Why should add a diode next to the relay?

The role of a diode to the relay

The function of the relay connected to the diode: the diode is called "freewheeling diode". It is named for its function of freewheeling in the circuit. Generally, a fast recovery diode or a Schottky diode is selected as the "freewheeling diode", which is in the circuit. Generally used to protect components from breakdown or burnout by induced voltage, connected in parallel to both ends of the element generating the induced electromotive force, and forming a loop with them, so that the high electromotive force generated by the circuit is consumed in a continuous current manner in the loop, thereby The components in the protection circuit are not damaged.