How to design Zener diode for a kickback voltage protection of motor?
simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. Two options.
The diodes sketched in your diagram will work. Figure 1a shows them drawn a little more clearly. Whichever way the motor is running the current will be diverted to the power supply - if it can take it.
Figure 1b uses two Zener diodes back-to-back to allow for forward and reverse. The Zener voltage needs to be &gt; V2. The peak power in the diodes will be \$ P = V_{ZD}I_{MOTOR} \$. The peak current will be \$ I_{MOTOR} \$.
I don't think you will find a 5 A Zener diode too easily. If your 5 A number is the running current you will have much higher current during a motor stall. Your protection circuit needs to survive this too.