The fast recovery diode is generally used in the freewheeling circuit to protect the components from being broken down or burned by the induced voltage. It is connected to the two ends of the component that generates the induced electromotive force in parallel and forms a loop with it, so that the high electromotive force generated by it is consumed in the loop in the freewheeling current mode, thus protecting the components in the circuit from being damaged. Its protection principle is that the freewheeling diodes are connected in parallel at both ends of the coil. When the coil passes through the current, it will generate induced electromotive force at both ends. When the current disappears, its induced electromotive force will generate reverse voltage to the components in the circuit When the reverse voltage is higher than the reverse breakdown voltage of components, components such as triodes and thyristors will be damaged The freewheeling diode is connected in parallel at both ends of the line. When the current flowing through the coil disappears, the induced electromotive force generated by the coil is consumed through the circuit composed of the diode and the coil, thus protecting the safety of other components in the circuit The freewheeling diode is in reverse parallel at both ends of the relay or inductance coil in the circuit. When the inductance coil is powered off, the electromotive force at both ends does not disappear immediately. At this time, the residual electromotive force is released through a diode.