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

Figure 1.5 Classification of overvoltage pulses
Figure 1.5 Classification of overvoltage pulses

The ESD protection diode is a type of Zener diode specifically designed to protect electronic circuits from overvoltage surge, particularly electrostatic discharge (ESD) events. ESD protection diodes provide protection mainly against short ESD pulses as well as lightning-induced and switching surge events that last for less than several microseconds. Zener diodes specifically designed for protection from surge events with a pulse duration larger than ESD are called surge protection Zener diodes. These Zener diodes are suitable for protecting electronic circuits from overvoltage pulses due to lightning-induced and switching surge events that last for more than several microseconds.

Table 1.1 Types of voltage surge

Type

Description

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 are specifically designed to protect electronic circuits from overvoltage surge, particularly from ESD events, without affecting the waveforms of signal lines. ESD protection diodes are available with a capacitance of 0.12 to 100 pF. Surge protection Zener diodes provide a wide junction so as to absorb large surge energy. With a total capacitance of 100 to 600 pF, these diodes are suitable for protection against lightning-induced and switching surge events. Table 1.2 shows the suitability of ESD protection diodes and surge protection Zener diodes for different types of overvoltage surge pulses: 

Table 1.2 Effects on surge protection

 

 Total capacitance

Purpose

Protection

ESD

Switching surge

Lightning-induced surge

Direct lightning surge

ESD protection diodes

Ct: 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

Ct: 100 to 600 pF

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

Good

Excellent

Good

Very poor

Note: Comparison of Toshiba’s diodes

1 What is a TVS diode (ESD protection diode)?

1 What is a TVS diode (ESD protection diode)?
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1-1 Reverse breakdown voltage
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1-3 Differences between protection diodes (ESD protection diodes and surge protection Zener diodes) and diodes for constant-voltage regulation
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