# 為何 Relay 的 coil 要加上 Flyback diode? Author: 家答 - [Inductive Flyback and Flyback Diodes](https://digilent.com/reference/learn/fundamentals/electronic-components/flyback-diodes/start) - [How to choose a flyback diode for a relay?](https://electronics.stackexchange.com/questions/110574/how-to-choose-a-flyback-diode-for-a-relay) [Diode package selection in flyback circuit for a relay](https://electronics.stackexchange.com/questions/404771/diode-package-selection-in-flyback-circuit-for-a-relay) ![image](https://hackmd.io/_uploads/rkbXUN-1lx.png) ### 沒加 flyback diode Maximum Inductive Kickback: 5.4kV ![image](https://hackmd.io/_uploads/rJRZDmWyxe.png) ![image](https://hackmd.io/_uploads/B1oHvmZkel.png) ### 有加 flyback diode Maximum Inductive Kickback: 743mV (D1 的順向偏壓) ![image](https://hackmd.io/_uploads/Sk7kP7Wkxx.png)