Quote Originally Posted by 2e0poz View Post
It does not make sense to just have a diode across the power lines as a protection circuit right?
Diodes have anodes and cathodes, the cathode is usually marked by a stripe, volts will flow anode to cathode but not vice versa.

A protection diode usually has it's cathode connected to the positice supply and it's anode connected above where you will break the circuit.

When the circuit breaks the supply to a coil the coil impedance wants to keep the current flowing. If it has nowhere to go the Volts go through the roof, probably exceeding the breakdown point of the transistors.

The diode carries the excess current back to the top of the coil so it can go round and round until the coil resistance eats it up.

Expect the cathode, stripe, to be at the positive supply end of the circuit.