TRIACs

A TRIAC is a 4-layer semiconductor device that conducts current in either direction when given a signal.

The name TRIAC is a generic trademark and is an abbreviation of TRIode for Alternating Current. The formal names for a TRIAC are bidirectional triode thyristor or bilateral triode thyristor, although these names are rarely used.

Schematic Symbol

The schematic symbol for the TRIAC is shown below:

The schematic symbol for the TRIAC, with pin names.

The anodes A1 and A2 may be called Main Terminal 1 (MT1) and Main Terminal 2 (MT2) respectively.

Component Parameter Descriptions

Repetitive Peak Off-State Voltage (50-60Hz)

The maximum repetitive peak voltage ($V_{DSM}$) allowed across the device. Remember that RMS voltage readings need to be multiplied by $\sqrt{2}$ to find the peak voltage (assuming a sinewave).

Non-repetitive Off-State Voltage

The maximum off-state peak voltage across A1 and A2 that is non-repetitive. Normally this is defined to pulses less than 10ms wide.

Gate Currents

A “normal” TRIAC might have a gate trigger current ($I_{gt}$) of 20-50mA. A “sensitive” TRIAC might have an $I_{gt}$ of 2-10mA.

Part Numbering

Many TRIACs begin with/include the three-letter term BTA.