A transient-voltage-suppression (TVS) diode, also transil, transorb or thyrector, is an

electronic component An electronic component is any basic discrete electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singula ...

used to protect

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

from

voltage spike In electrical engineering, spikes are fast, short duration electrical transients in voltage (voltage spikes), current (current spikes), or transferred energy (energy spikes) in an electrical circuit. Fast, short duration electrical transients ...

s induced on connected wires.

Description

The device operates by shunting excess current when the induced voltage exceeds the

avalanche breakdown Avalanche breakdown (or the avalanche effect) is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwis ...

potential. It is a clamping device, suppressing all overvoltages above its breakdown voltage. It automatically resets when the overvoltage goes away, but absorbs much more of the transient energy internally than a similarly rated crowbar device. Siemens NTBBA 40 183 340-100 - LCDA05-3328

Siemens NTBBA 40 183 340-100 - LCDA05-3328

A transient-voltage-suppression diode may be either unidirectional or bidirectional. A unidirectional device operates as a

rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as ''rectification'', since it "straightens" t ...

in the forward direction like any other avalanche diode, but is made and tested to handle very large peak currents. A bidirectional transient-voltage-suppression diode can be represented by two mutually opposing avalanche diodes in series with one another and connected in parallel with the circuit to be protected. While this representation is schematically accurate, physically the devices are now manufactured as a single component. A transient-voltage-suppression diode can respond to over-voltages faster than other common over-voltage protection components such as

varistor A varistor (a.k.a. voltage-dependent resistor (VDR)) is a surge protecting electronic component with an electrical resistance that varies with the applied voltage. It has a nonlinear, non- ohmic current–voltage characteristic that is similar ...

s or gas discharge tubes. The actual clamping occurs in roughly one picosecond, but in a practical circuit the

inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The electric current produces a magnetic field around the conductor. The magnetic field strength depends on the magnitude of the ...

of the wires leading to the device imposes a higher limit. This makes transient-voltage-suppression diodes useful for protection against very fast and often damaging voltage transients. These fast over-voltage transients are present on all distribution networks and can be caused by either internal or external events, such as lightning or motor arcing.

Transient voltage suppressor A surge protector, spike suppressor, surge suppressor, surge diverter, surge protection device (SPD), transient voltage suppressor (TVS) or transient voltage surge suppressor (TVSS) is an appliance or device intended to protect electrical devi ...

s will fail if they are subjected to voltages or conditions beyond those that the particular product was designed to accommodate. There are three key modes in which the TVS will fail: short, open, and degraded device. TVS diodes are sometimes referred to as transorbs, from the Vishay trademark ''TransZorb''. Combined TVS and rail-to-rail diodes

Characterization

A TVS diode is characterized by: *

Leakage current In electronics, leakage is the gradual transfer of electrical energy across a boundary normally viewed as insulating, such as the spontaneous discharge of a charged capacitor, magnetic coupling of a transformer with other components, or flow ...

: the amount of current conducted when voltage applied is below the maximum reverse standoff voltage. * Maximum reverse standoff voltage: the voltage below which no significant conduction occurs. *

Breakdown voltage The breakdown voltage of an insulator (electrical), insulator is the minimum voltage that causes a portion of an insulator to experience electrical breakdown and become electrically Conductor (material), conductive. For diodes, the breakdown vo ...

: the voltage at which some specified and significant conduction occurs. * Clamping voltage: the voltage at which the device will conduct its fully rated current (hundreds to thousands of

ampere The ampere ( , ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to 1 c ...

s). *

Parasitic capacitance Parasitic capacitance or stray capacitance is the unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other. When two electrical conductors a ...

: The nonconducting diode behaves like a

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

, which can distort and corrupt high-speed signals. Lower capacitance is generally preferred. * Parasitic inductance: Because the actual over voltage switching is so fast, the package inductance is the limiting factor for response speed. * Amount of energy it can absorb: Because the transients are so brief, all of the energy is initially stored internally as heat; a

heat sink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is thermal management (electronics), ...

only affects the time to cool down afterwards. Thus, a high-energy TVS must be physically large. If this capacity is too small, the over voltage will possibly destroy the device and leave the circuit unprotected.

References

External links

''Selection Method and Usage of TVS Diodes''
- Rohm app note
''TVS Diode (clamping) vs Trisil (crowbar) comparison'' - ST app note

''Transil Diode versus Varistor'' - ST app note
{{Electronic components Diodes Electric power systems components Voltage stability

Description

Characterization

See also

References

Further reading

External links