A TRIAC acts much like two SCRs connected back-to-back for bidirectional (AC) operation.

The TRIAC is a three-terminal device similar in construction and operation to the SCR. The TRIAC controls and conducts current flow during both alternations of an ac cycle, instead of only one.

The TRIAC ... If bidirectional (AC) operation is desired, two Shockley diodes may be joined in parallel facing different directions to form a new kind of thyristor, the DIAC: (Figure below)

A dimmer circuit arrangement is disclosed including a second control circuit (40) for controlling the operation of a triac (50) for delivering current to a load (60), and a first control circuit

OPERATION OF THE TRIAC ... In figure 7 the theoretical application of a TRIAC, analogous is brought back to that one of the SCR of figure 5.

1.0 TRIAC CONTROL; 1.1 Basic Triac Operation; 1.2 Triggering; 1.3 Zero Voltage Detection; 1.4 Direct Couple; 1.5 Pulse Transformer Interface; 1.6 False Turn-on;

When the triac is closed, both LEDs should be off. When it is open, both LEDs should be on. ... If the triac output comprises a sequence of pulses, such as a PWM (pulse-width-modulated) signal for

When the triac is closed, both LEDs should be off. When it is open, both LEDs should be on. ... If the triac output comprises a sequence of pulses, such as a PWM (pulse-width-modulated) signal for

They also require a bleeder circuit or holding current resistor between 3 and 5kΩ to ensure proper TRIAC operation.

The LM3445 includes a bleeder circuit to ensure proper triac operation by allowing current flow while the line voltage is low to enable proper firing of the triac.