Transient voltage suppression diode - AbsoluteAstronomy.com

A transient-voltage-suppression (TVS) diode is an electronic component

Electronic component

An electronic component is a basic electronic element and may be available in a discrete form having two or more electrical terminals . These are intended to be connected together, usually by soldering to a printed circuit board, in order to create an electronic circuit with a particular function...

used to protect sensitive electronics

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

from voltage spike

Voltage spike

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

s induced on connected wires.
The device operates by shunting excess current when the induced voltage exceeds the avalanche breakdown

Avalanche breakdown

Avalanche breakdown 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 insulators. It is a type of electron avalanche...

potential. It is a clamping device, suppressing all overvoltages above its breakdown voltage. Like all clamping devices, it automatically resets when the overvoltage goes away, but absorbs much more of the transient energy internally than a similarly rated crowbar

Crowbar (circuit)

A crowbar circuit is an electrical circuit used to prevent an overvoltage condition of a power supply unit from damaging the circuits attached to the power supply. It operates by putting a short circuit or low resistance path across the voltage source, much as if one dropped a tool of the same name...

device.

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

Rectifier

A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...

in the forward direction like any other avalanche diode

Avalanche diode

In electronics, an avalanche diode is a diode that is designed to go through avalanche breakdown at a specified reverse bias voltage. The junction of an avalanche diode is designed to prevent current concentration at hot spots, so that the diode is undamaged by the breakdown...

, but is made and tested to handle very large peak currents. The popular 1.5KE series allows 1500 W of peak power, for a short time.

A bidirectional transient-voltage-suppression diode can be represented by two mutually opposing avalanche diode

Avalanche diode

s 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

Varistor

A varistor is an electronic component with a "diode-like" nonlinear current–voltage characteristic. The name is a portmanteau of variable resistor...

s or gas discharge tubes. The actual clamping occurs in roughly one picosecond

Picosecond

A picosecond is 10−12 of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000 001 seconds. A picosecond is to one second as one second is to 31,700 years....

, but in a practical circuit the inductance

Inductance

In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...

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.

Characterization

A TVS diode is characterised by:

Leakage current: 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 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
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...

s).
Parasitic capacitance: The nonconducting diode behaves like a capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

, which can have a deleterious effect on high-speed signals. Lower capacitance is generally preferred.
Parasitic inductance: Because the actual overvoltage 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
Heat sink
A heat sink is a term for a component or assembly that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems and the radiator in a car...

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

External links

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