Triggering device
Encyclopedia
A Triggering device is an electronic circuit, such as a Schmitt trigger, which is used to control another electronic circuit.
speed control, electric welding
, and electric heating
. Although it is always possible to control the amount of electrical power delivered to a load by using a variable transformer
to create a variable secondary output voltage
, 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 1960, an alternative method, using thyristor
s, has been in use. Both silicon-controlled rectifier
s (SCR) and TRIAC
s are members of the thyristor family. The term thyristor includes all the semiconductor device
s, 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
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.
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.
Uses
In many 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 motorElectric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
speed control, electric welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
, and electric heating
Electric heating
Electric heating is any process in which electrical energy is converted to heat. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical appliance that converts electrical energy into heat...
. Although it is always possible to control the amount of electrical power delivered to a load by using a variable transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
to create a variable secondary output voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
, 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 1960, an alternative method, using thyristor
Thyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...
s, has been in use. Both silicon-controlled rectifier
Silicon-controlled rectifier
A silicon-controlled rectifier is a four-layer solid state device that controls current. The name "silicon controlled rectifier" or SCR is General Electric's trade name for a type of thyristor. The SCR was developed by a team of power engineers led by Gordon Hall and commercialized by Frank W...
s (SCR) and TRIAC
TRIAC
TRIAC, from Triode for Alternating Current, is a genericized tradename for an electronic component that can conduct current in either direction when it is triggered , and is formally called a bidirectional triode thyristor or bilateral triode thyristor.TRIACs belong to the thyristor family and are...
s are members of the thyristor family. The term thyristor includes all the semiconductor device
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...
s, 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
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
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.
Some thyristors can be gated
Logic gate
A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
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.