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

electronic component An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not ...

used to protect

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

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 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 otherwise good ...

potential. It is a

clamping A wheel clamp, also known as wheel boot, parking boot, or Denver boot, is a device that is designed to prevent motor vehicles from being moved. In its most common form, it consists of a clamp that surrounds a vehicle wheel, designed to preven ...

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. 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 reverse operation (converting DC to AC) is performed by an Power ...

in the forward direction like any other

avalanche diode In electronics, an avalanche diode is a diode (made from silicon or other semiconductor) that is designed to experience avalanche breakdown at a specified reverse bias voltage. The junction of an avalanche diode is designed to prevent current co ...

, 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 is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non- ohmic current–voltage characteristic that is similar to that ...

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 flow of electric current creates a magnetic field around the conductor. The 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. Siemens NTBBA 40 183 340-100 - LCDA05-3328

Siemens NTBBA 40 183 340-100 - LCDA05-3328

Transient voltage suppressor A 'surge protector'' (or spike suppressor, surge suppressor, surge diverter, surge protection device (SPD) or transient voltage surge suppressor (TVSS) is an appliance or device intended to protect electrical devices from voltage spikes in alt ...

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 Vishay Intertechnology, Inc. is an American manufacturer of discrete semiconductors and passive electronic components founded by Poland, Polish-born businessman Felix Zandman. Vishay has manufacturing plants in Israel, Asia, Europe, and the Ameri ...

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 of cu ...

: 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 is the minimum voltage that causes a portion of an insulator to experience electrical breakdown and become electrically conductive. For diodes, the breakdown voltage is the minimum reverse voltage that mak ...

: the voltage at which some specified and significant conduction occurs. *

Clamping voltage A wheel clamp, also known as wheel boot, parking boot, or Denver boot, is a device that is designed to prevent motor vehicles from being moved. In its most common form, it consists of a clamp that surrounds a vehicle wheel, designed to preven ...

: 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 elect ...

s). * Parasitic capacitance: The nonconducting diode behaves like a

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

, which can distort and corrupt high-speed signals. Lower capacitance is generally preferred. *

Parasitic inductance In electrical networks, a parasitic element is a circuit element ( resistance, inductance or capacitance) that is possessed by an electrical component but which it is not desirable for it to have for its intended purpose. For instance, a resis ...

: 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 dissipated away from the device, th ...

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

''What are TVS diodes'', Semtech Application Note SI96-01

''Transient Suppression Devices and Principles'', Littelfuse Application Note AN9768

''Transil™ / Trisil™ Comparison'', ST application note AN574

''Transient Protection Solutions: Transil™ diode versus Varistor'', ST application note AN1826
{{Electronic components Diodes Voltage stability Electric power systems components

Description

Characterization

See also

References

Further reading

External links