Trisil is a trade name for a
thyristor
A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current t ...
surge protection device, an electronic component designed to protect electronic circuits against
overvoltage
When the voltage in a circuit or part of it is raised above its upper design limit, this is known as overvoltage. The conditions may be hazardous. Depending on its duration, the overvoltage event can be transient—a voltage spike—or perm ...
. Unlike a
transient voltage suppression diodes, such as Transil, a Trisil acts as a
crowbar
A crowbar, also called a wrecking bar, pry bar or prybar, pinch-bar, or occasionally a prise bar or prisebar, colloquially, in Britain and Australia sometimes called a jemmy or jimmy (also called jemmy bar), gooseneck, or pig foot, is a tool ...
device, switching ON when the voltage on it exceeds its breakover voltage.
Overview
A Trisil is bidirectional, behaving the same way in both directions. It is principally a voltage-controlled
triac without gate. The behavior of a Trisil is similar to a
SIDAC, but unlike SIDAC, Trisil devices are commonly used to protect circuits from overvoltage. They act faster and can handle more current. In 1982, the only manufacturer was
Thomson SA; a successor company,
ST Microelectronics continues to make the devices.
This type of crowbar protector is widely used for protecting telecom equipment from lightning-induced transients and induced currents from power lines. Other manufacturers of this type of device include Bourns (TISP) and
Littelfuse
Littelfuse, Inc is an American electronic manufacturing company headquartered in Chicago, Illinois. The company primarily produces circuit protection products but also manufactures a variety of electronic switches and automotive sensors. Littelfus ...
(SIDACtor). Rather than using the natural breakdown voltage of the device, an extra region is fabricated within the device to form a
Zener diode
A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the ''Zener voltage'', is reached.
Zener diodes are manufactured with a great var ...
. This allows a much tighter control of the breakdown voltage.
It is also possible to make gated versions of this type of protector. In this case, the gate is connected to the telecom circuit power supply (via a diode or transistor) so that the device will crowbar if the transient exceeds the power supply voltage. The main advantage of this configuration is that the protection voltage tracks the power supply, thus eliminating the problem of selecting a particular breakdown voltage for the protection circuit.
See also
*
Transil
*
Zener diode
A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the ''Zener voltage'', is reached.
Zener diodes are manufactured with a great var ...
References
External links
Overvoltage protection''Trisil/Transil Comparison'', ST Application Note (PDF)
Solid state switches
Voltage stability
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