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The coil is also an inductor, which means it stores energy. When you
disconect the coil the energy will be released. It's a spike of opposite
polarity from the drive signal which can play havoc with the coil drive
circuit (esp. if it's electronic). The diode routes this back EMF
(electromotive force) back through the coil to dissipate the energy in a
safe way. This is very common practice, though usually the diode is in
the external circuit.
- SteveS
Michael S Briggs wrote:
I retested the relay and it worked so the blown diode did not ruin the
relay.
Hm, interesting. Still, why put it in there in the first place?