Ne znam tacno, ne secam se detalja, ali pitacu sigurno kada bude prilike. Uglavnom, i racunari imaju taj vid zastite na americkim kolima.
EDIT:
Nasao sam o cemu se radi. Tacno si pretpostavio da se dioda vezuje paralelno, vezuje se na pobudu i sluzi da spreci obrnut tok struje prilikom prestanka pobude jer se u namotaju indukuje nesto struje, ako sam dobro shvatio.

Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is turned off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil that wants to flow in the opposite direction which can cause damage to a ECM, PCM or ICs. A quenching protection diode or suppression resistor allows the induced voltage a path to block and dissipate. This prevents spiked voltage becoming high enough to cause damage to a electronic control module or a IC.


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