An example of applying an abnormal and steady reverse voltage to a power line of devices is shown on this slide. The left side shows a case where a steady reverse voltage comes into a power line that uses a middle power diode of 1 W or 2 W for protection. The reverse voltage is clamped at the forward voltage VF of the Zener diode, a steady large current flowing into the diode. After a while, a fuse located at the entry of a power line will melt to protect the load from reverse voltage, and the device will be stopped safely. The right side shows a case where a steady reverse voltage comes into a power line that uses a middle power diode of 200 mW for protection. A reverse voltage is clamped at the forward voltage VF of the Zener diode, a steady large current flowing into the diode. After a while, the Zener diode will be damaged due to a large current, resulting in applying a reverse voltage to the load. In this case, the device will be in an unsafe state and might be damaged or occasionally smoke or ignite. For steady reverse voltage, a middle-class Zener diode of 1 W or 2W is required because the voltage has extremely high electric energy.