A transient voltage suppression diode, also known as a TVS, is an electrical device designed to shunt or divert voltage spikes away from a circuit to protect it. TVS diode electronic components are also useful for protecting circuits from electrostatic discharge (ESD). Electrostatic discharge occurs when someone makes physical contact or nearly so with a circuit holding a different electric potential, and it can destroy or damage sensitive electrical components. For this reason, computer hardware and other valuable electronics must pass ESD testing to be able to withstand some level of electrostatic discharge before they can be sold. The transient voltage suppression diode is an important part of this protection scheme.
Two common types of circuit protection diode are often used in TVS applications. They are the Silicon-avalanche diode (SAD) and the Zener diode. When voltage in a circuit exceeds a breakdown level as it reaches a TVS diode, the diode conducts the voltage back in a reverse direction. Both the SAD and Zener diode perform in this manner. Where they differ is in the temperature changes that they undergo in reversing voltage, which can be important in circuits where the timing of temperature fluctuations is critical. Zener diodes see a temperature increase as voltage resistance decreases and SADs have a temperature increase as voltage resistance increases.
The transient voltage suppression diode most often used in sensitive circuits such as in cameras, cell phones, and handheld computer devices is the SAD design. They are wired in opposite directions in series in the circuit so that they can protect against both positive and negative voltage surges. Typically, they offer a reverse stand-off voltage where they activate five volts and a breakdown voltage where they shunt the current away from the circuit of 10 volts, both in direct current (DC).
Since a transient voltage suppression diode converts voltage spike resistance into heat, its physical size determines how much voltage it can suppress. A small transient voltage suppression diode could be destroyed by a peak voltage spike and still leave the circuit functional yet unprotected. Larger potential voltage spikes, therefore, call for larger TVS components.
The TVS diode also has to be placed in the circuit where the signal or electrical current first enters, otherwise it would fail to protect elements of the circuit upstream of its location. Another function of a TVS diode is that it engages at what is called a clamping voltage, which is the maximum voltage it will allow to pass. This voltage level is below whatever peak voltage the circuit is capable of handling without suffering damage, and offers an additional margin of safety in protecting the circuit.
