A Triggering device is an electronic circuit, such as a

Schmitt trigger In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input ...

, which is used to control another electronic circuit.

Uses

In many of industrial operations, the delivery of a variable and controlled amount of electrical power is necessary. The most common of these operations include electric lighting,

electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...

speed control, electric

welding Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as bra ...

, and

electric heating Electric heating is a process in which electrical energy is converted directly to heat energy at around 100% efficiency, using rather cheap devices. Common applications include space heating, cooking, water heating and industrial processes. ...

. Although it is always possible to control the amount of electrical power delivered to a load by using a variable

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

to create a variable secondary output

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

, these transformers are physically large and expensive and need frequent maintenance (in high power ratings). There are other methods of controlling power to a load, but they are mostly not available for high power applications. Since 1961, an alternative method, using

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 ...

s, has been in use. Both

silicon-controlled rectifier A silicon controlled rectifier or semiconductor controlled rectifier is a four-layer solid-state current-controlling device. The name "silicon controlled rectifier" is General Electric's trade name for a type of thyristor. The principle of four ...

s (SCR) and

TRIAC A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised trade ...

s are members of the thyristor family. The term thyristor includes all the semiconductor devices, which show inherent ON-OFF behavior, as opposed to allowing gradual changes in conduction. All thyristors are regenerative switching devices, and they cannot operate in linear manner. Thus, a

transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

is not a thyristor even though it can operate like a switch (ON-OFF). The transistor is not inherently an ON-OFF device, and it is possible for a transistor to operate linearly.{{cite news, title=Trigger Device, url=http://transparentc.com/catalogue/trigger-device, accessdate=22 July 2016, work=transparentc Some thyristors can be gated into the ON state. Other thyristors cannot be gated ON, but they can be turned ON when the applied voltage reaches a certain breakover value.

References

Digital electronics Electronic circuits