How does diode protection relay on coils work? - Quora
what is the purpose of the diode connected to the coil of the relay in the circuit - YouTube
Can Transistor Protection without Diode but a relay - ...I have a project...what hardware do I need? - Unitronics Support Forum: Programmable Controllers (PLC + HMI All-in-One)
Flyback diodes on relays to stop voltage spikes | The Garage Journal