P3602ACMC datasheet(172/212 Pages) TECCOR

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Overvoltage Protection Comparison

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SIDACtor® Data Book and Design Guide

Overvoltage Protection Comparison

The four most commonly used technologies for overvoltage protection are:

• SIDACtor devices

• Gas Discharge Tubes (GDTs)

• Metal Oxide Varistors (MOVs)

• TVS diodes

All four technologies are connected in parallel with the circuit being protected, and all exhibit

a high off-state impedance when biased with a voltage less than their respective blocking

voltages.

SIDACtor devices

A SIDACtor device is a PNPN device that can be thought of as a TVS diode with a gate.

Upon exceeding its peak off-state voltage (VDRM), a SIDACtor device will clamp a transient

voltage to within the device’s switching voltage (VS) rating. Then, once the current flowing

through the SIDACtor device exceeds its switching current, the device will crowbar and

simulate a short-circuit condition. When the current flowing through the SIDACtor device is

less than the device’s holding current (IH), the SIDACtor device will reset and return to its

high off-state impedance.

Advantages

Advantages of the SIDACtor device include its fast response time (Figure 5.3), stable

electrical characteristics, long term reliability, and low capacitance. Also, because the

SIDACtor device is a crowbar device, it cannot be damaged by voltage and it has extremely

high surge current ratings.

Restrictions

Because the SIDACtor device is a crowbar device, it cannot be used directly across the

AC line; it must be placed behind a load. Failing to do so will result in exceeding the

SIDACtor device’s surge current rating, which may cause the device to enter a permanent

short-circuit condition.

Applications

Although found in other applications, SIDACtor devices are primarily used as the principle

overvoltage protector in telecommunications and data communications circuits. For

applications outside this realm, follow the design criteria in "SIDACtor Device Selection

Criteria" on page 5-5.

Gas Discharge Tubes

Gas tubes are either glass or ceramic packages filled with an inert gas and capped on each

end with an electrode. When a transient voltage exceeds the DC breakdown rating of the

device, the voltage differential causes the electrodes of the gas tube to fire, resulting in an

arc, which in turn ionizes the gas within the tube and provides a low impedance path for the

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