Editing TRIAC (section)

===Gate threshold current, latching current, and holding current===

A TRIAC starts conducting when a current flowing into or out of its gate is sufficient to turn on the relevant junctions in the quadrant of operation. The minimum current able to do this is called '''gate threshold current''' and is generally indicated by I<sub>GT</sub>. In a typical TRIAC, the gate threshold current is generally a few milliamperes, but one has to take into account also that:

* I<sub>GT</sub> depends on the temperature: The higher the temperature, the higher the reverse currents in the blocked junctions. This implies the presence of more free carriers in the gate region, which lowers the gate current needed.
* I<sub>GT</sub> depends on the quadrant of operation, because a different quadrant implies a different way of triggering ([[#Operation|see here]]). As a rule, the first quadrant is the most sensitive (i.e. requires the least current to turn on), whereas the fourth quadrant is the least sensitive.
* When turning on from the off state, I<sub>GT</sub> depends on the voltage across the two main terminals MT1 and MT2. Higher voltage between MT1 and MT2 cause greater reverse currents in the blocked junctions, thus requiring less gate current to trigger the device (similar to high temperature operation).  In datasheets I<sub>GT</sub> is generally given for a specified voltage between MT1 and MT2.

When the gate current is discontinued, if the current between the two main terminals is more than what is called the '''latching current''', the device continues to conduct. Latching current is the minimum current that keeps the device internal structure latched in the absence of gate current.  The value of this parameter varies with:

* gate current pulse (amplitude, shape and width)
* temperature 
* quadrant of operation

In particular, if the pulse width of the gate current is sufficiently large (generally some tens of microseconds), the TRIAC has completed the triggering process when the gate signal is discontinued and the latching current reaches a minimum level called '''holding current'''. Holding current is the minimum required current flowing between the two main terminals that keeps the device on after it has achieved commutation in every part of its internal structure.

In datasheets, the latching current is indicated as I<sub>L</sub>, while the holding current is indicated as I<sub>H</sub>. They are typically in the order of some milliamperes.