1-2 Using different types of protection diodes (ESD protection diodes and Zener diodes for overvoltage protection)

Electrostatic discharge (ESD)

Electrostatic discharge (ESD) is a sudden flow of electricity between two electrically charged objects due to the discharging of stray capacitance that occurs when they are brought into contact or close together. Although ESD events can reach thousands of volts, their pulse duration is on the order of nanoseconds. Because of lower surge energy, ESD events are relatively easier to protect from than lightning-induced and switching surge events. ESD strikes occur frequently at low humidity. Accompanying the prevalence of smartphones and other mobile devices that are prone to malfunction due to an ESD strike, ESD protection is becoming increasingly important.

Lightning-induced surge

Lightning-induced surge is a type of surge that is induced to the inductance of long wires such as power supply and communication lines because of the effect of electromagnetic pulses emitted by lightning strikes. As is the case with ESD events, lightning-induced surge events reach thousands of volts. However, lightning-induced surge events have larger energy because their pulses last for microseconds to milliseconds. Compared to ESD protection devices, surge protection devices become relatively large so as to pass large energy to ground. In contrast to lightning-induced surge, a type of surge caused by a direct lightning strike is called direct lightning surge. It is difficult to protect from a direct lightning surge because of its extremely high energy.

Switching surge

Switching surge is an overvoltage transient induced during the on/off switching of a switch or a relay because of a sharp change in current, circuit inductance, and wire inductance. Since a circuit’s inductance and capacitance cause switching surge, its voltage is lower than that of ESD and lightning surge. However, switching surge pulses last for several nanoseconds to even milliseconds. Switching surge events with a long pulse duration have higher energy than ESD surge events. Protection devices are selected according to the magnitude of a circuit’s inductance and capacitance.

ESD protection diodes

C_t: 0.12 to 100 pF

Protection from overvoltage surge of a duration on the order of microseconds or less

Excellent

Poor

Poor

Very poor

Surge protection Zener diodes

C_t: 100 to 600 pF

Protection from overvoltage surge longer than microseconds (and from ESD strikes as well)

Good

Excellent

Good

Very poor