C can heat copper but doesn't present as a silicon short on a DMM. D shifts blame to the regulator yet doesn't explain the measured diode behavior upstream.

A: Recognizing the intrinsic diode path forces you to account for reverse feed, which matches real silicon behavior and DFMEA expectations. B mixes channel conduction with diode physics and drops an off-state hazard. C invents device type from a missing symbol, a classic drawing trap. D relies on documentation optimism instead of physics.

A: Working backwards, power times thermal resistance stacked on ambient gives the junction. B double-counts optimism from typical curves. C inflates temperature without a power basis. D invents convection gains without geometry or airflow.

A: Damaged BE junction explains low beta, temp-sensitive leakage, and higher Vce(sat). B would clamp voltages differently and usually kill gain entirely. C limits current but doesn't explain leakage growth. D is an operating issue, not a post-ESD signature.