What is transil and how it works?
Transil is a trademark from ST for its TVS diodes. TVS diodes behave somewhat like zener diodes: the current flows through them as soon as the voltage exceeds a given value. Contrary to Zener diodes, they are designed to get a huge power (600W and 1500W are standard power ratings) but only for a very short period of time. Moreover, they are generally designed to fail in short-circuit.