2920243

Surge protective devices such as transient voltage suppressors (TVS), metal oxide varistors (MOVs) and other styles of varistors, are used to protect electronic equipment from electrical transients caused by lightning strikes, electrostatic discharge (ESD), switching of electrical loads, and other similar electrical occurrences. Each type of surge protection device (SPD) has its own unique design and capabilities.

The 2920243 application field and working principle of these surge protection devices focus on diverting or dissipating high voltage and current spikes away from the protected device, and limited components of the surge to avoid immediate or near-term device damage. TVS devices are designed to clamp transient voltages by drawing current through a low-impedance path during a surge event. When a clamped transient voltage is present, the TVS device essentially acts as a low-resistance short-circuit between the positive and negative lines, causing the overvoltage to be dissipated as heat energy through the device itself.

The capability of the TVS to absorb this energy during a surge event is a direct result of the breakdown voltage of the device. The breakdown voltage is the point at which the protection device is designed to activate and protect the equipment from the high-voltage and current surge. As the surge current reaches a preset triggering point, the breakdown voltage of the TVS device reduces, and the device quickly conducts current away from the protected electronics, thus protecting the internal components within.

MOVs have also become popular for surge protection applications, although there are a few differences between MOVs and TVS devices. MOV devices are essentially varistors or voltage dependent resistors and are designed to limit voltage surges. When a surge occurs, MOVs will limit the voltage to a preset threshold by providing a low-impedance path to ground. This type of surge protection is achieved by slowly changing the resistance of the MOV device as the voltage rises, thus limiting the voltage level of the surge.

The greatest strength of MOVs is in their ability to drain off electrical energy caused by ESD. This is because MOVs have a much faster response time to voltage surges than do TVS devices. MOVs are also are capable of absorbing much more energy, allowing them to provide greater protection from electrical transients.

Although both MOVs and TVS devices have application fields and working principles for surge protection applications, the choice of which device to use must be based upon the specific configuration requirements of the protected equipment. MOVs are designed for applications that have high inrush current and require rapid response times, such as ESD protection. On the other hand, TVS devices are designed for applications that require higher energy protection, such as protection from lightning strikes. As such, the type of surge protection device that is required for a particular application must be determined before selecting the device in order to ensure adequate protection of the equipment.