Triacs

[tonilopezmr]

Triac are two transistors in parallel which mean it is bidirectional, and it is using for control AC loads with low voltage for switch on/off or potentiometer.

It is a substitute for a common relay with no sound, but it gets hot.

To be bidirectional, it means that it doesn't have Collector and Emitter, just T1 and T2 and a Base to control the voltage between T1 and T2.

Usage

It has different behavior depending on the current you use:

Direct Current

When you use a Direct current with a TRIAC, it acts as an SCR transistor which means once the base has a signal, even you stop signal to the base the Triac it still closes (when you switch on the first time, it won't switch off even you stop the signal to the base), for open the circuit you need to add a manual switch for open the circuit and receive 0v for switch off the TRIAC.

Alternating Current

When you use an Alternating Current it will act like an ordinary transistor with DC, but why? Because AC loads oscillate between + 0v and -0v, for example, 220v AC oscillates between +220v and -220v and when you switch on a TRIAC, for switch off, you need to open the circuit or receive 0v and AC loads will be 0v sometime then the TRIAC switch off.

Solid State Relays

Solid state relays are TRIACS with an integrated circuit for easy usage.

Reference

#29 Triacs usually uses Optocouplers
TRIAC BTA16-600B datasheet
Video Switch on/off lights with optocoupler and triac
Solid State AC Relays using Triacs