Just wondering, a flyback diode is typically used to protect the circuit.
Could the magnetic field generated by the flyback be captured to drive a reed switch and protect the circuit the same way a flyback diode does?
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The diode must (and can) respond very fast. A reed switch, being a mechanical device, will be much too slow (even when you could set it up to switch at the correct moment, which would be difficult if possible at all).
A coil that is carrying current and is then open-circuited will want to sustain that current until the energy in its magnetic field is zero. This continuation of current can't be diverted into the coil of a reed relay because the reed relay's coil will oppose the sudden surge in current and might as well become open-circuit for a few milli-seconds. This will generate a spark/high voltage that will inevitably harm semiconductors.
Short answer NO
Even if the switch was fast enough you would need to find some means to synchronize it precisely with the turn off spike. As Wouter says - its a slow mechanical device.
A diode automatically conducts and shorts out the reverse spike and costs a lot less than a reed switch.